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How to compare keys in yaml files?. <p>There are two ruby on rails internationalization yaml files. One file is complete and another one is with missing keys. How can I compare two yaml files and see missing keys in second file? Are there any tools for doing that?</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 |
Like a thief in the night!. | 0non-cybersec
| Reddit |
TIL a homeless girl who attended 12 schools in 12 years went to Harvard. She with her family used to move from shelter to shelter or sleep in bus stations or on the street. She was accepted to more than 20 universities before choosing Harvard.. | 0non-cybersec
| Reddit |
| Si .Se. Puede .Sax. en WordPress.com. | 0non-cybersec
| Reddit |
Where do I get the latest boost/libboost for 10.04?. <p>i'm unable to install libboost-all-dev package versions 1.42 or latest in ubuntu 10.04. only boost1.40 is installing. but i need 1.42. what should i do?
when i tried to install 1.48 boost i got the following error:</p>
<pre><code>robotics@robotics-desktop:~$ sudo dpkg -i libboost-all-dev_1.48.0.2_i386.deb
Selecting previously deselected package libboost-all-dev.
(Reading database ... 224047 files and directories currently installed.)
Unpacking libboost-all-dev (from libboost-all-dev_1.48.0.2_i386.deb) ...
dpkg: dependency problems prevent configuration of libboost-all-dev:
dpkg: error processing libboost-all-dev (--install):
dependency problems - leaving unconfigured
Errors were encountered while processing:
libboost-all-dev
</code></pre>
<p>what should i do? should upgrade to 11.10?</p>
| 0non-cybersec
| Stackexchange |
Convergence of $\sum_{n = 1}^\infty \frac{\sin n (1-\sin n)}{n}$. <p>How I can prove that this sum converges?
I can prove that $\frac{\sin n}{n}$ converges and that $(1-\sin n)$ is bounded.</p>
| 0non-cybersec
| Stackexchange |
[Schefter] Patriots now are re-signing WR Demaryius Thomas to a one-year deal, per source. Thomas was released with the idea of returning.. | 0non-cybersec
| Reddit |
$\operatorname{lcm}(a^2, ab, b^2) =\operatorname{lcm}(a^2, b^2)$. <blockquote>
<p>Let <span class="math-container">$a$</span> and <span class="math-container">$b$</span> be two integers. Is it true that <span class="math-container">$\operatorname{lcm}(a^2, ab, b^2) = \operatorname{lcm}(a^2, b^2)$</span> ?</p>
</blockquote>
<p><span class="math-container">$a, b$</span> are integers and the result that i tried to use, in this case,is <span class="math-container">$ \operatorname{lcm}(a^2,b^2)\gcd(a^2,b^2)=a^2 b^2$</span> but i don't know if it's true <span class="math-container">$\operatorname{lcm}(a^2,ab,b^2)\gcd(a^2,ab,b^2)=a^3 b^3$</span></p>
<p>I did some examples apparently it's true but I can't prove it. So could give me a hint?</p>
| 0non-cybersec
| Stackexchange |
Clear icon inside input text. <p>Is there a quick way to create an input text element with an icon on the right to clear the input element itself (like the google search box)?</p>
<p>I looked around but I only found how to put an icon as background of the input element. Is there a jQuery plugin or something else?</p>
<p>I want the icon inside the input text element, something like:</p>
<pre><code>--------------------------------------------------
| X|
--------------------------------------------------
</code></pre>
| 0non-cybersec
| Stackexchange |
Diagonalizing a $2\times 2$ matrix. <p>I am told that $A\in M_{2}(\mathbb{R})$ s.t $1-i$ is an eigenvalue
of $A$ with corresponding eigenvector $\begin{pmatrix}3+2i\\ 1+3i \end{pmatrix}$.</p>
<p>I wish to find a matrix $P$ s.t $P^{-1}AP=\begin{pmatrix}1-i & 0\\
0 & 1+i
\end{pmatrix}$. From what I understand since $\lambda_{1}=1-i$ is an eigenvalue
then also $\lambda_{2}=\bar{\lambda}_{2}=1+i$ is an eigenvalue and
since $\lambda_{1}\neq\lambda_{2}$ and $A$ is a $2\times2$ matrix
I conclude that such $P$ does exist.</p>
<p>My efforts for finding $P$ are: I said that if $v_{1}=\begin{pmatrix}3+2i\\
1+3i
\end{pmatrix}$ is an eigenvector corresponding to $\lambda_{1}$ then $v_{2}=\overline{v_{1}}$
is eigenvector corresponding to $\lambda_{2}$ hence $B=\{v_{1,}v_{2}\}$
is a basis of eigenvectors.</p>
<p>From what I remember $P$ is the matrix that transfers from the standard
base to $B$ (or the other way around ?), so I tried writing $\begin{pmatrix}1\\
0
\end{pmatrix}=\alpha v_{1}+\beta v_{2}$ and failed (I got that such $\alpha,\beta$ does not exist).</p>
<p>Can somene please help me understand what is my mistake and how to
find the matrix $P$ ?</p>
| 0non-cybersec
| Stackexchange |
Javascript's performance.now() and Nodejs. <p>I'm new to Nodejs and I'm confused about something when timing:</p>
<p>If Nodejs is Javascript, then why Javascript's performance.now() doesn't work on Nodejs and I'm forced to use console.time() or the like?</p>
<p>How can I know what other Javascript functions doesn't work on Node?</p>
<p>Thanks!</p>
| 0non-cybersec
| Stackexchange |
What is the characteristic formula for the addition of two lognormal distributions?. <p>If I have two lognormal processes ($X$ and $Y$) with mean and volatiilty for each and also correlation between the two, what is the characteristic formula of $X + Y$ (i.e. what is the new mean and new volatility of $X + Y$)? </p>
| 0non-cybersec
| Stackexchange |
Introduction to Networking | Network Basics for Beginners - Encryption 101. | 1cybersec
| Reddit |
No CD/DVD/BD writer found on k3b. <p>Even if it is seen into drives my system won't recognize the writer... since 15.04 update...</p>
<p>With k3b started as root the problem stays the same</p>
<p><img src="https://i.stack.imgur.com/cepP6.jpg" alt="system configuration problem">
<img src="https://i.stack.imgur.com/ClL8L.jpg" alt="even if seeing into drives"></p>
<p>Dont understand why I cannot write, is there a driver change on last kernel?</p>
<pre><code>sudo cat /proc/sys/dev/cdrom/info
CD-ROM information, Id: cdrom.c 3.20 2003/12/17
drive name: sr0
drive speed: 24
drive # of slots: 1
Can close tray: 1
Can open tray: 1
Can lock tray: 1
Can change speed: 1
Can select disk: 0
Can read multisession: 1
Can read MCN: 1
Reports media changed: 1
Can play audio: 1
Can write CD-R: 0
Can write CD-RW: 0
Can read DVD: 1
Can write DVD-R: 0
Can write DVD-RAM: 0
Can read MRW: 1
Can write MRW: 1
Can write RAM: 1
</code></pre>
| 0non-cybersec
| Stackexchange |
[SPOILERS] Game of Thrones | Season 8 | Official Tease: Aftermath (HBO). | 0non-cybersec
| Reddit |
Ruby on Rails - Import Data from a CSV file. <p>I would like to import data from a CSV file into an existing database table. I do not want to save the CSV file, just take the data from it and put it into the existing table. I am using Ruby 1.9.2 and Rails 3.</p>
<p>This is my table:</p>
<pre><code>create_table "mouldings", :force => true do |t|
t.string "suppliers_code"
t.datetime "created_at"
t.datetime "updated_at"
t.string "name"
t.integer "supplier_id"
t.decimal "length", :precision => 3, :scale => 2
t.decimal "cost", :precision => 4, :scale => 2
t.integer "width"
t.integer "depth"
end
</code></pre>
<p>Can you give me some code to show me the best way to do this, thanks.</p>
| 0non-cybersec
| Stackexchange |
Ubuntu 16.04 bootload grub2 problem?. <p>Ok, I have an internal SSD installed with Ubuntu 16.04 on it. Upon installation I deleted both partitions on both disks and installed Ubuntu on the SSD. I have a Lenovo V570 with the CD Drive replaced with a HDD 2.5 adapter holding a 1TB Hitachi. SSD installed in original HDD factory slot. I keep getting the issue of black screen and high fan usage when booting with the HDD connected. Even after Deleting and recreating both partitions on both disks, I still get this issue. The HDD did previously have Windows 7 installed on it. It has since had a new partition made on the device. I have looked everywhere for a solution. I have been unable to find out why this is happening. Can you give me some diagnostic commands to be able to find out what is happening?</p>
<p>P.S. Windows is not installed anymore. I have the most updated bios for that model: V43</p>
| 0non-cybersec
| Stackexchange |
Google Drive Api in Angular. <p>I am facing some difficulties in apply the google drive api to my angular web app. I tried copying the code from <a href="https://developers.google.com/drive/api/v3/quickstart/js" rel="nofollow noreferrer">https://developers.google.com/drive/api/v3/quickstart/js</a> to my components html but I keep getting an error that says</p>
<p><code>zone-evergreen.js:171 Uncaught {error: "idpiframe_initialization_failed", details: "Not a valid origin for the client: http://localhos…itelist this origin for your project's client ID."}</code></p>
<p>However, when I put it as a normal index.html without it being in an angular app, the client id is valid. Is it possible that it is because of how angular renders the components, resulting in 'async defer' to be not working? If so, how do I resolve this.</p>
<p>I tried using @types/gapi and gapi-auth2 but I also encounter errors that the module cannot be found. I did many fixes like adding the compilerType but it still does not work so I am trying to use the default html. Thank you.</p>
| 0non-cybersec
| Stackexchange |
The Darkness - I Believe In A Thing Called Love [Rock]. | 0non-cybersec
| Reddit |
Refeeding without carbs. Hi all, hope everyone is doing well. This post also has to do with intermittent fast.
I am going to undertake my second 72 hour fast. Recently I noticed a bit of discussion around refeeding. Has anyone done this? What does it look like for you? I was curious if one would just eat closer to maintenance macros or just increase calories during a single meal.
Thanks for any input in advance.
Cheers! | 0non-cybersec
| Reddit |
Logs from the Lincoln Interment Facility. ADMISSION REPORT:: Patient #00749
Patient was inducted after found with multiple self-inflicted lacerations to the neck, wrist, and chest. Patient has made repeated complaints of feelings of dread, hopelessness, and general melancholy. Also reporting insomnia and headaches.
Administered Triazolam 0.25mg for insomnia.
ADMISSION EVALUATION:: Patient #00749
Self harm has been confirmed. Definite somniphobia. Patient claims his self harm is meant to induce long periods of stimulation, refers to sleep with severe anxiety, possible agoraphobia. Issue of insomnia requires immediate attention.
Largely refused questioning except pertaining to his mental state. He claims to have a relationship with something he refers to as “other”.
I recommend we cancel Triazolam and instead supplant the patient with 5mg Diazepam.
ADMITTANCE REPORT:: Patient #00749
Patient remanded to Room 401. Occupants: Patient #00182 and Patient #00372
INCIDENT REPORT:: Patient #00749
During ward check, Patient #00182 requested immediate transfer from Room 401, reasoning that Patient #00749 is greatly disturbing her. Patient #00372 likewise requests to be moved into an isolated bed.
Requests denied.
INCIDENT REPORT (2):: Patient #00749
During ward check, Patient #00182 claims she has been ordered to be moved to isolation by observation staff. Patient #00372 corroborates her claims. There is no record of such a request, she is denied. Both patients become severely agitated. Require sedation.
Recommending more frequent follow-up checks to circumvent future conflict.
