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How to use spot instance with amazon elastic beanstalk?. <p>I have one infra that use amazon elastic beanstalk to deploy my application.
I need to scale my app adding some spot instances that EB do not support.</p>
<p>So I create a second autoscaling from a launch configuration with spot instances.
The autoscaling use the same load balancer created by beanstalk.</p>
<p>To up instances with the last version of my app, I copy the user data from the original launch configuration (created with beanstalk) to the launch configuration with spot instances (created by me).</p>
<p>This work fine, but:</p>
<ol>
<li><p>how to update spot instances that have come up from the second autoscaling when the beanstalk update instances managed by him with a new version of the app?</p>
</li>
<li><p>is there another way so easy as, and elegant, to use spot instances and enjoy the benefits of beanstalk?</p>
</li>
</ol>
<p><strong>UPDATE</strong></p>
<p>Elastic Beanstalk add support to spot instance since 2019... see:
<a href="https://docs.aws.amazon.com/elasticbeanstalk/latest/relnotes/release-2019-11-25-spot.html" rel="nofollow noreferrer">https://docs.aws.amazon.com/elasticbeanstalk/latest/relnotes/release-2019-11-25-spot.html</a></p>
| 0non-cybersec
| Stackexchange |
sometimes you just have to stop and smell the gunpowder. | 0non-cybersec
| Reddit |
A young Kenyan woman holds her pet deer in Mombassa, March 1909.. | 0non-cybersec
| Reddit |
Calculate $\sum_{n\geq 0}\frac{H_n}{10^n}$. <p>Question is like in the title and my attempt is</p>
<p>Let have sequence $$a_n = <\frac{H_0}{10^0},\frac{H_1}{10^1},\frac{H_2}{10^2},\dots>$$
where $H_n$ is n-th harmonic number.</p>
<p>And we have to construct $$b_n = \langle a_0,a_0+a_1,a_0+a_1+a_2,\dots\rangle$$
and it will be our answer.</p>
<p>Let's have generating function for sequence $a_n$: $$A(x) = \sum_{n=0}^\infty a_n x^n$$</p>
<p>And generating function for sequence $b_n$ will be $$B(x) = \frac{A(x)}{1-x}$$</p>
<p>I started making $\frac{H_n}{10^n}$ a bit easier(there are my doubts).</p>
<p>we can rewrite $H_n$ as $$1+\dfrac12+\dfrac13+\dots = 1+\frac{\frac{n(n+1)}{2}-\dfrac22}{n!} = 1+\frac{n(n+1)-2}{2*n!}$$
so now we can rewrite $a_n$ as $$a_n =\langle\frac{1}{10^n}+\frac{n(n+1)-2}{2*n!*10^n}\rangle$$</p>
<p>Generating function for $$\sum_{n=0}^\infty \frac{1}{10^n}x^n = \frac{1}{1-\frac{1}{10}x}$$ </p>
<p>But i'm having problem with second part of it...
And i'm not sure if i don't overcomplicated this task by making it "easier". I'd like to use generating functions cause it's task for them, but i'd be happy to see some other solutions. Thanks in advance.</p>
| 0non-cybersec
| Stackexchange |
How to use spot instance with amazon elastic beanstalk?. <p>I have one infra that use amazon elastic beanstalk to deploy my application.
I need to scale my app adding some spot instances that EB do not support.</p>
<p>So I create a second autoscaling from a launch configuration with spot instances.
The autoscaling use the same load balancer created by beanstalk.</p>
<p>To up instances with the last version of my app, I copy the user data from the original launch configuration (created with beanstalk) to the launch configuration with spot instances (created by me).</p>
<p>This work fine, but:</p>
<ol>
<li><p>how to update spot instances that have come up from the second autoscaling when the beanstalk update instances managed by him with a new version of the app?</p>
</li>
<li><p>is there another way so easy as, and elegant, to use spot instances and enjoy the benefits of beanstalk?</p>
</li>
</ol>
<p><strong>UPDATE</strong></p>
<p>Elastic Beanstalk add support to spot instance since 2019... see:
<a href="https://docs.aws.amazon.com/elasticbeanstalk/latest/relnotes/release-2019-11-25-spot.html" rel="nofollow noreferrer">https://docs.aws.amazon.com/elasticbeanstalk/latest/relnotes/release-2019-11-25-spot.html</a></p>
| 0non-cybersec
| Stackexchange |
pRovACaTiVE thReAT tO wOrLD peAcE. | 0non-cybersec
| Reddit |
Nexus 7 Successor Will Ditch Nvidia, Opt for Qualcomm Instead, Says Report. | 0non-cybersec
| Reddit |
How to use spot instance with amazon elastic beanstalk?. <p>I have one infra that use amazon elastic beanstalk to deploy my application.
I need to scale my app adding some spot instances that EB do not support.</p>
<p>So I create a second autoscaling from a launch configuration with spot instances.
The autoscaling use the same load balancer created by beanstalk.</p>
<p>To up instances with the last version of my app, I copy the user data from the original launch configuration (created with beanstalk) to the launch configuration with spot instances (created by me).</p>
<p>This work fine, but:</p>
<ol>
<li><p>how to update spot instances that have come up from the second autoscaling when the beanstalk update instances managed by him with a new version of the app?</p>
</li>
<li><p>is there another way so easy as, and elegant, to use spot instances and enjoy the benefits of beanstalk?</p>
</li>
</ol>
<p><strong>UPDATE</strong></p>
<p>Elastic Beanstalk add support to spot instance since 2019... see:
<a href="https://docs.aws.amazon.com/elasticbeanstalk/latest/relnotes/release-2019-11-25-spot.html" rel="nofollow noreferrer">https://docs.aws.amazon.com/elasticbeanstalk/latest/relnotes/release-2019-11-25-spot.html</a></p>
| 0non-cybersec
| Stackexchange |
I bought these boots recently and I would like your opinion on them. | 0non-cybersec
| Reddit |
How to use spot instance with amazon elastic beanstalk?. <p>I have one infra that use amazon elastic beanstalk to deploy my application.
I need to scale my app adding some spot instances that EB do not support.</p>
<p>So I create a second autoscaling from a launch configuration with spot instances.
The autoscaling use the same load balancer created by beanstalk.</p>
<p>To up instances with the last version of my app, I copy the user data from the original launch configuration (created with beanstalk) to the launch configuration with spot instances (created by me).</p>
<p>This work fine, but:</p>
<ol>
<li><p>how to update spot instances that have come up from the second autoscaling when the beanstalk update instances managed by him with a new version of the app?</p>
</li>
<li><p>is there another way so easy as, and elegant, to use spot instances and enjoy the benefits of beanstalk?</p>
</li>
</ol>
<p><strong>UPDATE</strong></p>
<p>Elastic Beanstalk add support to spot instance since 2019... see:
<a href="https://docs.aws.amazon.com/elasticbeanstalk/latest/relnotes/release-2019-11-25-spot.html" rel="nofollow noreferrer">https://docs.aws.amazon.com/elasticbeanstalk/latest/relnotes/release-2019-11-25-spot.html</a></p>
| 0non-cybersec
| Stackexchange |
Laplacian on coset spaces. <p>Edited after @J. Martel's comment: Let us consider the sphere $S^n$ (embedded in $\mathbb{R}^{n+1}$). We know that if $X_i$ represent the vector fields on $S^2$ giving the rotation about the $x_i$-axis, then the Laplacian on $S^2$ is given by $X^2_1 + X^2_2 + X^2_3$. My question is:</p>
<p>Can we have a similar expression for higher dimensional spheres? Specifically, if $Y_i$ generate the Lie algebra of $SO(n+1)$, can we conclude how the Laplacian would look like on $S^n$ from the fact that one can write $S^n$ as a coset space $SO(n+1)/SO(n)$?</p>
<p>Any help will be greatly appreciated. If there is a more general way of answering this question for coset spaces like $G/K$, I would be glad to know about it. Thanks...</p>
| 0non-cybersec
| Stackexchange |
Returning player needs advice!. Hi all! Long time fan been absent for the last 6 months. Any advice is appreciated but my main question relates to these remote raid passes. How can i know when there will be enough people at a raid? Is it as simple as just clicking on the raid as soon as it opens to see if there's people in the lobby? | 0non-cybersec
| Reddit |
Windows shortcut, Command Line and Perl. <p>I developed several scripts using the command line in windows (which is needed because there are several 'say' comments that need to be shown) and using the line:</p>
<pre><code>perl "D:/path to script"
</code></pre>
<p>That's all fine. But ...</p>
<p>This morning I created a series of shortcuts on Windows, the basic idea being they can click on the icon, and the CMD will open and start running the script. THAT is where I'm stuck !</p>
<p>In the target attribute of the shortcut, I have put:</p>
<pre><code>C:/system32/cmd.exe D:/path to perl script
</code></pre>
<p>That opens the command line, and sets the prompt to "D:/path to script_" (I also tried adding perl in between the two arguemennts as per when typing directly into window. That had no effect) I tried "perl D:/path to script" in quotes. That didn't work</p>
<p>I then wondered about batch files, but they appears to close the window once batch has run, so won't be able to display the say commands!</p>
<p>I have also heard of "pl2bat", but no idea if that would keep the CLI alive whilst rest of program run.</p>
<p>This is running client side, and NOT in browser, or sending data to a server, the idea being with Perl on a USB stick, it will be 'self contained' with nothing being installed on PC</p>
| 0non-cybersec
| Stackexchange |
Height of parent div is zero even if it has child with finite heights. <p>I have a website whose layout has been shown in the diagram. The body consists of a <code>main container</code>, which comprises of <code>header</code>, <code>parent div</code> and <code>footer</code>. The <code>parent div</code> further contains several <code>child div</code> as shown.</p>
<p><img src="https://i.stack.imgur.com/OIjF6.png" alt="Webpage Layout"></p>
<p>The problem being height of all the <code>child div</code> is finite. But the <code>parent div</code> contains nothing other than the child divs. All the child divs are visible but the height of the parent div is shown to be zero. I am also not fixing the height of the parent div by giving some pre-specified value as it may cause blunder if number of child increases in future.</p>
<p>The problem due to zero size of parent div is that my footer div is going up and clashing with the contents of the parent div. This can be resolved by giving a suitable margin-top, but that is not a solution I am looking for. </p>
<p>Can anyone suggest me some way so that the height of the parent div changes automatically according to the height of child divs present.</p>
<p>Please comment if I am unclear in asking my doubt !</p>
| 0non-cybersec
| Stackexchange |
How do I remove automatic line return in Word table?. <p>I am currently working in Excel and Word 2010 on a data table and want to transfer it to word. </p>
<p>Some columns contains long reference which only the first numbers are useful, other columns may contain important information and are plainly displayed. I removed the automatic line return so that full reference number are not entirely displayed. <a href="https://i.stack.imgur.com/9yEXC.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/9yEXC.png" alt="This is what it look like."></a></p>
<p>When I copy paste my table from excel to word, whatever the kind of copy paste, long reference are always displayed in full, thus removing lot of space for the important information, and also taking biggest line when there is no information. <a href="https://i.stack.imgur.com/GsGVn.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/GsGVn.png" alt="enter image description here"></a></p>
<p>I've tried to resize the column but the text wrapping is still the same.</p>
<p><a href="https://i.stack.imgur.com/Bxf95.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Bxf95.png" alt="enter image description here"></a></p>
<p>How do I remove this automatic return to the line in the first column (and only the first column) of the word table ? I want to keep the information but I want it to only be displayed partially like in Excel. I tought about pasting it as a picture but my table is very long and word does not handle multi page pictures well.</p>
| 0non-cybersec
| Stackexchange |
How to scroll down to a specific index of a list contained in a Scrollview ? (Nativescript-vue). <p>I'm writing a mobile application using <code>nativescript-vue</code>.</p>
<p>I have a list contained in a Scrollview (which is contained in a Tabview).
When my app goes to this tab, I want the Scrollview to scroll down to a specific index of the list that is contained.</p>
<p>I tried this : </p>
<pre><code><ScrollView id="ScrollView" @loaded="onLoaded">
<ListView for="item in items" class="list-group">
...
onLoaded() {
this.$refs.page.nativeView.getViewById("ScrollView").scrollToVerticalOffset(200, false);
}
</code></pre>
<p>This does not work, whatever the value for the offset parameter.</p>
<p>Do I miss something?</p>
<p>Thank you in advance.</p>
| 0non-cybersec
| Stackexchange |
[PI] "There exists a court that sentences people with "Would You Rather" questions. Whichever option the person picks, becomes reality.". Looking for constructive feedback, regarding characterizations and dialogue:
“Gina Smith, you have been found guilty by a jury of your peers.” The judge’s wig shed a few motes of white powder as the diminutive man puffed out his chest to deliver a sentence to the convict before him. “For your crimes against humanity, including but not limited to: mass murder, genocide, infanticide, matricide, regicide, jay-walking, and 32 counts of arson, your fate shall be accordingly left to… the cards!” The judge peered over his bench, and grabbed another book to stand on so that he could slam his gavel with slightly more force.
The crowd gasped, and Gina felt as though her spine had been transplanted to an arctic wasteland. Ever since the great robo-nuclear cross-species galactic war/plague that had devastated human civilization some hundreds of years ago, mankind had been struggling to rebuild what remained of their society. Of the relics that had survived the war, the cards were still one of the few that had still not been re-integrated into modern day procedures. Although many heinous crimes were committed every day, no one imagined someone could be so evil as to be labeled “horrible” even by the standards of the pre-apocalypse humans who had blatantly killed each other on the streets simply on the basis of their skin color or religious beliefs.
An armed procession had appeared in the courtroom now, guarding a black case that was now slowly making its way through the courthouse. From Gina’s perspective, she drolly observed that their helmets made it look as though a procession of ants were marching lockstep to deliver a small morsel of food up to the judge’s pulpit. Slight wrinkles creased the judge’s forehead as he saw the unassuming black box placed before him. He had a hushed conversation with the bailiff standing next to him before clearing his throat and puffing out his chest again.
“OPEN IT UP!” the judge screeched. The bailiff leaned in to quickly whisper in the judge’s ear again. “Oh, I just open it like this?” The judge reverently lifted the lid before gingerly placing it aside. The entire courthouse grew quiet as everyone craned their necks to get a better view of the proceedings.
“Gina Smith, it is now time for your sentencing,” said the judge. He took a trembling swig of water, coughed, choked, and spat some out before slowly reaching into the box. The dust of a bygone civilization floated out as he pulled out something that the audience couldn’t quite see, much to the general disappointment of the courtroom. The furrows in his brow grew deeper as he leaned in to have another hushed conversation with the bailiff. This time, the conversation seemed to be even more spirited, with animated gestures and wild shrugs flying between the two, before the judge threw up his arms and turned back around to face Gina. Once again, the crowd grew quiet as the judge seemed to inflate his chest yet another few inches.
“Gina, would you rather… die of dysentery?” A bead of sweat began traveling down the judge’s forehead. He shakily put aside whatever he had originally pulled from the box and consulted its depths once again. “Or… receive sp- spec… spectacular abs?” The crowd gasped. Gina paused, certain that there had been some sort of mistake. This was what the first civilization had planned for its most horrible of criminals?
“Um… excuse me?” was her only response. The judge’s fingers slipped as the man fumbled for his gavel.
