HTTPS filtering breaks some apps

Question: I have enabled HTTPS filtering in AdGuard. I installed AdGuard's certificates, and the Magisk module that moves the certificates to the system store. Nevertheless, some apps don't work. Why is this? If the certificate is in the system store how can they tell the difference? Also is there a way to tell which apps actually use HTTPS?
Answer: Most likely this happens because the apps not only perform certificate validation but also certificate pinning.
For certificate validation the validity of the server certificate and the certificates of the certificate chain (this is what you can bypass by installing the custom root CA certificate).
In addition, apps can do certificate pinning: The app includes a check if the used root CA certificate is the expected one. As the companies are buying their server certificate, they exactly know which CA certificate the connection should use. If the app then finds the AdGuard root CA certificate, the connection is rejected. A certificate pinning check cannot be bypassed without modifying the code of the app.
I know that Google (e.g. Play Store) and Facebook (various apps) use this certificate pinning to prevent breaking HTTPS connections.
Bypassing certificate pinning is possible on rooted devices, if the app is not too obfuscated. Those tools are usually based on LSPosed/Xposed or Frida. If AdGuard breaks all HTTPS connections, you could use TrusteMeAlready or JustTrustMe and enable it only for problematic apps (note that those modules not only try to disable pinning but also disable TLS security completely, so it is important that AdGuard intercepts those connections).
For Frida, there are various scripts that can disable pinning in some apps. A nice article about Frida and certificate pinning can be found here: Defeating Android Certificate Pinning with Frida
Comment: +1 i use Adguard too but surprisingly haven't come across any problems with Play Store as your answer indicates. Wonder why? //I added an answer to supplement yours
Answer: I use Adguard but haven't come across any problematic apps. To supplement Robert's answer, Adguard knowledgebase What is HTTPS filtering says

However, HTTPS filtering has its drawbacks. The most important one is that it hides from the browser the actual certificate of the website. Instead, the browser sees the certificate issued by AdGuard.

(Emphasis supplied)
While it talks of web based Adguard, the concept remains the same for Android apps. The only solution I see for such apps is to exclude those apps from Adguard using the app management icon in the center of icons displayed at bottom.
Maybe the latest version of the app (4.3) addresses this issue? Though from the release notes I don't see anything related, except for one specific app, which this release fixed.
You may as well raise the issue of the problematic apps in the Adguard forum for them to address, just as they did for the app linked above.
Comment: I agree, bypassing certain apps and/or domains is a common workaround for dealing with certificate pinning when performing https interception. At least for common apps like Play Store which don't have large ad banners that could be filtered and that are essential for most users.

HTTPS filtering breaks some apps


Definition of pole of a spherical mirror

Question: what can be a suitable definition to a pole of the spherical mirror. It cant be the geometrical center of a spherical mirror as if a mirror is cut then its pole does not change. moreover if a spherical mirror is cut into two parts then it does not have two poles.
Comment: Man, I'm having the same confusion. My physics teacher is not sure of the answer either.
Answer: The point where the principal axis pierces the mirror  is the pole. And this principlal axis can be any normal to the surface. It is what we assume according to our convenience.
Answer: It is twice the focus. Focus is the point where llght rays parrallel to principal axis will converge after getting reflected from the mirror.
Comment: i guess that is the definition of the radius of curvature of a spherical mirror