INCIDENT REPORT (3):: Patient #00372
Staff on Hall 1, Floor 4 report loud sounds from room 410 after facility lights out, disturbing other rooms and patients. Patient #00372 is found dead in northeast corner of the cell, both Patient #00182 and Patient #00749 are found struggling against their restraints, demanding the lights be turned back on before “she comes back”. Sedation approved and administered.
Recommending the use of antipsychotics in event of future incident.
INCIDENT REPORT(4):: Patient #00749
Staff on Hall 1, Floor 4 report loud sounds from room 410. Patient #00182 found dead from multiple lacerations to the upper body. Patient #00749 transferred to Isolation, room 626, given injected dose of 100mg Zuclopenthixol on attending physician’s orders to control acute psychosis.
Recommend video observation.
STAFF MEMO:
Something is very wrong here. Personnel observing Patient #00749’s cell have stated that they feel a heavy sense of dread, fear, anger, and general depression. Moral has dropped dramatically, and many observers have requested for immediate transfer.
This has officially gone far enough. I was confident that the men and women employed in this facility contained an iota of professionalism. Patient 749 is nothing new. He’s not the first patient with explosive episodes, or delusions, hell he isn’t even the first detainee to kill a cellmate! I do not understand why this man in particular has disturbed this staff so greatly.
It also pains me to report that it seems we’ve had multiple personnel attempt to breach 749’s isolation. The culprit has not come forward, rest assured whoever you are will be punished swiftly and severely.
Until otherwise noted I will not approve of any shift changes from scheduled Isolation hours. This matter is closed, and I want to hear no further mention of it.
~Administrator
INCIDENT REPORT (5):: Patient #00749
Patient #00749 requests that lights be left on after designated lights-out time. After consultation with attending physician and therapist, request granted. Patient then requests sleep lights be dimmed. Patient understands that low-level light is necessary for room observation – as quoted, “that’s why I want them off.” Patient then warned camera operator against ‘her’. Request denied.
Patient becomes increasingly agitated. Sedation has no effect, dosage doubled. Following sedation, it is noted that several bolts from the patient’s restrains were dislocated.
STAFF MEMO (2)::
I have been hearing talk around the halls that some of you are AFRAID of this man. He is bound to a bed, under the highest sedation we can medically provide. This is getting ridiculous.
Regardless of the reason, I will NOT permit untrained orderlies to begin interfering in the care provided to our patients.
~Administrator
INCIDENT REPORT (6)::
half the damn staff is gone and i dont know what to do. thomas left, said he couldn’t do this to his kids. are we watching this crazy fuck or is he
patient #00749 just stopped screaming. i don’t know why. i think he’s gone.
i pray she’s gone too
i only need a needle to stop the pain
STAFF MEMO (3)::
NO ONE IS TO ENTER ISOLATION 626 WITHOUT EXPRESS PERMISSION
INCIDENT REPORT (7)::
we.all.fall.down.
STAFF MEMO (4)::
To: [email protected]
From: [email protected]
Okay Robert, I think I have the situation under control. The staff is in the nurse’s station, I took some freedom with gathering them, but I don’t I’m going to get a reprimanding for it.
Ever since Patient #00372 was killed, something odd has been happening. I’ve noticed a large quantity of dextroamphetamine has gone missing from the medical bay. A greater amount of needles have also gone missing. You want to know what the side effects of overdose are? Paranoia, compulsiveness, confusion, and severe agitation. Sound familiar?
I started looking over the video feed for 00749, and I found something interesting. Each night in Isolation, the camera feed cut out for approximately 5 minutes between shifts. Every night. As if someone had made it so that the cameras wouldn’t record a specific incident.
The thought occurs to me that 00372 and 00182 both were killed the same way, lacerations. But did you notice in each report, 00749 was restrained when the bodies were discovered? Surely he could not have released himself and re-restrained himself!
The worst part is, the past few days, I’ve been circling the grounds and checking our records, counting staffers. As far as I can tell, there are more staff on the grounds than we have on payroll.
Security says it doesn't make sense, but I think we have one extra.
COMPANY MEMO:
Seal 749’s body in Isolation. Make him look alive. Wait her out. Security and I will be in there with 16g of pentobarbital. When all's said and done, cremate both bodies.
The administration is taking this opportunity to apologize for its conduct in light of the situation. Indeed, there are risks inherent in this profession, risks we all knew about upon assuming it, but that is the burden we bear to render aid to those who find themselves under our care.
We’re taking this opportunity to also remind our staff that counselors are always available during standard hours for those who need to consult with someone in light of the recent event and associated workplace anxiety.
Let’s just hope the rest of us don’t wind up needing time in these beds as well.
| 0non-cybersec
| Reddit |
iBook G4 hard disk issue - how to repair broken HFS filesystem?. <p>The OS does not boot, it stays in blue blank screen with scrolling bar.</p>
<p>I restarted to single user mode and tried fsck - it said it cannot repair fs.</p>
<p>Restarting with OSX install diskette: it did not show the hard disk in the list of target drives.</p>
<p>Any ideas, how to check if the HD is physically broken?</p>
<p>By pressing D during boot (with install disk inserted) did not seem to do anything (according to Google, shouldn't it open hardware test?)</p>
| 0non-cybersec
| Stackexchange |
Fundamental solution for Helmholtz equation in higher dimensions. <p>The fundamental solution for Helmholtz equation $(\Delta + k^2) u = -\delta$ is $e^{i k r}/r$ in 3d and $H_0^1(kr)$ in 2d (up to normalization constants).
Is there an explicit expression (eventually in terms of special functions) for the fundamental solution in dimension $\geq 4$? How can one derive it?</p>
| 0non-cybersec
| Stackexchange |
The Joker.. | 0non-cybersec
| Reddit |
Is there something similar to pseudorandom generators but in the opposite direction?. <p>Pseudorandom generators (<a href="http://en.wikipedia.org/wiki/Pseudorandom_generator" rel="nofollow">PRG</a>) are functions that takes a random small input (called the Seed) and maps it into much larger output .</p>
<p>However, the mapping process must be unpredictable in order for the PRG to be used securely in cryptography.</p>
<p>My question is: Are there any tool the does the opposite? i.e. takes a long random string and maps it to a smaller random unpredictable output? </p>
<p>And if not, can we use <a href="http://en.wikipedia.org/wiki/S-box" rel="nofollow">s-box</a> for this purpose? </p>
| 0non-cybersec
| Stackexchange |
TIL That Finland gave 2,000 random unemployed people $640 USD a month, no strings attached, for two years as part of a study.. | 0non-cybersec
| Reddit |
Proving properties of Random Graphs. <p>I am asking the question on a slightly abstract level and it may depend on the specifics but it would be great to have related references or ideas.</p>
<p>Consider the random graph model $G_{n,p}$ where its a random graph on n vertices and each edge is selected with probability $p$. I want to prove that a certain property $P$ is satisfied by graphs in this model with high probability ($\rightarrow 1$ as $n \rightarrow \infty$). I know/can prove the following two facts</p>
<ol>
<li>Conditioned on the event that the graph obtained from the sample is regular, the probability of the property being satisfied is very high (something like $1 - 1/n^c$)</li>
<li>Given any graph G and any other graph G' that can be obtained by removing edges from G. If G satisfies the property then so does G'. </li>
</ol>
<p>Can the above two statements be enough to make a general statement about the probability of the satisfaction of the property in $G_{n,p}$</p>
<p>Any references would be very helpful? </p>
| 0non-cybersec
| Stackexchange |
derive formula for height of tower on a hill. <p>I'm working through a book to learn trig on my own and I got stuck with the following. This is the image given and the text in the book reads:</p>
<blockquote>
<p>Suppose you are standing an unknown distance away from a cliff of height <span class="math-container">$h$</span>. You need to know the height <span class="math-container">$t$</span> of a tower located on top of the cliff. You know that the angle of elevation of the bottom of the tower is <span class="math-container">$B$</span> and the angle of elevation of the top of the tower is <span class="math-container">$A$</span>. Derive a formula for the height of the tower.</p>
</blockquote>
<p><img src="https://i.stack.imgur.com/rLVuI.png" alt=""></p>
<p>The solution they gave is <span class="math-container">$t = h\left({{tan A}\over{tan B}}-1\right)$</span>. I don't quite understand how to derive that answer. I think that the height is going to be <span class="math-container">$d(tanA - tanB)$</span> where <span class="math-container">$d$</span> is the unknown adjacent side. I get stuck after that. The more verbose the answer the better. Thanks!</p>
| 0non-cybersec
| Stackexchange |
Fourth Amendment Caucus defeats Patriot Act expansion in Congress. | 0non-cybersec
| Reddit |
Well... Its unique at least.. | 0non-cybersec
| Reddit |
American currency is printed with magnetic ink.. | 0non-cybersec
| Reddit |
Black dogs allegedly facing discrimination. | 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 |
How to prevent chapter titles from appearing in the header on the first page of each chapter in ConTeXt?. <p>To place the chapter title in the header of my document, I used:</p>
<pre><code> \setupheadertexts[{\getmarking[chapter]}][][][{\getmarking[chapter]}]
</code></pre>
<p>My document is not double-sided. Whenever the chapter title appears on the first page of the chapter, it produces the odd result of seeing the chapter title in the header directly above the actual chapter title, e.g.:</p>
<pre><code> _______________
| Chapter 1 |
| |
| CHAPTER 1 |
| Once upon |
| a time, ... |
|_______________|
</code></pre>
<p>How can I place a chapter title in the header, but prevent it from appearing on the first page of each chapter?</p>
| 0non-cybersec
| Stackexchange |
Restricting access to Share using both an AD user using a specific Computer. <p>The Environment:
One AD domain that is not managed by local admins (can’t edit, can’t add GPO, etc.) Users have accounts here. Call this AD alpha
This AD Alpha has a trust to a local AD domain (Call this one Zeta) that local admins administer. Contains computer accounts. Has accessible network shares</p>
<p>Goal:
Set permissions on AD Zeta’s network shared folders using AD Alpha’s user accounts and AD Zeta computer accounts for folder access.</p>
<p>Reason:
To make sure that when a users using credentials from Alpha accesses a share on Zeta, they can only do so if they are also accessing that share from a machine they would normally use during working hours.</p>
<p>Example:
User A logged in with computer A = grant access
User A logged in with computer B= no access</p>
<p>User B logged in with computer B = grant access
User B logged in with computer A= no access</p>
| 0non-cybersec
| Stackexchange |
Why don't CPUs have dedicated instruction sets for compression?. Computers built in the last decade generally take advantage of the [x86 AES instruction set](https://en.wikipedia.org/wiki/AES_instruction_set), which is hardware acceleration in the CPU that speeds up the task of encryption or decryption using the standard AES algorithm. Even obsolete processors like mine can encrypt multiple gigabytes per second (!). This vastly exceeds the speed of hard drives, so the result is that there's negligible performance loss for encrypting your data and you might as well encrypt everything all the time.