“Order in the court! Gina! You must choose! The cards dictate it!” The judge tried roaring as best he could, but his tiny vocal cords were not enough to overwhelm the storm of whispers that had flooded the court.
“The spectacular abs, then,” said Gina, as she turned to face her state-appointed lawyer. The lawyer could only raise an eyebrow back.
“There must be a mistake!” The judge screeched as he reached for the box again. He pulled out another card. “Gina! Would you rather… have dead babies? Or…” The crowd drew in once again, eager to see how this most horrible criminal would be punished. The judge’s hand began to shake as he looked at the next card he had drawn. “…Become obscenely rich…?” The judge’s voice had petered off into a squeak.
Gina’s lawyer leapt to his feet. “Objection! This is double jeopardy!” The lawyer hadn’t been able to do much, given the horrible nature of Gina’s crimes, but at least he was competent enough to recognize that Gina couldn’t be tried twice for the same crimes.
“No, no, it’s fine,” said Gina cheerily. “I’ll take the riches, please.”
The judge’s chest had shrunk back down to its original diameter. “Very well. You have been sentenced,” came the barely audible whisper. “With spectacular abdominal muscles, an-and… obscene riches. That is the verdict of the Cards against Humanity.” The judge gave one last feeble bang with his gavel as the courtroom erupted into chatter.
| 0non-cybersec
| Reddit |
Does this girl not want to talk to me?. So theres this girl that I've been friends with for a while, and I'd like to ask her out soon. So to start, I figured I would just start talking to her as a friend so I can get to know her better. I don't think I'm creepy or annoying in anyway, but almost every single time I message her she's takes **hours** to reply. I started getting the feeling that she didn't really wanna talk to me, due to the long response times, and the final nail in the coffin was when I messaged her and six hours later, she opened it without responding.
So my question is, how do I know if I'm being annoying? If she really doesn't want to talk to me, how do I get over it?
Edit: after reading all of the comments, it seems like I'm just overthinking or something along those lines. Thanks everyone for the help! | 0non-cybersec
| Reddit |
This woman who stole a ball from this girl.. | 0non-cybersec
| Reddit |
If Reddit wants NA to have a good soloqueue again, it doesn't stop at the pro level, EVERYONE has to be trying in soloqueue.. I've been seeing everyone talking about how NA's soloqueue is trash because no one cares in high elo, but I haven't heard a whole lot of talk of people saying that THEY will start trying hard to make NA soloqueue better. Those high elo players weren't always high elo, if you want NA soloqueue to be good, you have to try hard yourself. Stop pretending that it's on the duty of high elo players to do everything, even if the bronze 3 teemo is trying hard, that's one more person trying their best to up the quality of soloqueue. I encourage everyone who truly wants NA to be great to put their 100% into every game, win or lose. | 0non-cybersec
| Reddit |
polynomial modulus question. <p>I have to solve $x^2 + x ≡ 44 \mod 56$. For part A and B I had to use trial and error to find the solutions to $x^2 + x ≡44 \mod 8$ and $x^2 + x ≡44 \mod7$.</p>
<p>For $x^2 + x ≡44 \mod 8 $ I found the solutions were $x≡ 3 \mod 8$ and $x ≡ 4 \mod 8$.</p>
<p>For $x^2 + x ≡44 \mod 7$ I found the solutions were $x≡ 1 \mod 7$ and $x ≡ 5 \mod 7$.</p>
<p>I know these are correct since I double checked them. But the problem is I have to use the Chinese remainder theorem to solve solutions as a system meaning</p>
<p>$$ x ≡ 3 \mod 8 $$
$$ x ≡ 4 \mod 8 $$
$$ x ≡ 1 \mod 7 $$
$$ x ≡ 5 \mod 7 $$</p>
<p>but it won't work since the gcd's of the moduli are not pairwise disjoint. Or am I doing it wrong?</p>
| 0non-cybersec
| Stackexchange |
Netgear CEO Patrick Lo on Jobs' Medical Leave: "Once Steve Jobs goes away, which is probably not far away, then Apple will have to make a strategic decision on whether to open up the platform." . | 0non-cybersec
| Reddit |
Saw a little piece of heaven in Lake Banyoles, the site for the water event in Barcelona Olympics. Girona, Catalonia, Spain. | 0non-cybersec
| Reddit |
I turn 40 today. I feel my life is basically over.. I'm 40 years old today.
I can hardly believe it. I feel the same. I got up this morning, went to work.... just another Monday.
And then it hit me. I'm 40. The hair on my chest is going white. The lines around my eyes are there to stay now.
How did it get so late? How did I lose so much time?
If I close my eyes and take a deep breath, I remember turning 30. Hanging out with friends on a Wednesday night, pigging out on pizza and video games. I was broke as shit, but happy and never lonely.
Another breath, and I remember turning 25. I was fat, depressed, tired of my corporate job. I drank too much and gambled a lot. But I was still young.
Then, easy as breathing, I remember turning 20. I had all my hair. I was in amazing shape. I had a new girlfriend and the world was my oyster.
I still my mind just a little, I remember being 15. I can look down and see my own body, nearly man-sized but hairless. I can run my tongue across my teeth and feel the rasp of the orthodontics. I remember the thrill of cashing my first paycheck, the rush of holding a girl's hand.
And for just a fleeting instant, between breaths, between heartbeats, I remember being 8. I'm a little boy, too smart, too fat, too wordy. I remember getting my first puppy, a shaggy Collie mix that I loved dearly but was dead within the year.
Soon, I too will be dead. Just a few more breaths. One breath, and I'll be 50 and saying good-bye to my parents. Another breath, I'll be 60 and starting to worry about my health. And maybe on the next breath, or the breath after, I'll have to say good-bye to wife.
Being young, you could look forward to things, to experiences. You thought about your life in terms of "firsts". First tooth fallen out, first bike, first trip away from home, first kiss, first job...
And now... now I'm entering the age of "lasts".
Today I'm 40 years old. And I'm not celebrating.
I'm so sad, I feel old.
And scared. So very scared.
| 0non-cybersec
| Reddit |
ar
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1
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Noname manuscript No.
(will be inserted by the editor)
Innovative methods of correlation and orbit determination
for space debris
Davide Farnocchia · Giacomo Tommei ·
Andrea Milani · Alessandro Rossi
Received: date / Accepted: date
Abstract We propose two algorithms to provide a full preliminary orbit of an Earth-
orbiting object with a number of observations lower than the classical methods, such
as those by Laplace and Gauss. The first one is the Virtual debris algorithm, based
upon the admissible region, that is the set of the unknown quantities corresponding to
possible orbits for objects in Earth orbit (as opposed to both interplanetary orbits and
ballistic ones). A similar method has already been successfully used in recent years for
the asteroidal case. The second algorithm uses the integrals of the geocentric 2-body
motion, which must have the same values at the times of the different observations for
a common orbit to exist. We also discuss how to account for the perturbations of the
2-body motion, e.g., the J2 effect.
Keywords Space debris · Orbit determination · Admissible region · Keplerian
integrals
1 Introduction
The near-Earth space, filled by more than 300000 artificial debris particles with diam-
eter larger than 1 cm, can be divided into three main regions: the Low Earth Orbit
(LEO), below about 2000 km, the Medium Earth Orbit (MEO), above 2000 km and
below 36000 km, and the Geosynchronous Earth Orbit (GEO) at about 36000 km of
altitude. Currently the orbits of more than 12000 objects larger than about 10 cm are
listed in the so called Two Line Elements (TLE) catalogue. To produce and maintain
D. Farnocchia, G. Tommei, A. Milani
Department of Mathematics, University of Pisa, Largo Bruno Pontecorvo 5, 56127 Pisa, Italy
E-mail: [email protected]
G. Tommei
E-mail: [email protected]
A. Milani
E-mail: [email protected]
A. Rossi
ISTI/CNR, Via Moruzzi 1, 56124 Pisa, Italy
E-mail: [email protected]
http://arxiv.org/abs/0911.0149v1
2
such a catalogue a large number of optical and radar observations are routinely per-
formed by the United States Space Surveillance Network. Nowadays also Europe has
launched its Space Situational Awareness (SSA) initiative aimed to increase the knowl-
edge of the circumterrestrial environment. In this context the availability of efficient
methods and algorithms for accurate orbit determination is extremely important.
Given two or more sets of observations, the main problem is how to identify which
separate sets of data belong to the same physical object (the so-called correlation
problem). Thus the orbit determination problem needs to be solved in two stages: first
different sets of observations need to be correlated, then an orbit can be determined;
this combined procedure is called linkage in the literature [Milani 1999].
In this paper we describe two different linkage methods, for both optical and radar
data. By using the attributable vector (Sec. 2) we summarize the information contained
in either optical or radar data. In Sec. 3 we describe the admissible region and the Vir-
tual debris algorithm [Tommei et al. 2007] and we propose a general scheme to classify
observed objects. Sec. 4 deals with the Keplerian integrals method, first introduced by
[Gronchi et al. 2009] for the problem of asteroid orbit determination. Furthermore, the
inclusion of the effect due to the non-spherical shape of the Earth is discussed. Finally,
in Sec. 5, a sketch of the general procedure for the full process of correlation of different
observations is outlined.
2 Observations and attributables
Objects in LEO are mostly observed by radar while for MEOs and GEOs optical sensors
are used. In both cases, the batches of observations which can be immediately assigned
to a single object give us a set of data that can be summarized in an attributable, that
is a 4-dimensional vector. To compute a full orbit, formed by 6 parameters, we need to
know 2 further quantities.
Thus the question is the identification problem, also called correlation in the debris
context: given 2 attributables at different times, can they belong to the same orbiting
object? And if this is the case, can we find an orbit fitting both data sets?
Let (ρ, α, δ) ∈ R+×[0, 2π)×(−π/2, π/2) be spherical coordinates for the topocentric
position of an Earth satellite. The angular coordinates (α, δ) are defined by a topocen-
tric reference system that can be arbitrarily selected. Usually, in the applications, α is
the right ascension and δ the declination with respect to an equatorial reference system
(e.g., J2000). The values of range ρ and range rate ρ̇ are not measured.
We shall call optical attributable a vector
Aopt = (α, δ, α̇, δ̇) ∈ [0, 2π)× (π/2, π/2) × R2 ,
representing the angular position and velocity of the body at a time t in the selected
reference frame.
Active artificial satellites and space debris can also be observed by radar: because
of the 1/ρ4 dependence of the signal to noise for radar observations, range and range-
rate are currently measured only for debris in LEO. When a return signal is acquired,
the antenna pointing angles are also available. Given the capability of modern radars
to scan very rapidly the entire visible sky, radar can be used to discover all the debris
above a minimum size while they are visible from an antenna, or a system of antennas.
When a radar observation is performed we assume that the measured quantities (all
with their own uncertainty) are the range, the range rate, and also the antenna pointing
3
direction, that is the debris apparent position on the celestial sphere, expressed by two
angular coordinates such as right ascension α and declination δ. The time derivatives
of these angular coordinates, α̇ and δ̇, are not measured.
We define radar attributable a vector
Arad = (α, δ, ρ, ρ̇) ∈ [−π, π)× (−π/2, π/2)× R
+ × R ,
containing the information from a radar observation, at the receive time t.
To define an orbit given the attributable A we need to find the values of two
unknowns quantities (e.g., ρ and ρ̇ in the optical case, α̇ and δ̇ in the radar case), that,
together with the attributable, give us a set of attributable orbital elements:
X = [α, δ, α̇, δ̇, ρ, ρ̇]
at a time t̄, computed from t taking into account the light-time correction: t̄ = t− ρ/c.
The Cartesian geocentric position and velocity (r, ṙ) can be obtained, given the observer
geocentric position q at time t, by using the unit vector ρ̂ = (cosα cos δ, sinα cos δ, sin δ)
in the direction of the observation:
r = q+ ρρ̂ , ṙ = q̇+ ρ̇ρ̂ + ρ
dρ̂
dt
,
dρ̂
dt
= α̇ρ̂α + δ̇ρ̂δ ,
ρ̂α = (− sinα cos δ, cosα cos δ, 0) , ρ̂δ = (− cosα sin δ,− sinα sin δ, cos δ) .
3 Admissible region theory
Starting from an attributable, we would like to extract sufficient information from it
in order to compute preliminary orbits: we shall use the admissible region tool, as
described in [Tommei et al. 2007]. For easy of reading we recall here the basic steps of
the theory.
The admissible region replaces the conventional confidence region as defined in the
classical orbit determination procedure. The main requirement is that the geocentric
energy of the object is negative, that is the object is a satellite of the Earth.
3.1 Optical admissible region
Given the geocentric position r of the debris, the geocentric position q of the observer,
and the topocentric position ρ of the debris we have r = ρ + q. The energy (per unit
of mass) is given by
E(ρ, ρ̇) = 1
2
||ṙ(ρ, ρ̇)||2 − µ
||r(ρ)||
,
where µ is the Earth gravitational parameter. Then a definition of admissible region
such that only satellites of the Earth are allowed includes the condition
E(ρ, ρ̇) ≤ 0 (1)
that could be rewritten as
2E(ρ, ρ̇) = ρ̇2 + c1ρ̇+ T (ρ)−
2µ
p
S(ρ)
≤ 0 ,
4
T (ρ) = c2ρ
2
+ c3ρ+ c4 , S(ρ) = ρ
2
+ c5ρ+ c0
and coefficients ci depending on the attributable [Tommei et al. 2007]:
c0 = ||q||2 , c1 = 2 q̇ · ρ̂ , c2 = α̇2 cos2 δ + δ̇2 = η2 ,
c3 = 2 (α̇ q̇ · ρ̂α + δ̇ q̇ · ρ̂δ) , c4 = ||q̇||
2
, c5 = 2q · ρ̂ ,
where η is the proper motion. In order to obtain real solutions for ρ̇ the discriminant
of 2E (polynomial of degree 2 in ρ̇) must be non-negative:
∆ =
c21
4
− T (ρ) + 2µp
S(ρ)
≥ 0 .
This observation results in the following condition on ρ:
2µ
p
S(ρ)
≥ Q(ρ) = c2ρ2 + c3ρ+ γ , γ = c4 −
c21
4
. (2)
Condition (2) can be seen as an inequality involving a polynomial V (ρ) of degree 6:
V (ρ) = Q
2
(ρ)S(ρ) ≤ 4µ2 .
Studying the polynomial V (ρ) and its roots, as done by [Milani et al. 2004], the con-
clusion is that the region of (ρ, ρ̇) such that condition (1) is satisfied can admit more
than one connected component, but it has at most two. In any case, in a large number
of numerical experiments with objects in Earth orbit, we have not found examples with
two connected components.
The admissible region needs to be compact in order to have the possibility to
sample it with a finite number of points, thus a condition defining an inner boundary
needs to be added. The choice for the inner boundary depends upon the specific orbit
determination task: a simple method is to add constraints ρmin ≤ ρ ≤ ρmax allowing,
e.g., to focus the search of identifications to one of the three classes LEO, MEO and
GEO. Another natural choice for the inner boundary is to take ρ ≥ hatm where hatm
is the thickness of a portion of the Earth atmosphere in which a satellite cannot remain
in orbit for a significant time span. As an alternative, it is possible to constrain the
semimajor axis to be larger than R⊕ + hatm = rmin, and this leads to the inequality
E(ρ, ρ̇) ≥ − µ
2rmin
= Emin , (3)
which defines another degree six inequality with the same coefficients but for a different
constant term. The qualitative structure of the admissible region is shown in Fig. 1.
