Asymptotic symmetry algebra

Question: So after a lot of research, and tons and tons of papers that I've went through, I finally have some idea how to solve the equations that will give me candidates for the asymptotic symmetry group for Kerr/CFT correspondence. One has boundary conditions $h_{\mu\nu}$, and metric that behaves like $g_{\mu\nu}=\bar{g}_{\mu\nu}+h_{\mu\nu}$, where $\bar{g}_{\mu\nu}$ is the background metric (in this case it's taken as near horizon extreme Kerr metric), and $h_{\mu\nu}$ are perturbations (given).
So the task is finding diffeomorphisms $\xi$ for which this metric will transform according to
$$\bar{g}_{\mu\nu}+\mathcal{L}_\xi \bar{g}_{\mu\nu}=g_{\mu\nu}=\bar{g}_{\mu\nu}+h_{\mu\nu}$$
And one solves that by solving equations
$$\mathcal{L}_\xi g_{\mu\nu}=\mathcal(r^m)$$
where $\mathcal{O}(r^m)$ are boundary conditions, given in terms of radial coordinates.
From this, and the fact that $h_{\mu\nu}=h_{\nu\mu}$ I get ten equations.
Now my issue is this: What to take as ansatz for $\xi$?
In some papers, they take this:
$$\xi^\mu=\xi^\mu_0(t,\theta,\phi)+r\xi^\mu_1(t,\theta,\phi)+\mathcal{O}(r^2)$$
But in certain papers I've found that authors take this form (see after eq. 4.4 here, or here eq 5.1)
$$\xi^\mu=\sum\limits_{n=-1}^\infty \xi^\mu_n r^{-n}$$
such that we have subleading contributions (a falloff in radial coordinate).
Now, I'm inclined to use the second one, since the diffeomorphism given in Guica et. al is given with subleading terms.
I should solve this by putting a certain few terms in, and see what the boundary condition says. For instance we have
$$\mathcal{L}_\xi g_{tt}=\mathcal{O}(r^2)$$
That means that all $\mathcal{O}(r^2)$ contributions will cancel, and only equations with $r$, or smaller $r$ contributions will survive. But the answer is drastically different if I take first or second ansatz.
So what to take? Am I on the right track? If I take second one, what n should I start from? $n=-1$ or $n=-2$?
Oh and I finally got how to solve this by looking at this article and following how they got it in appendix A
EDIT:
I've been thinking. Does the fact that in their article, the metric, and the ansatz goes with powers of $v$, means that since their equations are limited by $\mathcal{O}(v)$ onward all higher power will cancel each other? In that case, since I'm taking only subleading terms in metric, and boundary conditions (different for each of 10 terms), and if I take that my ansatz falls off as $r^{-n}$, that means that all lower order correction cancel out?
The question is still: what n to take? Since it's not the same if my $\xi$ starts with $r^2$, or $r$ :\
EDIT2:
I'll put one component to show what I'm doing. Although I think something is wrong, since I'm getting complicated equations (when things get too complicated, it's kind of a show that things might not be going in the right direction, at least that's what experience showed me)
So, my metric is $g_{\mu\nu}=\bar{g}_{\mu\nu}+h_{\mu\nu}$, as explained above. The first question that comes to my mind: do I put manually $h_{\mu\nu}$ in this expression, or do I use the given boundary conditions? I could say that $h_{\mu\nu}$ is arbitrary, and my metric has to have a power fall off perturbations, so that my $tt$ component would be
$$g_{tt}=-\Omega^2(\theta)(1+r^2(1-\Lambda^2(\theta)))+r^{-1}h_{tt}(t,\theta,\phi)+\mathcal{O}(r^{-2})\quad (\star)$$
I removed $2GJ$ since it's just a factor in front of the metric, not depending on any of the variables ($t,r,\theta,\phi$), and it doesn't contribute to diffeomorphisms.
I will try this after I finish what I did.
However, I just put the given boundary conditions. For $tt$ component I have
$$\mathcal{L}_\xi g_{tt}=\mathcal{O}(r^2)=\xi^\sigma\partial_\sigma g_{tt}+g_{\sigma t}\partial_t\xi^\sigma+g_{t\sigma}\partial_t\xi^\sigma$$
Since $g_{tt}$ depends on $r$ and $\theta$, I have two components in the first argument. In the second and third arguments are the same since $g_{t\phi}=g_{\phi t}$. So I have
$$\xi^\theta\partial_\theta g_{tt}+\xi^r\partial_r g_{tt}+2(g_{tt}\partial_t\xi^t+g_{t\phi}\partial_t \xi^\phi)=\mathcal{O}(r^2)$$
$$(\xi^\theta_{-1}r+\xi^\theta_0+\xi^\theta_1r^{-1}+\mathcal{O}(r^{-2}))(-2\Omega\Omega'+2\Omega(\Lambda\Lambda'\Omega-\Omega'(1-\Lambda^2))r^2+\mathcal{O}(r^2))+(\xi^r_{-1}r+\xi^r_0+\xi^r_1r^{-1}+\mathcal{O}(r^{-2}))(-2\Omega^2(1-\Lambda^2)r+\mathcal{O}(r))+2((-\Omega^2-\Omega^2(1-\Lambda^2)r^2+\mathcal{O}(r^2))(\partial_t\xi^t_{-1}r+\partial_t\xi^t_0+\mathcal{O}(r^{-1}))+(\Lambda^2\Omega^2r+\mathcal{O}(1))(\partial_t\xi^\phi_{-1}r+\partial_t\xi^\phi_0+\partial_t\xi^\phi_1 r+\mathcal{O}(r^{-2})))=\mathcal{O}(r^2)$$
After sorting all out, and saying that all the corrections of $\mathcal{O}(r^2)$ vanish, I end up with
$$(\Lambda\Lambda'\Omega-\Omega'(1-\Lambda^2))\xi^\theta_{-1}-\Omega(1-\Lambda^2)\partial_t\xi^t_{-1}=0$$
But, this one is relatively ok, the other ones sometimes have six or more components ($\xi^\mu$). I'll work all of them out, and then try with $(\star)$ as an assumption and see if things simplify...
EDIT 3:
So things aren't simplifying. But one thing I've learned: I need to solve asymptotic Killing equation.
My next try, the one I think is a fast and relatively good try, is to just see what the leading orders of components should be, such that they satisfy the asymptotic Killing equations, given by boundary conditions. Then I'll try to do explicit calculation.
For instance (and I hope I'm on a right track) for $tt$ component I would have
$$\mathcal{L}_\xi g_{tt}=\mathcal{O}(r^2)$$
$$\xi^\theta\partial_\theta g_{tt}+\xi^r\partial_r g_{tt}+2(g_{tt}\partial_t\xi^t+g_{t\phi}\partial_t \xi^\phi)=\mathcal{O}(r^2)$$
$$\xi^\theta\mathcal{O}(r^2)+\xi^r\mathcal{O}(r)+\mathcal{O}(r^2)\partial_t\xi^t+\mathcal{O}(r)\partial_t\xi^\phi=\mathcal{O}(r^2)$$
So for this to be true (LHS=RHS) I should have
$$\xi^r\to\mathcal{O}(r)$$
$$\xi^\theta\to\mathcal{O}(1)$$
$$\partial_t\xi^t\to\mathcal{O}(1)$$
$$\partial_t\xi^\phi\to\mathcal{O}(r)$$
I hope I'm on a right track.
I got a hint how Guica et. al did it.
First we need to guess what the symmetries are and then generate boundary conditions by acting with those diffeomorphisms, and then check that the charges are finite and integrable.
So it's more a guessing game than exact solving :S
EDIT 4:
So far (by solving asymptotic Killing equations) I only get the $\xi^\theta$ component right. That is I have
$$\xi^\theta_0=\xi^\theta_{-1}r$$
which, when I put in the ansatz I get
$$\xi^\theta=\xi^\theta_{-1}r+\xi^\theta_0+\xi^\theta_1r^{-1}+\mathcal{O}(r^{-2})$$
$$\xi^\theta=\xi^\theta_1 r^{-1}+\mathcal{O}(r^{-2})$$
which is exactly the one in the article by Guica et. al. But no luck with other components.
If only there was some info on what I need to put in asymptotic Killing equation after the equal sign...
EDIT 5:
I'll write the equations I got by putting $\mathcal{L}_\xi g_{\mu\nu}=\mathcal{O}(r^n)$ where $\mathcal{O}(r^n)$ are given by boundary conditions:
$$tt:\quad (\Lambda \Lambda' \Omega+(\Lambda^2-1)\Omega')\xi^\theta_{-1}+(\Lambda^2-1)\Omega \partial_t\xi^t_{-1}=0$$
$$t r:\quad (\Lambda^2-1)r(\xi^t_{-1}+\xi^t_0r^{-1})+(\Lambda^2-1)r^3(\xi^t_{-1}+\xi^t_0r^{-1}+\xi^t_1r^{-2}+\xi^t_2r^{-3})-$$
$$-r(\xi^t_{-1}+\xi^t_0r^{-1})+\Lambda^2\xi^\phi_{-1}+\Lambda^2r^2(\xi^\phi_{-1}+\xi^\phi_0r^{-1}+\xi^\phi_1r^{-2})+\partial_t\xi^r_{-1}=0$$
$$t\theta:\quad (\Lambda^2-1)r^2(\partial_\theta\xi^t_{-1}r+\partial_\theta\xi^t_0+\partial_\theta\xi^t_1r^{-1}+\partial_\theta\xi^t_2r^{-2})-(\partial_\theta\xi^t_{-1}r+\partial_\theta\xi^t_0)+$$
$$+\Lambda^2r(\partial_\theta\xi^\phi_{-1}r+\partial_\theta\xi^\phi_0+\partial_\theta\xi^\phi_2r^{-1})+(\partial_t\xi^\theta_{-1}r+\partial_t\xi^\theta_0)=0$$
$$t\phi:\quad (2\Lambda(\Lambda'\Omega+\Lambda\Omega'))(\xi^\theta_{-1}r+\xi^\theta_0)+\Lambda^2\Omega\xi^r_{-1}+$$
$$+(\Omega(\Lambda^2-1))(\partial_\phi\xi^t_{-1}r+\partial_\phi\xi^t_0+\partial_\phi\xi^t_1r^{-1})-\Omega\partial_\phi\xi^t_{-1}+$$
$$+\Lambda^2\Omega(\partial_\phi\xi^\phi_{-1}r+\partial_\phi\xi^\phi_0)+\Lambda^2\Omega(\partial_t\xi^\phi_{-1}r+\partial_t\xi^t_0)+\Lambda^2\Omega\partial_t\xi^\phi_{-1}=0$$
$$rr:\quad \xi^\theta_{-1}r+\xi^\theta_0=0$$
$$r\theta:\quad \partial_\theta\xi^r_{-1}+(\xi^\theta_{-1}r+\xi^\theta_0)=0$$
$$r\phi:\quad (\xi^t_{-1}r+\xi^t_0)+\xi^\phi_{-1}=0$$
$$\theta\theta:\quad \Omega'(\xi^\theta_{-1}r+\xi^\theta_0)+\Omega(\partial_\theta\xi^\theta_{-1}r+\partial_\theta\xi^\theta_0)=0$$
$$\theta\phi:\quad (\partial_\phi\xi^\theta_{-1}r+\partial_\phi\xi^\theta_0)+\Lambda^2r(\partial_\theta\xi^t_{-1}r+\partial_\theta\xi^t_0+\partial_\theta\xi^t_1r^{-1})+$$
$$+\Lambda^2(\partial_\theta\xi^\phi_{-1}r+\partial_\theta\xi^\phi_0)=0$$
$$\phi\phi:\quad (\Omega\Lambda'+\Lambda\Omega')\xi^\theta_{-1}r+\Lambda\Omega r(\partial_\phi\xi^t_{-1}r+\partial_\phi\xi^t_0)+$$
$$+\Lambda\Omega\partial_\phi\xi^\phi_{-1}r=0$$
The problem is, the only equation I can get some information, about how my vector should behave in components is $rr$, from which I get the general form of $\xi^\theta$ component of diffeomorphism.
From $r\theta$ I get that the $\xi^r_{-1}$ term is a constant that doesn't depend on $\theta$, and $\theta\theta$ equation will just confirm that $rr$ one is correct.
I guess from the fact that $\xi^r_{-1}$ is not zero I could say that the $r$ component will start at that term (like in the article).
EDIT 6:
I have added the bounty to raise awareness to this, if anyone knows if what I did so far is correct, and what to do next, please do tell :)
Comment: This might be relevant: [_Glenn Barnich: 2016 Lectures on BMS symmetry_](http://homepages.ulb.ac.be/%7Egbarnich/notes.html).
Answer: So the way these equations are solved is by looking what order we have at the equations,
this means that when we put the ansatz inside the equations, we keep all the orders that are greater than the ones equating the equation.
Then we collect all terms with the powers of $r$ (for $tt$ equation all the powers greater than $r^2$ are that of $r^3$, for $tr$, all powers greater than $r^0$ are $r^4,\ r^3,\ r^2$ and $r$, etc.) and set them equal to zero respectively. This in turn gives us 25 equations in total. From those I got only that:
$$\xi^t_{-1}=0,\ \xi^t_0=0,\xi^t_1=C(t,\phi)$$
$$\xi^r_{-1}=C_1(t,\phi)$$
$$\xi^\theta_{-1}=0,\ \xi^\theta_0=0$$
$$\xi^\phi_{-1}=0,\ \xi^\phi_0=C_2(t,\phi)$$
From additional equations I only got that $\xi^\phi_1=-\partial_t\xi^r_{-1}$, and $\xi^t_2=\partial_t\xi^r_{-1}$, that is $\xi^\phi_1+\xi^t_2=0$.
Now in principle that gives me a relatively good solution, it's just that in original article it's not specified what those constants are. Not only that, but the $\xi^r_{-1}$ constant shouldn't depend on $t$.
That way $\xi^\phi_1=0$, and $\xi^t_2=0$, and that is ok by the article. But I have no way of proving that, so it would be kinda presumptuous of me to just assume that.
So this is only a partial answer. If anyone got anything different do tell.
Maybe I should include even higher powers of $r$? Like $r^2$ in my ansatz. That would give me more components, but would also make this work even more cumbersome.
EDIT:
I used Mathematca to simplify things, and I get the correct answer finally. The only thing that is kinda unresolved is why did the authors assumed that none of the components will depend on $t$. My guess is because $U(1)$ is enhanced to Virasoro, and $U(1)$ Killing vector doesn't have $t$ dependence.
But all in all I finally have the correct answer.