However, another common task, possibly even more common with even more standardized algorithms, is data compression. As far as I can tell there's no hardware acceleration for this. Is there a technical reason why that's not feasible? Something to do with a larger or much more active buffer? What might be the advantages of different compression algorithms for dedicated hardware acceleration? | 0non-cybersec
| Reddit |
In $\mathbb{Z}/(n)$, does $(a) = (b)$ imply that $a$ and $b$ are associates?. <p>[<strong>Update</strong>: Based on the hints provided by @zcn and @whacka, I believe I have found a solution. See my answer below.]</p>
<p>Below, $R$ is a commutative ring with $1$.</p>
<p>In John J. Watkins' <em>Topics in Commutative Ring Theory</em>, the author observes that if $a$ and $b$ are associates in $R$, then they generate the same ideal: $(a) = (b)$. This is clearly true, because $a = ub$ and $b = va$ for some units $u$ and $v$, and so $a \in (b)$ and $b \in (a)$, whence $(a) \subset (b)$ and $(b) \subset (a)$. Indeed, we didn't even require $u$ and $v$ to be units to reach this conclusion.</p>
<p>The author then claims that if $R$ is not a domain, then the converse may not be true: we may have $(a) = (b)$ even if $a$ and $b$ are not associates. As a "counterexample" he gives $R = \mathbb{Z}/(6)$, with $a = 2 + (6)$ and $b = 4 + (6)$. Clearly these elements generate the same ideal: $(a) = (b) = \{0, 2 + (6), 4 + (6)\}$. The author asserts that $a$ and $b$ are not associates, but this is false: $5 + (6)$ is a unit, and $(2 + (6))(5 + (6)) = 4 + (6)$, so $a$ and $b$ actually are associates.</p>
<p>I figured that the author botched the example but that surely the basic fact must be true: if $R = \mathbb{Z}/(n)$ then there may be nonassociates $a,b \in R$ with $(a) = (b)$. However, I was not able to find a counterexample and eventually resorted to writing a computer program and found that there are no counterexamples in $\mathbb{Z}/(n)$ for $n \leq 100$.</p>
<p>So now I'm starting to think that there is no counterexample in $\mathbb{Z}/(n)$ at all, but I have not yet been able to prove this.</p>
<p>My questions:</p>
<ol>
<li><p>If I am correct that $(a) = (b)$ in $\mathbb{Z}/(n)$ implies that $a$ and $b$ are associates, I would appreciate a nudge in the right direction toward a proof. (But if the proof is elementary, please give only a hint, not a solution :-) I'll post my solution once I have one.</p></li>
<li><p>In either case, could you please point me to a genuine counterexample? If there is one in $\mathbb{Z}/(n)$ for some $n$, that would be ideal (no pun intended), otherwise a counterexample in any commutative ring with $1$ would be great.</p></li>
</ol>
| 0non-cybersec
| Stackexchange |
xargs - place the argument in a different location in the command. <p>Let's say I want to write a script that does <code>ls</code> with a prefix for each filename. I tried this</p>
<pre><code>ls | xargs -n 1 echo prefix_
</code></pre>
<p>But the result was</p>
<pre><code>prefix_ first_file
prefix_ second_file
...
</code></pre>
<p>How can I remove the space between the prefix and the filename? I.e. how to I make xargs put the variable after the command, without space? (Or in any other place for that matter)</p>
| 0non-cybersec
| Stackexchange |
Found a Polaroid 690 at a garage sale and can't seem to price it.. eBay has some pretty ridiculous listings, so I don't really believe them (like $600-$800 range; I can't find a completed auction either). Any help would be much appreciated!
Here's a picture of it:
http://i.imgur.com/Jc35gFq.jpg | 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 |
How do you get Google product rich snippets working on WooCommerce. <p>I have just set up a WooCommerce site and I am trying to get the reviews on it to show up in the Google rich snippets. How can i do this? Is there any out-the-box plugins to make it work?</p>
<p>Currently it pulls in some data in the Rich Snippets Structured Data Testing Tool but it does not show the 'Star rating' and 'Price' in the search results?</p>
| 0non-cybersec
| Stackexchange |
OnLive Desktop hits the Market. | 0non-cybersec
| Reddit |
Why are partitons not automatically mounting?. <p>After installing Ubuntu 12.04.3 LTS, the Windows 7 partition and an extra backup partition are no longer mounting automatically as they used to do in 10.04.2 LTS.</p>
<p>I have an ATA HardDisk.</p>
<p>What could be the problem? Any insights will be highly appreciated.</p>
| 0non-cybersec
| Stackexchange |
Unique unordered combinations of varying length. <p>Given random set of integers. I.e. </p>
<p>$\{1,2,2,3,3,3,5\}$</p>
<p>Find the number of <strong>unique, unordered</strong> <em>of varying length</em> sets that can be created.</p>
<hr>
<h2>My Workings</h2>
<hr>
<p>This is <em>not</em> a homework problem, but rather, I'm trying to develop an algorithm to calculate the number of divisors a number has after knowing all of its factors. For example, 36 has</p>
<p>$$1*36$$
$$2*18$$
$$3*12$$
$$4*9$$
$$6*6$$
A total of <strong>9</strong> <em>unique</em> divisors.</p>
<p>I have broken this problem down in the the above description, but I haven't been able to consolidate everything.</p>
<p>My approach is to consider every unordered combination, and then remove the duplicates.</p>
<p>I begin by not considering the 1 since it will not give additional divisors (I just add 2 in the end).</p>
<p>$\{2, 2, 3, 3, 3, 5\}$</p>
<p>Let $L$ be length $= 6$</p>
<h3>Consolidating Varying Length</h3>
<p>I approach this by considering each length from $n$ to $L$ separately.</p>
<p>Groups of $n$ Where $ 1<= n <=L$</p>
<p>$L\choose{n}$ $=\frac{L!}{n!(L-n)!}$</p>
<p>This would give the number of unordered combinations for a given length $n$. </p>
<h3>Consolidating Repeated Factors</h3>
<p>Now I consider each subset of repeated integers $\{2,2\}$ $\{3,3,3\}$</p>
<p>For the set of length 3 the duplicates will be found as follows:</p>
<ol>
<li><p>$\underline{R}\space \underline{U} \space \underline{U}$ </p></li>
<li><p>$\underline{R}\space \underline{R} \space \underline{U}$ </p></li>
<li><p>$\underline{R}\space \underline{R} \space \underline{R}$ </p></li>
</ol>
<p>Where $R$ is an unordered subset of a duplicate set $\{3, 3\} \{2\}$ and $U$ is an unordered subset of the unique set $\{2, 3, 5\}$</p>
<p>So, for 1. if I'm considering the duplicate set $\{3,3\}$ I would remove the amount equal to: $2\choose{1}$ $*$$3\choose{2}$ </p>
<p>For 2. It would be $2\choose{2}$ $*$$3\choose{1}$ </p>
<p>Then for 3. I wouldn't subtract anything for the subset of $\{3,3\}$ since it's not long enough.</p>
<hr>
<h2>Roadblock</h2>
<hr>
<p>Using this method, I've been able to predict the divisor count of <em>some</em> numbers, though my brain is mushy right now and I could have mistakes I don't realize. </p>
<ol>
<li>Is there any easier way to do this?</li>
<li>Why doesn't my method work for all cases? Like if the factors were: $\{1, 2, 2, 2, 2\}$</li>
</ol>
| 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 |
Game of Thrones House Stark Wolf Glass Bracelets. | 0non-cybersec
| Reddit |
CURSED SNACC. | 0non-cybersec
| Reddit |
FedEx Founder: Tax hikes on top 2% as job killer is ‘mythology’. | 0non-cybersec
| Reddit |
Deploying SSIS (SQL Server 2012) Project Outside Network. <p>I have built an SSIS project on my PC, and am connecting to an SQL 2012 Server outside our network (via SQL Authentication) while executing the package. It is now time to deploy the project to that same server, but I have hit a wall. While going through the built-in deployment wizard, I enter the Server Name (just as I have entered it to connect to the database withing the connection managers) and get an “untrusted domain” error (it is requiring Window’s Authentication rather than SQL Authentication). </p>
<p>I think it may also be relevant that I am using parameters to set environment-specific values in the project. </p>
<p>How do I deploy an SSIS project to a SQL Server outside the network?</p>
<p>I should also add that in my searches, I did come across someone who was struggling to do this with a VPN connection (with no resolution posted), is that how this is typically done?</p>
| 0non-cybersec
| Stackexchange |
Show system of equations with one number and centered. <p>I have an equation which I rearrange in several steps. I want to show this, by having a single numbered equation, which has an aligned equal sign on the right, and the terms left of the equal sign are centered in each line.
So basically it looks like this:</p>
<pre><code> (a+b)^3 =
(a+b)(a+b)^2 =
(a+b)(a+b)(a+b) = (1)
(a^2+2ab+b^2)(a+b) =
(a^3+3a^2b+3ab^2+b^3) =
</code></pre>
<p>I know about aligned, gather and split, but neither seems to achieve, what I want.</p>
<p>Update:
This is no duplicate to the linked question, as I want a fixed sign on the right, and a horizontal centered alignement on the left. The linked question has no horizontal centering in it.</p>
| 0non-cybersec
| Stackexchange |
Knit error in RStudio: pandoc conversion failed with error 23. Extension ascii_identifiers is not supported for markdown. <p>Trying to knit a doc into html, RStudio would hang on the conversion to html part. I looked around and it looked like this happened to other folks when they were using an out of date pandoc version. I updated pandoc to 2.8. I received the error in the title. Looking around again, it appeared that v 2.5 seemed stable. I installed that, restarted my computer, and still get the same error.</p>
<p>repex is the default example when you create an RMarkdown file in RStudio: file -> New file -> R Markdown -> html.</p>
<pre><code>---
title: "repexpandocerror23"
author: "Adam Korejwa"
date: "11/22/2019"
output: html_document
---
```{r setup, include=FALSE}
knitr::opts_chunk$set(echo = TRUE)
```
## R Markdown
This is an R Markdown document. Markdown is a simple formatting syntax for
authoring HTML, PDF, and MS Word documents. For more details on using R
Markdown see <http://rmarkdown.rstudio.com>.
When you click the **Knit** button a document will be generated that
includes both content as well as the output of any embedded R code chunks
within the document. You can embed an R code chunk like this:
```{r cars}
summary(cars)
```
## Including Plots
You can also embed plots, for example:
```{r pressure, echo=FALSE}
plot(pressure)
```
Note that the `echo = FALSE` parameter was added to the code chunk to
prevent printing of the R code that generated the plot.
</code></pre>
| 0non-cybersec
| Stackexchange |
Performance Analysis of AES-CBC Software Implementation
AES-CBC Software Execution Optimization
Razvi Doomun*, Jayramsingh Doma, Sundeep Tengur
Computer Science and Engineering,
University of Mauritius
[email protected], [email protected], [email protected]
Abstract
With the proliferation of high-speed wireless
networking, the necessity for efficient, robust and
secure encryption modes is ever increasing. But,
cryptography is primarily a computationally
intensive process. This paper investigates the
performance and efficiency of IEEE 802.11i
approved Advanced Encryption Standard (AES)-
Rijndael ciphering/deciphering software in Cipher
Block Chaining (CBC) mode. Simulations are used to
analyse the speed, resource consumption and
robustness of AES-CBC to investigate its viability for
image encryption usage on common low power
devices. The detailed results presented in this paper
provide a basis for performance estimation of AES
cryptosystems implemented on wireless devices. The
use of optimized AES-CBC software implementation
gives a superior encryption speed performance by 12
– 30%, but at the cost of twice more memory for
code size.
1. Introduction
Wireless technologies have exploded into
prominence over the last few years, with newer and
more advanced standards emerging all the time. As
wireless traffic becomes more pervasive, the
requirement for high quality security becomes even
more important. All the recent standards have
included security from the start, with the older
standards like IEEE 802.11 being brought up to date
with its 802.11i security extensions. Users are
expecting to secure data transmission and storage on
wireless mobile devices, which require efficient
cryptographic algorithms. Hence, there is increasing
need for efficient AES-CBC software implementation
since it has become a key ingredient in IEEE 802.11i
wireless security protocol [1]. Many of the IEEE
standards, such as 802.11, 802.15 and 802.16 use
AES-CCM [2][1] as the basis for their security; and
this is a good choice because it provides both
encryption and authentication in a single efficient
solution. Security and performance considerations are
therefore both imperative during the design phase of
encryption algorithms.
With the advent of AES in IEEE 802.11i, as
considered in this work, and the high prospects of
wireless systems, this research holds a prominent
position in the evaluation and analysis of the
structure of the Rijndael algorithm (AES-CBC) from
the resource constraint wireless systems point of view.