Another possible way to find an inner boundary is to exclude trajectories impacting
the Earth in less than one revolution, that is to use an inequality on the perigee rP ,
already proposed in [Maruskin et al. 2009]:
rP = a(1− e) ≥ rmin. (4)
Note that this condition naturally implies (3) and ρ ≥ hatm. To analytically develop
the inequality (4) we use the 2-body formulae involving the angular momentum:
c(ρ, ρ̇) = r× ṙ = Dρ̇+Eρ2 + Fρ+G (5)
5
0 1 2 3 4 5 6 7 8
−150
−100
−50
0
50
100
150
E=0
E=E
min
ρ=ρ
min
ρ=ρ
max
ρ (R
⊕
)
d
ρ
/d
t
(R
⊕
/d
a
y
)
Fig. 1 An example of admissible region, optical case, in the (ρ, ρ̇) plane. The region (painted
in grey) is bounded by two level curves of the energy, (E = Emin) and (E = 0), and by the
two conditions on the topocentric distance (ρ = ρmin and ρ = ρmax).
D = q× ρ̂, E = ρ̂ × (α̇ρ̂α + δ̇ρ̂δ),
F = q̂× (α̇ρ̂α + δ̇ρ̂δ) + q̇× ρ̂, G = q× q̇
and substituting in (4) we obtain:
s
1 +
2E||c||2
µ2
≤ 1 + 2Ermin
µ
. (6)
Since the left hand side is e ≥ 0, we need to impose 1 + 2Ermin/µ ≥ 0: this is again
a ≥ rmin. By squaring (6) we obtain:
||c||2 ≥ 2rmin(µ+ Ermin) .
The above condition is an algebraic inequality in the variables (ρ, ρ̇):
(r
2
min − ||D||
2
)ρ̇
2 − P (ρ)ρ̇− U(ρ) + r2minT (ρ)−
2r2minµ
p
S(ρ)
≤ 0 , (7)
P (ρ) = 2D ·Eρ2 + 2D · Fρ+ 2D ·G− r2minc1 ,
U(ρ) = ||E||2ρ4 + 2E · Fρ3 + (2E ·G+ ||F||2)ρ2 + 2F ·Gρ+ ||G||2 − 2rminµ .
The coefficient of ρ̇2 is positive, thus to obtain real solutions for ρ̇ the discriminant of
(7) must be non negative:
∆P = P
2
(ρ) + 4(r
2
min − ||D||
2
)
U(ρ) + r
2
minT (ρ) +
2r2minµ
p
S(ρ)
!
≥ 0 .
6
This condition is equivalent to the following:
2µ
p
S(ρ)
≥ W (ρ) = −4(r
2
min − ||D||
2)(U(ρ) + r2minT (ρ)) + P
2(ρ)
4r2min(r
2
min − ||D||2)
. (8)
Note that the inequality (8) is similar to (2). However, in this case, the function in
the right hand side is much more complicated, and there is no easy way to use the
condition (4) to explicitly describe the boundary of the admissible region; e.g., we do
not have a rigorous bound on the number of connected components. This condition (4)
will be used only a posteriori as a filter (Sec. 3.3).
0 1 2 3 4 5 6 7 8
−150
−100
−50
0
50
100
150
r
P
=r
min
r
A
=r
max
ρ (R
⊕
)
d
ρ
/d
t
(R
⊕
/d
a
y
)
Fig. 2 The same example of Fig. 1, with the two further conditions on the pericenter (rP ≥
rmin) and the apocenter (rA ≤ rmax) distances.
Fig. 2 shows also this inner boundary; note that the boundaries of the regions
defined by (3) and by ρ ≥ hatm are also plotted in the figure, but these constraints
are not necessary. We have also plotted an alternative outer boundary constraining the
apocenter rA at some large value rmax:
8
<
:
E ≤ − µ
2rmax
||c||2 ≥ 2rmax(µ+ Ermax)
;
this outer boundary can be used in the same way, as an a posteriori filter.
3.2 Radar admissible region
Given a radar attributable Arad, we define as radar admissible region for a space debris
the set of values of (α̇, δ̇) such that
E(α, δ) = z1α̇2 + z2δ̇2 + z3α̇+ z4δ̇ + z5 ≤ 0 , (9)
7
−150 −100 −50 0 50 100 150
−150
−100
−50
0
50
100
150
dα/dt cosδ (rad/day)
d
δ
/d
t
(r
a
d
/d
a
y
)
E=0
E=E
min
Fig. 3 An example of admissible region, radar case, in the (α̇ cos δ, δ̇) plane. The region
(painted in grey) is the circular annulus bounded by the two level curves of the energy (E =
Emin) and (E = 0).
where zij depend on the attributable [Tommei et al. 2007]:
z1 = ρ
2
cos
2
δ , z2 = ρ
2
, z3 = ρ q̇ · ρ̂α/2 ,
z4 = ρ q̇ · ρ̂δ/2 , z5 = ρ̇
2
+ c1ρ̇+ c4 −
2µ
p
S(ρ)
.
The boundary of the admissible region is then given by E(α̇, δ̇) = 0 and this equation
represents an ellipse with its axes aligned with the coordinate axes in the (α̇, δ̇) plane.
Actually, in a plane (α̇ cos δ, δ̇), with the axes rescaled according to the metric of the
tangent plane to the celestial sphere, the curves E(α̇, δ̇) = constant are circles.
The region defined by negative geocentric energy, the inside of a circle, is a compact
set, and the problem of defining an inner boundary is much less important than in
the optical attributable case. Anyway, it is possible to define an inner boundary by
constraining the semimajor axis a > rmin, that is by eq. (3), resulting in a concentric
inner circle, thus in an admissible region forming a circular annulus (see Fig. 3).
It is also possible to exclude the ballistic trajectories by imposing the condition (4)
in which α̇, δ̇ are to be considered as variables. The angular momentum is given by
c = r× ṙ = Aα̇+Bδ̇ +C , (10)
A = ρ r× ρ̂α , B = ρ r× ρ̂δ , C = r× q̇+ ρ̇q× ρ̂ .
The condition on the pericenter is expressed by a polynomial inequality of degree 2:
w1α̇
2
+ w2α̇δ̇ + w3δ̇
2
+ w4α̇+ w5δ̇ + w6 ≥ 0 ,
w1 = ||A||2 − 2r2minz1, w3 = ||B||
2 − 2r2min, w5 = 2(B ·C− r
2
minz4),
w2 = 2A ·B, w4 = 2(A ·C− r2minz3), w6 = ||C||
2 − 2rmin(rminz5 + µ).
8
−150 −100 −50 0 50 100 150
−150
−100
−50
0
50
100
150
dα/dt cosδ (rad/day)
d
δ
/d
t
(r
a
d
/d
a
y
)
r
P
=r
min
Fig. 4 An example of admissible region, with the further condition on the pericenter distance
(rP ≥ rmin), bounded by an ellipse.
−150 −100 −50 0 50 100 150
−150
−100
−50
0
50
100
150
dα/dt cosδ (rad/day)
d
δ
/d
t
(r
a
d
/d
a
y
)
r
P
=r
min
r
P
=r
min
Fig. 5 An example of admissible region, with the further condition on the pericenter distance
(rP ≥ rmin), bounded by an hyperbola.
Thus the admissible region can be geometrically described as a region bounded by
three conics: the first two are concentric circles, the third one can be either an ellipse
or an hyperbola (depending on the sign of w1w3 − w22/4), with a different center and
different symmetry axes. Fig. 4 and 5 show the possible qualitatively different cases.
9
0 1 2 3 4
x 10
−4
−6
−4
−2
0
2
4
6
x 10
−3
ρ (AU)
d
ρ/
d
t
(A
U
/d
a
y)
Fig. 6 An example of admissible region, defined by imposing negative geocentric energy,
for an optical attributable, with the Delaunay triangulation. The nodes of the triangulation
corresponding to the ballistic trajectories (on the left of the curve cutting the outer part of
the triangulation) can be discarded.
−1.5 −1 −0.5 0 0.5 1 1.5
−1
−0.5
0
0.5
1
dα/dt cosδ
d
δ/
d
t
Fig. 7 An example of admissible region, defined by imposing Emin ≤ E ≤ 0, for a radar
attributable, with the cobweb sampling. The nodes of the cobweb corresponding to the ballistic
trajectories (between the two branches of the hyperbola) can be discarded.
10
3.3 Virtual debris algorithm
The admissible region can be used to generate a swarm of virtual debris: we sample
it using the Delaunay triangulation [Milani et al. 2004] for the optical case and the
cobweb [Tommei et al. 2007] for the radar case, as shown in Fig. 6 and 7. The condi-
tion on the pericenter is not used at this step, because we could lose some important
geometrical properties: this condition is used as filter, the nodes with a low pericenter
are discarded.
The idea is to generate a swarm of virtual debris Xi, corresponding to the nodes
of the admissible region of one of the two attributables, let us say A1. Then we com-
pute, from each of the Xi, a prediction Ai for the epoch t2, each with its covariance
matrix ΓAi . Thus for each virtual debris Xi we can compute an attribution penalty
Ki4 [Milani and Gronchi 2009] and use the values as a criterion to select some of the
virtual debris to proceed to the orbit computation.
Thus the procedure is as follows: we select some maximum value Kmax for the
attribution penalty and if there are some nodes such that Ki4 ≤ Kmax we proceed to
the correlation confirmation. If this is not the case, we can try with another method,
such as the one described in Sec. 4.
3.4 Universal classification of objects
0 2 4 6 8 10 12 14 16 18 20
−500
−400
−300
−200
−100
0
100
200
300
400
500
ρ (R
⊕
)
d
ρ/
d
t
(R
⊕
/d
a
y)
E
earth
=0
r
p
=r
min
E
sun
=0
dρ/dt=0
L
R
ES
ES
A
A
ISC
ISC
ETA
ETL
IPR
IPL
Fig. 8 Partitioning of the (ρ, ρ̇) half plane ρ > 0 in regions corresponding to different popula-
tions, for an optical attributable with proper motion η = 10.1980. The labels mean: L Launch,
R Reentry, ES Earth Satellite, A Asteroid, ISC Interstellar Comet, ETA ET Arriving, ETL
ET Leaving, IPR Interplanetary Reentry, IPL Interplanetary Launch. rad/day.
11
−600 −400 −200 0 200 400 600
−600
−500
−400
−300
−200
−100
0
100
200
300
400
dα/dt cosδ (rad/day)
d
δ/
d
t
(r
a
d
/d
a
y)
E
earth
=0
E
sun
=0
r
P
=r
min
r
P
=r
min
L/R
ES
ES
A
A
ISC
ISC
ET ET
IPL/IPR
IPL/IPR
Fig. 9 Partitioning of the (α̇ cos δ, δ̇) plane in regions corresponding to different populations,
for a radar attributable with ρ = 1R⊕. The labels mean: L/R Launch or Reentry, ES Earth
Satellite, A Asteroid, ISC Interstellar Comet, ET interstellar launch/reentry, IPL/IPR Inter-
planetary Launch or Reentry.
The method of the admissible region is also useful to provide insight on the re-
lationship between the different populations, in particular how they can mix in the
observations. For a given optical attributable, supposedly computed from a short arc
of optical observations, the Fig. 8 shows the region in the (ρ, ρ̇) half-plane ρ > 0 where
Earth satellites (ES) can be, but also where ballistic trajectories (either launches L or
reentries R) can be, and where an asteroid serendipitously found in the same obser-
vations would be. Other more exotic populations, which are very unlikely, also have
their region in the half plane: e.g., there are regions for direct departure/arrival to the
Earth from interstellar space, which we have labeled as ET trajectories.
The same “universal” figure can be generated from a given radar attributable
(Fig 9). In this case the regions corresponding to different populations partition the
plane (α̇ cos δ, δ̇). The curve Esun = 0, for the heliocentric energy, has been computed
with formulas very similar to the ones for the geocentric energy.
4 Keplerian integrals method
We shall describe a method proposed for the asteroid case in [Gronchi et al. 2009]
and based on the two-body integrals, to produce preliminary orbits starting from two
attributables A1, A2 of the same object at two epochs t1, t2. We assume that the orbit
between t1 and t2 is well approximated by a Keplerian 2-body orbit, with constant
energy E and angular momentum vector c:
(
E(t1)− E(t2) = 0
c(t1)− c(t2) = 0
. (11)
12
4.1 Optical case
Using (5) and by scalar product between with the first equation of (11) and D1 ×D2
we obtain the scalar equation of degree 2:
(D1 ×D2) · (c1 − c2) = q(ρ1, ρ2) = 0 .
Geometrically, this equation defines a conic section in the (ρ1, ρ2) plane. By the formu-
lae giving ρ̇1, ρ̇2 as a function of ρ1, ρ2 derived from the angular momentum equations:
ρ̇1 =
(E2ρ
2
2 + F2ρ2 +G2 −E1ρ21 − F1ρ1 −G1)×D2
||D1 ×D2||2
;
ρ̇2 =
D1 × (E1ρ21 +F1ρ1 +G1 −E2ρ22 −F2ρ2 −G2)
||D1 ×D2||2
the energies E1, E2 can be considered as functions of ρ1, ρ2 only. Thus we obtain:
(
E1(ρ1, ρ2)− E2(ρ1, ρ2) = 0
q(ρ1, ρ2) = 0
,
a system of 2 equations in 2 unknowns, already present in [Taff and Hall 1977]: they
proposed a Newton-Raphson method to solve the system, but this results into a loss of
control on the number of alternate solutions. In [Gronchi et al. 2009] the authors have
applied the same equations to the asteroid problem, and proposed a different approach
to the solution of the system.
The energy equation is algebraic, but not polynomial, because there are denomi-
nators containing square roots. By squaring twice it is possible to obtain a polynomial
equation p(ρ1, ρ2) = 0: the degree of this equation is 24. Thus the system
(
p(ρ1, ρ2) = 0
q(ρ1, ρ2) = 0
has exactly 48 solutions in the complex domain, counting them with multiplicity. Of
course we are interested only in solutions with ρ1, ρ2 real and positive, moreover the
squaring of the equations introduces spurious solutions. Nevertheless, we have found
examples with up to 11 non spurious solutions.
We need a global solution of the algebraic system of overall degree 48, providing at
once all the possible couples (ρ1, ρ2). This is a classical problem of algebraic geometry,
which can be solved with the resultant method: we can build an auxiliary Sylvester
matrix, in this case 22 × 22, with coefficients polynomials in ρ2, and its determinant,
the resultant, is a polynomial of degree 48 in ρ2 only. The values of ρ2 appearing in
the solutions of the polynomial system are the roots of the resultant [Cox et al. 1996].
The computation of the resultant is numerically unstable, because the coefficients
have a wide range of orders of magnitude: we have to use quadruple precision. Once
the resultant is available, there are methods to solve the univariate polynomial equa-
tions, providing at once all the complex roots with rigorous error bounds [Bini 1996].
Given all the roots which could be real, we solve for the other variable ρ1, select the
positive couples (ρ1, ρ2) and remove the spurious ones due to squaring. If the number
of remaining solutions is 0, the attributables cannot be correlated with this method.