Asymptotic symmetry algebra


Error on upgrade 4.7.17

Question:
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Luckily this was on my sandbox site. I forgot that I was no longer logged in and tried to run:

http://mysite/wp-admin/admin.php?page=CiviCRM&q=civicrm/upgrade&reset=1

Now it wants to reinstall CiviCRM.
May I suggest that someone fix this before it happens on a live site.
Update 1: Looks like I forgot to copy back the civicrm.settings.php file. After changing the version in civicrm_domain back to 4.7.16, I ran it again and it died in 4.17.17.mysql.tpl trying to add the card_type.
ALTER TABLE civicrm_financial_trxn
  ADD card_type INT( 10 ) UNSIGNED NULL DEFAULT NULL COMMENT 'FK to accept_creditcard option group values' AFTER payment_instrument_id,
  ADD pan_truncation INT UNSIGNED NULL COMMENT 'Last 4 digits of credit card.' AFTER check_number;
After adding the card+type manually with no errors, Civicrm refuses to continue.
A copy of civicrm.settings.php could reside in ../uploads/civicrm. Then part one of the upgrade process would be to copy this file and stick in ../uploads/civicrm then copy it back as part one of the install if it exists?
Either that or dump the information in the wp_options table in WordPress and either reload them each time or recreate the file as part of the upgrade.
Given that I'm not emotionally attached to this sandbox database I'm going to get another one
Answer: It's not completely clear the whole history of what happened to the instance, but it appears that you managed to run the upgrade script twice, and it choked the second time because the fields had already been inserted on the first run of the upgrade.

Error on upgrade 4.7.17


Relative fractions of Kohanim and Levi'im

Question: Does anyone have reliable statistics (and barring that, reasonable anectdotal evidence) of the fraction of Kohanim, Levi'im, and Yisraelim in various Jewish communities today? By "communities" I don't necessarily mean geographic, but minhagic, like Chabad/Syrian/Litvak, etc.
Comment: Related: http://judaism.stackexchange.com/q/22549
Answer: Answer: Levites: 4%, Priests: 4%.
A scientific article which deals with the genetics of priests and Levites quotes a book from 1999 (not available for reading online) which estimates Levites and priests each at 4% of the general Jewish population.
Source:
http://www.sciencedirect.com/science/article/pii/S000292970763626X#bbib6
Referenced book:
"The genetic origins of Old Testament priests", CE Renfrew, Editor, Population specific polymorphisms, Cambridge University Press, Cambridge, United Kingdom (1999), pp. 31–44
Answer: The Persian community (mostly Shirazi) absorbed by Baltimore contains a high fraction of Cohanim and very few Leviim.
Comment: What could explain this strange distribution?
Comment: I had heard similar stats about the Syrian community in the US. One explanation (although I am personal skeptical) is that under the various persecutions in Syria in the past century or so, the community focused on getting the Cohanim safely out. Maybe some Leviim impersonated Cohanim in order to be safe too.
Comment: There's some discussion about how most of the Cohanim returned from Babylon to Israel with Ezra and Nechemiah, but very few Leviim did. I always wondered if that was related ...
Comment: @WAF Perhaps they are largely from the same ancestral family.
Comment: @WAF Of course I mean much more recently than Aharon haCohen :)
Answer: Djerba has almost all kohanim.
Comment: Hebrew Wikipedia points to a recent article in the Israeli weekly Makor Rishon - אליהו בירנבוים, אי הנפלאות 1 באוגוסט 2008 מקור ראשון
There were two primary centers of Jewish life, Kohanim founded דיגת, Israelites founded חארה כבירה. According to legend, the Israelites were from Zevulun since they maintained seafaring trade with nearby Phoenicians in Carthage. Also acc. to legend, because the inhabitants didn't return for the building of the Second Temple, Ezra cursed the Leviim on the island and they died off. To this day, Leviim aren't permitted to permanently reside for more than a year.
Comment: There's also an interesting article from the journal מחניים:
http://www.daat.ac.il/daat/history/nidhey/rabinovitsh.htm
Comment: @ShmuelBrill, true, but I knew it independently. I don't remember from where, though.
Comment: The article from Makor Rishon can be found here: http://musaf-shabbat.com/2011/01/18/%D7%90%D7%99-%D7%94%D7%A0%D7%A4%D7%9C%D7%90%D7%95%D7%AA-%D7%90%D7%9C%D7%99%D7%94%D7%95-%D7%91%D7%99%D7%A8%D7%A0%D7%91%D7%95%D7%99%D7%9D/


How to get rid of fear of fighting

Question: "How to get rid of fear of fighting". When i get hit i am scared to get beaten more. I am worried about my nose getting break which costs me to lose. But i love the sport.
Comment: Could you clarify what the _question_ is?  That makes it easier for people to answer.
Comment: @John Please edit and update your question accordingly and add that information.
Comment: i am sorry , i wanted to ask "How to get rid of fear of fighting". When i get hit i am scared to get beaten more.  I am worried about my nose getting break which costs me to lose. But i love the sport.
Comment: related: http://martialarts.stackexchange.com/questions/241/drills-for-reducing-your-natural-flinch-reaction
Answer: To be honest this is a tough question to answer because there is no one right answer or technique for this.
It is healthy to be scared in a match. If you are not scared then you are either highly experienced or somewhat mental.
I think the only way to overcome this (without some hypnotic reprogramming) is experience - which means getting hit. Overcoming pain and fear requires training, it requires that you face the fear and receive the pain and realize that you are still fine and you can carry on.
A smack on the nose can hurt and make you eyes water, ideally you should avoid it (keep your guard up, no be there Daniel-san). It might even break your nose, but after you've had a few of those you learn that it isn't so bad and you can continue.
When you fight you ideally want to be "in the zone", which is a state where you are not consciously thinking about what you are doing and what is happening around you. When in this state you will still feel the hits but won't consciously register the pain from it (this is kind of important especially when your thighs will be getting smashed during the match!) - the only way to achieve this is with ring experience and training.
Comment: Well thank you, My master even told the same. I believe i need to start fighting with my size of people first.
Comment: Exactly @John. But from time to time try also to spar someone more experienced. This will improve your skills, and you'll be able to push your limits much faster.
Answer: Yod Ruerngsa has a section on 'being hit' in Muay Thai - The Art of Fighting.
Here an excerpt:

If you want to evolve and grow as a human being, don't worry about
  what you'll  get from others...learn to give, to try, to extend
  yourself, and to concentrate on  what you're doing to and for others,
  not on what's being done to or for you.
  If you want to learn how to box, same thing:
  don't worry about what others will do  to you, learn
  to give, to try, to extend yourself with effort, and concentrate on
  what you're doing, not on what's being done to you.
Comment: The chapter goes into some more detail. I've linked to it [here](http://martialarts.stackexchange.com/questions/1774/terminology-list-of-all-boxing-and-muay-thai-technique-terms-with-example-photo/1780#1780)
Answer: Good old body conditioning / body beating worked for me. First I got a guy with the same height as me to punch me around. I did not defend.
It mostly consisted of