Many cryptographic algorithms, such as AES-
Rijndael, which are compact and efficient to
implement on high-performance microprocessors,
may not be implementable efficiently on smaller and
less powerful microprocessors found in low-power
mobile devices. A resource-constrained wireless
system’s efficiency is invariably related to the size of
the code [3]. The efficiency of a program increases,
as the code size decreases and the execution speed
increases. Therefore, implementation of
cryptosystems on with very tight memory constraints
mobile devices introduces new challenges. In [4], the
authors investigate the speed measurement of several
cryptographic system libraries to determine if they
are feasible for Palm devices or if they are too
complex. The main finding is that it can be valuable
to encrypt real-time data if pre-computation of certain
steps is allowed but it may cause a problem for
devices with very limited space. Hence, optimization
is often possible through a closer inspection of the
encryption software algorithms.
The security suites can be more broadly classified
by their properties: encryption only (AES-CTR),
followed by authentication only (AES-CBC MAC),
and finally encryption and authentication (AES-CCM)
[1]. AES-CTR (counter mode of cryptographic
operation with AES) means that the CTR mode uses
AES as the block cipher; and provides access control,
data encryption and optional sequential freshness.
Authentication is done using the cipher block
chaining with message authentication code (CBC-
MAC), which creates a message integrity code using
a block cipher in CBC mode, and computes a MAC
over the packet and includes the length of the
authenticated data. The code can be computed upon
packet reception and can be compared with the one
received.
AES-CCM is a combination of the encryption and
authentication suites detailed above. It has three
inputs; the data payload to be encrypted and
authenticated, the associated data (header etc.) to be
authenticated only, and the nonce to be assigned to
the payload and the associated data [1]. There are
varying MAC lengths to choose from for AES-CBC-
MAC and AES-CCM modes of operation (4, 8 or 16
bytes), allowing for some scalability of security
depending on application requirements.
In this paper, we study the performance of AES-
CBC software execution and its operation complexity.
An overview of Rijndael algorithm and complexity is
presented in section 2. The CBC mode is described in
section 3. Simulation results are analyzed and
discussions are provided in section 4 and 5
respectively. Finally, we conclude and summarize the
main findings of the paper.
2. Rijndael block cipher algorithm
The Advanced Encryption Standard (AES)- Rijndael
[5][6] is an iterated symmetric key block cipher with
a variable block length and a variable key length that
can be independently specified to 128, 192 and 256
bits. The four main functions that comprise the AES
algorithm are Add Round Key, Substitute Byte, Shift
Rows and Mix Columns. A data block to be
processed by Rijndael is partitioned into an array of
bytes, called State, and each cipher operation is byte-
oriented. Add Round Key, the first step in the
transformation, performs a bitwise XOR of the state
and the round key matrix. This transformation is its
own inverse. Then, the Sub-Byte transformation is a
non-linear byte substitution operation that is
composed of two sub-transformations: multiplicative
inverse and affine transformation. In typical software
implementations [7], these two sub-steps are
combined into a single table lookup called
substitution box or S-box. The ShiftRows function is
a linear diffusion process that operates individually
on the last three rows of the state matrix. A simple
byte transposition cyclically shifts to the left the
bytes in the rows by an offset varying from one to
three. The second, third and four rows’ elements are
shifted one byte, two bytes and three bytes to the left,
respectively. For full encryption, the data is passed
through Nr rounds (Nr=10, 12, 14) that are governed
by the four transformations, as shown in figure 1.
Most software based AES implementations are
written in the C/C++, assembler or Java
programming languages. Since these
implementations are based on different APIs,
processors, compilers and various design
assumptions, they are hard to compare. Some
researchers however, have tried to compare the AES
performance in an efficient way on various platforms.
Figure 1 AES transformation
Paper [8] claims that the fastest software based AES
implementation requires 237 cycles to encrypt one
data block. This result was obtained on a Pentium II
450 MHZ platform and the software implementation
was optimized on the basis of several large pre-
calculated tables. Furthermore, the work also
assumed that all data variables are directly available.
AES-Rijndael computational analysis
There are two methods commonly used in order to
distinguish between time critical operations and non
time-critical AES operations [10]. The first method is
based on analyzing AES transformations on
arithmetical or mathematical level, while the second
method is based on analyzing the transformations on
the amount of executed instructions. The basis of the
first method is: what are the arithmetical operations
and how many clock cycles will these operations
require. The second method will be performed by
using a simulator that will give a detailed profiling
information of the executed instructions.
An mathematical analysis of AES computational
cost is given in [9][10], and each AddRoundkey is
implemented with 8Nb bytewise-ANDs and 4Nb
bytewise-ORs, where is Nb = block length/32, each
SubByte operation incurs 3Nb bytewise-ANDs and
2Nb bytewise-ORs, each ShiftRows consists of 3Nb
shifts of bytes and 3Nb bytewise-ORs and each round
operation with 19Nb bytewise-XORs, 8Nb bytewise-
ORs and 64Nb shifts; or 38Nb bytewise-ANDs, 27Nb
bytewise-ORs and 64Nb shifts. AES for one block of
data is a function of the block size, the key size, the
number of encryption rounds (Nr) and the number of
processing cycles required for performing basic
operations bytewise-AND (Ta), bytewise-OR (To),
and bytewise shift (Ts) and expressed in general
terms as:
TAES-ENCRYPT = (46Nb Nr – 30Nb)Ta + [31Nb Nr +
12(Nr – 1) – 20Nb ]To + [64Nb Nr + 96(Nr – 1) – 61
Nb]Ts.
A significant limitation of AES is related to its
decryption because the cipher and its inverse make
use of partially different code. The decryption code
has Inverse MixColumns operation, which uses a
transformation with another polynomial, 0Bx3 + 0Dx2
+ 09x + 0E. This leads to extra processing complexity
for decryption as multiplication by bigger
coefficients is more complex. The difference in
computation between one Inverse MixColumn and
MixColumn operation is [96NbTa + 72NbTo –
32NbTs].
Therefore, the total number of processing cycles in
computational effort required for AES decryption of
one block of data is given:
TAES-DECRYPT = TAES-ENCRYPT + {[96 NbTa + 72 NbTo –
32 NbTs] × (Nr – 1)}.
On analyzing AES transformations on arithmetical
level, showed that the MixColumn and the Inverse
MixColumn transformation are the most time-critical
operation. The second method, which was based on
the simulation tests, showed that the MixColumn and
the Inverse MixColumn transformation contain the
most executed instructions, and that most of these
instructions are related to integer computations.
Therefore one can conclude that the MixColumn and
Inverse MixColumn transformation are indeed the
most time-critical operations.
3. CBC mode
The Cipher Block Chaining (CBC) [12] is a popular
block cipher mode operation where each plaintext is
XORed with the previous ciphertext block before
being encrypted. Hence, each ciphertext is dependent
on all plaintext blocks up to that stage. A plaintext
message M is divided into t n-bit blocks Mi and the
ciphertext Ci is given as:
)( 1−⊕= iiki CMEC , i= 1, 2, …t.
In the CBC mode, the value Ci-1 is used to randomize
the plaintext by combining with data blocks Mi to
hide patterns and repetitions. To enable the
encryption of the first plaintext block (i=1), C0 is
defined as the Initial Value (IV), which should be
randomly chosen and transmitted securely to the
recipient.
Figure 2: CBC model
CBC mode is as secure as the underlying block
cipher against standard attacks. In addition, any
patterns in the plaintext are concealed by the XORing
of the previous ciphertext block with the plaintext
block. Note also that the plaintext cannot be directly
manipulated except by removal of blocks from the
beginning or the end of the ciphertext. The
initialization vector should be different for any two
messages encrypted with the same key and is
preferably randomly chosen. It does not have to be
encrypted and it can be transmitted with (or
considered as the first part of) the ciphertext. CBC
overcomes the security deficiency of the electronic
codebook mode; the input to the encryption algorithm
consists of the XOR of the plaintext block and the
ciphertext produced from the previous plaintext block
as illustrated in figure 2. This makes it more difficult
for a cryptanalyst to beak the code using strategies
that look for patterns in the ciphertext, patterns that
may correspond to the known structure of the
plaintext. With this chaining scheme, the ciphertext
block for any given plaintext block becomes a
function of all the previous ciphertext blocks.
4. Simulation results
Software encryption is still being widely used due to
the software features of portability and flexibility.
However, unoptimized software encryption is very
slow and is insecure in many aspects of key
management and program manipulation. The coding
of the program was performed in the C language,
which is a high-level language defined at higher
abstract levels and is programmer-friendly. The high-
level language needs to be compiled into a low-level
language before execution. The main advantage of
using a high-level language is code portability i.e. the
ability of the code to be transferred to a different
system or environment with minimal amounts of
modification and redevelopment.
Modularization of encryption software is the
technique of splitting a large program into smaller
modules. The advantage of modularization is the ease
of maintenance and code debugging. Modularization
helps in code-reuse, which reduces run-time memory.
A cryptographic system is developed as a separate
module with sub-modules implementing the details.
In the C language, modularization is achieved by
dividing the code into various functions. When the
embedded system needs to encrypt or decrypt data it
invokes the corresponding module, which executes
its tasks and then returns the output to the host
function. The main program was divided into
different modules termed encrypt(), decrypt()and
KeyExpansion() functions.
Optimization
Maintaining pre-computed tables to simplify program
operations and improve performance is a common
practice. For AES, a method to combine different
operations of the round transformation in a single set
of table lookups was suggested in [11]. This approach
basically combines the matrix multiplication required
in the MixColumn operation with the S-box, and
involves 4 tables with 256 4-byte entries, i.e., 4
KByte of memory. Because encryption and
decryption must use different tables, the total
memory requirement amounts to 8 KByte. Another
solution is to trade memory for speed, and use two
256-byte lookup tables for the SubByte and
InvSubByte operations, while implementing the Mix-
Column/Inverse MixColumn operations separately.
Here, again, various trade-offs are possible. Each call
to the MixColumn or InvMixColumn operations
results in sixteen field multiplications. A
straightforward implementation of the multiplication
operation in the field is MIPS-intensive. Since one of
the multiplicands is fixed (with values limited to 6
field elements, i.e., f01g; f02g and f03g for
MixColumn and f0bg; f0dg, and f09g for
InvMixColumn), a conventional field multiplication
operation can be replaced by a table lookup, requiring
a new 6x256 table, each element of which is 8-bit
wide. Image specifications used for simulation are
summarized in table 1.
Table 1: Image Type and Size
Recursive tasks have an overhead that needs to be
checked when the instruction sequence should jump
out of the loop. For a small number of repetitions, the
overhead could be removed altogether by replacing
the loop with the code components for that fixed
number of times. This technique is called loop
unrolling. When two loops are being executed with
similar tasks that can be sequentially adjusted, it is
better to combine the two loops into a single loop.
This technique is called loop merging. This reduces
the total overhead time of executing multiple loops to
the overhead of a single loop.
AES-ECB with increasing key size/rounds e.g.
128/10, 192/12 and 256/14 causes: AddRound Key
execution time to increase by 13 – 16 %; SubBytes
execution time increases by 17 – 22%; ShiftRow
execution time increases 20 – 22 % and Mixcolumn
execution time increase 21 – 25%. When the number
of AES rounds is increased by 2 stepwise (i.e. 2, 4, 6,
8…), the encryption time for a data block of 16 bytes
is augmented by a margin of 14-19% whereas a 15-
30% rise is observed in the decryption time.
After software optimisation techniques were applied:
• SubBytes()showed a performance gain of 20
% in terms of execution speed.
• ShiftRows() displayed a performance of 30
% in terms of execution speed.
• AddRoundKey() displayed a performance
gain of 21 % in terms of execution speed.
• Mixcol() displayed a performance gain of 13
% in terms of execution speed.