13
4.2 Radar case
The formulae for geocentric energy and angular momentum are given by (9) and (10),
polynomials of degree 2 and 1 in the unknowns (α̇, δ̇), respectively. The system (11)
has overall algebraic degree 2: such a system can be solved by elementary algebra.
The angular momentum equations are
A1α̇1 +B1δ̇1 +C1 = A2α̇2 +B2δ̇2 +C2 (12)
that is a system of 3 linear equations in 4 unknowns (α̇1, δ̇1, α̇2, δ2) and can be solved
for three unknowns as a function of one of the four. For example, by scalar product
between (12) and B1 ×A2 we have
α̇1 =
A2 · (B1 ×B2)δ̇2 − (C1 −C2) · (A2 ×B1)
B1 · (A1 ×A2)
and in a similar way we obtain
δ̇1 =
B2 · (A1 ×A2)δ̇2 − (C1 −C2) · (A1 ×A2)
B1 · (A1 ×A2)
,
α̇2 =
A1 · (B1 ×B2)δ̇2 − (C1 −C2) · (A1 ×B1)
B1 · (A1 ×A2)
.
When the equations for, say, (α̇1, α̇2, δ̇1) as a function of δ̇2 are substituted in
the equation for the energies E1(α̇1, δ̇1) = E2(α̇2, δ̇2) we obtain a quadratic equation
in δ̇2, which can be solved by elementary algebra, giving at most two real solutions.
Geometrically, equation (12) can be described by a straight line in a plane, e.g., in
(α̇2, δ̇2), where the energy equation defines a conic section.
4.3 Singularities
There are some cases in which the Keplerian integrals method can not be applied.
In the optical case we have to avoid the condition D1×D2 = (q1×ρ̂1)×(q2×ρ̂2) =
0. This can happen when:
– q1 is parallel to ρ̂1, i.e. the observation at time t1 is done at the observer zenith;
– q2 is parallel to ρ̂2, i.e., the observation at time t2 is done at the observer zenith;
– q1, q2, ρ̂1 and ρ̂2 are coplanar. This case arises whenever a geostationary object
is observed from the same station at the same hour of distinct nights.
As it is normal, the mathematical singularity is surrounded by a neighborhood in which
the method is possible for zero error (both zero observational error and zero rounding off
in the computation), but is not applicable in practice. E.g., for nearly geosynchronous
orbits, even if they are not geostationary, and for hours of observations in different
nights different by few minutes, this method fails.
In the radar case the procedure fails only if the four vectors A1, A2, B1 and B2
do not generate a linear space of dimension 3, i.e., when:
(
Ai · (B1 ×B2) = 0
Bi · (A1 ×A2) = 0
i = 1, 2.
14
For i = 1 we obtain
(
ρ21ρ2[ρ̂δ2 · (r1 × r2)][r1 · (ρ̂α1 × ρ̂δ1)] = 0
ρ21ρ2[ρ̂α2 · (r1 × r2)][r1 · (ρ̂δ1 × ρ̂α1)] = 0
and for i = 2 the formulae are analogous. Thus there is singularity when:
– r1 is parallel to r2;
– ri · (ρ̂δi × ρ̂αi) = cos δi(qi · ρ̂i + ρi) = 0, but this can never happen, apart from
coordinate singularities, because qi · ρ̂i ≥ 0;
– r1 · (ρ̂δ1 × ρ̂αi) = 0 and r1 · (ρ̂δ1 × ρ̂δi) = 0, i.e., ρ̂αi and ρ̂δi for i = 1, 2 belong to
the orbital plane.
4.4 Preliminary orbits
Once a solution of (11) is computed the values of attributable elements can be obtained
for the epochs t̄1 and t̄2, and they can be converted into the usual Keplerian elements:
(aj , ej , Ij , Ωj , ωj , ℓj) , j = 1, 2 ,
where ℓj are the mean anomalies. The first four Keplerian elements (aj , ej , Ij , Ωj) are
functions of the 2-body energy and angular momentum vectors Ej , cj , and are the
same for j = 1, 2. Thus the result can be assembled in the 8-dimensional vector:
H = (V, Φ1, Φ2) , V = (a, e, I,Ω) , Φ1 = (ω1, ℓ1) , Φ2 = (ω2, ℓ2) . (13)
There are compatibility conditions between Φ1 and Φ2 to be satisfied if the two at-
tributables belong to the same object:
ω1 = ω2 , ℓ1 = ℓ2 + n(t̄1 − t̄2) , (14)
where n = n(a) is the mean motion. We cannot demand the exact equality in the
formulae above, because of various error sources, including the uncertainty of the at-
tributable, and the changes on the Keplerian integrals due to the perturbations with
respect to the 2-body model. Thus we need a metric to measure in an objective way
the residuals in the compatibility conditions.
4.5 Covariance propagation
The two attributables A1,A2 used to compute the coefficients of equations (11) have
been computed from the observations by using a least squares fit to the individual
observations, thus 4 × 4 covariance matrices ΓA1 and ΓA2 are available; they can be
used to form the block diagonal 8 × 8 covariance matrix for both attributables ΓA.
The Keplerian integral method allows to compute explicitly the vector H of (13) and,
by means of the implicit function theorem, its partial derivatives, thus it is possible
by the standard covariance propagation formula [Milani and Gronchi 2009][Sec. 5.5] to
compute also ΓH , the covariance of H . With another transformation we can compute
the average elements Φ0 = (Φ1 + Φ2)/2 (as the best value for the angular elements at
15
time t̄0 = (t̄1 + t̄2)/2) and the discrepancy ∆Φ in the compatibility conditions (14),
and to propagate the covariance also to this 8-dimensional vector:
ΓA =⇒ ΓH =⇒ ΓV,Φ0,∆Φ .
The above argument is a generalization of the one in [Gronchi et al. 2009], where ex-
plicit computations are given for the optical attributables case.
In the 8×8 covariance matrix ΓV,Φ0,∆Φ, the lower right 2×2 block is the marginal
covariance matrix of ∆Φ, from which we can compute the normal matrix and the χ2:
C∆Φ = Γ
−1
∆Φ , χ
2
∆Φ = ∆Φ · C∆Φ ∆Φ ,
which can be used as control, that is the discrepancy in the compatibility conditions is
consistent with the observation error and the correlation between the two attributables
is considered possible only if χ2∆Φ ≤ χ
2
max.
The upper left 6× 6 block is the covariance matrix of the preliminary orbit, that is
of the orbital elements set (V, Φ0) (at epoch t̄0). Although this preliminary orbit is just
a 2-body solution, it has an uncertainty estimate, arising from the (supposedly known)
statistical properties of the observational errors. This estimate neglects the influence of
perturbations, such as the spherical harmonics of the Earth gravity field, the lunisolar
differential attraction and the non-gravitational perturbations; nevertheless, if the time
span t̄2 − t̄1 is short, the covariance obtained above can be a useful approximation.
4.6 Precession model
We can generalize the method, including the effect due to the non-spherical shape of
the Earth. The averaged equation for Delaunay’s variables ℓ, g = ω, z = Ω, L =
√
µa,
G = L
√
1− e2 and Z = G cos I are [Roy 2005][Sec. 10.4]:
8
>
>
>
>
>
>
>
>
>
>
>
<
>
>
>
>
>
>
>
>
>
>
>
:
¯̇
ℓ = n− 3
4
n
„
R⊕
a
«2
J2(1− 3 cos2 I)
(1− e2)3/2
¯̇g =
3
4
n
„
R⊕
a
«2
J2(4− 5 sin2 I)
(1− e2)2
¯̇z = −3
2
n
„
R⊕
a
«2
J2 cos I
(1− e2)2
¯̇
L =
¯̇
G =
¯̇
Z = 0
, (15)
where J2 is the coefficient of the second zonal spherical harmonic of the Earth gravity
field. To apply in this case the Keplerian integrals method, we can not use the equations
assuming conservation of the angular momentum. From (15) we can replace (11) with:
8
>
>
>
>
<
>
>
>
>
:
E1 = E2
c1 · ẑ = c2 · ẑ
||c1||2 = ||c2||2
cos(z2) = cos(z1) cos(¯̇z(t̄2 − t̄1))− sin(z1) sin(¯̇z(t̄2 − t̄1))
. (16)
In the optical case the first equation is algebraic and by squaring twice is possible to
obtain a polynomial equation; in the radar case this relation is already polynomial. The
16
second and the third equations are always polynomial, while the last equation needs
to be linearized in the parameter ¯̇z(t̄2 − t̄1):
cos z2 = cos z1 − ¯̇z(t̄2 − t̄1) sin z1 . (17)
The following relationships hold:
cos zi =
ẑ× ci
||ẑ× ci||
· x̂ , sin zi =
ẑ× ci
||ẑ × ci||
· ŷ , a(1− e2) = ||c1||
2
µ
,
cos I =
c1 · ẑ
||c1||
, n =
s
−
8E3
1
µ2
, ¯̇z(t2 − t1) =
ξ
q
−8E3
1
(c1 · ẑ)
||c1||5
where ξ = −3µJ2R2⊕(t̄2 − t̄1)/2. Substituting in (17) we obtain
ẑ× c2
||ẑ× c2||
· x̂ = ẑ× c1
||ẑ × c1||
· x̂−
ξ
q
−8E3
1
(c1 · ẑ)
||c1||5
ẑ× c1
||ẑ× c1||
· ŷ .
Since ||ẑ× c|| = ||c|| sin I is constant we have:
||c1||5[ẑ× (c2 − c1)] · x̂ = −ξ
q
−8E3
1
(c1 · ẑ)(ẑ× c1) · ŷ ,
that is an algebraic equation. Furthermore, by squaring twice in the optical case and
only once in the radar case it is possible to obtain a polynomial equation.
Finally the new compatibility conditions, in place of (14) need to take into account
the precession of the perigee and the secular perturbation in mean anomaly:
g1 = g2 + ¯̇g(t̄1 − t̄2) , ℓ1 = ℓ2 + ¯̇ℓ(t̄1 − t̄2) .
The overall degree of system (16) is summarized in Table 1. We conclude that this
method is unpractical for optical attributables, could be used for radar attributables,
with computational difficulties comparable with the optical case without precession.
Table 1 Degrees of the equations in system (16)
Optical case Radar case
E1 = E2 16 2
c1 · ẑ = c2 · ẑ 2 1
||c1||
2 = ||c2||
2 4 2
cos z2 = cos z1 − ¯̇z(t̄2 − t̄1) sin z1 54 12
Total 6912 48
To solve the problem (even in the optical case) we begin by considering the para-
metric problem ¯̇z = K, where K is constant. Thus we replace (11) with:
(
E1 − E2 = 0
R c1 −RT c2 = 0
where R is the rotation by ∆Ω/2 = K(t̄2− t̄1)/2 around ẑ. This means that for a fixed
value of K the problem has the same algebraic structure of the unperturbed one. The
17
only thing needed is to substitute D1, E1, F1 and G1 with RD1, RE1, RF1 and RG1
in the optical case and A1, B1 and C1 with RA1, RB1 and RC1 in the radar case;
similarly the vectors with index 2 are multiplied by RT .
The compatibility conditions contain the precession of the perigee and the secular
perturbation in mean anomaly, related to the one of the node by linear equations
g1 = g2 +KCg (t̄1 − t̄2) , ℓ1 = ℓ2 + (n+KCℓ)(t̄1 − t̄2) ,
where the coefficients Cg, Cℓ can be easily deduced from (15). Thus we can compute
the χ2∆Φ(K) and set up a simple procedure to minimize this by changing K, then the
control on the acceptability of the preliminary orbit is
min
K
χ
2
∆Φ(K) ≤ χ
2
max .
5 Correlation confirmation
The multiple orbits obtained from the solutions of the algebraic problem are just pre-
liminary orbits, solution of a 2-body approximation (as in the classical methods of
Laplace and Gauss), or possibly of a J2-only problem. They have to be replaced by
least squares orbits, with a dynamical model including all the relevant perturbations.
Even after confirmation by least squares fit, it might still be the case that some
linkages with just two attributables can be false, that is the two attributables might
belong to different objects. This is confirmed by the tests with real data reported in
[Tommei et al. 2009] for the Virtual debris method and in [Milani et al. 2009] for the
Keplerian integrals method. [Gronchi et al. 2009] have found the same phenomenon in
a simulation of the application of the same algorithm to the asteroid case. Thus every
linkage of two attributables needs to be confirmed by correlating a third attributable.
The process of looking for a third attributable which can also be correlated to
the other two is called attribution [Milani 1999,Milani et al. 2001]. From the available
2-attributable orbit with covariance we predict the attributable AP at the time t3 of
the third attributable, and compare with A3 computed from the third set of obser-
vations. Both AP and A3 come with a covariance matrix, we can compute the χ2 of
the difference and use it as a test. For the attributions passing this test we proceed
to the differential corrections. The procedure is recursive, that is we can use the 3-
attributable orbit to search for attribution of a fourth attributable, and so on. This
generates a very large number of many-attributable orbits, but there are many dupli-
cations, corresponding to adding them in a different order.
By correlation management we mean a procedure to remove duplicates (e.g., A =
B = C and A = C = B) and inferior correlations (e.g., A = B = C is superior to both
A = B and to C = D, thus both are removed). The output catalog after this process
is called normalized. In the process, we may try to merge two correlations with some
attributables in common, by computing a common orbit [Milani et al. 2005].
6 Conclusions
We have described two algorithms to solve the linkage problem, that is to compute
an orbit for an Earth-orbiting object observed in two well separated arcs. The first
method exploits the geometric structure of the admissible region of negative geocentric
18
energy orbits, which is sampled to generate virtual orbits. The latter are propagated
in time to find other observations which could belong to the same object. The second
method exploits the integrals of the 2-body problem, which are constant even over a
significant time span and thus should apply to both observed arcs of the same object.
This top level description is enough to understand that the Virtual debris algo-
rithm should be applied to short time intervals between observed arcs, less than one
orbital period or at most a few orbital periods. The Keplerian integrals method can
be used for longer time spans, spanning several orbital periods; it is near to a sin-
gularity for very short time spans and in some other near-resonance conditions, such
as observations of a geosynchronous orbits at the same hour in different nights. We
conclude that each method should be used in the cases in which it is most suitable.
Both algorithms have been tested for the optical case with real data from the ESA Op-
tical Ground Station [Tommei et al. 2009,Milani et al. 2009] with good results. The
analogous algorithms have been tested for asteroids in simulations of next generation
surveys [Milani et al. 2005,Gronchi et al. 2009]. Future work should include the tests
of the radar case and the solution of other related problem, like orbit identification
between two objects for which an orbit is already available.
Acknowledgements Part of this work was performed in the framework of ESOC Contract
No. 21280/07/D/CS, “Orbit Determination of Space Objects Based on Sparse Optical Data”.
References
Bini 1996. Bini, D.A.: Numerical Computation of Polynomial Zeros by Means of Aberth’s
Method. Numerical Algorithms. 13, 179–200 (1996).
Cox et al. 1996. Cox, D. A., Little, J. B., O’Shea, D.: Ideals, Varieties and Algorithms.
Springer (1996).
Gronchi et al. 2009. Gronchi, G.F., Dimare, L., Milani, A.: Orbit Determination with the two-
body Integrals. Submitted (2009).