Punches to the abdomen (with gloves on)
Punches to the chest.
Jabs to the face
Hooks to the face
Slap kicks to the thigh
Slaps on my stomach
Front kick to the chest
Slap kicks on my shoulder

This hurt for a few days, but after a month my body had got used to it. So I upgraded to a tall bloke (So that I did not get intimidated in an actual fight)
Basically you make yourself subconsciously used to get beaten up. I learned this from Kalari, where I was handed weapons on the first day. It seems daunting at first, the instinct of getting hurt/or hurting others just goes away over time.
Answer: When I just started learning martial arts (Seido) I was in the same position that you refer to. The solution for me was sparring with black belts or a kyu at least two ranks above mine. They will have the experience to be able to control their strikes so you don't get hurt too much. An added bonus is if you make a mistake while sparring you will know immediately. Also keep practicing the basics eventually you will see their applications in sparring, osu.
Answer: I can offer some advice from my experience working with Tony Blauer. In Tony's system we do some drills called Emotional Climate Training (ECT) where the purpose is to think about how an attack or situation makes you "feel" on an emotional level.
How it works, starting with an attack such as haymaker is you stand there while an opponent tosses the haymaker at you in slow motion. What you do is a couple of things. First watch the attack, mental blueprint what a haymaker or whatever attack/situation looks and sounds like. Takes a good bad guy to do this part. Next think about how the attack makes you feel emotionally. Keep doing this attack over and over. Remember you are not making any defense movements, just analyze and think about the attack. This part of the drill can go on for a while. You stop when you start feeling "comfortable" with the attack on an emotional level.
From here we would usually progress to describing the attack. Same as above except now you are verbally describing what you see and hear from the attacker. Again, repeat this drill, maybe 10-20 times or till you feel comfortable with describing the aspects of the attack.
The next part of the drills just keep building upon this same thing. Next would be describing the safe/unsafe parts of the attack (unsafe is when the attacker is making contact, safe is all other times) and then working on defensive responses. Doing this in class can take a couple of hours but it does work in helping with fear management and analyzing attacks.
Answer: try some like-sparring drills (like sticky hands from Wing Chun) - those drills will give you lots of confidence without much of a danger.
update:
1) The sticky hands drill presumes a very short distance of "fighting" (the distance is one thing lots of people and uncomfortable about)
2) the drill can be done as hard (aggressive) or soft as needed
3) since the contact is kept all the time, the danger is much less than during "conventional" sparring; I can't post an essay about Wing Chun and it's philosophy, so you would have to believe me or do some research on your own (or just ignore my post alltogether)
Comment: -1 this avoids sparring instead of dealing with the issue.
Comment: @DaveLiepmann - have you tried any of that or you are theoritising? I have seen how it works and done it myself.
Comment: I've never had the problem, so I can't say I've tried it directly. However I've dabbled with sticky hands and am quite confident in describing that drill as "not sparring" and "not fighting". Since the question asks for ways to fight and spar, an answer that recommends doing something **instead** of fighting and sparring seems unhelpful.
Comment: @DaveLiepmann - perhaps, the version you have seen was different from what I have practiced (sticky hands drill can have as much sparring as both participants want). In short, it IS fighting; try to dabble it again, perhaps it will change your confedency.
Comment: Do you have any video examples of what you're referring to? Perhaps a ruleset? I've seen it be a useful drill, but never rise to the level of sparring.
Comment: @DaveLiepmann  - here is a good one
https://www.youtube.com/watch?v=Y4TKgoybvBs
Comment: let us [continue this discussion in chat](http://chat.stackexchange.com/rooms/8069/discussion-between-dave-liepmann-and-steve-v)
Comment: Chi Sao is fitted for Wing Chun but i doubt other styles will benefit from this. It's training to just react instead of thinking about your next moves. You are just rsponding to your opponents force.
Comment: @Jeroen please try it ;). If (during the real street fight) your opponent would "react" to your move and poke you in the eye - will the knowledge that this move **has not been planned** make you feel better?
Comment: I'm practicing Wing Chun for some years now. And Chi Sau highly focuses on the main WC techniques. Bong sau, Tan sau, Fook sau, etc... Chi Sao is only effective if you really invest a lot of time so when you have to fight you can use these 'reflexes' instead of planning your fight. Basically you should switch to full WC training ;) But i agree Chi sao is a perfect way to close the gap between training and a real fight.
Answer: I'd like to echo Reno's answer. We do a lot of body conditioning. Basically we let the partner pummel us with kicks and punches, without defending. After a while, your body and mind are used to being hit. It's no big deal, really.
Naturally, we don't go 100% from day one. With beginners it's just light contact, and then the intensity is built up as they become tougher.
When it comes to strikes to the head, it's a bit different ballgame, because you can't conditioning your soft, squishy brain to be hit all the time. However, our method is almost the same. We put some gloves on, and do some light contact boxing. Instead of targeting the fragile parts of the head, like the nose or jaw, we aim for the forehead or side of the head.
Now, conditioning is only part one. Part two is actually building up the courage and try to be a more aggressive fighter when you spar in class. This is easier, the more regularly you do sparring. Pick a good match (one that is more skilled than yourself), and put some pressure on. You might be hit more often, but it's no big deal. You might even be hit less frequently, because you leave your opponent less space to attack!
Part three is taking it completely outside the comfort zone. So far you've only been in a controlled environment (dojo/gym) with people you trust. The next step is to fight at a tournament, but only when you feel reasonably "comfortable" with that. It's never really "comfortable". All fighters are a little bit scared, and that's natural and actually healthy (keeps you focused – it's dangerous to be careless). The hardest and most frightening fight, is your first one. As soon as you've been there a few times, you get used to it.
Sidenote: tournament fighting is not for all. Some people simply don't see the point, and that is fair – however, if this is secretly a dream of yours, you should most definitely pursue it, even if you don't have ambitions to be an elite fighter. Too many martial artists skip tournaments, because they don't believe they are up to it.
However, no matter how courageous and skilled you are, you will one day get hit really hard in the face. It's unavoidable. When that day comes, the important question is how well you handle it. The worst thing you can do is to panic. The best thing you can do (if you are still conscious), is to shrug and settle the score. :)
Be prepared, and good luck!
Answer: <code>Sure, you can get rid of fear through daily practice & meditation.
</code>

Through daily meditation, your mind will become calm and
accurate.
Through daily martial arts practicing, you will become
stronger and healthier.

And finally a calm, accurate, stronger and healthier person will not
  afraid of anything other than God.

<code> "Mind and Body are two parts of a coin"
</code>
Comment: How would daily practicing and meditation help exactly? Please elaborate.
Comment: This is a set of assertions, not an objective answer backed by evidence. I accept that the statements are true for you, but SE is about objective answers that are supported by evidence and can be applied generally.
Comment: @MarkC.Wallace yes, the statements are true for me and I hope this is generally applicable. thanks

How to get rid of fear of fighting


Has anyone encountered problems with Trash drives on NTFS partitions?

Question: I have my SSD on EXT4 and my shared data drive on NTFS. Unless anyone can think of good reason not to, I want to move the Trash folder out of the cramped SSD onto the NTFS partition.
Any horror stories or problems?
Answer: My guess is that you will run into problems, since NTFS does not support Unix permissions. Try out deleting and restoring a few files before you move your trash there for good.
That said, I found that a regular backup is a much more safe solution than Trash, and you can back up on the NTFS partition just fine.


Which language is most similar to Esperanto?

Question: I'm just curious about which languages Esperanto is closest to, in order to know for whom it would be easiest to learn this language! For example, could a Spanish speaker learn it more quickly than a French speaker?
Comment: Now you can also ask on the Esperanto Stack Exchange!   http://esperanto.stackexchange.com/questions
Comment: Thank you @fi12 :)
Answer: Let me break your question into several parts and answer them one by one.
How much would a person not knowing Esperanto understand from a newspaper article in Esperanto?
If you are asking solely about vocabulary, then from my experiences of teaching Esperanto worldwide, German speakers can recognize the origin of about 70% words and can directly understand about 40%. My French students at first understand about 30% of the vocabulary, but go up to 70% too once they learn some basic principles of the vocabulary building. Russian students can understand about 20-25% of usual Esperanto texts (unlike the common belief of 40%!), and again go up to the same level when becoming more advanced.
As pointed out in a comment, the reason for that might lie also in population bias, for:

For most of the Russian students Esperanto is the first foreign language where they reach the level of fluent speech (usual schools teach languages only up to level A2 that does not include fluent conversation), and they primarily study Esperanto to participate in the social activities of Esperanto-movement, not due to linguistic reasons.
European students are usually fluent at least in one (English), but many also in several foreign languages and social aspect of learning is much less pronounced here.

Would native speakers of certain language learn Esperanto much faster than the others?
Since Esperanto has an a-priori grammar (see below for explanations!), learning the language itself it similar for everybody irrespective of their mother's tongue.
The grammar of Esperanto is well balanced, so that if Russian native speakers might have less problems to understand the system of active and passive participles (naturally existing in Russian), the speakers of Romane languages have much less problems with a definite article la that does not exist in Slavic languages.
Speaking about vocabulary, one need to admit that speakers of Romane and Slavic languages have some advantages in memorizing Esperanto words, as they often resemble words that exist in their languages (international lexis, see below). However, since "internationalism" is just one of several principles of Esperanto vocabulary (see below), learning the correct spelling of the word is required for everyone.
To be honest, native speakers of Asian languages, especially those employing a different writing system (Chinese, Korean) might require more time to learn Esperanto, because they need to get used to the new alphabet. But from my experience, all Asian students already knew at least one European language and were past this step.
If we compare, however, learning Esperanto as a second language vs. English as Second Language (ESL), the former requires about one eights (1/8) of the learning time to reach the comparable level (meaning that the level that one reaches in English in 2 years can be reached in Esperanto after 2/8 = 1/4 years).
How is Esperanto similar to natural languages?
But talking about similarities between constructed and natural languages, one should understand two basic principles of language design:

a priori languages are created "from scratch", without any reference to existing (natural, creole or other constructed languages) languages, rather they try to introduce other principles (schematicity, regularity, predicate logic, laws of musical harmony etc.) to language construction.
a posteriori languages borrow principles from already existing languages, trying to mimic the latter ones while eliminating their disadvantages (like irregularity, difficult to pronounce sounds, irregular stress etc.).