This shows that a 20 – 30 % performance gain was
obtained by optimizations for encrypt() function
ShiftRows() experienced the best ratio of
optimisation than all other sub-functions.
MixColumns() was one of the least optimized
function. This was due to the implementation of a
look-up table for the GF multiplication. . Simulations
were performed on a Pentium-4 3.0 GHz with 512
MB DDR RAM. Figure 3 shows the encryption time
results for different optimization scenario and cipher
parameters. We examined the performance of
encryption/decryption by optimizing the round
transformation operations. Alternate round execution
gives a trade-off between minimizing code size and
reducing execution time.
AES-ECB 128/10 rounds partially optimized with
alternate rounds (Opt1) gives 13% less encryption
time compared to original unoptimized. AES-ECB
128/10 partially optmized with two alternate rounds
(Opt2) gives a performance gain of 12 % on
encryption time. AES-ECB 128/10 fully optimized
(OptF) improved encryption time by 20% but with
memory storage for code size that is doubled.
Figure 3: Encryption time v/s varying image
size (117, 263, 468 Kbytes) for different key
size 128/10, 192/12, 256/14 and optimization
scenarios.
5. Results discussion
In many cases, programs have a high-cost critical
path that needs to be optimized. It is therefore
necessary to optimize the critical paths to a higher
extent than the less critical paths. A complex
mathematical can be made simple by dividing it into
smaller components so that they can be executed in
parallel. Observations from the various stages of the
code optimizations revealed that the MixColumns()
function was consuming more time than other sub-
modules combined in the encrypt() function. This
was due to the mul() function in the MixColumns()
function, which was used to perform the Galois Field
(GF) multiplication on the data operands. GF
multiplication was performed by implementing a
look-up table to defeat any timing attacks. The results
reveal that decrypt() takes more time than encrypt().
This is due to the added complexity of the GF
multiplication in InvMixColumns() of decrypt().
The InvMixColumns() needs to perform four
multiplications while the MixColumns() needs to
perform only two multiplications per each byte of the
state. Complex functions in AES can be made
simpler by exploring other alternatives such as look-
up tables and bit-manipulation. The SubBytes() can
be implemented by using the formula but it
consumes lot of processor cycles. So, SubBytes()
was implemented by using a look-up table. Some
tasks in a program need to be executed a finite
number of times. Recursive tasks have an overhead
that needs to be checked when the instruction
sequence should jump out of the loop. For a small
number of repetitions, the overhead could be
removed altogether by replacing the loop with the
code components for that fixed number of times. This
technique is called loop unrolling. Code Sample A
presents the loop unrolling for AddRoundKey() and
Code Sample B presents loop unrolling for
SubBytes().
Initial code:
int i, j;
for (i=0; i<4; i++)
for(j=0; j<4; j++) a[i][j] ^= rk[i][j];
Modified code:
int i;
for (i=0; i<4; i++)
{
a[i][0] ^= rk[i][0];
a[i][1] ^= rk[i][1];
a[i][2] ^= rk[i][2];
a[i][3] ^= rk[i][3];
}
Code Sample A: Loop unrolling for AddRoundKey( )
Initial code:
int i, j;
for (i=0; i<4; i++)
for(j=0; j< BC; j++)
a[i][j] = box[a[i][j]];
Modified code:
int i;
for (i=0; i<4; i++)
{
a[i][0] = box[a[i][0]];
a[i][1] = box[a[i][1]];
a[i][2] = box[a[i][2]];
a[i][3] = box[a[i][3]];
}
Code Sample B: Loop unrolling for SubBytes( )
When two loops are being executed with similar
tasks that can be sequentially adjusted, it is better to
combine the two loops into a single loop. This
technique, called loop merging, reduces the total
overhead time of executing multiple loops to the
overhead of a single loop. Code Sample C presents
the loop unrolling and merging with constants
substitution for ShiftRows( ).
Initial code:
int i, j;
for (i=0; i<4; i++)
{
for(j=0; j< BC; j++)
tmp[j] = a[i][(j + shifts[BC-4][i]) % BC];
for(j=0; j< BC; j++) a[i][j] = tmp[j];
}
Modified code:
int i;
for (i=1; i<4; i++)
{
tmp[0] = a[i][(0 + i) % BC];
tmp[1] = a[i][(1 + i) % BC];
tmp[2] = a[i][(2 + i) % BC];
tmp[3] = a[i][(3 + i) % BC];
a[i][0] = tmp[0];
a[i][1] = tmp[1];
a[i][2] = tmp[2];
a[i][3] = tmp[3];
}
Code Sample C: Loop unrolling and merging
To maintain a balance between optimization and code
size, only internal loops have been unrolled. Loop
unrolling makes the code run smoothly in low
processor-intense devices while monitoring the code
size ensures efficient use of memory. This is because
small mobile devices such as smart phones and PDAs
have small embedded memory and might not be able
to fit the program in the memory if the code is bulky.
AES encryption and decryption code size for
optimized and unoptimized versions are given in
table 2.
Table 2: Unoptimised v/s Optimised AES
Code Size
(a) (b) (c)
Figure 4: (b) AES-ECB v/s (c)AES CBC
Figure 5a: AES-ECB using increasing
number of rounds (2,4,10)
Figure 5b: AES-ECB using varying number of
rounds (2, 4, 10)
Figure 5c: AES-CBC for any number of
rounds
(a) before encryption
(b) after encryption
Figure 6: Image histograms before and after
encryption
When the image contains homogeneous texture zones,
all the identical blocks having same content also
produce same output after AES-ECB ciphering. The
AES-ECB mode of operation failed to conceal all the
hidden details (visual texture patterns) of a bitmap
image and AES-CBC had the highest encryption time.
Hence, the AES-ECB encrypted image will also
contain textured zones and the entropy of the image
is not maximum, as shown in figure 4 and figure 5.
As the number of AES-ECB encryption rounds
increases, the visual texture patterns are concealed to
higher degree. An ideal encrypted image shows a flat
histogram distribution of pixels values. The image
histogram in figure 6 shows the distribution of RGB
pixel values for the unencrypted image and the three
encrypted colour channels. Various colour peaks can
be noted, showing that textures and visual
components exist in the unencrypted image. Previous
simulations have demonstrated that the AES
algorithm performs well for encryption and the
resultant images are scrambled. However, it is true
that for some types of images, mainly single objects
on a plain monochrome background, the AES-ECB
encrypted image still holds some visual information
about the original image such as shape and texture in
some cases.
6. Conclusion
There are many design tradeoffs to consider when
implementing the AES-CBC algorithm in software.
In resource-constrained platform, the memory
requirements, power consumption and throughput are
important considerations. The AES-ECB and CBC
image encryption software is analyzed thoroughly in
this paper. Our experimental results show that AES-
CBC achieves the higher security performance
compared to AES-ECB scheme, although the speed
of encryption degrades marginally. Visual
appearance of test images demonstrates the superior
confusion and diffusion properties of AES-CBC
since there is full scrambling.
As future work, we are investigating further memory
optimization using pre-computed tables to enhance
the round operations, such as SubByte/InvSubByte, by
exploiting similarities between encryption and
decryption. As the AES encryption scheme becomes
more widely used, the concept of mixed software and
hardware design is also a growing new area of
interest.
7. References
[1] IEEE Standard for Information Technology –
Telecommunications and Information Exchange between Systems
– Local and Metropolitan Networks – Specific requirements, Part
II Amendment 6: Medium Access Control (MAC) Security
Enhancements, IEEE Std 802.11i – 2004.
[2] R. Struik, “Formal specification of the CCM* Mode of
operation.” Doc no. IEEE 15-04-0537-00-004b.
[3] Rainer Leupers, “Code Optimization Techniques for Embedded
Processors –Methods, Algorithms, and Tools”, Kluwer Academic
Publishers, 2000.
[4] Duncan S. Wong, Hector Ho Fuentes, Agnes H. Chan, “The
Performance Measurement of Cryptographic Primitives on Palm
Devices” In the Proceedings of the 17th Annual Computer Security
Applications Conference, December 2001.
[5] NIST-FIPS Standard “Announcing the Advanced Encryption
Standard (AES),” in Federal Information Processing Standards
Publication no. 197, November 2001.
[6] J. Daemen, V. Rijmen, "The block cipher Rijindael",
Proceedings of the Third International Conference on smart card
Research and Applications, CARDIS’98, Lecture Notes in
computer Science, vol.1820, Springer, Berlin, 2000, pp.277-284.
[7] G. Bertoni, L. Breveglieri, P. Fragneto, M. Macchetti and S.
Marchesin, ” Efficient Software Implementation of AES on 32-bit
platforms” in Cryptographic Hardware and Embedded Systems
CHES 2002, pp. 159-171.
[8] K. Aoki1 and H. Lipmaa, “Fast implementations of AES
candidates”, Third AES Candidate Conference (New York City,
USA), April 2000.
[9] R. Doomun, KMS Soyjaudah, D. Bundhoo, “Energy
Consumption and Computational Analysis of Rijndael-AES”,
Third IEEE International Conference in Central Asia on Internet
The Next Generation of Mobile, Wireless and Optical
Communications Networks, ICI 2007, September 26-28, 2007.
[10] R. Doomun, KMS Soyjaudah, “Analytical Comparison of
Cryptographic techniques for Resource Constrained Wireless
Security”. http://ijns.nchu.edu.tw/ International Journal of Network
Security. (accepted Feb 2008)
[11] J. Daemen., Rijmen, V., “AES Proposal: Rijndael”, AES
submission, 1998. Available at
<http://csrc.nist.gov/encryotion/aes/aes_home.htm>.
[12] William Stallings, “Cryptography and Network Security”, 2nd
Edition, Prentice Hall, 1999.
| 1cybersec
| arXiv |
Testing against -n option in BASH scripts always returns true. <p>I am writing a bash script, in which I am trying to check if there are particular parameters provided. I've noticed a strange (at least for me) behavior of <code>[ -n arg ]</code> test. For the following script:</p>
<pre><code>#!/bin/bash
if [ -n $1 ]; then
echo "The 1st argument is of NON ZERO length"
fi
if [ -z $1 ]; then
echo "The 1st argument is of ZERO length"
fi
</code></pre>
<p>I am getting results as follows:</p>
<ol>
<li><p><strong>with no parameters:</strong></p>
<pre><code>xylodev@ubuntu:~$ ./my-bash-script.sh
The 1st argument is of NON ZERO length
The 1st argument is of ZERO length
</code></pre></li>
<li><p><strong>with parameters:</strong></p>
<pre><code>xylodev@ubuntu:~$ ./my-bash-script.sh foobar
The 1st argument is of NON ZERO length
</code></pre></li>
</ol>
<p>I've already found out that enclosing <code>$1</code> in double quotes gives me the results as expected, but I still wonder <strong>why both tests return true when quotes are not used and the script is called with no parameters?</strong> It seems that <code>$1</code> is null then, so <code>[ -n $1 ]</code> should return false, shouldn't it?</p>
| 0non-cybersec
| Stackexchange |
AITA for telling my husband of 15 years that I never want to have sex again?. My husband and I have been married for about 15 years, dating for much longer. He's my soulmate and I can't imagine being with anyone other than him, he feels the same way. I've never really enjoyed sex that much, but my husband has an incredibly high sex drive so we used to have sex every other day. I've had sex with many partners (upwards of 30) in both relationships and hookups and I've just never really enjoyed it. It's inevitable that you're going to ask, but yes they can make me orgasm, I just don't like orgasming with a partner versus orgasming with myself. It just doesn't feel good to me.
​
There's something about sex that I just don't really like (please don't say I need therapy, it's insulting to think that everybody must LOVE sex. I've also been to therapy before and we've come to the conclusion that it's mostly just a preference). I also don't identify as asexual though, because I do get horny and love masturbating, but I find it more of a release if that makes sense? It's more of an intimate moment with myself. I can try and explain more in the comments if this doesn't really make sense, but it's more a nonsexual release and enjoyment of exploring my own body.