Maruskin et al. 2009. Maruskin, J. M., Scheeres, D. J., Alfriend, K. T.: Correlation of Optical
Observations of Objects in Earth Orbit. Journal of Guidance, Control, and Dynamics. 32,
194–209 (2009).
Milani 1999. Milani, A.: The Asteroid Identification Problem I: recovery of lost asteroids.
Icarus. 137, 269–292 (1999).
Milani et al. 2001. Milani, A., Sansaturio, Chesley, S.R.: The Asteroid Identification Problem
IV: Attributions. Icarus. 151, 150–159 (2001).
Milani et al. 2004. Milani, A., Gronchi, G.F., de’ Michieli Vitturi, M., Knežević, Z.: Orbit
Determination with Very Short Arcs. I Admissible Regions. Celestial Mechanics & Dynamical
Astronomy. 90, 59–87 (2004).
Milani et al. 2005. Milani, A., Gronchi, G.F., Knežević, Z., Sansaturio, M.E., Arratia, O.:
Orbit Determination with Very Short Arcs. II Identifications. Icarus. 79, 350–374 (2005).
Milani and Gronchi 2009. Milani, A. , Gronchi, G.F.: Theory of orbit determination. Cam-
bridge University Press (2009).
Milani et al. 2009. Milani, A., Gronchi, G. F., Farnocchia, D., Tommei, G., Dimare, L.: Opti-
mization of space surveillance resources by innovative preliminary orbit methods. Proc. of the
Fifth European Conference on Space Debris. 30 March–2 April 2009, Darmstadt, Germany,
SP-672 on CD-Rom.
Roy 2005. Roy, A. E.: Orbital Motion. Institute of Physics Publishing (2005).
Taff and Hall 1977. Taff, L. G., Hall, D. L.: The use of angles and angular rates. I - Initial
orbit determination. Celestial Mechanics & Dynamical Astronomy. 16, 481–488 (1977).
Tommei et al. 2007. Tommei, G., Milani, A., Rossi, A.: Orbit Determination of Space Debris:
Admissible Regions. Celestial Mechanics & Dynamical Astronomy. 97, pp. 289–304 (2007).
Tommei et al. 2009. Tommei, G., Milani, A., Farnocchia, D., Rossi, A.: Correlation of space
debris observations by the virtual debris algorithm. Proc. of the Fifth European Conference
on Space Debris. 30 March–2 April 2009, Darmstadt, Germany, SP-672 on CD-Rom.
Introduction
Observations and attributables
Admissible region theory
Keplerian integrals method
Correlation confirmation
Conclusions
| 0non-cybersec
| arXiv |
Are digit separators allowed before the digits in a hex or binary number?. <p>C++14 introduced the concept of digit separators into literals, along the lines of <code>3'141'592'653'589</code>. Now this is a <em>great</em> feature for readable code but I was wondering whether it allowed quotes <em>before</em> the numeric portion of a <code>0x/0b</code>-type literal. It seems to me that:</p>
<pre><code>unsigned int topThreeBits = 0b'1110'0000;
unsigned int hexNum = 0x'dead'beef;
</code></pre>
<p>is more readable than the one <em>without</em> a leading separator:</p>
<pre><code>unsigned int topThreeBits = 0b1110'0000;
unsigned int hexNum = 0xdead'beef;
</code></pre>
<p>because it clearly delineates the base from the digits.</p>
<p>Since I don't yet have a C++14 compiler, I need confirmation one way or another as to whether it allows this.</p>
<p>I know it doesn't make sense for un-prefixed numbers like <code>'123'456</code>, especially since the parser wouldn't know if it was meant to be a <code>char</code> variable or a numeric literal.</p>
<p>But, for prefixed literals, I can't see there's any confusion as to what the token is meant to be at the point the first <code>'</code> arrives - the <code>0x/0b</code> has already dictated it's going to be a numeric literal.</p>
| 0non-cybersec
| Stackexchange |
It's "Drug Test Day" at work tomorrow, what could possibly go wrong?. | 0non-cybersec
| Reddit |
Vortex radio waves could boost wireless capacity "infinitely" - Thoughts?. | 0non-cybersec
| Reddit |
USB-C Charging Speeds / Charger Outputs. <p>I own a 2016 Macbook (with the USB-C charging) - at the time and in response to all of the reports of poor cables and poor chargers, I bought a meter so I could see what the <strong>throughput of my cables/chargers</strong> was. However, having run some tests I'm now not sure <strong>what to consider normal / what is harmless to the battery</strong>. </p>
<p>For all tests I used an original Apple C-C cable - though was able to replicate with two third party cables I own.</p>
<p>I have the original Apple block charging at 14.3 V / 1.99 A and a third party block that charges the same.</p>
<p>Another third party block which advertises USB PD and 3 A is currently charging at 20 V / 1.43 A</p>
<p>I've done some research online but I can't find any articles that indicate <strong>what a normal USB PD output is relative to the devices that connect to it</strong> and would appreciate any guidance / assistance. </p>
<p>TL;DR: Have Apple charger which charges at one voltage/amperage. Bought several others advertised at PD which are higher voltage, lower amperage. Not sure what is 'safe', or 'fast', or does least overall damage to battery. </p>
| 0non-cybersec
| Stackexchange |
[Spoilers] Pop Team Epic Episode 10 Discussion. *Pop Team Epic*, Episode 10 「銀座ホステス探偵」
[~~*Hoshiiro Girldrop*, The 10th Star「満天のキス」~~](https://i.imgur.com/5vWMZur.jpg)
[A Part seiyuus](https://i.imgur.com/1jGaWyt.jpg) ([Tokui Sora](https://myanimelist.net/people/11361/Sora_Tokui), [Mimori Suzuko](https://myanimelist.net/people/11359/Suzuko_Mimori))
[B Part seiyuus](https://i.imgur.com/qvNuYnE.jpg) ([Koyama Rikiya](https://myanimelist.net/people/113/Rikiya_Koyama), [Takagi Wataru](https://myanimelist.net/people/133/Wataru_Takagi))
--------------------
*Streams*:
[Crunchyroll](http://www.crunchyroll.com/pop-team-epic)
[Funimation](https://www.funimation.com/shows/pop-team-epic)
[HIDIVE](https://www.hidive.com/tv/pop-team-epic)
[Asian Crush](https://www.asiancrush.com/series/018652s/pop-team-epic/)
[Midnight Pulp](https://www.midnightpulp.com/series/012965s/pop-team-epic/)
[Aniplus Asia](https://www.aniplus-asia.com/show/pop-team-epic/)
[AbemaTV](https://abema.tv/video/title/115-48)
[niconico](http://ch.nicovideo.jp/hoshiiro) / [nicolive](http://live.nicovideo.jp/watch/lv310201523)
---
**Show Information:**
[MAL](https://myanimelist.net/anime/35330/Poputepipikku)
[aniDB](https://anidb.net/perl-bin/animedb.pl?show=anime&amp;aid=13067)
[Official site](http://hoshiiro.jp/)
~~[Official site](http://hoshiiro.jp/hoshiiro-girldrop/)~~
[Official PV](https://www.youtube.com/watch?v=otfYAvJzoRE)
~~[Official PV](https://www.youtube.com/watch?v=4EW-9VH_iZI)~~
---
**Previous Discussions**
[Official PV discussion](https://www.reddit.com/r/anime/comments/7jisuh/pop_team_epic_official_pv/)
[Episode 1 discussion](https://www.reddit.com/r/anime/comments/7ok8bk/spoilers_pop_team_epic_episode_1_discussion/)
[Episode 2](https://www.reddit.com/r/anime/comments/7q5dtu/spoilers_pop_team_epic_episode_2_discussion/)
[Episode 3](https://www.reddit.com/r/anime/comments/7rrbnw/spoilers_pop_team_epic_episode_3_discussion/)
[Episode 4](https://www.reddit.com/r/anime/comments/7teaxq/spoilers_pop_team_epic_episode_4_discussion/)
[Episode 5](https://www.reddit.com/r/anime/comments/7v0bel/spoilers_pop_team_epic_episode_5_discussion/)
[Episode 6](https://www.reddit.com/r/anime/comments/7wmhh7/spoilers_pop_team_epic_episode_6_discussion/)
[Episode 7](https://www.reddit.com/r/anime/comments/7y7mwr/spoilers_pop_team_epic_episode_7_discussion/)
[Episode 8](https://www.reddit.com/r/anime/comments/7zxp3m/spoilers_pop_team_epic_episode_8_discussion/)
[Episode 9](https://www.reddit.com/r/anime/comments/81r54x/spoilers_pop_team_epic_episode_9_discussion/)
----
Bonus: [Best Girldrop](https://i.imgur.com/cRfgANQ.jpg) | 0non-cybersec
| Reddit |
Going to see Margaret Atwood tomorrow! Reddit, what are some good questions to ask during the Q&A session?. | 0non-cybersec
| Reddit |
Destination host unreachable using Virtualbox. <p>I just need to be able to call service on client from host and vice versa, unfortunately I just can't make it work.</p>
<p>Host: Windows 7 Professional</p>
<p>Client: Windows 7 Professional with Guest Additions 4.3</p>
<p>I've set up a host-only network.</p>
<p>Host ipconfig:</p>
<pre><code>Ethernet adapter Ethernet:
Link-local IPv6 address . . . : fe80::2901:db57:33a3:d585%11
IPv4 Address: 192.168.1.150
Subnet Mask: 255.255.255.0
Default Gateway: 192.168.1.250
Ethernet Virtualbox Host-only Network:
Link-local IPv6 address . . . : fe80::c4f6:a7be:24ae:59e7%13
IPv4 Address . . . . . . . . . . . : 192.168.56.1
Subnet Mask . . . . . . . . . . : 255.255.255.0
Default Gateway . . . . . . . . . . :
...
</code></pre>
<p>Client ipconfig:</p>
<pre><code>IPv4 Address: 192.168.56.101
Subnet Mask: 255.255.255.0
Default Gateway:
...
</code></pre>
<p>The firewall on client is turned off, and there is no antivirus. When I try to ping the host from client, it says </p>
<pre><code>ping 192.168.56.1
Reply from 192.168.56.101: Destination host unreachable
</code></pre>
<p>Similar message appears when pinging client from host. I'd like to ask what could the problem be. I'd be thankful for any advice.</p>
<p>EDIT:
route print</p>
<pre><code>IPv4 Route Table
===========================================================================
Active Routes:
Network Destination Netmask Gateway Interface Metric
0.0.0.0 0.0.0.0 192.168.1.250 192.168.1.150 266
127.0.0.0 255.0.0.0 On-link 127.0.0.1 306
127.0.0.1 255.255.255.255 On-link 127.0.0.1 306
127.255.255.255 255.255.255.255 On-link 127.0.0.1 306
192.168.1.0 255.255.255.0 On-link 192.168.1.150 266
192.168.1.150 255.255.255.255 On-link 192.168.1.150 266
192.168.1.255 255.255.255.255 On-link 192.168.1.150 266
192.168.56.0 255.255.255.0 On-link 192.168.56.1 266
192.168.56.1 255.255.255.255 On-link 192.168.56.1 266
192.168.56.255 255.255.255.255 On-link 192.168.56.1 266
224.0.0.0 240.0.0.0 On-link 127.0.0.1 306
224.0.0.0 240.0.0.0 On-link 192.168.1.150 266
224.0.0.0 240.0.0.0 On-link 192.168.56.1 266
255.255.255.255 255.255.255.255 On-link 127.0.0.1 306
255.255.255.255 255.255.255.255 On-link 192.168.1.150 266
255.255.255.255 255.255.255.255 On-link 192.168.56.1 266
===========================================================================
Persistent Routes:
Network Destination Netmask Gateway Metric
0.0.0.0 0.0.0.0 192.168.1.250 Default
===========================================================================
</code></pre>
| 0non-cybersec
| Stackexchange |
[WP] Wizard thinks they're a talented summoner capable of summoning a demon, but in truth, his summoning is pitiful, you're just opening the portal from the other side, you're not even bound to him or anything, you're just being nice.. | 0non-cybersec
| Reddit |
"Those Were the Days," Aliya Chen, Digital, 2016. | 0non-cybersec
| Reddit |
That boy’s name?. | 0non-cybersec
| Reddit |
Ubuntu 12.10 Installation Hangs at 'Preparing to Install Ubuntu'. <p>I have downloaded the Ubuntu 12.10 i386 Desktop ISO both via HTTP & Torrent Download.
I have attempted the install via CD & Bootable USB (created using YUMI from Pendrive Linux), each using a different ISO (to rule out corruption).</p>
<p>I can boot from CD & USB and use the live Ubuntu, but each time I try to Install it, Ubiquity hangs at the "Preparing to Install Ubuntu" screen.