Clock distribution for low-jitter audio DAC

Question: I am building a 10-channel audio DAC using 10 ES9018 converters and an ultra low phase noise clock (Pulsar) with femtosecond jitter. What would be the best way to distribute the clock's signal to the 10 converters? It is assumed that the clock's board will be mounted directly on the PCB where the 10 converters are soldered. The clock's frequency is 100 MHz.
Comment: The device you listed is an ADC not a DAC.
Comment: and I am not sure what jitter and distribution have in common. I'd say that the distribution would affect skew, not jitter. And without knowing your clock frequency little help can be given.
Comment: My mistake! I'm working on both an ADC and a DAC converter, and I got confused between the two devices. The DAC uses the ES9018. Sorry.
Comment: The clock's frequency is 100 MHz.
Comment: well 100MHz is borderline, just keep the traces short and nice and you'll be good.
Answer: For jitter the big thing you want to avoid is noise coupling into the clock lines.  Your clock device is single-ended, so that's a strike against you, but you can still consider routing it with shielding.  That is, route ground traces next to the clock as much as possible, but avoid vias on the clock line (keeping it all on one layer should be paramount).  For skew (also may be important for you), keep the electrical length of the clock lines equal to each converter.
Also, follow these suggestions closely:  A Short Course in PCB Layout for High-Speed ADCs


what happens if you don't get the chance to say the shahada

Question: so let say you are a good Muslim you prayer 5 times read the Quran and fast, but when its time for you to go.
What will happen if you cant say the shahada like you died to quick or your throats injured?
Comment: Salam and welcome to IslamSE the Q&A site about Islam. To learn more about our site and model consider taking the [tour] and checking our [help]. Could you please explain what you mean by "what happens..." in this context as it is clear that one would die as any other soul would die. Do you mean to ask whether it is something bad to die this way? Or what?
Answer: Reciting the shahada is done either as an act of entering into of Islam or as a dhikr.
Saying the shahada once during life is what makes a person a Muslim. As long as a person accepted Islam once and then died without committing Kufr, they would be treated as a Muslim and they would enter paradise eventually and be saved from an eternity in Hell.
Repeating the shahada as a dhikr at the time of death is a recommended and virtuous act for one who is able (Muslim 917 ,  Abu Dawud 3116), but it does not change the status of a person. And there are several Muslims who die without getting this opportunity, such as those who die in their sleep - and they all still fall under the meaning of the other texts:

وعد الله المؤمنين والمؤمنات جنات تجري من تحتها الأنهار خالدين فيها
Allah has promised the believing men and believing women gardens beneath which rivers flow, wherein they abide eternally
— Quran 9:72

 ما من أحد يشهد أن لا إله إلا الله وأن محمدا رسول الله صدقا من قلبه إلا حرمه الله على النار
There is none who testifies sincerely that none has the right to be worshipped but Allah and Muhammad is his Apostle, except that Allah, will save him from the Hell-fire.
— Bukhari 128
Comment: thansk for clearing taht up i was confused
Answer: Not saying the sahahdah at the moment of death isn't as sign of a bad ending
First of all if the question is whether not being able to perform the shahadah is something bad for the life in the hereafter? Then the answer is no.
A Muslim remains a Muslim as long as he didn't commit shirk or kufr and what at the end of his life counts are his deeds.
Secondly if one is not able to do something Allah the Almighty would know this better than any of His creation and His Mercy and Justness wouldn't allow to count something behind a servants possibilities as bad. Allah says:

Allah does not charge a soul except [with that within] its capacity. ... (2:286)

However in case of a choice there are levels of good and levels of bad deeds. The best is always what our prophet () taught us beyond Allah's orders and the worst is what Allah clearly forbid.
Saying the sahahda at the moment of death is a sign of a good ending
As stated in the hadith which was graded as sahih by some scholars, saying the shahadah at the moment of death is a sign of a good ending:

The Messenger of Allah (ﷺ) as saying: If anyone's last words are "There is no god but Allah" he will enter Paradise. (Sunan abi Dawod)

So this hadith only states one of the signs of a good ending (among many more) and one of the signs of entering Jannah (among many more) so its statement isn't to be understood as exclusive. End even if it was there would be special cases.
At the end whatever will let us enter Jannah is first Allah's endless mercy, secondly our good deeds.
Scholars used to say a good believer lives between two states: hope and fear: The hope of entering Jannah due to Allah's mercy and the fear of Allah's punishment.
Further some scholars regard it as a virtuous to exhort relatives to say the shahadah if one fears their death to be coming soon based on some sahih hadith (see in Sunan abu Dawod, Sunan ibn Majah here, here and here-qulified as da'if-, Sunan an-Nasa-i here and here, Jami' at-Tirmidhi, Sahih Muslim here and here . However there's a difference of opinion on this:
Some scholars say one should remind them, others would say it is one should say it in front of them in order that they repeat it or hear it and this or saying it when they have died instead of them is a strongly disputed topic.
See also islamqa fatwa #114666 (available in Urdu and Arabic).