Speaking about similarity between languages, we can talk separately about similarity of grammar and similarity of vocabulary.
Esperanto is a constructed language with a-priori grammar (not similar in any way to any existing language, i.e. created completely from scratch), and a-posteriori vocabulary (every Esperanto word, except those derived directly from grammar constructions (like ina, ree, arigi etc.), has an origin in an existing language).
Similarities in grammar
Despite being an a-priori language from a grammatical viewpoint, the only pure a-priori part here is the so-called correlatives (tiam, kiam, iam ...), the other affixes are usually selected so that the resulting word sounds similar to a word or affixes existing in natural languages (like -ar- for grouping, similar to English arity (unary, binary, ternary) etc.), hence even memorizing these affixes is usually very natural for speakers of any major Romance language).
Principles of Esperanto vocabulary and similarities
The vocabulary of Esperanto is, in its turn, based on so-called international lexis, i.e. the words used in most of the languages (both as inherent and borrowed). This is somewhat similar to the concept of "common denominator" in mathematics, for these words are known to representatives of many nations, either directly (with the same meaning) or indirectly (as foreign words or parts of borrowed words).

Let me give you some examples now.
Nation is nacio in Esperanto, and many words derived from its root (naci-), like inter-nacia, naci-isto, naci-ismo are understandable for me as a native Russian speaker (and definitely to English, French, German, Spanish and Italian speakers too).
Looking at the first word, inter-nacia, you can see that in Esperanto you can use this pattern to derive further words, like inter-urba (something going from one city to another, a "long distance" [train, call, taxi]), and again I know the root urb- (=city) from other borrowed words in Russian, like urbanization (this is an example of that "international lexis"), even though the word "city" is completely different in Russian (gorod).

"Internationalism" is not the only principle of Esperanto vocabulary.
Another principle is simple pronunciation, that makes some words get "crippled" to fit into Esperanto vocabulary: bread => pano (most likely from Italian "pane", but also French "du pain"), sausage => kolbaso (from Russian "kolbasa" etc.). If several international words exist, the one with the simpler pronunciation for most of the nations is selected (compare pano vs. bredo). Sometimes it leads to Esperantization of quite unexpected words, like bulko (=bread roll or loaf).
One more principle is avoidance of homonyms. Hence "planet" is in Esperanto planedo, not planeto, that could also be understood as plan-eto (=small plan).
The latter principles make Esperanto sound or write less similarly to natural languages, but they contribute to its other features, like easiness to learn and pronounce, comprehension (both written and speaking) etc.
Comment: To what extent (if any) do you think a form of population bias applies?  Native German speakers tend to be quite well-taught in foreign languages compared to some other countries, *especially if they show an interest in languages* which you could probably assume if they're learning Esperanto
Comment: @ChrisH: Excellent question! I edited my answer trying to address it.
Comment: "not similar in any way" is a bit strong!
Answer: I found a quick breakdown in the Esperanto.net FAQ:

About 75 % of Esperanto's vocabulary comes from Latin and Romance languages (especially French), about 20 % comes from Germanic languages (German and English), and the rest comes mainly from Slavic languages (Russian and Polish) and Greek (mostly scientific terms).

And I got to learn something about the common ground with Russian!

The words derived from Romance languages were chosen to be as recognizable as possible throughout the world. For example, the word "radio", although technically Romance, is now used internationally. Someone knowing only Russian and looking at a text in Esperanto would immediately recognize perhaps 40 % of the words, without even having studied the language.
Answer: The majority of Esperanto's original vocabulary came from French, German and English, so if you already speak any of these languages it would certainly give you a head start.  According to La deveno de Esperanto by Geraldo Mattos, by 1987 an estimated 84% of Esperanto's basic vocabulary was Latinate, 14% Germanic, and 2% Slavic and Greek.  The French language, specifically, has had a strong influence on Esperanto; however, Esperanto pronunciation is entirely phonetic, unlike French, and this could hinder reading comprehension for French speakers.
Comment: English isn't the most phonetic language on the planet, but Esperanto's phonetic-ness didn't hinder my reading comprehension, so I don't think that would be the case for French either.
Answer: According to the proportion of common lexemes, French, English and Italian are the most similar to Esperanto.
The proportion of lexemes that are common to Esperanto and other languages: 91.64 percent French; 89.50 percent English; 89.12 percent Italian; 87.79 percent Portuguese; 87.12 percent Spanish; 81.70 percent German; 64.78 percent Latin; 53.26 percent Russian.
Source: Language Learning Research
Answer: The closest well known language is Ido. There are some other offsprings that are perhaps closer, but they are all rather esoteric ones.
Knowing Ido would give you almost immediate good passive understanding of Esperanto, but active usage might suffer a lot from interference.
Comment: Well, yes. Much like Italian is a "descendant" of Latin, or English is a "descendant" of Anglo-Saxon or. lojban is a descendant of loglan or the American Sign Language a descendant of (old) French Sign Language... The differences between Ido and Esperanto are quite substantial, even if much of the vocabulary is similar (but not identical). Nobody would claim these to be two forms of one language.
Comment: But isn't Ido just a form of esperanto? Wikipedia says 'the language is a "descendant" of Esperanto'.


Where is the ringing telephone in Arkham City?

Question: In Batman: Arkham City I've overheard several prisoners in the Bowery talking about a ringing telephone, saying that whoever answers it will die. Where can I find the phone in question?
Answer: This is a side-mission: there are several payphones throughout Arkham City, which have a random chance of ringing when you get close. They will be called out on your HUD. If you reach one in time (you can't be in combat, though it'll wait for you) you'll be able to advance the mission. If you miss a ringing phone, you won't be penalised; however, during the mission, you may have to pick up a phone before a timer expires, and missing this phone will penalise you.
As a hint, there's one Batman villain whose modus operandi involves making an innocent choice that leads to your inevitable demise/release. He also appeared in Arkham Asylum.
Comment: I've actually finished all the sidequests since I posted this, I forgot to mark a solution as accepted.
Answer: I found one in Park Row, northeast of the court house, under the overpass. Didn't realize it also gave me the Ring Ring achievement. From what I see, there are quite a few ringing phones to find.
Answer: Sooner or later in the game Zsas will call you on one of these phones. When you hear it ringing, use detective mode to see it ringing . Kinda of like a bat's sonar.


What is 'wala' of a slave?

Question: Its mentioned in several ahadith (like this) that the 'wala' of a slave is for the one who buys the slave, and that 'wala' should not be bought and sold.
This 'wala' comes up a lot in the ahadith concerning slavery.
What does it mean ?
Answer: In short wala in Arabic means loyalty.
Why is it so important?
Wala is one of the conditions of Iman. Allah has stated:

And if they had believed in Allah and the Prophet and in what was revealed to him, they would not have taken them as allies; but many of them are defiantly disobedient.﴾٨١﴿

It is not just for slaves, you will find many Ahadith that shows that loyality to Allah should never be bought or sold as it is one of the basics of islam.
Comment: While this explains a little bit the word "wala", it does not respond to the OP's question.
Answer: The word wala in your question's context has a legal meaning that comes with rights and duties. Therefore there is no direct translation.
The meaning has elements of similar yet different concepts. Among others you find in it the notions of:

guardianship, custodianship, wardship
tutelage, trusteeship, curatorship, fosterage
maybe there are other nuances
Comment: I have already needed to delete multiple comments on this post, all of which were nothing to do with the question asked nor how well this answer *answered* the question asked, rather they were arguing about the tangential claims which I have now removed. If you wish to argue that they are actually necessary for *answering the question asked*, please take it to meta.

What is 'wala' of a slave?


How can I get flash video to work?

Question: I'm trying to watch NBC Sports Gold, I assume it's flash but I don't really know. The video will not load. I have tried Chrome, Firefox and Epiphany. Flash appears to be installed. What do I do? I'm using Juno. Thanks.
Answer: open terminal (applications > terminal > )
paste the below command:
sudo apt install flashplugin-installer

follow the prompts.
there may be security popups on your selected browser that will need to be enabled for the popup or content to be displayed.
hope this helps.
""Cheers
G
Comment: Thanks, yeah that's how I originally installed it. I just get a blank screen where the video should be displayed with "loading..." in the top, left corner. I manually allowed Flash in Chrome, don't know how to do it in Epiphany.
Answer: this is showing the same problem for some users:
https://askubuntu.com/questions/64164/flash-player-in-epiphany
I'm suing FireFox for flash and probably why i haven't run into this problem as the last post in the link explains.

NPAPI plugins are (unfortunately) no longer supported by major web
  browsers. PPAPI is the new way. Fortunately, a very good open source
  project called Freshplugin allow any browser to use flash player PPAPI
  from Chrome in Linux.It means that the last flash player update will
  be used in any browser, even epiphany. You must have Chrome installed.
  https://github.com/i-rinat/freshplayerplugin

it may be that due to having FF installed before i installed flash its now available and working in Epiphany.
the link has multiple other fixes to try.
let me know how you go.
""Cheers
G
Answer: Also, as written on NBC Gold troubleshoot page:

You will need to unblock 3rd party cookies, in order to view video.

(As this is a must, try unblocking 3rd party cookies in your browser, and see if it will enable video streaming.)
Answer: Why the duck you want to install flash which you will have to remove with the end of the 2020 year? Flash will be banned and abandoned by Adobe. It will be no support, no patch and finally this format will die definitelly and will be erased from the Internet. Besides remove Epiphany.
sudo apt purge epiphany

Install Firefox which all Elementary OS developers are using, or Chromium at least. I recommend Vivaldi browser.

How can I get flash video to work?


Sudoku puzzles and propositional logic

Question: I am currently reading about how to solve Sudoku puzzles using propositional logic. More specifically, they use the compound statement
$$\bigwedge_{i=1}^{9} \bigwedge_{n=1}^{9} \bigvee_{j=1}^{9}~p(i,j,n)$$
where $p(i,j,n)$ is the proposition that is true when the number
$n$ is in the cell in the $ith$ row and $jth$ column, to denote that every row contains every number. I know that this is what the entire compound statement implies, but I am trying to read each individual statement together. Taking one single case, does
$$\bigwedge_{i=1}^{9} \bigwedge_{n=1}^{9} \bigvee_{j=1}^{9}~p(i,j,n)$$
say that in the first row, the number one will be found in the first column, or second column, or third column, etc?
Comment: I think you're correct.
Answer: The formula says "for every allowed value of the row $i$ and the value $n$, there is at least one column $j$ for which the $(i,j)$ location of the grid is filled with the value $n$".
The translation of Sudoko to propositional logic does not make the problem fundamentally easier.  Any logic problem can be rewritten as a Sudoku, too, and solving either type of problem in general is computationally difficult (NP-complete).

does $\bigwedge_{i=1}^{9} \bigwedge_{n=1}^{9} \bigvee_{j=1}^{9}~p(i,j,n)$ say that in the first row, the number one will be found in the first column, or second column, or third column, etc?

No, the formula saying that is $\bigvee_{j=1}^{9}~p(1,j,1)$ which is the $i=1$,$n=1$ specialization of the first formula. The disjunction indexed by $j$ unpacks to "p(1,1,1) OR p(1,2,1) OR p(1,3,1) OR ... p(1,9,1)".
Comment: I added some more to directly answer the question.
Comment: So, is what we have both said essentially the same, yours being more general?
Answer: Although expressible as propositional logic, for practical solutions, it is computationally more effective to view Sudoku as a Constraint Satisfaction Problem. See Chapter 6 of Russell and Norvig: Artificial Intelligence - A Modern Approach, for example.