It doesn't matter if i check or uncheck the 'Download updates while installing' and/or 'Install this third party software' options.</p>
<p>I am attempting install on a Dell Inspiron 6000 Notebook (Pentium M 1.60GHz, 2.0GB RAM, 160GB HDD) with an existing Windows Partition. The install from CD worked without incident on my Triple Boot MacBook Pro.</p>
<p>Also, the System Log app will not open, unsure if this is related.</p>
| 0non-cybersec
| Stackexchange |
Bootstrap with a fixed width grid and images that should span the window width. <p>I would like to display the image outside the containers <code>width</code>, filling up to right edge of the browser.</p>
<p>At the moment I'm doing this with JavaScript, but I feels and looks clumsy, and SEO is unfriendly because of missing ALT-tags and also introduces problems when the css triggers different viewport settings for smaller screens. </p>
<p>Is there a documentation chapter I've missed?</p>
<p>My current set up:</p>
<pre><code><div class="container-fluid screen-image" style="background: url('image.png') no-repeat;" data-position-object="screen1">
<div class="container">
<div class="col-md-6">
my content
</div>
<div class="col-md-6" id="screen1">
</div>
</div>
</div>
</code></pre>
<p>Javscript:</p>
<pre><code>$(document).ready(function () {
setScreenPositions();
$(window).on('resize', function() {
setScreenPositions();
});
function setScreenPositions() {
$('.screen-image').each(function() {
var $this = $(this),
$positionObject = $('#' + $this.attr('data-position-object'));
$this.css('background-position', $positionObject.position().left + 'px 60px');
});
}
});
</code></pre>
<p>To better illustrate what I'm after, I've put my Word drawing skills to the test since I'm not at my own computer at the moment ;)
<a href="https://i.stack.imgur.com/Vu25Q.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Vu25Q.png" alt="enter image description here"></a></p>
| 0non-cybersec
| Stackexchange |
Best way to parse nested json from an api response. <p>So I have some code to generate a json response from an api:</p>
<pre class="lang-py prettyprint-override"><code>r4 = requests.get(url, params=mlp)
mlpr = r4.json()
</code></pre>
<p>1 row of the response looks like this.</p>
<pre><code>'command': 'SELECT', 'rowCount': 134, 'oid': None, 'rows': [{'match_id': 5334428840, 'start_time': 1586029157, 'leagueid': 11823, 'patch': '7.25', 'name': 'ESL One Los Angeles 2020 Online powered by Intel', 'radiant_team': 'Cyber Legacy', 'dire_team': 'B8', 'picks_bans': [{'is_pick': False, 'hero_id': 98, 'team': 0, 'order': 0}, {'is_pick': False, 'hero_id': 95, 'team': 1, 'order': 1}, {'is_pick': False, 'hero_id': 66, 'team': 0, 'order': 2}, {'is_pick': False, 'hero_id': 43, 'team': 1, 'order': 3}, {'is_pick': False, 'hero_id': 49, 'team': 0, 'order': 4}, {'is_pick': False, 'hero_id': 110, 'team': 1, 'order': 5}, {'is_pick': False, 'hero_id': 79, 'team': 0, 'order': 6}, {'is_pick': False, 'hero_id': 106, 'team': 1, 'order': 7}, {'is_pick': True, 'hero_id': 96, 'team': 0, 'order': 8}, {'is_pick': True, 'hero_id': 86, 'team': 1, 'order': 9}, {'is_pick': True, 'hero_id': 129, 'team': 1, 'order': 10}, {'is_pick': True, 'hero_id': 50, 'team': 0, 'order': 11}, {'is_pick': False, 'hero_id': 12, 'team': 0, 'order': 12}, {'is_pick': False, 'hero_id': 77, 'team': 1, 'order': 13}, {'is_pick': True, 'hero_id': 128, 'team': 1, 'order': 14}, {'is_pick': True, 'hero_id': 121, 'team': 0, 'order': 15}, {'is_pick': True, 'hero_id': 41, 'team': 1, 'order': 16}, {'is_pick': True, 'hero_id': 42, 'team': 0, 'order': 17}, {'is_pick': False, 'hero_id': 126, 'team': 1, 'order': 18}, {'is_pick': False, 'hero_id': 65, 'team': 0, 'order': 19}, {'is_pick': True, 'hero_id': 31, 'team': 0, 'order': 20}, {'is_pick': True, 'hero_id': 45, 'team': 1, 'order': 21}]}
</code></pre>
<p>As you can see the picks_bans "Column has a nested dictionary of 3 additional columns I need to pull out and spread across each match ID.</p>
<p>Here is the code I am using to put my response into an initial <code>Dataframe</code>, but it is only getting me to the initial level.</p>
<pre class="lang-py prettyprint-override"><code>mlpr_df = pd.DataFrame(mlpr.get('rows'))
mlpr_df
</code></pre>
<p>[example dataframe][1]</p>
<p>How do I go about unnesting the <code>picks_bans</code> column appropriately?</p>
<p>Edit: I attempted to change the code to:</p>
<pre><code>r4 = requests.get(url, params=mlp)
mlpr = r4.json()
data = mlpr.get('rows')
df = pd.concat([pd.DataFrame(data),
json_normalize(data['picks_bans'])],
axis=1).drop('picks_bans', 1)
</code></pre>
<p>I receive and error that says "list indices must be integers or slices, not str"</p>
| 0non-cybersec
| Stackexchange |
Given a positive integer n, if for all integers a and b, n|ab implies n|a or n|b, then n is prime.. <p>I'm new here and I'm stuck on a problem with my homework. I know that if ab/n=m, a/n=p, and b/n=q where m, p and are integers and I have to show that n can only be divided by one and itself but I'm not sure how to get there. Any help will be appreciated. Thanks</p>
| 0non-cybersec
| Stackexchange |
Spanish royal's property impounded in corruption case. | 0non-cybersec
| Reddit |
Is there a Twitter-like app that can be installed for a corporate intranet?. <p>I think that the Twitter model of communication would work very well for disseminating information and informal discussion in the corporate world.</p>
<p>Is there a Twitter-like web-app that can be installed at the corporate level to provide this?</p>
| 0non-cybersec
| Stackexchange |
How to get callback from Room Database android Kotlin. <p>I want to get just row count as Int value from room database,
not from initialized <code>LiveData</code> such as <code>livedata.value?.size</code></p>
<p><strong>Dao class</strong></p>
<pre><code> @Dao
interface MyDao {
@Query("SELECT COUNT(*) FROM User")
fun getUserCount(): Int
}
</code></pre>
<p><strong>Repository class</strong></p>
<pre><code>class MyRepository(private val myDao: MyDao) {
fun getUserCount() = myDao.getUserCount()
}
</code></pre>
<p><strong>ViewModel class</strong></p>
<pre><code>class MyViewModel(application: Application) : AndroidViewModel(application) {
fun getUserCount() = myRepository.getUserCount()
}
</code></pre>
<p>This is what I want. But as you know we need to access room database at background thread, not at mainthread</p>
<p>so I changed the code like <a href="https://codelabs.developers.google.com/codelabs/android-room-with-a-view-kotlin/#8" rel="nofollow noreferrer">this</a></p>
<p><strong>Dao class</strong></p>
<pre><code> @Dao
interface MyDao {
@Query("SELECT COUNT(*) FROM User")
suspend fun getUserCount(): Int
}
</code></pre>
<p><strong>Repository class</strong></p>
<pre><code>class MyRepository(private val myDao: MyDao) {
suspend fun getUserCount() = myDao.getUserCount()
}
</code></pre>
<p><strong>ViewModel class</strong></p>
<pre><code>class MyViewModel(application: Application) : AndroidViewModel(application) {
fun getUserCount() = viewModelScope.launch {
myRepository.getUserCount()
}
}
</code></pre>
<p>if row count is 1, How can I get "1" as callback?</p>
| 0non-cybersec
| Stackexchange |
IPhone UITextField not showing edit caret or clearing placeholder text when tapped. <p>I have a window within an iPhone application, which is displayed modally to allow the user to enter their settings for a web service upon 'first run'. </p>
<p>The text fields have helper text set, and when you tap them the keyboard shows and allows you to enter text.</p>
<p>Unfortunately the text fields do not clear the helper text, show the edit caret or show the text being entered (as in the screenshot below).</p>
<p><a href="https://i.stack.imgur.com/C3naD.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/C3naD.png" alt="The wonderful issue..."></a>
</p>
<p>Any suggestions? </p>
<p>The window is being displayed with <code>[self presentModalViewController:<controller_name> animated:YES];</code>, which may or may not be the cause of this issue - when I run the UI via the Interface Builder 'test' application the text boxes respond like normal.</p>
<p><code>Clear when editing begins</code> has been set for both fields.</p>
<p>Thanks in advance!</p>
<p><em>Edited: More information</em>
After the info Bart Gottschalk provided I thought I should add some more information. First, the application is a Navigation Based Application.</p>
<p>Secondly, the test app Bart recommended worked fine, so that takes the modal window and the view out of the equation.</p>
<p>Third, I was presenting the modal view when the <code>-(void)viewWillAppear...</code> delegate method was being called - which may very well be the wrong place... however I'm not 100% sure if I should be presenting the modal view from within the <code>didFinishLaunchingWithOptions</code> of the App Delegate...</p>
<p>(this is happening on Simulator and iPhone 3.1.3)</p>
| 0non-cybersec
| Stackexchange |
When is clone() and fork better than pthreads?. <p>I am beginner in this area.</p>
<p>I have studied <code>fork()</code>, <code>vfork()</code>, <code>clone()</code> and pthreads.</p>
<p>I have noticed that <code>pthread_create()</code> will create a thread, which is less overhead than creating a new process with <code>fork()</code>. Additionally the thread will share file descriptors, memory, etc with parent process.</p>
<p>But when is <code>fork()</code> and <code>clone()</code> better than pthreads? Can you please explain it to me by giving real world example?</p>
<p>Thanks in Advance.</p>
| 0non-cybersec
| Stackexchange |
How to use spot instance with amazon elastic beanstalk?. <p>I have one infra that use amazon elastic beanstalk to deploy my application.
I need to scale my app adding some spot instances that EB do not support.</p>
<p>So I create a second autoscaling from a launch configuration with spot instances.
The autoscaling use the same load balancer created by beanstalk.</p>
<p>To up instances with the last version of my app, I copy the user data from the original launch configuration (created with beanstalk) to the launch configuration with spot instances (created by me).</p>
<p>This work fine, but:</p>
<ol>
<li><p>how to update spot instances that have come up from the second autoscaling when the beanstalk update instances managed by him with a new version of the app?</p>
</li>
<li><p>is there another way so easy as, and elegant, to use spot instances and enjoy the benefits of beanstalk?</p>
</li>
</ol>
<p><strong>UPDATE</strong></p>
<p>Elastic Beanstalk add support to spot instance since 2019... see:
<a href="https://docs.aws.amazon.com/elasticbeanstalk/latest/relnotes/release-2019-11-25-spot.html" rel="nofollow noreferrer">https://docs.aws.amazon.com/elasticbeanstalk/latest/relnotes/release-2019-11-25-spot.html</a></p>
| 0non-cybersec
| Stackexchange |
rDNS 'zone [xxx] has no address record (A or AAAA). <p>teaching myself some server tricks.</p>
<p>Getting trouble with bind9 on debian8.</p>
<pre><code>named-checkzone pro.lan db.pro.lan.inv
zone pro.lan/IN: NS 'server.pro.lan' has no address records (A or AAAA)
</code></pre>
<p>my db.pro.lan.inv</p>
<pre><code> $TTL 604800
@ IN SOA server.pro.lan. root.pro.lan. (
2015052402
604800
86400
2419200
604800
)
@ IN NS server.pro.lan.
254 IN PTR server.pro.lan.
10 IN PTR nas.pro.lan.
</code></pre>
<p>Any idea ?</p>
<p>Thks.</p>
| 0non-cybersec
| Stackexchange |
Dry-aged ribeye sous vide (second attempt to get it right!). | 0non-cybersec
| Reddit |
gnome window top corners problem. <p>As you can see on the screenshot below, there is a problem on top of the windows. How can I fix this?</p>
<p>I installed ubuntu 16.04 then switched to gnome on login screen.</p>
<p><a href="https://i.stack.imgur.com/dRiPJ.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/dRiPJ.png" alt="screenshot"></a></p>
| 0non-cybersec
| Stackexchange |
Install a specific RHEL point release. <p>Is there a way to effectively <code>yum update</code> to a specific point release in RHEL 5 and 6?</p>
<p>When a new point release is rolled out, the powers that be in my organisation put it through acceptance testing, which can take some time to complete - currently I've heard that the fairly newly released RHEL 6.7 breaks something to do with Veritas that a large proportion of the organisation uses and so we have not yet accepted it.</p>
<p>There are also times when we are building a server for a project and the project have already agreed that a vendor can have a specific version of RHEL (we seem to have a number of vendors that say their applications are only certified to run on specific versions).</p>
<p>The majority of our servers are virtualised (VMware) and are 'built' by deploying a pre-made/tested/QAd/approved template, then configured with the correct network settings/users/etc. - we note that there are better ways, and they are being explored and set through - ah hem- various acceptance testing...</p>
<p>We have a couple of mirror repo servers (one for 5, one for 6), but no Satellite.</p>
<p><strong>So, if I have just deployed a VM which is sitting at RHEL 6.5 and I want to get to the latest <em>accepted</em> version of 6.6, is there anyway I can do this?</strong></p>
<p>It seems that it <em>should</em> be easy, just install the package versions that comprise a specific release, but I can't find a way to easily do this, or even scrape a list and have it upgrade...</p>
| 0non-cybersec
| Stackexchange |
El Capitan, Yosemite National Park [3024x4032] [OC]. | 0non-cybersec
| Reddit |
How to show that the matrix exponential is invertible for non-diagonalizable matrix A,. <p>I have shown the easy case, when A is diagonalizable.</p>
<p>But I am stuck on the case when A is not.</p>
<p>So, I put A in its Jordan canonical form. Then say A = $SJS^{-1}$.</p>
<p>Then $e^A = Se^JS^{-1}$, </p>
<p>where $e^J$ is an upper triangular matrix with the Jordan blocks exponentiated. </p>
<p>Now for each Jordan block, I have that </p>
<p>$$e^{J_i} = e^{\lambda_i I + N}$$</p>
<p>where N is elementary nilpotent. But since scalar matrices commute with all matrices, it commutes with N.</p>
<p>Then
$$e^{J_i} = e^{\lambda_i I + N} = e^{\lambda_i}e^{N}$$
where $e^{\lambda_i}$ is a diagonal matrix with non-zero diagonal, hence it is invertible / has non-zero determinant. What can I do with the $e^N$ factor? I know that it has a finite expansion, since it is nilpotent:</p>
<p>$$e^N = I + N + ... + \frac {N^k}{k!}$$</p>
<p>I'm not sure where to go from here...</p>
<p>Thanks,</p>
| 0non-cybersec
| Stackexchange |
Tattoo care in the sun. Hey, I'm currently in Thailand where I'm going to be around the beach a lot and in the sun regularly. I got a half sleeve done on my lower arm so it's always going to be exposed.
Today at the beach, I was whacking on 50+ SPF on my tattoo and I still managed to get burnt a little bit on it. Previously in the trip I was using 110 SPF spray, but I still tanned on my arm.