Why is it proclaimed for astronauts to be "falling"?

Question: My physics teacher explained that the reason why it looks like astronauts are floating is because they are "falling". However, the way I think of it is that the outwards inertial force of the astronaut as he/she orbits the earth is equal to and opposite the force of gravity from the planet. Therefore, the net force is 0. But I don't see how this means the astronaut is "falling".
Comment: The earth is spherical with 6000 km radius. Have an astronaut float 100km from the surface. Make the origin [0,0,0] the center of the earth. Let the astronaut start at position [6100,0,0]. Give this astronaut an initial [0,8,0] km/sec velocity. The earth mass is 6 x 10^24 kg. The astronaut mass is 100 kg. The force exerted on her is F=GMm/r^2. The vector acceleration at this instant is [0, -GM/r^2, 0]. Find the vector position of the astronaut after 1 sec. Calculate the next position and repeat. You will find that she is orbiting the earth, using only this pull! It's a marvel.
Comment: Related: [Why doesn't the Moon fall onto the Earth?](https://physics.stackexchange.com/q/9049/2451)
Answer: We always need to be careful with fictitious forces, of which the centrifugal force is one. In the reference frame of the earth, there is only one force acting on an astronaut in orbit, and that is gravity.
From the earth's frame, the astronaut is falling with some acceleration (g or perhaps a little less than that if they're far away) but they never hit the earth because they're also travelling with a large velocity around the earth. (This is after all what orbiting is).
If we instead look at the forces in the frame of the astronaut we need to be careful, because the astronaut's frame is a non-inertial frame of reference, and so fictitious forces are present. In the astronauts frame there is the force of gravity, and a fictitious centrifugal force that exactly balances it.
At the end of the day whether we really call what is happening "falling" or not doesn't matter very much. Most correctly there is only one force acting on the astronaut, gravity, just like it would be if they were on earth, but the astronaut happens to have a huge horizontal velocity, so when they "fall" towards the earth, they have already moved partway around the earth.
Comment: That is, of course, the approved Newtonian way to look at it. But it's also OK to use centrifugal force: it yields the same answer in problems like this. And in General Relativity, the force of gravity is just as fictitious as centrifugal force.
Answer: Falling can have slightly different experiences/observations. From the pov of a person falling freely inside some capsule/cabin, he won't experience any normal reaction from the walls of the cabin, as the whole system fall with equal acceleration. However, from the POV of the ground observer, he sees the cabin falling toward the ground.
Falling can be defined as moving under the influence of the gravity of the celestial body, whether it be an asteroid having its course changed, or rain falling.
The astronaut is said to be falling around the earth instead of falling towards the earth. This is because of horizontal velocity with respect to the ground of the cabin which keeps it going around in orbit, albeit always under influence of gravity. So the astronaut is falling, but around, not directly downwards. The equation of force can be written as:
$$F_g=F_{centripetal}$$
$$\frac{GmM}{r^2}=\frac{mv^2}{r}$$