Sudoku puzzles and propositional logic


Is the 51% attack the only technical reason no country will adopt Bitcoin as a state currency?

Question: Is the 51% attack the only technical reason no country will adopt Bitcoin as a state currency?
Lets suppose a country with GDP size less than 300 Billion USD adopt the Bitcoin as an official currency. It will be very easy to crush or take control of state currency if a country like US or China invest to run 51% of mining pool.
Comment: A lot of companies used to be (and some still are) uneasy about leaving critical infrastructure to open-source development.  It's hard to believe either US or China would be comfortable with their currency being maintained by developers out of their control.
Comment: Related: https://bitcoin.stackexchange.com/q/256/63872
Answer: If what you mean by adopt bitcoin as a state currency means replace their existing fiat currency; I believe there would a lot bigger problems to consider. If they did do that, it would essentially be saying that their money no longer has any value, which would cause a massive panic within their population. A type of panic similar to when India banned the 500 and 1000 Rupee notes.
You'd also have to consider countries that have that type of GDP, they would need the infrastructure for everyone to be able to be connected to the internet and have devices to use Bitcoin. Also they would need everyone to be tech savy enough to understand how to use bitcoin.
Also, with the lightning network at its current state, bitcoin transactions can't scale to an entire countries' economic activity.
So I would say that a 51% attack is pretty low concern for a country looking to adopt bitcoin as a state currency. A better approach would probably be to start stock piling bitcoin and perhaps even use it to back their fiat currency to strengthen it.
Answer: You would not do PoW if you have a state as central authority and trust anchor. You would simply switch to Proof of Authority or other strategies, e.g. permission-ed blockchains. Further, you could use other Decentralized Ledger Technologies.
PoW is so great because everyone can join the network without revealing their identity.


Why upgrading iPhone from iOS 3 to iOS 5 displays USB and iTunes icons?

Question: I upgraded my iPhone from iOS 3 to iOS 5. It is now blocked: it shows a USB icon and the iTunes icon. How to proceed?
Answer: Start iTunes on your computer (ideally on the one you used to sync your iPhone with) and connect the iPhone via USB.
You will get an error message or number if there is something else amiss, but usually getting iTunes to do the download and then the restore will fix things up for you.
Answer: This is a normal part of the installation. When updating iTunes puts the phone into recovery mode. Obviously an error occurred whilst updating. Plugging it back into you computer should fix this.


If I have 51% of the capacity of the entire network, can I mine absolutely all the blocks faster than the network?

Question: I'm really wondering can I mine absolutely all the blocks in the network faster than rest miners with their 49% hashing power not for the purpose of conducting double-spend attack?
Answer: Can you mine absolutely? No. If you have 51% share of the network hash rate then the probability (not certainty) that you will mine the next block is 51%. It is theoretically possible that you may never find a solution to the block ever. However, if you continue to mine on the blocks that only you generate, then practically you can build a chain that consists entirely of the blocks that you mine after the forking point.
Comment: This is not necessarily correct. If you truly have more than 50% of the hashrate, and the ability to maintain that state for an extended period of time, you can broadcast your blocks just fine. However, you only choose to extend your own blocks,   not any blocks that others happen to mine. If you have >50% this is guaranteed to eventually result in a majority chain that consists entirely of your blocks after the forking point.
Comment: Note that if anyone actually did this, it would be quite apparent as all other miners would never get any rewards. It's likely that this would prompt a rule change, for example, to a different mining algorithm.
Comment: @PieterWuille Now that I think about it, your reasoning seems to make sense. I had to not include the possibility of the miner mining on the honest blocks.


Why does the torque due to a reaction wheel shift to the center of mass of the spacecraft?

Question: In a spacecraft, even if a reaction wheel is placed at some distance from the center of mass, the satellite always rotates through an axis which passes through its CoM? What is the reason behind this? Why is the torque vector treated as free vector?
Comment: What do you mean by a "free vector?"
Answer: The reason for this is Newton's first law of motion:

When viewed in an inertial reference frame, an object either remains
  at rest or continues to move at a constant velocity, unless acted upon
  by a net force

(from here). This is the version for point-like objects. For extended objects, the law applies to the center of mass.
When it activates its reaction wheel, the satellite is not acted upon by external forces (ignoring gravity): the wheels only create an internal force, which cannot impact the trajectory of the center of mass.
Answer: "Because Newton's first law says..." is an answer but it's not really a "because" type answer. Newton's laws of motion are observations. He noticed these things about how the world seems to work and wrote them down. They are not explanations.
Asking why does an object's center of mass tend not to move (or change velocity) when there is no external force, and answering because objects tend not to move (or change velocity) when there is no external force - and we call that Newton's Law is not really an answer to why?
Richard Feynman sometimes got a little prickly when asked "the why question" in physics himself. He is usually very careful to remind us over and over "we don't know why" something happens, but it just does.
So in my alternate answer, I've expressed Newton's first law in more familiar rather than formal terms. But really, no matter how you look at it, it's simply an observation of how the world appears to work. Every time we check, no matter how we check, it keeps happening this way. Most people call it a law, but this is only because we haven't found a case yet when it doesn't happen.
We should really call these Newton's observations. He noticed it and noted his observations, and he couldn't find exceptions, and it helped him predict more complicated things and those thinks also always seem to happen the way he predicted. For humans, a law is something we should or must do. But, in physics, a law is no more than an observation that something seems to keep happening and no exceptions have been seen yet.

Very good question! I had to think about it. The center of mass can't suddenly move on its own, without an external force - like thrust from it's rocket or somebody pushing on it. Floating there in space, if you don't see it interacting with anything, not thrust or magnetic fields or beams of light or solar wind, then it's gotta just stay right there. That's what Newton sez in this excellent answer.
If something (symmetric like a wheel around its axis) is turning inside the spacecraft - even a tape recorder - the whole thing can rotate in place, but it can't move from one place to another.
If something moves (translates) inside, then the whole spacecraft can appear to move from the outside, but its center of mass will still be in the same place.
Comment: I totally agree with you that the answer to the question is "that's the way things seem to work", and that any "why" question on the fundamental principles of physics can be answered the same way.


How can pilots differentiate runways and taxiways during landing?

Question: There have been many incidents where pilots landed or attempted to land the aircraft on a wrong surface (for example Continental 1883 and Air Canada 759). Are there any tips for pilots to avoid that? Especially during nights or low visibility scenarios.
Comment: Can you point out a particular *accident* that happened when a pilot landed on a taxiway? Usually these don't result in accidents, they are classified as "pilot deviations" or incidents. I don't know of any "accident" caused by landing on a taxiway... There have been accidents involving landing aircraft coming down on top of, or running into aircraft *on the runway* during low visibility...
Comment: You might find this interesting: https://www.skybrary.aero/index.php/Runway_Identification
Comment: [Closely related](https://aviation.stackexchange.com/q/24023/62)
Comment: @VvV Please don't hesitate to roll back if you don't like my edit!
Comment: I think this website should provide interesting reading for you: https://www.skybrary.aero/index.php/Inappropriate_use_of_Runway_or_Taxiway . I will not create an answer here, because I don't have the time to spare to copy-paste what you can find there. In particular, look into the document under "Further Reading" (direct link: http://www.skybrary.aero/bookshelf/books/4058.pdf )
Comment: Simple flowchart. Are you a pilot? N--> Doesn't matter Y--> Are you Harrison Ford? N-->You're landing on a runway Y--> [You might be landing on a taxyway.](https://www.ainonline.com/aviation-news/general-aviation/2017-05-16/faa-opts-out-punishment-harrison-ford-taxiway-landing)
Answer: During daytime and good visibility, it should be pretty obvious that runway markings are white and taxiway markings are yellow. Runways have the runway designator in big white numbers at the end and a dashed centerline, while taxiways have a narrow continuous yellow centerline.

During nighttime, you will notice that runway lights are white or yellowish while taxiway lights are green (center) end blue (edge). Additionally, many runways have approach lighting, which taxiways obviously do not.

During low visibility, you won't be trying to identify the runway visually, since you will be performing an instrument approach, which will usually take you all the way to the threshold. For non-precision approaches, where some visual maneuvering is required, the information above regarding markings and lights apply equally.
In addition, taxiways are generally narrower than runways. While many runways do have parallel taxiways that run for the full length of the runway, in many cases the taxiways will have a few bends or be at a slight angle, whereas the runway will be completely straight and wider.
You should always study aerodrome charts and familiarize yourself with the airport layout before attempting to land at an airport. When doing so, pay attention to the airport layout, and try to notice any areas where confusion is likely (such as long straight taxiways that run parallel to a runway). If you come prepared, and pay attention to the details mentioned above, you should be home safe.
Comment: Dusseldorf Tower: "Taxiway Alpha to Romeo to X-ray.  Why are you confused, have you ever flown to Dusseldorf?  British Airways pilot: "Twice, in 1944, but it was dark, and I didn't land."
Answer: ExpediteDescent has done an excellent job of describing how pilots distinguish runways and taxiways. In addition to what he has posted, I would like to add that it boils down to situational awareness and proper prior planning. Runways and taxiways are very well identifiable from there markings, lights, and signs. And, only specially equipped aircraft with pilots who have received special initial and recurrent training and certification are allowed to land on a runway that they can not visually identify the runway environment. Aviation safety is built on redundancy. So, identification is not left up to chance.
For instance:

The markings, signs, and lights for runways are distinctly different from those of taxiways.
Runways are named and listed according to their magnetic heading/ground track
During taxiing, pilots should check their magnetic compass and  Directional Gyro/Heading Indicator against the known headings of identified taxiways.
Pilots should always check their magnetic compass and Directional Gyro/Heading Indicator prior to takeoffs and landings to ensure they are lined up with the correct runway.
Different runways of the same airport will have different runway lead-in lights (MASLR, ALSF, etc). Which type of leads in lights used will be indicated in charts, diagrams, and chart supplements.
Runways will usually have visual vertical guidance equipment next to them. Which side of the runway the equipment is on will usually be indicated in charts, diagrams, and chart supplements.
Even during good visibility, pilots can use ILS or RNAV equipment to double check they are landing on the correct runway.
Plenty of panel mounted and handheld electronics have the option to show the extended centerline of a chosen runway. I personally use this feature to double check the runway alignment of the airport on each landing. Especially those at unfamiliar airfields. It is as simple as hitting OBS on the Garmin and dialing in the magnetic heading of the desired runway.
Plenty of panel mounted and handheld electronics have the option to show the aircraft's GPS derived position relative to their ground location on the map.
Plenty of panel mounted and handheld electronics have the option to show the aircraft's GPS derived position relative to their ground location on sectionals, charts, and airport taxi diagrams. Many call this geo-referencing. I believe Garmin has trademarked the name SafeTaxi for this feature.
The airport taxi diagrams and chart supplements list areas on the airport surface where there might be confusion or a preponderance of error of mistaking one airport surface for another. These are labeled and described as Hot Spots for the pilot to exercise increased diligence.