Is there anyway to completely stop my lower arm from getting burnt/tanned? (Other then staying out of the sun)
If not, any tips on how to reduce the impact the sun has on my tat? | 0non-cybersec
| Reddit |
Does anyone else prefer games that go with an actual art style, rather than trying to mimic real life?. | 0non-cybersec
| Reddit |
Difference between hardware based virtualization and software based virtualization in VPS Hosting?. <p>I want to know the difference between these two kinds of virtualization in VPS Hosting. Which one is used by hosting companies? And also tell which one is best? Commonly used software for software based partitioning?</p>
| 0non-cybersec
| Stackexchange |
Happy Fathers day!. | 0non-cybersec
| Reddit |
Do both versions (invariant and primary) of the Fundamental Theorem for Finitely Generated Abelian Groups hold at the same time?. <p>So there are the two versions of the Fundamental Theorem for Finitely Generated Abelian Groups (FTFGAG). I take the following from A First Course in Abstract Algebra by Fraleigh. The first is as follows:</p>
<p>FTFGAG 1: Every finitely generated abelian group $G$ is isomorphic to a direct product of cyclic groups in the form
$$ G \cong \mathbb{Z}_{p_1^{r_1}} \times \cdots \times \mathbb{Z}_{p_n^{r_n}} \times \mathbb{Z} \times \cdots \times \mathbb{Z}$$
where $p_i$ are primes (not necessarily distinct) and $r_i$ are positive integers. </p>
<p>But then we also have the second version:</p>
<p>FTFGAG 2: Every finitely generated abelian group $G$ is isomorphic to a direct product of cyclic groups in the form
$$ G \cong \mathbb{Z}_{m_1} \times \cdots \times \mathbb{Z}_{m_r} \times \mathbb{Z} \times \cdots \times \mathbb{Z}$$
where $m_1 | m_2 | \cdots | m_r$.</p>
<p>My question is whether these two hold at all times? So say for $\mathbb{Z}_{20}$, do we have $\mathbb{Z}_{20} \cong \mathbb{Z}_2 \times \mathbb{Z}_2 \times \mathbb{Z}_5 \cong \mathbb{Z}_4 \times \mathbb{Z}_5 \cong \mathbb{Z}_2 \times \mathbb{Z}_{10}$, even though $10$ is not a power of a prime (though of course $2|10$)?</p>
<p>I've also seen statements of the Chinese Remainder Theorem (CRT) which say that $\mathbb{Z}_{nm} \cong \mathbb{Z}_n \times \mathbb{Z}_m$ if and only if $\gcd(n,m)=1$. Does this not contradict $\mathbb{Z}_{20} \cong \mathbb{Z}_2 \times \mathbb{Z}_{10}$ from above? Or is treating $\mathbb{Z}_n$ and $\mathbb{Z}_m$ as rings in the CRT what makes the situation different? I guess what I'm asking in a nutshell is: why don't the primary and invariant forms of the structure theorems for abelian groups (and also modules over PIDs, etc) contradict each other?</p>
<p>Many thanks for any answers.</p>
<hr>
<p><strong>Edit:</strong> So it seems that I didn't see <a href="https://math.stackexchange.com/questions/361239/why-doesnt-the-chinese-remainder-theorem-contradict-the-fundamental-theorem-of?rq=1">this</a> question which basically answers mine. CRT gives us a way of decomposition but FTFGAG only tells us that <em>some</em> decomposition is always possible. So for FTFGAG 1, $\mathbb{Z}_4 \times \mathbb{Z}_5$ suffices, for FTFGAG 2, $\mathbb{Z}_{20}$ suffices, and for the CRT $\mathbb{Z}_{20} \cong \mathbb{Z}_4 \times \mathbb{Z}_5$ works.</p>
| 0non-cybersec
| Stackexchange |
StateT over Cont. Why is my state not being reset?. <p>I'm playing with the <code>Cont</code> monad tricks described <a href="https://mail.haskell.org/pipermail/haskell-cafe/2005-July/010623.html" rel="noreferrer">here</a> and in <a href="https://stackoverflow.com/questions/5193876/goto-in-haskell-can-anyone-explain-this-seemingly-insane-effect-of-continuation">this SO question</a>.</p>
<p>This function lets you "jump back" to earlier in the computation, taking a parameter so you can do things differently:</p>
<pre><code>import Control.Monad.Cont
import Control.Monad.State.Strict
import Control.Monad.Writer.Strict
getCC' :: MonadCont m => a -> m (a,a -> m b)
getCC' x0 = callCC (\c -> let f x = c (x, f) in return (x0, f))
</code></pre>
<p>I have these toy examples of monad transformers on top of <code>Cont</code>:</p>
<pre><code>foo :: WriterT String (Cont String) ()
foo = do
(stop,loop) <- getCC' False
if stop
then do tell "bbb"
else do tell "aaa"
loop True
foo' :: StateT String (Cont String) ()
foo' = do
(stop,loop) <- getCC' False
if stop
then do modify $ \s -> s ++ "bbb"
else do modify $ \s -> s ++ "aaa"
loop True
</code></pre>
<p>In the first example (as <a href="https://stackoverflow.com/a/5203603/1364288">explained</a> in the linked SO question) the effects of <code>Cont</code> have "priority" over the effects of the <code>WriterT</code>. When we reset the computation, the log is lost:</p>
<pre><code>*Main> print $ runCont (execWriterT foo) id
"bbb"
</code></pre>
<p>The second example does exactly the same thing, only using <code>StateT</code> instead of <code>WriterT</code>. However, in this case the log is preserved!</p>
<pre><code>*Main> print $ runCont (execStateT foo' "") id
"aaabbb"
</code></pre>
<p>What is the explanation of this discrepancy?</p>
| 0non-cybersec
| Stackexchange |
The seasons in the overview should be sorted from current to old. | 0non-cybersec
| Reddit |
dell inspiron 15 3552 ubuntu 18.04 lts installation. <p>I'm trying to install ubuntu 18.04 lts on my laptop dell inspiron 15 3552. It's in the list of the supported devices. I create a bootable usb using the "Startup disk creator" but when I load from this usb I see the menu with the point "install ubuntu". I click on it and then get nothing but a black screen. Could you please point me ti the right direction? What's the problem?</p>
<p>Thanks.</p>
| 0non-cybersec
| Stackexchange |
Eliminate certificate warning when users access Outlook/Exchange 2010 on split domain setup. <p>I have an internally-hosted Exchange 2010 Server with an internal domain, <code>EXCHANGE0.COMPANY.COM</code>.</p>
<p>I have configured all users to access Outlook (even internally) using Outlook-over-HTTP. To do so I have set up a client access certificate for the externally-facing domain <code>mail.company.com</code>.</p>
<p>The problem is that whenever users open Outlook they are promptly greeted by certificate warnings of the mismatch between <code>mail.company.com</code> and <code>EXCHANGE0.COMPANY.COM</code>. I would like to eliminate these warnings and I feel there is a way to do so either through DNS or through Exchange. I am just not sure what to do.</p>
<p>AutoDiscover is configured using the SRV method if that matters at all.</p>
<p>EDIT: Configuration on clients looks as follows</p>
<p>Exchange Server: EXCHANGE0.COMPANY.COM
Connect using Outlook Anywhere (HTTP): on fast and slow connections, connect to mail.company.com and only trust msstd:mail.company.com</p>
<p>Name on certificate is mail.company.com, but Outlook was expecting EXCHANGE0.COMPANY.COM</p>
| 0non-cybersec
| Stackexchange |
My friend works at a pet store and she sent me this.... | 0non-cybersec
| Reddit |
Is an anonymous FTP user always a risk (even if this user doesn't have access to anything)?. <p>I found some FTP servers in a network that seem to allow login with an anonymous FTP user. I confirmed this with the <code>ftp-anon</code> NSE script in Nmap.</p>
<pre><code>PORT STATE SERVICE
21/tcp open ftp
|_ftp-anon: Anonymous FTP login allowed (FTP code 230)
</code></pre>
<p>But when I try to connect with an anonymous user using an FTP client like FileZilla, it seems that this FTP user does not have any rights.</p>
<pre><code>Status: Connecting to X.X.X.X:21...
Status: Connection established, waiting for welcome message...
Status: Insecure server, it does not support FTP over TLS.
Status: Server does not support non-ASCII characters.
Status: Logged in
Status: Retrieving directory listing...
Command: PWD
Response: 257 "/" is current directory
Command: TYPE I
Response: 200 Command successful
Command: PASV
Response: 227 Entering Passive Mode(X,X,X,X,004,001)
Command: LIST
Error: The data connection could not be established: EAI_NONAME - Neither nodename nor servname provided, or not known
Error: Connection timed out after 20 seconds of inactivity
Error: Failed to retrieve directory listing
Status: Disconnected from server
</code></pre>
<p>So am I right to assume that this FTP server does allow a connection with an anonymous user but that anonymous user doesn't have any rights? If so, would the right recommendation still be to disallow anonymous FTP users or won't that make any difference? Also, what are the risks of above scenario?</p>
| 0non-cybersec
| Stackexchange |
Launch Icons: how do I get rid of them?. <p>After browsing a commercial site www.kohls.com I suddenly got some "launch icons" in my bottom bar towards the right side. They automatically go to pages on Kohl's website. I cannot get rid of them - tried everything, including even uninstalling and reinstalling Firefox. This has never happened on other websites. Could Kohl's website be installing malware? In any case, how do I get rid of them, short of a complete Ubuntu reinstall? I am using Ubuntu 12.04, correctly updated, but with Gnome GUI instead of "unity" which I do not like at all.</p>
<p>Screenshot at: <a href="https://i.imgur.com/ijAVoIE.png?1" rel="nofollow noreferrer">http://i.imgur.com/ijAVoIE.png?1</a></p>
| 0non-cybersec
| Stackexchange |
Why does GNOME Shell Extensions installation from website not work?. <p>I'm trying to install some GNOME Shell Extensions on Ubuntu 16.04 (64bit) from the web site extensions.gnome.org. I'm using Gnome 3.18 with LightDM.</p>
<p>I verified that Firefox has the Gnome Shell Integration plugin enabled, and the extension page loads with the on/off slider correctly displayed.</p>
<p>When I switch the slider to "on", I accept the dialog about installation but then nothing happens. After reloading the page, the slider is still "off".
Thus the extension is actually NOT installed and the directory .local/share/gnome-shell/extensions/ remains unchanged.</p>
<p>I read older discussions whereas someone were suggesting to reset GNOME settings to default, as discussed here: <a href="https://askubuntu.com/questions/56313/how-do-i-reset-gnome-to-the-defaults">How do I reset GNOME to the defaults?</a>, but that did not solve the issue.</p>
| 0non-cybersec
| Stackexchange |
Circles tangential to the real line. <p>For any two <em>distinct</em> points $a,b$ in the upper half plane, prove that there is a circle passing through $a$ and $b$ that is tangential to the extended real line.</p>
<p>Seems obvious, but how would you go about proving this?</p>
| 0non-cybersec
| Stackexchange |
Prove that $\sum (-1)^n f_n(x) $ uniformly converges in I. <p>I need some clue on the proof of the following question:</p>
<p>Suppose $f_n$ is a series of functions which are defined in I, descending there to 0. Assume that:
$\exists a \in I : f_n(x) \leq f_n(a)$
for every $x \in I$ and $n \in \mathbb{N}$</p>
<p>Prove that $\sum (-1)^n f_n(x) $ uniformly converges in I</p>
<p>Thanks :)</p>
| 0non-cybersec
| Stackexchange |
I teach myself to draw by drawing everything I see. | 0non-cybersec
| Reddit |
Dokku redirects to another domain when requested site is down. <p>I have Dokku installed on a server, with multiple sites/domains deployed to it. When one of my sites goes down, all HTTP requests to it get redirected (for some reason) to another site. This is confusing. I'm expecting Dokku to show some error page in this case. Is it the default behavior or I did something wrong?</p>
<p>PS. This is the problem: <a href="https://github.com/dokku/dokku/issues/2602" rel="noreferrer">https://github.com/dokku/dokku/issues/2602</a></p>
| 0non-cybersec
| Stackexchange |
NTFS wrong used space count. <p>So I have this NTFS HD drive and when I select all the files and directories in it's root (including hidden and system files) the total <em>Size on disk</em> is 460 GB, but when I look on the disk properties it says that the <em>used space</em> is 464 GB. There must be something wrong...</p>
<p>P.S.: I run Win XP Pro SP3, don't know if this matters.
P.P.S: No, it's not about GiB vs GB.</p>
| 0non-cybersec
| Stackexchange |
cmake not compiling with qt4. <p>I am trying to build AMAROK on ubuntu 12. I have although installed Qt5 already but i am getting the following error. Please help me.</p>
<pre><code>CMake Error at /usr/share/cmake-2.8/Modules/FindPackageHandleStandardArgs.cmake:108 (message): Could NOT find Qt4: Found unsuitable version "4.8.2", but required is at least "4.8.3" (found /usr/bin/qmake) Call Stack (most recent call first): /usr/share/cmake-2.8/Modules/FindPackageHandleStandardArgs.cmake:313 (_FPHSA_FAILURE_MESSAGE) /usr/share/cmake-2.8/Modules/FindQt4.cmake:1393 (FIND_PACKAGE_HANDLE_STANDARD_ARGS) CMakeLists.txt:83 (find_package)
</code></pre>
| 0non-cybersec
| Stackexchange |
All colorations of horses. | 0non-cybersec
| Reddit |
Pi vs arduino rule of thumb. | 0non-cybersec
| Reddit |
Someone got bored at HTC. http://i.imgur.com/3SV30Ew.jpg | 0non-cybersec
| Reddit |
How to draw this pyramid with TeX?. <p>I draw this pyramid with GeoSpacw. How to draw this figure with TeX?</p>
<p><img src="https://i.stack.imgur.com/RWPTr.gif" alt="enter image description here"></p>
<p>Where:</p>
<ul>
<li><p><em>M</em> is midpoint of the segment <em>SA</em>;</p></li>
<li><p><em>I</em> is midpoint of the segment <em>SD</em>;</p></li>
<li><p><em>H</em> is project of the point <em>A</em> on the line <em>SO</em>;</p></li>
<li><p><em>ABKE</em> is a is a parallelogram;</p></li>
<li><p>The line passing through <em>S</em> and parallel to the line <em>AB</em>.</p></li>
</ul>
| 0non-cybersec
| Stackexchange |
PSA to Wedding and Event Coordinators. If your event feeds the photographer and other vendors, feed them first. As a photographer, I have worked too many events and weddings where we were served after all of the guests. The problem with this is that as soon as the guests are done eating, we as vendors need to be working. If we are served after the guests, we are lucky if we have enough time to eat by the time we need to be working again. Friday night, I worked a wedding and we were fed after the guests. We had about five minutes to shovel down our food before we had to be shooting again. Last night, I shot another wedding and they fed us before the guests. We had plenty of time to relax for a bit and eat our food. So, please feed us first.
tl;dr Feed your photographers and vendors before the guests. | 0non-cybersec
| Reddit |
Its like catching it at a wedding, but better.. | 0non-cybersec
| Reddit |
How can I remove the bar in the react-select?. <p>I am trying to improve my UI for the react-select. I did some researches online, but I still cannot figure out how to remove the bar in the select.</p>
<p>Can I style the control component to remove the bar? How？</p>
<pre><code>import React from 'react';
import chroma from 'chroma-js';
import { colourOptions } from './docs/data';
import Select from 'react-select';
const dot = (color = '#ccc') => ({
alignItems: 'center',
display: 'flex',
':before': {
backgroundColor: color,
borderRadius: 10,
content: ' ',
display: 'block',
marginRight: 8,
height: 10,
width: 10,
},
});
const colourStyles = {
control: styles => ({ ...styles, backgroundColor: 'white' }),
option: (styles, { data, isDisabled, isFocused, isSelected }) => {
const color = chroma(data.color);
return {
...styles,
backgroundColor: isDisabled
? null
: isSelected ? data.color : isFocused ? color.alpha(0.1).css() : null,
color: isDisabled
? '#ccc'
: isSelected
? chroma.contrast(color, 'white') > 2 ? 'white' : 'black'
: data.color,
cursor: isDisabled ? 'not-allowed' : 'default',
};
},
input: styles => ({ ...styles, ...dot() }),
placeholder: styles => ({ ...styles, ...dot() }),
singleValue: (styles, { data }) => ({ ...styles, ...dot(data.color) }),
};
export default () => (
<Select
defaultValue={colourOptions[2]}
label="Single select"
options={colourOptions}
styles={colourStyles}
/>
);
</code></pre>
<p><a href="https://codesandbox.io/s/qqj3vv9zzj" rel="noreferrer"><img src="https://codesandbox.io/static/img/play-codesandbox.svg" alt="Edit react-codesandboxer-example"></a></p>
| 0non-cybersec
| Stackexchange |
PsBattle: water buffalo in a hotel bar. | 0non-cybersec
| Reddit |
Can Windows 7 pagefile be turned off if 4GB of hi-speed RAM present?. <blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="https://superuser.com/questions/30345/any-reason-not-to-disable-the-windows-pagefile-given-enough-physical-ram">Any reason not to disable the Windows pagefile given enough physical RAM?</a> </p>
</blockquote>
<p>I believe that there is enough of memory for everything used at the moment to be stored and that nothing needs to be paged to disk. Is this true?</p>
| 0non-cybersec
| Stackexchange |
Hackers hit Pittsburg schools with ransomware attack. | 1cybersec
| Reddit |
HP buys Palm. | 0non-cybersec
| Reddit |
Gardeners, could you help a grad student out by taking a short survey?. Hello --
Would you be willing to help me gather information on your gardening habits for my master's thesis? I'm hoping to build a business plan for a snazzy new gardening publication with a digital extension. The more data I can get, the better, so I'd be hugely grateful for your responses. All data collected will be used solely for the use of my thesis, and I will not use any personally identifying information.