​
As we've gotten older with kids we've stopped having sex as frequently, two to three times a month *at most.* He knows I've never been a huge fan of sex, but I've recently told him that I want to stop having sex. I find it more a chore and I don't really gain much pleasure from it. He was so hurt and upset saying that I'm going to trap him in a loveless and sexless marriage.
​
I told him that if he really wanted to have sex with other people, he could have sex with other women, I just wouldn't wanna know about it. He was so upset and said that I was the only woman he wants to have sex with and that he could never imagine having sex with somebody else. A couple days ago he caught me mastubating (something I do once a day) and he was even more hurt. He said how come you get horny but you don't want to have sex with me? I tried explaining what I typed above but he got even more hurt. We really love each other and have an amazing relationship aside from this, but he thinks I'm an asshole for making an executive decision about our sex life and trapping him in a lifetime without sex. So AITA for having a preference?
​
tl;dr have never really liked sex, decided I still want to masturbate but no longer have sex with my husband
​
edit: everyone seems to think my husband is going to divorce me over this, we've discussed it and divorce isn't even something he's considering. Redactors are so quick to pull the divorce card when in reality there are so many other aspects to a heathy relationship that can't be explain in 3000 characters. Our marriage is strong, supportive and loving in many other ways. I don't feel like we need sex to still love each other | 0non-cybersec
| Reddit |
I think I just interrupted a meeting I wasnt supposed to know about. | 0non-cybersec
| Reddit |
secure certain data on my webserver. <p>I've developed a website where people add their sensitive data. Not credit cards, but lets say they share things about themselves which are private and it wouldn't be good if other people see that info. Some of the data is private, some is public.</p>
<p>I want to keep the private data private as in... If someone breaks into the server I want them to be able to extract encrypted versions, rather than plane text about my users' accounts.</p>
<p>What I've thought about so far is the following.
1. SSL certificate (doesn't really protect the data on the server, but the connection)
2. the data which is market private to be encrypted by a series of algorithms (I would imagine that would be heavy on the server)
3. encrypt the php functions which encodes/decodes the data.</p>
<p>I'm not very well prepared for this tho, so I would like to know what is considered best practice for my situation? Am I overcomplicating the process?</p>
<p>The thing is that the app is not generating any income so I can't afford a sys admin, nor I'm able to look after the traffic 24/7. I'm looking for a solution which will take care on its own. Also I can't spend $$$ on sophisticated software that would do the job. I'm looking to bootstrap the app as much as possible. I can afford the SSL cert but not a 600$ Zend Guard for instance.</p>
<p>PS.
I've used codeigniter so far to write my php code if that matters.</p>
<p>Suggestions?</p>
| 0non-cybersec
| Stackexchange |
How to cross join unnest a JSON array in Presto. <p>Given a table that contains a column of JSON like this:</p>
<pre><code>{"payload":[{"type":"b","value":"9"}, {"type":"a","value":"8"}]}
{"payload":[{"type":"c","value":"7"}, {"type":"b","value":"3"}]}
</code></pre>
<p>How can I write a Presto query to give me the average <code>b</code> value across all entries?</p>
<p>So far I think I need to use something like Hive's <a href="https://cwiki.apache.org/confluence/display/Hive/LanguageManual+UDF#LanguageManualUDF-explode" rel="nofollow noreferrer">lateral view explode</a>, whose equivalent is <a href="https://prestodb.io/docs/current/migration/from-hive.html#use-unnest-to-expand-arrays-and-maps" rel="nofollow noreferrer">cross join unnest</a> in Presto.</p>
<p>But I'm stuck on how to write the Presto query for <code>cross join unnest</code>.</p>
<p>How can I use <code>cross join unnest</code> to expand all array elements and select them?</p>
| 0non-cybersec
| Stackexchange |
When you think you'll get away with a hit and run but your license plate stays behind. | 0non-cybersec
| Reddit |
Disallowed Welbeck goal vs. Bayern. | 0non-cybersec
| Reddit |
Don't worry, Obelix is here is watch over your kids at the pool.. | 0non-cybersec
| Reddit |
Introducing a fellow gif maker to the crazy, wonderful people of HQG.. | 0non-cybersec
| Reddit |
I think whoever made this one wins.. | 0non-cybersec
| Reddit |
White Roses and Lilacs | Megan Mac @ Mercy Seat Tattoo; Kansas City MO. | 0non-cybersec
| Reddit |
The Torbjorn Balancing Act. As we've learned from Star_'s first impressions video, Torbjorn might be dramatically underpowered at the moment. Much like the Engie in TF2, he needs scrap to build his turrets. Unlike the Engie in TF2, he doesn't have an easy supply to it. Apparently the only way to get it is by killing enemies and cleaning up dead bodies, which puts him in a front-lines position where he's likely much less useful that most direct-combat heroes like Reaper or McCree.
I think the Shoutcast demonstration match showed these problems off as well. We didn't see Torbjorn hardly at all short of his "Kill Dozer" near the end, which required his ult.
So how can we help our poor Svedish Dwarf not be a one-trick pony that's only useful when he gets his ult up? My recommendation would be allowing him to gradually generate metal over time. Not enough that him being in the fight and gathering off of corpses wouldn't still be key, but still allow him to get some lvl 2 or lvl 3 sentries up without his ult.
Thoughts? | 0non-cybersec
| Reddit |
Flushing numpy memmap to npy file. <p>Is there a method to save a numpy memmap array into a <code>.npy</code> file? Apparently, there is a method to load such an array from a <code>.npy</code> file as follows</p>
<pre><code>data = numpy.load("input.npy", mmap_mode='r')
</code></pre>
<p>but flushing the file is not equivalent to storing it in a <code>.npy</code> format.</p>
<p>If flushing is the only way to go then is there a way to infer the shape of the stored array? I would prefer to have dynamic shape which is automatically stored and retrieved (possibly as memmap again) in another script.</p>
<p>I have searched on various places about this but didn't find get any result. I way to store into <code>.npy</code> I do now is</p>
<pre><code>numpy.save(output.filename, output.copy())
</code></pre>
<p>which defeats the idea of using memmap but preserves the shape.</p>
<p><strong>NOTE:</strong> I know about hdf5 and h5py but I was wondering if there is a pure numpy solution to this.</p>
| 0non-cybersec
| Stackexchange |
How to show alert message when closing a window?. <blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="https://stackoverflow.com/questions/333665/how-to-prevent-closing-browser-window">How to prevent closing browser window?</a> </p>
</blockquote>
<p>I want to show an alert message "Please logout before closing the window" with an logout button, when an user tries to close the window and after clicking on logout button the window can be closed. How to achieve this?</p>
| 0non-cybersec
| Stackexchange |
An application of Holder's Inequality. <p>Suppose <span class="math-container">$1\leq p,q\leq \infty$</span> and <span class="math-container">$1/p+1/q=1$</span>. Let <span class="math-container">$f\in\mathcal{L}^p(E)$</span>. Show that <span class="math-container">$f=0$</span> a.e. if and only if
<span class="math-container">\begin{align*}
\int_E f\cdot gdm=0
\end{align*}</span>
for all <span class="math-container">$g\in \mathcal{L}^q(E)$</span>. Hint: Choose a smart <span class="math-container">$g$</span> so that <span class="math-container">$\int_Ef\cdot gdm=\|f\|_p^p$</span>.</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 |
Leigh Alexander writes a piece that is relevant to the gaming community at large, but I think should particularly be heard by /r/gaming.. | 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 |
April fool's: Google trends. | 0non-cybersec
| Reddit |
iOS Firebase Crash Reporting - Error running build script. <p>I get the following error when running the script to upload symbol files (everytime I try and build my project):</p>
<blockquote>
<p>upload-sym-util.bash:351: error: symbolFileUploadLocation: The API Key and the authentication
credential are from different projects.</p>
</blockquote>
<p>Here is my build script:</p>
<pre><code>if [ "$CONFIGURATION" == "Debug" ]; then
GOOGLE_APP_ID=<app-id>
"${PODS_ROOT}"/FirebaseCrash/upload-sym "${SRCROOT}"/<app>/Firebase/CrashReportingKey-Dev.json
else
GOOGLE_APP_ID=<app-id>
"${PODS_ROOT}"/FirebaseCrash/upload-sym "${SRCROOT}"/<app>/Firebase/CrashReportingKey.json
fi
</code></pre>
<p>Things I've done/checked:</p>
<ol>
<li>The <code>GOOGLE_APP_ID</code> and <code>CrashReportingKey*.json</code> are associated with the same project.</li>
<li>My <code>GoogleService-Info*.plist</code> files have the <code>API_KEY</code> field.</li>
<li>Checking "Run script only when installing" box, which allows me to run the app, but doesn't actually run the script in a development environment. So crashes are sent to Firebase, but they aren't symbolicated.</li>
</ol>
<p>I'm open to any ideas. Thanks!</p>
| 0non-cybersec
| Stackexchange |
Why not seeing shell globs as a "dialect" of regex?. <p>I often confuse Bash 3.x shell globs:</p>
<pre><code>? # Match any single character.
* # Match any string of characters (up until the asterisk).
[set] # Match any character in set (but not the entire set itself).
[!set] # Match any character not in set.
</code></pre>
<p>with regex (especially <a href="https://en.wikipedia.org/wiki/Perl_Compatible_Regular_Expressions" rel="nofollow noreferrer">PCRE</a>).</p>
<p>My question is why not seeing these as "Bash regex" (just as we have "JavaScript regex" for example)?</p>
<p>Why not seeing these as just another "dialect" of regex?</p>
<p>Of course it would be unorthodox, but I'm not sure there isn't any formal-logical reason not to.</p>
| 0non-cybersec
| Stackexchange |
sys.getrefcount() prints one more than the expected number of references to an object?. <p>I would like to know why this code prints <code>4</code> instead of <code>3</code>. Where is the fourth reference?</p>
<pre><code>import sys
def f(a):
print(sys.getrefcount(a))
a = [1, 2, 3]
f(a)
</code></pre>
| 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 |
Retired Master Cpl. Paul Franklin, who lost both legs in Afghanistan to a suicide bomber in 2006, says every year he has to prove to Canadian Veterans Affairs that he still has no legs and needs a wheelchair.. | 0non-cybersec
| Reddit |
Bash Terminal colors for filetypes. <p>Bash terminal seems to not have colors for certain types of files, such as docx, pdf...</p>
<p>Is it possible to add colors for these in the output of <code>ls</code>, or no?</p>
| 0non-cybersec
| Stackexchange |
What tape backup device can read a DC 2120 XL cartridge?. <p>While preparing to move to a new house, I came across two forgotten tape backup mini cartridges from 1996. I know they hold the only backup I made of my original Remote Access BBS, with all my original Star Trek themed ANSI art, DOS/OS2 shareware, and 1000+ users.</p>
<p>I'd love to be able to resurrect this time-capsule, but what hardware device can actually read this?</p>
<p>I think I originally used a 50pin Wide-SCSI external backup, narrower & longer than an external CD-Rom drive (caddy-style). Backup restoration software I'm not worried about as I'm certain I can find something on Linux to suffice, I just need to find the hardware ;)</p>
<p>Here is the mystery cartridge in question:</p>
<p><img src="https://i.stack.imgur.com/xqeOU.jpg" alt="DC 2120 XL Minicartridge"></p>
<p>The cartridge size is:</p>
<ul>
<li>3 3/16"(w) x 2 3/8"(h) x 5/8"(d), or</li>
<li>8cm(w) x 6cm(h) x 1.5cm(d)</li>
</ul>
<p>Thanks!</p>
| 0non-cybersec
| Stackexchange |
I decided to try braving the harsh wilderness that is the rest of Reddit. My face when I finally come back to r/trees.. | 0non-cybersec
| Reddit |
mongoDB: querying for a document that has an object reference. <p>I have a widgets collection that has records like this:</p>
<pre><code>{ "_id" : ObjectId("55a6abe193819c033d4d755a"), "name" : "widget1"}
{ "_id" : ObjectId("55a6abe193819c033d4d755a"), "name" : "widget2", "loc" : ObjectId("55a69475da314d9984fc6201") }
</code></pre>
<p>I also have a locations collection that looks like this: </p>
<pre><code>{ "_id" : ObjectId("55a69475da314d9984fc6201"), "abbrev" : "CAN", "description" : "Canada" }
{ "_id" : ObjectId("55a6948eda314d9984fc6202"), "abbrev" : "USA", "description" : "United States" }
{ "_id" : ObjectId("55a69496da314d9984fc6203"), "abbrev" : "MEX", "description" : "Mexico" }
</code></pre>
<p>If I want to find all widgets that are located in Canada, using the Objectid, I know I can do this: </p>
<pre><code>> db.widgets.find( { loc: ObjectId("55a69475da314d9984fc6201")})
{ "_id" : ObjectId("55a6abe193819c033d4d755a"), "name" : "widget2", "loc" : ObjectId("55a69475da314d9984fc6201") }
</code></pre>
<p>But what if I want to search for locations not using the objectid but the abbreviation or the description? How would I do that? </p>
| 0non-cybersec
| Stackexchange |
A 2.0l Nissan 240SX was de-stroked to 1.5l and turbo charged to set a land speed record in its class. | 0non-cybersec
| Reddit |
Restore SQL database to newer version. <p>I'm using Drupal 7 on Windows and its using SQL Server 2008 RS2 (SP2).