These various methods and their redundancies work. Case in point: My local airport decided to build a longer runway parallel to their existing runway. They designated the old runway as a second, main taxiway. The configuration is new runway on the East, old (main outbound) taxiway on the West, old runway/new (main inbound) taxiway in the center. All running North-South. They still maintain the old runway as if it were still an active runway. They just changed the markings, signs, and lights. They have even had an opportunity to use the old runway/new taxiway as an emergency landing surface when the new/actual runway was shut down due to a wheels up belly landing. Since the new and the old runways are identical except for their markings, signs and lights, and they both start right next to each other on the North end, it would be very easy to mistake one for another. Through situational awareness and the redundancies listed above, that does not happen.
Comment: "Runways are named Andrew listed according to their magnetic heading/ground track", but I've called my George! I will hold him and pet him and take off from him. Actually, that looks like your train of thought jumped track right in the middle. Want to revisit that and/or make a further explanation to the non-pilots in the room?
Comment: I realized that was probably the problem. Right after I hit `` on my comment. I figured I'd leave it since I was pulled out a good dad joke so early in the morning. ;)
Comment: @FreeMan - Darn spellcheck. That should be "Runways are named **and** listed according to their magnetic heading/ground track". Thanks. I did not catch that Apple had changed what I had typed.


Android PlayStore App/ Launcher icon

Question: I am designing an App for Android PlayStore and have a launcher icon related question. I know there used to be a set rounded corner radius of 5% for all launcher icons, but I see many free form App/ Launcher icons on the PlayStore these days.  Does anyone know if this is a strict design regulation anymore? Or will Google still feature (Editors Choice) your App with a free form App launcher icon?
Thanks
Answer: From Android launcher icon design guidelines:

Style
Use a distinct silhouette. Three-dimensional, front view, with a
  slight perspective as if viewed from above, so that users perceive
  some depth.

Android PlayStore App/ Launcher icon


Is there a way to learn Icelandic phonetics online?

Question: I want to learn Icelandic online, but am struggling to produce some phonemes.  I am unable to find an IPA translator for Icelandic and think it'd be easier for me if I could see some of what I learn in IPA if possible. Any ideas?
Comment: http://en.wikipedia.org/wiki/Icelandic_phonology ?
Comment: skoli.eu offers (paid) online courses including lessons and exams via Skype. Check it out. Otherwise take a trip to Iceland, it's the best method.
Answer: Have you taken a look at Icelandic Online? It's a free online Icelandic language course created at the University of Iceland. It's been designed with an emphasis on immersion and trial-by-error, so you aren't spoonfed everything in every lesson. Pronunciation is no exception to this, so this may not be what you're looking for.
That said, if you stick with it it might prove useful in the pronunciation arena. One of the tricky things about Icelandic is that there is a lot of lenition, contraction, etc. that happens in the context of full utterances, so that the pronunciation of a phrase may not be the literal "sum of its parts" (think going to --> gonna in English), but these pronunciation changes aren't indicated in any way in the orthography the way we sometimes use apostrophes or changes in spelling to express such phenomena in English. This is of course true for a lot of languages to varying degrees, but my anecdotal experience as a linguist and a native speaker of English is that Icelandic presents a more extreme case along this spectrum.
What's useful about the Icelandic Online program is that it provides tons of recordings (by native speakers) of both full dialogues and individual words. By listening to the carefully articulated pronunciations of the individual words you start to build a sense of how the orthography--and therefore the phonology--works, especially if you supplement it with the Wikipedia article on Icelandic phonology, which gives you IPA information. Then, if you listen to the dialogue recordings you start to get a sense of how things get "slurred" and lenited in continuous speech.
I hope that helps!


Is there a reason to upgrade Internet Explorer on Windows Server?

Question: I never use Internet Explorer on my Windows Servers. Is there any reason I should upgrade Internet Explorer (version 6 or 7 to 7 or 8)?
Answer: Keep in mind that while you may not directly use IE, the IE rendering engine or other components may be used by other applications you may run.
I think it should kept it up to date.
Answer: Definitely. If you have it installed, I'd rather run a more the most up-to-date version regarding security. Featurewise it's a moot point, but I'd rather not have admins browsing around in IE6 on my servers.
Optimally noone uses IE on servers, but we know sh** happens.
Comment: @David Schmitt: http://www.saveie6.com/ ;-)
Comment: I'm going to buy saveie6.com off that guy and put up a redirect to getfirefox.com
Answer: Someone else (person or application) might use it, now or in the future - so keep the patch level of all installed applications as recent as possible at all times.
Answer: The main benefit I see would be security.
That alone is worth upgrading and the other reasons mentioned: other apps may use it, other individuals may use it, and for testing are defiantly worth considering.
However, the best bet might be to wait a couple weeks so the initial bugs get ironed out then do the upgrade.
There always seems to be one big security flaw in new IE releases.
Answer: Like many things in this world, it depends:
If you have web based applications in your shop that you might have to access from one of these servers (*) and that app doesn't work with IE7 or IE8, then no. Otherwise, I don't see anything wrong with updating the version of IE as part of your regular upgrade cycle , but I wouldn't bother rushing it.
(*) In general, you shouldn't have to use a browser on a server to access any web application. That's what workstations are for; and again, if you or your users depend on IE6, then no, don't upgrade it. Setup a test box in IE7/IE8 and audit your web applications.
Answer: Most systems need IE for Windows updates, so yes, keep it up to date.
Comment: Not if you have WSUS.
Comment: +1 Indeed, that is a valid exception.
Answer: Even if you don't upgrade, i don't think it will be a problem: thanks to the uber-protective securty policy applied to internet explorer by default, IE6 is already crippled to a state that renders it useless
btw, ie6 it is like a bug compilation, i would strongly suggest to upgrade
Answer: Until such time as we get a server version without IE it needs to be updated. IE has always had more than its fair share of vulnerabilities and your server needs to be protected.
Answer: Oddly, not upgrading IE protected me from the nimda virus.
I used to run a SCM server that used NT 4.0, which comes with IE 2, and I had never upgraded.  Despite the fact I had the server configured to only allow connections from internal IP address, nimda had infected our exchange server so it still managed to get on to my server using the ..\.. alt encoding trick. However, nimda failed to infect my server because it  used a fnc in WININET that wasn't in the IE 2.0 WININET.  My IIS logs were full of these failed attempts.  It took quite some time to figure out why my server didn't actually have a nimda infection.
Had I upgraded to IE3, my server would have been infected as well. (I'd prefer not to have IE installed at all).
Answer: I upgrade IE selectively.  If the server runs or is managed by a web app I absolutely will not upgrade until I am certain the app supports it.   Otherwise if the thing should never be used or launched I will upgrade right away.  I have had web admin tools broken by IE upgrades and had to downgrade before I could resolve issues.


Why didn't Daenerys take help from Daario Naharis?

Question: As observed in S8E4, Daenerys needs all the people she can get to fight Cersei. Why didn't she ask Dario Naharis and second sons to join the war?
Comment: +1 and Yara and her iron fleet too, and probably the south (they hate the Lannisters)
Comment: @Anu7 I think it's stated, or at least implied, that the ships they use to get to Dragonstone are Yara's, it's just we don't see Yara.
Comment: The beacons didn't work........
Comment: On a side note, I'd say Daario Naharis is probably the best strategist Dany has, surely better than Tyrion or Jon, who made lots and lots of blunders recently. He was the one who correctly understood that the Unsullied were ineffective against the Sons of the Harpy, and the Second Sons would have done a better job.
Comment: Yara was at the iron islands, so not in a position to (quickly) help.
Comment: @TheLethalCarrot oh !!! those are Yara's ships ? I did not know that. But yes good to know.
Answer: They are on the other side of the world. Reaching them with the message and then waiting for them to sail to Westeros is not something Daenerys would be willing to wait for. Remember that she refused to give her troops even a few days rest after the Battle for Winterfell before marching on King's Landing.
Her (dubious) reasoning for this was that her army would be getting weaker, while Cersei's grows stronger by the day.
Comment: Yup. After the battle of Winterfell, she controls the iron islands (taken to Cersei's side), Dorne, and part of Stormlands thanks to Gendry, while Cersei needs to pay the golden company every day. Time is definitely helping Cersei...
Comment: She has no real control over the Stormlands.  The only people that might recognize her authority to appoint him its lord were already right there.  And right there wasn't the Stormlands.  It was little more than a ceremonial gesture, which would only bear fruit well into the future.
Comment: @zibadawatimmy which is relevant... why?
Answer: Dany was insulted and looked ready to start burning people when it was suggested that they try to rest from the battle of Winterfell.
When Tyrion and others arrive at the camp outside King's Landing on the night before battle he tells Jon and the others that Dany wants the attack to begin "immediately." Glances were exchanged and Jon said they would attack the following morning.  It won't surprise me if Dany brings up that delay in ep 6 next week.
With that level of urgency from Dany, there is simply no way that she was going to sit around waiting to see if the Second Sons could make it across the sea from Essos without being sunk by Euron's fleet.
And beyond the issues of time and logistics, if Dany wanted to keep having sex with Daario then she would have brought him with her in the first place.  She left him behind because he was not suitable as a queen's consort and nothing about that has changed.  Daario is probably the last person she would call to her side.
Answer: Don't forget he was essentially appointed as the head of law enforcement on her departure.  She tasked him with keeping the peace and keeping Mereen from reverting to slavery or just generally crumbling into chaos. Removing him would basically mean accepting that Mereen may crumble and her changes undone.
Also, they probably couldn't fit his abs into the budget.


How many shots should one take to get a reliable estimate in a quantum program?