Here's the link to the short survey:
https://docs.google.com/spreadsheet/viewform?formkey=dERlZFBLLUNJQ2lnOXVTWlYwZXVmZFE6MQ#gid=0
Thank you for your help!
Diana | 0non-cybersec
| Reddit |
Open Letter to Steve Huffman and the Board of Directors of Reddit, Inc– If you believe in standing up to hate and supporting black lives, you need to act. | 0non-cybersec
| Reddit |
Even smoll clouds need a checkup from time to time!. | 0non-cybersec
| Reddit |
Show that $E(X|\mathcal{F}_\tau)=\sum\limits_{n\in\mathbb{N}}E(X|\mathcal{F}_n)\mathbf{1}_{\{\tau=n\}}$. <blockquote>
<p>If <span class="math-container">$\mathbf{E}X<\infty$</span> and <span class="math-container">$\tau$</span> is a stopping time, then <span class="math-container">$$\mathbf{E}(X|\mathcal{F}_\tau)=\sum_{n\in\mathbb{N}}\mathbf{E}(X|\mathcal{F}_n)\mathbf{1}_{\{\tau=n\}}.$$</span></p>
</blockquote>
<p>My attempt: First assume that <span class="math-container">$X$</span> is nonnegative. The general case will follow directly from nonnegative case.</p>
<p>Let <span class="math-container">$A\in \mathcal{F}_\tau.$</span> Then <span class="math-container">$A\cap \{\tau=n\}\in \mathcal{F}_n$</span> for every <span class="math-container">$n\in\mathbb{N}.$</span> Therefore, <span class="math-container">\begin{align*}
\int_{A}\sum_{n\in\mathbb{N}}\mathbf{E}(X|\mathcal{F}_n)\mathbf{1}_{\{\tau=n\}}d\mathbf{P}&=\sum_{n\in\mathbb{N}}\int_{A}\mathbf{E}(X|\mathcal{F}_n)\mathbf{1}_{\{\tau=n\}}d\mathbf{P}=\sum_{n\in\mathbb{N}}\int_{A\cap \{\tau=n\}}\mathbf{E}(X|\mathcal{F}_n)d\mathbf{P}\\&=\sum_{n\in\mathbb{N}}\int_{A\cap \{\tau=n\}}Xd\mathbf{P}=\int_A Xd\mathbf{P}
\end{align*}</span>
where the first equality follows from monotone convergence theorem, third follows from the definition of the conditional expectation.</p>
<p>Question: (1) To prove that <span class="math-container">$\sum_{n\in\mathbb{N}}\mathbf{E}(X|\mathcal{F}_n)\mathbf{1}_{\{\tau=n\}}$</span> is indeed the conditional expectation of <span class="math-container">$X$</span> wrt <span class="math-container">$\mathcal{F}_\tau$</span>, I have to prove that it is <span class="math-container">$\mathcal{F}_\tau$</span>-measurable. How should I do so?</p>
<p>(2) Since the stopping time can take infinite value, my calculation of the integration above holds only when <span class="math-container">$\tau<\infty$</span> almost surely. Is the condition <span class="math-container">$\tau<\infty$</span> a.s. necessary here?</p>
<p>Thanks in advance!</p>
| 0non-cybersec
| Stackexchange |
A simple solution for documents left unattended on a printer. | 0non-cybersec
| Reddit |
Is it possible to break on thread exit with specific error code?. <p>I was wondering if it was possible to configure visual studio 2008 debugger to stop execution when a thread exits with a precise error code (or at least any non-zero value). My app use a tremendous number of threads, so it's impossible to track them all manually. </p>
<p>Is there a way to tell VS2008 to break when ANY thread in the program hits "exit(X);" (X being different from 0) and display source ?</p>
| 0non-cybersec
| Stackexchange |
Jacoco Coverage Report issues. <p>I am trying to define the location, where jacoco will create the coverage file for instrumentation tests running on real devices.</p>
<p>From the <code>--debug</code> run of the gradle task I see this log:</p>
<pre><code>[DEBUG] [org.gradle.api.Task] DeviceConnector 'Nexus 5X - 6.0.1': installing /home/martin/workspace/lib/my-lib/build/outputs/apk/my-lib-debug-androidTest-unaligned.apk
[INFO] [org.gradle.api.Task] Starting 1 tests on Nexus 5X - 6.0.1
[INFO] [org.gradle.api.Task] de.my.lib.utils.UtilsTest testMyTest[Nexus 5X - 6.0.1] [32mSUCCESS [0m
[DEBUG] [org.gradle.api.Task] DeviceConnector 'Nexus 5X - 6.0.1': fetching coverage data from /data/data/de.my.lib.test/coverage.ec
[DEBUG] [org.gradle.api.Task] DeviceConnector 'Nexus 5X - 6.0.1': uninstalling de.my.lib.test 13:46:14.538
[DEBUG] [org.gradle.api.internal.tasks.execution.ExecuteAtMostOnceTaskExecuter] Finished executing task ':my-lib:connectedDebugAndroidTest'
</code></pre>
<p>I tried 3 ways to define the location:</p>
<p>Using the <code><instrumentation></code> tag in the manifest file didn't change anything.</p>
<pre><code><?xml version="1.0" encoding="utf-8"?>
<manifest
package="de.my.lib.test"
xmlns:android="http://schemas.android.com/apk/res/android">
<instrumentation
android:name="android.support.test.runner.AndroidJUnitRunner"
xmlns:tools="http://schemas.android.com/tools"
android:targetPackage="de.my.lib.test"
tools:replace="android:targetPackage">
<meta-data
android:name="coverage"
android:value="true" />
<meta-data
android:name="coverageFile"
android:value="/sdcard/coverage.ec" />
</instrumentation>
</manifest>
</code></pre>
<p>I tried it with gradle but the output was the same:</p>
<pre><code>defaultConfig {
// unimportant stuff
testApplicationId "de.my.lib.test"
testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
testInstrumentationRunnerArgument('coverageFile', '/sdcard/coverage.ec')
}
</code></pre>
<p>And finally I tried it with <code>adb</code> command:</p>
<pre><code>adb shell am instrument -w -e coverage true -e coverageFile /sdcard/coverage.ec de.my.lib.test/android.support.test.runner.AndroidJUnitRunner
</code></pre>
<p>But there I get 2 errors:</p>
<blockquote>
<p>de.my.lib.utils.UtilsTest:.
Could not find class: org.jacoco.agent.rt.internal_773e439.CoverageTransformer
.
Time: 0,072</p>
<p>OK (1 test)</p>
<p>Error: Failed to generate emma coverage.</p>
</blockquote>
<p>I am completely lost here. Any ideas?</p>
<p><strong>Background</strong> Why I need it to have it stored in another place: There is a bug with <code>adb shell run-as</code> command on some devices and Android version so I have devices in my test device farm which return 0% coverage because the file can't be pulled. So I need the file to be stored in a publicly available location.</p>
| 0non-cybersec
| Stackexchange |
Problem with determining the shape and direction of the Huffman Diagram. <p>I have the phrase <strong>"abracadabra"</strong> and I want to encode it through the Huffman method. I first took the frequencies of each letters;
$$a=5$$
$$b=3$$
$$c=1$$
$$d=2$$
$$r=2$$
But I'm not sure as to how the diagram should look like. I made a few and some of them are correct. Also what determines the direction the branches take? Is there any fixed criteria for it?</p>
<p><a href="https://i.stack.imgur.com/i1z3R.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/i1z3R.jpg" alt="enter image description here"></a>
<a href="https://i.stack.imgur.com/NRtE6.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/NRtE6.jpg" alt="enter image description here"></a></p>
| 0non-cybersec
| Stackexchange |
gevent does not install properly on Ubuntu. <p>I want to experiment with <a href="http://gevent.org">gevent</a>, but after installing it I can't load any gevent module.</p>
<p>The installation steps are:</p>
<pre><code>sudo apt-get install libevent-dev
sudo pip install greenlet
sudo pip install gevent
</code></pre>
<p>The environment setup is Ubuntu 10.10 x86_64 GNU/Linux.</p>
<p>When I try to do a simple test, I get:</p>
<pre><code>>>> import gevent
>>> from gevent import socket
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ImportError: cannot import name socket
</code></pre>
<p>I suspect the installation not doing what it should, but I'm not sure what wrong. </p>
| 0non-cybersec
| Stackexchange |
DFS setup with large initial folder. <p>I have two offices that both use a similar network share structure, and often generate the same files. I would like to implement DFS between the two locations, but am concerned that the main folder at each location is too large for the amount of time to sync.</p>
<p>HeadOffice has a folder A:\files\ with 18,000 files @ 120gb</p>
<p>RemoteOffice has a folder B:\files\ with 28,000 files @ 133Gb</p>
<p>Currently HeadOffice is running 2012r2 and RemoteOffice is 2003r2. I understand 2003 will not work, so I will set up a new 2012r2 machine just for DFS. I would mimick the same folder setup and copy from 2003 to 2012 locally.</p>
<p>There is a lot of duplicates between these two offices, which I want to get into sync with DFS.</p>
<p>The VPN link between the two locations can handle 16mbps. If I throttle it to 10mbps, best case is 30hours to copy from Remote to HeadOffice.</p>
<p>Would there be an initial scan to see which files already exist at the other location and ignore those? What about copying the contents to a flash or usb hdd and shipping it to the other location and getting them 'almost' in sync. </p>
<p>I can dedicate downtime (weekend) to sync the folders if DFS will initially scan for differences.</p>
<p>Can anyone offer suggestions how to best implement this to limit the bandwidth for the initial setup? </p>
<p>Thanks in advance.</p>
| 0non-cybersec
| Stackexchange |
$ \mathbb{C} $-characters of $ A_5 $. <p>How can we find all of five irreducible $ \mathbb{C} $-characters of $ A_5 $?
Precisely how can we construct the character table with the aid of orthogonality relations?</p>
| 0non-cybersec
| Stackexchange |
[NSFW and possible SPOILERS] I make Free! gifs and edit things into scenes. | 0non-cybersec
| Reddit |
Inner product (functions) tending to infinity. <p>I have a quite simple question, which I'm not really able to answer. Assume that you have to functions $f,g$ on an infinite dimensional function (normed) space. Define the usual inner product on a given interval $[0,b]$ as $$\langle f,g \rangle = \int_{0}^{b} f(t)g(t)dt$$</p>
<p>Now assume that I would like to approximate the function $f$ by a suitable finite subset of basis functions $\{\phi_i\}_{i}^{N}$, which can be done by using the aforementioned inner product.</p>
<p>Ok, my question is the following: Can I define this inner product if $b\to\infty$? Do I need any hypothesis on the set of $\phi$'s or the function $f$? </p>
<p>Thanks!!!!!</p>
| 0non-cybersec
| Stackexchange |
Quick way to tell if an installed application is 64-bit or 32-bit. <p>I've got a third-party application (in this case Cognos Data Manager) installed on 64-bit Windows Server 2003.</p>
<p>Is there a quick way to determine if an application has been built/compiled as a 64-bit application or as a 32-bit application?</p>
<p>By default a program wanted to be installed in Program Files (x86). I'm guessing that means that it is a 32-bit version. I had to get it to talk to an Oracle database and to get that working I eventually reinstalled it in a directory path which didn't have brackets "(" and ")" in it, as that was causing a problem. I've also installed both 64-bit and 32-bit Oracle clients.</p>
<p>For future reference, I'd like to be able to type a command
"xxxx fred.exe"
and have it tell me whether fred.exe would be needing 32-bit or 64-bit setup (eg ODBC data sources etc).</p>
| 0non-cybersec
| Stackexchange |
Call it magic call it true. | 0non-cybersec
| Reddit |
Safari has a problem displaying certain images. <p>Safari does not display certain images properly.</p>
<p>The latest example is <a href="https://i.imgur.com/GqQchYM.jpg" rel="nofollow noreferrer">http://i.imgur.com/GqQchYM.jpg</a> which is perfectly loadable in firefox.</p>
<p>In Safari however the picture is displayed properly while it is loading/as long as it is only partially loaded. When it should display the whole picture all I get is black or white box. It can be clicked to zoom in though.</p>
<h2>Safari</h2>
<p><img src="https://i.imgur.com/kTgkGZQ.png?1" alt="Safari 7.0.3" title="safari"></p>
<h2>Firefox</h2>
<p><img src="https://i.imgur.com/WMuboNZ.png?1" alt="Firefox" title="firefox"></p>
<p>I've had the same problem once before. That time I found this thread: <a href="https://discussions.apple.com/thread/3796427" rel="nofollow noreferrer">https://discussions.apple.com/thread/3796427</a></p>
<p>and was able to get it working by deleting:</p>
<pre><code>~/Library/Caches/com.apple.Safari/Cache.db
</code></pre>
<p>I've tried that this time as well, but the picture is still failing.</p>
<p>The system is updated. My version of Safari is 7.0.3 (9537.75.14). The operating system is OS X 10.9.2 (13C1021).</p>
<p>What can I do to get the browser working again?</p>
<p>EDIT:</p>
<p>I've tried removing all extensions from the browser.
<img src="https://i.imgur.com/oR47GDv.png" alt="Extensions" title="extensions"></p>
<p>I only had <a href="http://redditenhancementsuite.com" rel="nofollow noreferrer">Reddit enhancement suite</a> installed before cleaning.</p>
<p>EDIT2: problem persists after updating to Safari Version 7.1 (9537.85.10.17.1)</p>
<p>EDIT3: Problem solved in Safari Version 8.0 (10600.1.25)!</p>
| 0non-cybersec
| Stackexchange |
Converting string into xstring without using function module. <p>I want to convert a string into a xstring. I know that there is a function module named "SCMS_STRING_TO_XSTRING" </p>
<p>But since it is not a good habit to use function modules anymore, a class based solution would be my prefered way to go. </p>
<p>I know that there is a class </p>
<pre><code>cl_abap_conv_in_ce
</code></pre>
<p>but I can only validate, that this class can convert xstrings into string. I wand to have the reverse case. Does anyone have experience on how to do that class based?</p>
| 0non-cybersec
| Stackexchange |
How to use spot instance with amazon elastic beanstalk?. <p>I have one infra that use amazon elastic beanstalk to deploy my application.
I need to scale my app adding some spot instances that EB do not support.</p>
<p>So I create a second autoscaling from a launch configuration with spot instances.
The autoscaling use the same load balancer created by beanstalk.</p>
<p>To up instances with the last version of my app, I copy the user data from the original launch configuration (created with beanstalk) to the launch configuration with spot instances (created by me).</p>
<p>This work fine, but:</p>
<ol>
<li><p>how to update spot instances that have come up from the second autoscaling when the beanstalk update instances managed by him with a new version of the app?</p>
</li>
<li><p>is there another way so easy as, and elegant, to use spot instances and enjoy the benefits of beanstalk?</p>
</li>
</ol>
<p><strong>UPDATE</strong></p>
<p>Elastic Beanstalk add support to spot instance since 2019... see:
<a href="https://docs.aws.amazon.com/elasticbeanstalk/latest/relnotes/release-2019-11-25-spot.html" rel="nofollow noreferrer">https://docs.aws.amazon.com/elasticbeanstalk/latest/relnotes/release-2019-11-25-spot.html</a></p>
| 0non-cybersec
| Stackexchange |
Mormon Studies Attracts More Scholars and Attention, The Mormon Lens on American History.. | 0non-cybersec
| Reddit |
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