Now, I have to move my site and new server using SQL Server 2016.</p>
<p>How can I restore my database to new server? Is it possible?</p>
<p>Thanks.</p>
| 0non-cybersec
| Stackexchange |
McRegion to be officially implemented in Minecraft?. | 0non-cybersec
| Reddit |
Statue identification?. Looking to identify who or what is portrayed in this statue
http://i.imgur.com/pVQYXSt.jpg | 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 |
Minina and maxima (2-variable function). <p>I need to find a minima and maxima of a function $z = x^2 - 12x + y^2 - 2y$ that is limited by points $A(-7,-5)$, $B(5;-5)$ and $C(5,10)$ but i do not clearly understand the algorithm $><$</p>
<p>What should i do? Especially with equation of $CA$ line ($y = 1.25x + 3.75$)</p>
| 0non-cybersec
| Stackexchange |
TIFUpdate: TIFU by possibly tearing the cords of my eyeball. [I'M OK! :D]. Just got back from the optometrist in Peterborough!
The eyedrops made my pupils dilate to the point where there was like a 2mm ring around my pupil, nothing more. Couldn't see shit.
The optometrist said that what happened was most likely inflammation caused by dryness in the eye.
The cause of this? My hypothyroidism.
I was given some eyedrops to take if it happens again.
I have two more appointments for this on the 19th of April and on the 1st of May.
tl;dr: Why would you need one?
Actual tl;dr: Had Optic Neuritis, but it was NOT linked to MS.
-----------------------------------------------
Previous update thread: http://www.reddit.com/r/tifu/comments/1b5dhb/tifupdate_tifu_by_possible_tearing_the_cords_of/
-----------------------------------------------
Original post: http://www.reddit.com/r/tifu/comments/1b0jy2/tifu_by_possibly_tearing_the_cords_of_my_eyeball/ | 0non-cybersec
| Reddit |
Python: sending data between two computers via sockets. <p>I am working on a script that would transmit the data between two distinct computers with access to the internet. I am using python's socket standard module. It works fine when I run both client and server on single computer but I am not able to make the things work when they run on different computers. </p>
<p>Here is a part of my server code:</p>
<pre><code>import socket, time,os, random
class Server():
def __init__(self,Adress=('',5000),MaxClient=1):
self.s = socket.socket()
self.s.bind(Adress)
self.s.listen(MaxClient)
def WaitForConnection(self):
self.Client, self.Adr=(self.s.accept())
print('Got a connection from: '+str(self.Client)+'.')
s = Server()
s.WaitForConnection()
</code></pre>
<p>And here is a part of my client code:</p>
<pre><code>import socket
class Client():
def __init__(self,Adress=("Here is the IP of the computer on which the \
server scrip is running",5000)):
self.s = socket.socket()
self.s.connect(Adress)
c = Client()
</code></pre>
<p>When I run these scripts on two different computers with internet access the client is unable to connect and raises an error and the server is waiting for connections forever. </p>
<p>What am I doing wrong?</p>
| 0non-cybersec
| Stackexchange |
Creamy Scallop Fettuccine with Lemon and Capers. | 0non-cybersec
| Reddit |
Using ActionCable with multiple identification methods. <p>I develop a Ruby on Rails 5.1 application using ActionCable. <a href="https://rubytutorial.io/actioncable-devise-authentication/" rel="noreferrer">User authentification via Devise</a> works fine for several channels. Now, I want to add a <strong>second type of channels</strong> which does not require any user authentification. More precisely, I would like to enable anonymous website visitors to chat with support staff.</p>
<p>My current implementation of <code>ApplicationCable::Connection</code> for authenticated users looks like this:</p>
<pre><code># app/channels/application_cable/connection.rb
module ApplicationCable
class Connection < ActionCable::Connection::Base
identified_by :current_user
def connect
self.current_user = find_verified_user
end
protected
def find_verified_user
user = User.find_by(id: cookies.signed['user.id'])
return user if user
fail 'User needs to be authenticated.'
end
end
end
</code></pre>
<p>Anonymous users will be identified by some random UUID (<a href="https://ruby-doc.org/stdlib-2.2.3/libdoc/securerandom/rdoc/SecureRandom.html#method-c-urlsafe_base64" rel="noreferrer"><code>SecureRandom.urlsafe_base64</code></a>).</p>
<p><strong>Question:</strong></p>
<p>How do I best add this new type of channels? Could I add a boolean flag <code>require_authentification</code> somewhere, override it in my inherited channel class for anonymous communication, and switch the identification method in <code>Connection</code> depending on this attribute? Or would I rather have to implement a completely new module, say <code>AnonymousApplicationCable</code>?</p>
| 0non-cybersec
| Stackexchange |
Fucking wife's hot friend. A guy had a crush on his wife's hot friend, so he invited her for a camping trip.
while camping he wanted to get rid of his wife so he told her:Honey, why don't you go grab us some flowers? as soon as the wife went.
husband: I'll give you 20$ for a blowjob
friend: No
husband:50$
friend:No
husband:75$
random stranger passing by:75$ for a blow job!! you are a moron man, there is a lady picking flowers down there who let me fuck her in the ass for 2$ | 0non-cybersec
| Reddit |
[Build Complete] First build, done by my dad and me.. I am a teenager who has had interest in building a PC for a while now. And since I have a lot of time now with it being summer I decided to approach my dad about the whole thing. He said he'd be willing to do it with me, so we picked our parts over a few days. We wanted to go with more or less the cheapest build possible that was still practical and we came out with this:
[PCPartPicker part list](http://ca.pcpartpicker.com/p/sjdJdC) / [Price breakdown by merchant](http://ca.pcpartpicker.com/p/sjdJdC/by_merchant/)
Type|Item|Price
:----|:----|:----
**CPU** | [AMD 2650 1.45Ghz Dual-Core Processor](http://ca.pcpartpicker.com/part/amd-cpu-sd2650jahmbox) | $34.00 @ DirectCanada
**Motherboard** | [ASRock AM1B-M Micro ATX AM1 Motherboard](http://ca.pcpartpicker.com/part/asrock-motherboard-am1bm) | $32.75 @ Vuugo
**Memory** | [Patriot Viper Xtreme 4GB (1 x 4GB) DDR3-1600 Memory](http://ca.pcpartpicker.com/part/patriot-memory-px34g1600c11) | $29.35 @ DirectCanada
**Storage** | [Patriot Blaze 60GB 2.5" Solid State Drive](http://ca.pcpartpicker.com/part/patriot-internal-hard-drive-pb60gs25ssdr) | $46.80 @ shopRBC
**Case** | [Fractal Design Core 1100 MicroATX Mini Tower Case](http://ca.pcpartpicker.com/part/fractal-design-case-fdcacore1100bl) | $54.75 @ Vuugo
**Power Supply** | [EVGA 400W ATX Power Supply](http://ca.pcpartpicker.com/part/evga-power-supply-100n10400l1) | $37.25 @ Vuugo
**Keyboard** | [Logitech MK120 Wired Slim Keyboard w/Optical Mouse](http://ca.pcpartpicker.com/part/logitech-keyboard-920002565) | $11.01 @ DirectCanada
| *Prices include shipping, taxes, rebates, and discounts* |
| Total (before mail-in rebates) | $255.91
| Mail-in rebates | -$10.00
| **Total** | **$245.91**
| Generated by [PCPartPicker](http://pcpartpicker.com) 2015-08-16 11:32 EDT-0400 |
After few weeks of waiting for stuff to get here we built the thing yesterday. I did roughly 75% of the building with my dad helping out when some elbow grease was required. We finished the build in about two and a half hours and I installed Linux Mint on it. We also plan on slowly upgrading it over time instead of building other builds from scratch when we want do do more of this stuff.
[Here](http://imgur.com/a/Lvems) are the pictures of parts taken by my dad. Anyway I hope you found this interesting and feel free to leave advice and feedback on the build in the comments. I have a lot of learning to do. | 0non-cybersec
| Reddit |
HDD/ATA password incorrect after system crash. <p><strong>Initial situation</strong></p>
<p>I have an Acer Aspire V 15 Nitro with Win 8.1 and 2 hard drives.
mSATA Liteon SSD (256 GB) - operating system
Samsung SSD 840 EVO 500GB - Data</p>
<p>More than a year ago I set a password in the BIOS for both hard disks and the BIOS itself (the same for all three). When switching on I was asked for the passwords and after input, the hard disks were unlocked and the system started.</p>
<p>My problem and how it happened. I have working for a while as always and around noon the system hung/crashed, windows not responding then I did a hard reset (pressed long the power key). After that I have restarted and as with every start, the passwords promt for the hard disks pops up. I could unlock the first hard disk, then entered the password for the second hard disk and I get "Incorrect Password" message. Since then I can't unlock the hard drive.</p>
<p>It's been a week now and since then I can't unlock the hard drive and I've read and tried many things but without success.</p>
<p><strong>Summary Samsung Support</strong></p>
<p>I have contact the Samsung Support, that's the result.
They claim that they didn't have something like this yet and just offer me to send the SSD to them and they delete it completely after that I can use it again. However, no option for me I need the data.</p>
<p>The ATA security concept knows two different passwords, the user password and the master password. I got this back on the request of the master password:</p>
<blockquote>
<p>Unfortunately, we have no instruction on how the ATA security concept
works. Please contact the motherboard manufacturer directly and ask
how to unlock the hard drive. Unfortunately we don't have a special
tool or master passwords. We can only unlock the SSD in our Repair
Center.</p>
</blockquote>
<p>But according to <a href="https://www.samsung.com/us/pdf/memory-storage/840PRO_25_SATA_III_Spec.pdf" rel="nofollow noreferrer">this document</a> there is such a password<br>
At point 5.2.1 SECURITY (page 11) the master password is mentioned.</p>
<blockquote>
<p>5.2.1 SECURITY mode default setting
The 840 PRO is shipped with master password set to 20h value (ASCII blanks) and the lock function disabled.