Question: When testing my quantum programs, I wonder how many shots I must take to get a specific accuracy.
Are there any papers that you can recommend that analyze this?
Answer: This is depends on what algorithm you are executing.
For example, if you look at the Bernstein-Vazirani algorithm then theoretically the number of shot you need is 1 if you have a perfect quantum computer. This is because the end result that you are looking for collapsed onto a single eigenstate. However, because of noise, we would like to do more. In term of how many more, this is depends on the device. Not all device have the same noise level. You can, actually, look at the gate fidelity on the machines (at least you can do that for IBM's machines) and work out the probability that your circuit will fail, then from there determine the number of shots you might want to use. However, without doing that analysis, then you can just be on the safe side by using the maximum number of shots giving to you. For IBM's machines this works out to be 8192 shots. However, you can run multiple jobs to collect the statistics if you think you need more shots than this. Now, of course, if your quantum circuit is too long, the errors will built up so much that your circuit will "essentially" guarantee to fails, then additional shots will not help.
The above discussion is for quantum algorithms that only need $O(1)$ shots/samples. This is not true for algorithm like VQE. For VQE, we need to do $O(1/\epsilon^2)$ shots to achieve error of $\epsilon$. For chemical accuracy, which is for $\epsilon = 10^{-3}$, you would need to do ~$10^6$ shots at each iteration... which is insane!
Now if you just create a random circuit, which output a state that could be in super-position of $2^n$ eigenbasis then you will need $O(2^n)$ shots to able to able to extract the output probabilities. This why, designing a quantum algorithm is like an art. Therefore, You can't just do some operations on a quantum computers, and claim that because you did it on a quantum computer, it must be faster than doing it classically. You do not have access to the state of the qubits! This is also the reason why you can't just perform Quantum Fourier Transform ( essentially doing Discrete Fourier Transform on a quantum computer) and claim that you have a speed-up. Although, QFT does give you an exponential speed-up over DFT or even FFT (Fast Fourier Transform), doing it randomly will output a generic quantum state that in superposition of $2^n$ eigenbasis... Extracting out this state would take exponential amount of samples which then defeat the entire purpose.
Comment: Thankyou :) How has the accuracy of $\mathcal{O}(1/\epsilon^2) $ been proven? Is there a paper in which it is that I can read?
Comment: @Hannah The $O(1/\epsilon^2)$ samples needed for VQE is a direct result of the Chebyshev inequality https://en.wikipedia.org/wiki/Chebyshev%27s_inequality . Also, if you want a paper reference then in the original paper: https://arxiv.org/abs/1304.3061  you can look at the first paragraph of page 9 for their discussion on this as well. Hope this help.
Comment: In this paper is the shot-number needed for QAOA with gradient-descent otimizers analysed. This is super interesting! https://arxiv.org/pdf/1910.01155.pdf
Comment: thank you so much ! :)
Answer: One way of this estimation is to analyze how many states will be there. Suppose there will be $N$ states and the shots are $N$, then the average observation of each should be 1, which is easy to forget some states, while if you change to $N^2$ shots the risk is decreased.
For $N$ states, if you take $n$ shots, the probability that a state has not been detected is $n \choose 1$=$(\frac{1}{N})^n$, where degeneracy is ignored.
Another way is rather interesting, I think the shots number only influence the running time slightly. Here comes my observation:

The first case is to search the number 24 from the range [0,31], the second case is to search number 64 from the range [0,127], the last one is printed on the figure (in my code, the number of qubits needed is 3*len(bin(24/64/128)[2:]), three times of the binary length).
According to this observation, I think the time-consuming part of computing is to get the state vector, and the role this 'shot' variable plays is to generate output based on the state vector. So, if you just want to save the running time of your script, maybe you do not need to change the number of shots.
NOTICE that this test is not sophisticated, loopholes maybe continue hidden.
Comment: FINE, I will, later.
Comment: Could you please replace the first picture with actual text?


Difference between multiple voices and chorus

Question: There is many software synthesizer providing controls for both "voices" and "chorus" effect. I guess that both works by adding more oscillators layers with little differences, but what exactly change between the two functions?
Answer: Voices are separate oscillators, chorus is merely a delay-based effect.
Usually the number of voices in a synth actually refers to the number of oscillator groups. For example, an analog synth with "six voices, each with two oscillators" means that you can separately program two different oscillator programs (e.g., wave shape, frequency, etc.), and then play six different notes at the same time, each note playing two oscillator programs. So there are a total of twelve oscillators, but you can only program them in banks of six.
Chorus is a delay based effect where whatever signal comes in is copied and delayed slightly, usually pitch-shifted also, and then the copy is played back with the original. The delay and pitch changes are usually varied over time to make it sound like more than one instrument is playing the same part.
Answer: 'Chorus' is a similar effect because it is also achieved by adding similar voices together. It is technically correct so long as the voices still create a sound that is perceived as a 'chorus' and not as distinct voices or pitches:
Sometimes you can have oscillator voices synchronized in Unison mode, or otherwise have their phase playback "freely". In the latter case, detuning the voices creates a stronger chorus-like effect, due to the various "beating" introduced by superimposition of the waves at various phases. This is similar to introducing one or more delays. When the Osc phase is put in "sync" mode, generally a sharper flanger-like effect is heard, as the voices cycle in and out of phase uniformly, from the master oscillator.
Comment: It should be noted that not all controls labelled "Sync" or "Osc Sync" do what you describe here. For instance, the "1->2 Sync" button on the Moog Little Phatty is not a phase or transient sync, it's an oscillator reset sync, which creates psuedo-FM modulation when the frequencies are set correctly. Oscillator sync controls on Dave Smith Instruments synths behave like the Moog control as well. Hardware analog synths are less likely to use extra voices for an effect called "Chorus" because analog oscillators are more expensive than BBDs.


How is this question too broad?

Question: The question How can I highlight matches using GNU grep? got closed for being too broad. I would like to know why this question is considered as too broad? Was it because of the first edit today? Or for different reasons? Answer can hopefully improve my close-voting behavior.
Comment: I'm thankful it's no longer titled "Pimp my...". Sexual slavery and human trade are pressing yet unrelated issues.
Answer: I started the close process (though originally as "primarily opinion based", not "too broad") on that question because it popped up on the front page because someone posted a new answer.
The version of the question as of then had a title of "Pimp my GNU grep", and a body containing "How do you configure GNU grep best" which is very subjective. Most of the answers were also supporting this as they had basically become everyone's favorite way of using grep.
So the close was because it was a subjective question, and to get people to stop posting answers to it.
Additionally, closing sends a message that such questions are not a good fit for the site, while still keeping it around as it has value. Otherwise people see the question, and think they can ask ones similar to it.
Comment: That your name gets attached to a reason you did not pick when close-voting also bothers me a bit.

How is this question too broad?


Opening plastic soda bottles on Yom Tov

Question: In regards to opening plastic soda bottles on Shabbos I'm sure everyone knows there is a maklokes in this. Is the same maklokes applicable on Yom Tov, or is Yom Tov different so that according to everyone it is muter to open the bottles? (My sofek (doubt) is based on there being a heter to do some malachos on Yom Tov l'tzrich ochel nefesh (for the purpose of food for humans).)
Comment: Wouldn't it depend what the reasons of those who prohibit are? If so, why aren't you including those details in your question when they seem extremely relevant?
Comment: @Ariel In his defense, that isn't his link. See the revision history. To the best of my knowledge he is right about there being a machloket on the matter.
Comment: What maklokes? I quote from your link: "It is permissible to unscrew a plastic cap, even if it separates and leaves a ring around the bottle neck." The only bottle cap with a question is the metal one that has tabs that break on the bottom when you unscrew it.
Comment: Certainly it would depend on the reasons for those that say it's ossur. Sorry for not listing those I simply pointed out that there is a maklokes in this. Those who prohibit it are for a few reasons. Either m'chatek or making a cli, etc. In regards to Yom Tov we permit the malachos "m'lisha v'eliech" in the seder of the malachos. My question is do these chashashes in regards to Shabbos fall into the category of malachos that are permitted on Shabbos or are ossur. Perhaps there are other points to take into account that someone could point out to me.
Comment: I dont do it cause its tearing.
But we deduced that biased off of the plain meaning of the prohibition and didnt factor in later heters by non authoritative rabbi's. But i do have to admit that im from a school of thought that goes with the stringent approach in most cases if there is a doubt.
Comment: In Eretz Yisrael the maklokes is quoted that R' Shlomo Zalman Aurbach was matir and R' Eliyashuv held that it's ossur (to open the plastic caps on Shabbos.)
Answer: Some poskim have indeed raised concerns when opening a bottle cap on Shabbat or Yom Tov, e.g., turning the cap into a receptacle (kli), completing the formation of a utensil (make bepatish), tearing (korea) and more (see e.g., here).
Shemirat Shabbat Kehilchata (9:22), after explaining one cannot remove the bottle cap of a bottle if that act converts it into a usable top which can be replaced and removed at will, writes

The various rules set out above are equally applicable on both Shabbat
  and Yom Tov.

And indeed the melachot possibly relevant to opening a soda bottle cap are not part of those permitted on Yom Tov for the sake of ochel nefesh (see here for the list).
R Doniel Neustadt (here) also doesn't note a difference, nor does dinonline.
For the avoidance of doubt, and as noted by Chacham Nisan in comments, there are many poskim who are lenient regarding soda bottles on both Shabbat and Yom Tov.

Opening plastic soda bottles on Yom Tov


How do I get past the turrets at the beginning of test chamber 15, chapter 3

Question: The turrets whose sight you can block with the light bridge at the beginning, how do I get past them?
Pic:

Thanks!
Answer: I actually came up with a different solution myself.  I stood by the portal and noticed that despite looking like the bridge is keeping you from using it, you still have half a usable portal.  So I walked through and picked up the turret and tossed it back through the portal.
Comment: Added a picture that I think describes what you're talking about
Answer: Simply ignore the four turrets to the right; the bridge is in front of them so they're harmless.
As for the other one: with a portal, shoot a heavy light bridge in front of the single turret (like in the screenshot). Walk to the just-shooted bridge, and re-shoot the portal so the bridge disappears. If you're standing to the left or right of the turret, you can simply pick it up without it noticing you.
Answer: I used a very low tech solution. First, I crouched down by the turrets on the right and grabbed one of the fallen ones. Using that, I knocked over the two that were still standing. I then walked over to the turret on the left and did the same thing. I've no idea if that was the intention, but it worked for me. :)
Answer: If you want a fool-proof method, just grab the turret's leg below the light wall and toss it.  You might need to move the portal up a tiny bit so it's not hard on the floor, but it's impossible to get shot this way.

Move up to the wall...

and grab it's leg.

I prefer just being quick; shooting the portal that was sourcing the bridge (the blue portal) further on into the room and hustling through.
Answer: Crouch in front of the light bridge.
grab the turret.
Wiggle the left stick or tap the WASD keys (depending on what system your using.)
Stop grabbing it.
Then it should fall over than shut off.
rinse and repeat for all turrets.


What exercises are recommended to build strength for hiking?