The system manufacturer/dealer may set a new master password by using the SECURITY SET PASSWORD command, without enabling the lock function.</p>
</blockquote>
<p>However, the support did not react directly to the document.</p>
<p><strong>My attempts to unlock the SSD with hdparm</strong></p>
<pre><code>ubuntu@ubuntu:~$ sudo hdparm -I /dev/sdb
/dev/sdb:
ATA device, with non-removable media
Model Number: Samsung SSD 840 EVO 500GB
Serial Number: S1DHNSAD903633N
Firmware Revision: EXT0BB6Q
Transport: Serial, ATA8-AST, SATA 1.0a, SATA II Extensions, SATA Rev 2.5, SATA Rev 2.6, SATA Rev 3.0
Standards:
Used: unknown (minor revision code 0x0039)
Supported: 9 8 7 6 5
Likely used: 9
Configuration:
Logical max current
cylinders 130 130
heads 16 16
sectors/track 63 63
--
CHS current addressable sectors: 131040
LBA user addressable sectors: 268435455
LBA48 user addressable sectors: 976773168
Logical Sector size: 512 bytes
Physical Sector size: 512 bytes
Logical Sector-0 offset: 0 bytes
device size with M = 1024*1024: 476940 MBytes
device size with M = 1000*1000: 500107 MBytes (500 GB)
cache/buffer size = unknown
Nominal Media Rotation Rate: Solid State Device
Capabilities:
LBA, IORDY(can be disabled)
Queue depth: 32
Standby timer values: spec'd by Standard, no device specific minimum
R/W multiple sector transfer: Max = 1 Current = 1
DMA: mdma0 mdma1 mdma2 udma0 udma1 udma2 udma3 udma4 udma5 *udma6
Cycle time: min=120ns recommended=120ns
PIO: pio0 pio1 pio2 pio3 pio4
Cycle time: no flow control=120ns IORDY flow control=120ns
Commands/features:
Enabled Supported:
* SMART feature set
* Security Mode feature set
* Power Management feature set
* Write cache
* Look-ahead
* Host Protected Area feature set
* WRITE_BUFFER command
* READ_BUFFER command
* NOP cmd
* DOWNLOAD_MICROCODE
SET_MAX security extension
* 48-bit Address feature set
* Device Configuration Overlay feature set
* Mandatory FLUSH_CACHE
* FLUSH_CACHE_EXT
* SMART error logging
* SMART self-test
* General Purpose Logging feature set
* WRITE_{DMA|MULTIPLE}_FUA_EXT
* 64-bit World wide name
Write-Read-Verify feature set
* WRITE_UNCORRECTABLE_EXT command
* {READ,WRITE}_DMA_EXT_GPL commands
* Segmented DOWNLOAD_MICROCODE
* Gen1 signaling speed (1.5Gb/s)
* Gen2 signaling speed (3.0Gb/s)
* Gen3 signaling speed (6.0Gb/s)
* Native Command Queueing (NCQ)
* Phy event counters
* READ_LOG_DMA_EXT equivalent to READ_LOG_EXT
DMA Setup Auto-Activate optimization
Device-initiated interface power management
* Asynchronous notification (eg. media change)
* Software settings preservation
* SMART Command Transport (SCT) feature set
* SCT Write Same (AC2)
* SCT Error Recovery Control (AC3)
* SCT Features Control (AC4)
* SCT Data Tables (AC5)
* reserved 69[4]
* DOWNLOAD MICROCODE DMA command
* SET MAX SETPASSWORD/UNLOCK DMA commands
* WRITE BUFFER DMA command
* READ BUFFER DMA command
* Data Set Management TRIM supported (limit 8 blocks)
Security:
Master password revision code = 65534
supported
enabled
locked
not frozen
not expired: security count
supported: enhanced erase
Security level high
2min for SECURITY ERASE UNIT. 8min for ENHANCED SECURITY ERASE UNIT.
Logical Unit WWN Device Identifier: 50025388a0031dde
NAA : 5
IEEE OUI : 002538
Unique ID : 8a0031dde
Checksum: correct
</code></pre>
<p>This <a href="https://serverfault.com/questions/712849/how-to-unlock-a-ssd-disk-with-hdparm/733784#733784">article</a> served as help.</p>
<p>I have tried all security-unlock and disable commands with and without --user-master m, and pass the password also as scancode.</p>
<pre><code>sudo hdparm --security-unlock $(printf '\x12\x12\x12\x12\x12\x12') /dev/sdb
</code></pre>
<p>Anything without success, always get SG_IO: bad/missing sense data</p>
<pre><code>ubuntu@ubuntu:~$ sudo hdparm --security-unlock "password" /dev/sdb
security_password: "password"
/dev/sdb:
Issuing SECURITY_UNLOCK command, password="password", user=user
SG_IO: bad/missing sense data, sb[]: 70 00 05 00 00 00 00 0a 04 51 40 01 21 04 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
</code></pre>
<p>This is what I found about the code</p>
<pre><code>70 response code=Current information (about the error etc.)
00
05 sense code=Illegal Request
00 00 00 00 (not valid)
0a additional 10 bytes
04 51 40 01 (command specific)
21 04 additional sense code=Unaligned Write Command
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
</code></pre>
<p>Master passwords I found and tested in every possible length from 1 - 32 characters and also as ScanCode:</p>
<ul>
<li>my password</li>
<li>Blank (" ")</li>
<li>"ttttttttttttttttttttttttttttttttttttttttttttt" (32 times t)</li>
<li>h20insyde</li>
</ul>
<p>Since the security level of the SSD is set to "high" it means that you can unlock the hard disk with the master password without losing the data and according to the master password revision code = 65534 the master password has not been changed and should still have the default value.</p>
<p>I also built the Samsung SSD into an identical notebook and a computer all without success.</p>
<p>The university of texas has published an interesting article <em><a href="https://security.utexas.edu/education-outreach/BreakingATA" rel="nofollow noreferrer">Breaking ATA Password Security</a></em>, they could remove the ATA Password with A-FF Repair Station but I can not try the software because the website is offline, via the web archive I could download the software but you need a login and this can not be created.</p>
<p>I hope one of you can help me to unlock the SSD.</p>
| 0non-cybersec
| Stackexchange |
Tokyo Olympics Committee President Proposes Manga Parade at 2020 Games. | 0non-cybersec
| Reddit |
multi line equation with full left brace, small right brace and text at right bottom of right brace. <p>I want to write a three line equation with left curly brace for all three, right curly brace for bottom two ones and some text at right bottom of right curly brace. All with proper alignment. I wrote following code.</p>
<pre><code>\documentclass{article}
\usepackage{amsmath,amssymb,amsfonts}
\usepackage{flexisym}
\begin{document}
\begin{equation*}
\begin{aligned}
K_{\mathbb{A}_{Ui}} =\begin{cases}
D =\ g^{ \frac{ (\alpha + r) }{\beta} }\\
\left.\begin {aligned}
&D_j &=\ &g^r . H(j)^{r_j} \\
&D_j\textprime &=\ &g^{r_j}
\end{aligned}\right\} \forall j \in \mathbb{A}_{Ui}
\end{cases}
\end{aligned}
\end{equation*}
\end{document}
</code></pre>
<p>It is giving some problems.</p>
<ol>
<li><p>Second and Third lines are aligned but they are not aligned with the first one. I want alignment to occur at start of "D", "=" and "g" for all three.</p></li>
<li><p>Right now, the text at right of right curly brace is coming at center. I want it to shift down and come at bottom.</p></li>
</ol>
<p>Please help. Thanks in advance.</p>
| 0non-cybersec
| Stackexchange |
Decorator or Facade. <p>I face an issue if to use a decorator or facade pattern to accomplish my needs.</p>
<p>Imagine a client wants to play a video. He can use the interface </p>
<pre><code>public interface IVideoPlayer
{
// Prepares everything to set up and plays the video
void Play();
}
</code></pre>
<p>The client should not be concerned with the preparation, so the interface's method's summary states that preparation is done by the <code>Play()</code> method.</p>
<p>Preparation may include different things like connecting to the internet, logging in to the service and so on. There are different preparation steps for different systems.</p>
<h1>Facade pattern</h1>
<p>I could implement <code>IVideoPlayer</code> using the facade pattern as follows</p>
<pre><code>VideoPlayerFacade : IVideoPlayer
{
ctor(...)
void Play()
{
_internetConnection.Connect();
_loginService.Login();
_actualVideoPlayer.Play();
}
}
</code></pre>
<p>What I dislike with this approach:</p>
<ul>
<li>The preparation (connecting, logging in) seems more like an addition to the actual playing algorithm, which leads me more to the decorator pattern. I rather understand the facade pattern to compose some "equal level" steps to achieve a common goal, like <code>CreateCar()</code> delegating to <code>CreateEngine()</code>, <code>CreateCarBody()</code> and so on.</li>
<li>I face a naming issue because the interface the type of <code>_actualVideoPlayer</code> implements could also be named <code>IVideoPlayer</code>, because it IS the actual video player, which also guides me to the decorator pattern. I would need two almost identical interfaces (one with and one without preparation) with quite similar names, which I cannot imagine at the moment.</li>
</ul>
<h1>Decorator pattern</h1>
<p><code>IVideoPlayer</code> could be implemented with the actual playing algorithm as follows</p>
<pre><code>VideoPlayer : IVideoPlayer
{
void Play()
{
// do stuff and algorithms
}
}
</code></pre>
<p>The preparation could be done in a decorator as follows</p>
<pre><code>PreparatingVideoPlayer : IVideoPlayer
{
ctor(...)
void Play()
{
_internetConnection.Connect();
_loginService.Login();
_decoratee.Play();
}
}
</code></pre>
<p>What I dislike with this approach:</p>
<ul>
<li><p>Actually the <code>VideoPlayer</code> violates the LSP because it does not conform to the interface by not doing all preparation in the <code>Play()</code> method, which rather leads me to the facade pattern. Or doesn't it violate the LSP because it will always be decorated by the <code>PreparatingVideoPlayer</code> when it is injected into the system?</p></li>
<li><p>What if another client wants to play video without preparation (because the client knows everything is prepared or prepared everything himself)? He wouldn't be able to because letting <code>IVideoPlayer</code> be injected will always result in getting the <code>PreparatingVideoPlayer</code>, which would lead me to the facade pattern again.</p></li>
</ul>
<h1>Conclusion</h1>
<p>So which pattern is more appropriate or are these patterns appropriate at all? Are my concerns valid?</p>
| 0non-cybersec
| Stackexchange |
Imma plank across the two hand rails on the escalator. WCGW?. | 0non-cybersec
| Reddit |
proving the composition of two linear transformations is a linear transformation. <p>$U$ and $V$ are vector spaces, their Cartesian product is defined by</p>
<p>$$U\times V = [(u,v): u \in U, v \in V]$$</p>
<p>addition and multiplication defined by</p>
<p>$$(u_1,v_1) + (u_2,v_2) = (u_1+u_2, v_1+v_2)$$
$$r(u,v) = (ru,rv)$$</p>
<p>Let the $T_1: V \rightarrow W$ and $T_2:V\rightarrow W$ be linear transformations, and define a transformation $S: V \times V \rightarrow W \times W$ by</p>
<p>$$S[(v_1,v_2)] = (T_1(v_1),T_2(v_2)$$</p>
<p>how do I go about proving the linear transformation here? I know the idea behind proving linear transformations for composition when they are $T_1(T_2(v_1))$ for example but I am not sure how to prove it in this case.</p>
<p>To prove addition I have gotten this far but I don't know where to go from here:</p>
<p>$$S[(v_1,v_2)+(v_3,v_4)] = S[(v_1,v_2)] + S[(v_3,v_4)]$$
$$=[T_1(v_1),T_2(v_2)] + [T_1(v_3),T_2(v_4)]$$</p>
| 0non-cybersec
| Stackexchange |
PsBattle: A Snail on a Mushroom Reaching Towards a Drop of Water on a Raspberry. | 0non-cybersec
| Reddit |
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