Question: I've not had much opportunity to go hiking for any decent distance recently and I feel the next time I do my body will probably complain a lot. However, I've access to a gym with a lot of equipment so what exercises and equipment should I be using regularly to ensure my first hike back is lacking in pain?
Answer: There's no better hiking excercise than hiking :) Seriously, if you can walk to work, with your dog, to the shop, do it. Regularly. If you have some time during the weekend, go out for a few kilometers. Running is also fun, and depending on the weather where you live, you could easily run through the whole year.
Running will build up some strength in your feet and prepare your whole body to take the load, especially the heart and the lungs. Swimming works like that, too. I'd certainly take any "natural" activity rather than stay in the gym (but that's just my opinion, of course).
Comment: I'm not sure I agree that running helps.  I know a lot of people that do both, but most of the people I meet who only run do not have an easy transition to hiking.  I also know several people (including myself) who can hike 15+ miles but can't run very much at all. (+1 all the same because hiking is the best exercise for hiking)
Comment: I'm not saying that good hiker is a good runner, but running will get you into shape, which is why I think it will help to prepare for a hike.
Answer: Train by hiking, start small, do it every week.
After my injury, when I could not hike, I started by hiking less than a mile, but I did it every week.  Even only once a week, this will help.  Pick a trail that's a length just a little hard for you.  This is best if you have a nearby park with lots of interlocking trails.  Interlocking is good because you can mix and match the path to increase distance.
Increase distance before you increase weight.  I would not recommend adding weight until you can hike 5 miles comfortably.
Once you get to 5 miles, start carrying an empty pack.  Next add your layer clothes (maybe it's cool enough for a jacket, but not needed when you warm up)  Next add just a water bladder for drinking.  To the extent that you can, I recommend packing things you will actually hike with.  One, the weight is more representative, and two, the weight is going to be dispersed more realistically for actual hiking.  If you train with other things in your pack just for weight you are more likely to train for a pack that's off balance.
Buy and learn how to use hiking poles.  They really do help, even starting out.
If at all possible, exercise doing something you like, or in a place you like.  If training is just misery you go through to learn to hike, you're less likely to train (and hike).  Pick the day, time, and place that you are least likely to skip every week.  Pick someone to go with you who will encourage you to never miss a hike.
If you seriously overweight, I would suggest first shedding the pounds by taking up swimming.  This will greatly reduce the strain on your knees.
Comment: Great answer. I would only add that to shred the pounds the *best* way is to focus on nutrition, alongside with exercise.
Answer: As others have mentioned, the best exercise you can get is simply hiking. To train for weight, it's recommended to fill the backpack with water or sand that can be thrown out at the top to prevent knee injuries.
If you live in the flatlands like I do, there's not much elevation changes. The closest in the gym is to use an incline treadmill or a stepmill. I've even filled up a bag with weights to use on the stepmill.
As for specific weightlifting exercises, hiking requires a lot of lower body strength and endurance. Various squats and deadlifts can help strengthen your quads, hamstrings, glutes, and back.
General cardio (running, biking, or swimming) is always helpful since it'll build endurance, and if you can shave some pounds off your body, that's less weight you have to carry.
Alpine Ascents has a training program to prepare for Denali, which, while a little bit overboard for hiking, still shares the same concepts.
Body Results also has provides some mountaineering training DVDs which also share similar concepts.
Answer: Like others have said, the best training to hike is hiking.
If you are concerned about being able to climb large vertical distances (mountains?), try climbing stairs.  I don't mean the stair-climber at the gym (although it does help), but put on a pack with weight and find a tall building.  Clear this with any security the building may have (or management/owner), and climb the fire stairs for a half hour.  Once your body starts to acclimate to the challenge, increase the time that you climb the stairs.
Answer: It all depends on how far you want to hike! Its probably good to do stretching before any exercise such as hiking or running! Lunges and squats may also help as well.
Although you may look a bit silly in the gym, you could carry a backpack on a treadmill and use it on an incline to strengthen your legs.
I would also considering doing short burst of jogging as well to get your endurance levels up.


How to migrate customer data from magento 1.9 to 2

Question: How to migrate customer data from magento 1.9 to 2?
Comment: I hope its done and if not then I will post answer.
Answer: Default Magento 2 Migration tool.
Guide Link : http://devdocs.magento.com/guides/v2.0/migration/bk-migration-guide.html
Install tool for a migration :
https://github.com/magento/data-migration-tool/
OR
UberTheme migration tool.
This is easier way to migrate Magento 1.9.X to Magento 2.X.X
Guide Link :
https://www.ubertheme.com/magento-news/magento-2-data-migration-pro-release/
Install tool for a migration :
https://github.com/ubertheme/magento2_data_migration/releases/tag/Version0.1.0
Comment: First of all you have to export magento 1.9.X CSV then download magento 2 demo export CSV. Create format like magento 2 .But this is way is too much time taking and Not easy .Because for attribute and some other filed you have to merge and all that.so batter way it migrate date using tool.
Comment: this tool is the pro version only to migrate customer option..
Comment: Batter way is that, You just migrant all data and then export data of customer, then import into your website .
Comment: with out install tool can not do this one?.. in csv import any possible way ..
Comment: i ask without tool install it not possibility ?.
Comment: ok i try to this tool UberTheme Migration tool.


Are hashes (such as md5) legal in the US

Question: If I were to implement a remote computer control system using amateur radio, would using hashes (such as md5, sha-*, etc...) for authentication be permissible under the United States rules?
Answer: Yes, they are. Generally speaking, authentication is legal, obfuscating is not legal. So you could do a cryptographically signed hash that would be legal in the United States to transmit over Amateur Radio.
It's worth mentioning that there is some debate as to how legal a cryptographically signed hash would be. I believe it would be legal, so long as it was a signature, intended to ensure that the message came from a particular person.
MD5 type hashes are definitely legal, they merely provide a signature of data already sent, and are used to ensure the data that was sent is correct.
Comment: [citation needed]
Comment: I'm sure as an error detection mechanism is legal. It's basically a fancy checksum.  A more interesting question is the use of a cryptographic signature. This usually means that the hash is encrypted with the private key of the sender. The receiver, if he has the sender's public key, can verify who really sent it and conversely, the sender cannot deny that he sent it. Is that legal? Maybe it's a gray area but I think probably yes provided that the message content is not encrypted.
Comment: The word Encryption doesn't actually appear in Part 97, only the word Obscure. I don't believe this obscures the meaning to have a crypto signature, but I'm not an expert in the law, so...
Comment: CRC checksums in APRS packets are also allowed. This would set the precedent for hashes like MD5 and friends as well.
Answer: Please see:
§97.309   RTTY and data emission codes.
(a) Where authorized by §§97.305(c) and 97.307(f) of the part, an amateur station may transmit a RTTY or data emission using the following specified digital codes:
(1) The 5-unit, start-stop, International Telegraph Alphabet No. 2, code defined in ITU-T Recommendation F.1, Division C (commonly known as "Baudot").
(2) The 7-unit code specified in ITU-R Recommendations M.476-5 and M.625-3 (commonly known as "AMTOR").
(3) The 7-unit, International Alphabet No. 5, code defined in IT--T Recommendation T.50 (commonly known as "ASCII").
(4) An amateur station transmitting a RTTY or data emission using a digital code specified in this paragraph may use any technique whose technical characteristics have been documented publicly, such as CLOVER, G-TOR, or PacTOR, for the purpose of facilitating communications.
(b) Where authorized by §§97.305(c) and 97.307(f), a station may transmit a RTTY or data emission using an unspecified digital code, except to a station in a country with which the United States does not have an agreement permitting the code to be used. RTTY and data emissions using unspecified digital codes must not be transmitted for the purpose of obscuring the meaning of any communication. When deemed necessary by a Regional Director to assure compliance with the FCC Rules, a station must:
(1) Cease the transmission using the unspecified digital code;
(2) Restrict transmissions of any digital code to the extent instructed;
(3) Maintain a record, convertible to the original information, of all digital communications transmitted.
[54 FR 25857, June 20, 1989, as amended at 54 FR 39537, Sept. 27, 1989; 56 FR 56172, Nov. 1, 1991; 60 FR 55486, Nov. 1, 1995; 71 FR 25982, May 3, 2006; 71 FR 66465, Nov. 15, 2006; 80 FR 53753, Sept. 8, 2015]
Answer: While some of this discussion ventures into cryptography terminology, your understanding of it may not automatically mean that the FCC will see it the same way. A hash is a one-way cryptographic function, and as such, it cannot be "decoded" on the other end with a password (or key). This is clearly not obfuscation.
Now, if this hash is sent out in the open as a "signature", there is no guarantee that someone else cannot intercept it and send it from his or her own station later. One way to prevent that is to have a list of one-time strings shared in advance, out of band (off-air). Once a string is used, it is scratched off by both parties. (You can automate this process with an OTP mobile app based on just one pre-shared string. These strings are strictly used for authentication, and can change every few seconds. Nobody can predict the next one without access to the secret string. They also only take a few digits, so they do not look suspicious as "obfuscation".)
The vague area comes from encrypting a hash with a private key. As the name of the process implies, it is actual encryption, since you use the recepient's public key that derived from his private key, and your private key remains secret. The purpose of Public Key Cryptography is in fact, would satisfy the FCC's definition of obfuscation, because the process hides the meaning of the message from those who intercept the transmission. That would be a clear violation of FCC rules.
In addition, someone intercepting the message would not immediately know that your string is "just a hash signature"; you may be accused of sending an AES-256 encrypted string, which is actually two-way encryption, and as such, "obfuscation".
The rules were most likely not written with all these technicalities in mind, so the best bet is to keep it safe and minimize cyphertext traffic.
Comment: I don't agree with your third paragraph. Firstly, it's technically incorrect. If I sign a message, I hash it and then encrypt the hash with my private key. The recipient uses my public key to decrypt the hash, and then compares it with the hash that he computes. No recipient key is involved. Assuming the message content is sent in clear text, what is being obscured? Anyone can receive the message without my key. They just can't be sure that I sent it. I know it hasn't been ruled on by the FCC so nobody knows the real answer but ... I find it hard to see how this would be against the rules.
Comment: Someone could accuse me of putting encrypted messages into my RST reports, too. So should I avoid those too?
Comment: KT1F, you are correct, I made the assumption in that paragraph that we were talking about using private and public keys to encrypt the message itself. In fact, the subject I should have been discussing was limited to the signature, not the message.


Will a constant remain the same between iOS updates?

Question: There is a constant I'm using from the iOS SDK. I printed out the value of the constant (which were int's) and it was 0. Can I assume that constant will always remain zero between iOS builds? The reason I need to use the actual value and not the constant directly is because I want to keep it in a plist that ships in the main bundle. And since a plist doesn't take a constant variable name, I need to place a constant value in the plist.
Answer: You shouldn't assume an enum won't change its value, just to be safe, even though it probably won't. (They'll almost certainly keep it constant so old apps run correctly on future OS versions.)
Instead, save a string to your plist (say, "standard" under the key "map type"), and then initialize the actual value at runtime with an if statement. This has the added benefit of actually saying what you mean explicitly, which makes it easier to look at your plist (and your code!) and see what it does.
Comment: Yes that's what I'm doing, I was hoping to reduce the if statements, but I guess to make sure the app will remain compatible I should keep them. Thanks.
Answer: It's very likely that it will stay the same for at least the life of your application, if not longer.