Upper bounds on the irrationality measure of the arctan of an algebraic number

Question: Let $x$ be an algebraic number.  Must $\arctan(x)/\pi$ have finite irrationality measure?  Are there any useful upper bounds?
Comment: Yes. The number has finite irrationality measure. A bound is obtained from Baker-Wustholtz theorem, but probably very big. https://en.wikipedia.org/wiki/Baker%27s_theorem
Comment: Yes they are. The bound will depend on the degree of the algebraic number x.
Comment: @SungjinKim: perhaps you can convert your comment into an answer? Could you explain how does it follow from Baker's Theorem?
Comment: What if $x=\sqrt{2}$?
Comment: I don't know.  Is there a reason $\sqrt{2}$ is special here?
Comment: Thanks.  My question though is whether the irrationality measure is finite for all choices of x, with x algebraic.
Answer: Let $\alpha=\frac{1+xi}{\sqrt{1+x^2}}$. There are some cases $(\arctan x) /\pi$ is rational. For example, $x=1, \sqrt3$. In these cases, $(\arctan x)/\pi$ has the irrationality measure $1$. These occur precisely when  $\alpha$ is a root of unity.
Since $x$ is algebraic, so is $\alpha$. Then $\arctan x = \arg \alpha = (\log \alpha)/i$. Using $\log(-1)=i\pi$, we have $(\arctan x)/\pi= (\log \alpha)/\log (-1)$. Here, we need a fixed determination of logarithms of complex numbers.
Suppose that $\alpha$ is not a root of unity. We must have that $(\arctan x)/\pi$ is irrational. That is, there is no nonzero rational solutions to $\beta_1 \log \alpha + \beta_2 \log(-1) = 0$. By Gelfond-Schneider theorem, $(\log \alpha)/\log(-1)$ is transcendental. Thus, the irrationality measure of $(\arctan x)/\pi$ is at least $2$. Note that the transcendence of $(\arctan x)/\pi$ also follows from the argument below.
For the upper bound of the irrationality measure, we apply Baker-Wustholz theorem. The logarithmic form $$L=\beta_1 \log\alpha + \beta_2 \log (-1)$$ is nonvanishing for any pair of integers $(\beta_1,\beta_2)\neq (0,0)$. Let  $n=2$ and let $d$ be the degree of $\alpha$ over $\mathbb{Q}$. Then the theorem yields
$$
\log |L| > -C(2,d)h'(\alpha)h'(-1)h'(L)
$$
where
$C(2,d)= 905969664 \ d^4\log(4d)$, $h'(-1)=1$, $h'(\alpha)$ is a modified height of $\alpha$ defined by
$$
h'(\alpha)=\frac1d \max(h(\alpha), |\log \alpha|, 1)
$$
and $h(\alpha)$ is the logarithmic Weil height of $\alpha$. We may use $h'(L)=\log (\max(|\beta_1|/b, |\beta_2|/b))+1$ although the definition is slightly different in the note. Also, $b=\gcd (\beta_1,\beta_2)$.
Hence, there are positive numbers $A(d,\alpha)$, $B(d,\alpha)$ such that for any integer $p$ and any positive integer $q$,
$$
\left|\frac{\log \alpha}{\log(-1)}- \frac pq \right|> \frac{A(d,\alpha)}{q^{B(d,\alpha)}}.
$$
As we see above, the number $B(d,\alpha)$ is quite huge, but it gives an upper bound of the irrationality measure of $(\arctan x)/\pi$.


What does it mean for someone to "join narratives to explain their experiences"?

Question: Describing the Blue Whale Challenge, an online phenomenon where participants perform tasks with the final task being suicide, we have the following:

Dr Achal Bhagat, a psychiatrist in Delhi, told the BBC he had not encountered a single Blue Whale case, although he speaks to young people every day.
"People join narratives to explain their experiences," said Dr Bhagat, adding that is possibly why some children have said they participated in the rumoured challenge despite there being no proof of its existence.
Aparna Alluri, Why is 'Blue Whale' hysteria gripping India?, BBC News, Delhi, 2017

I don't understand what "people join narratives to explain their experiences" means, and how its relevant to the context.  It seems to imply that people are making up they've participated in a Blue Whale Challenge (i.e., they join the narrative) because of some (unstated) events in their lives.  The quote also indicates it holds more generally, i.e., it's not only true for the Blue Whale Challenge.
Question: What does it mean for someone to "join narratives to explain their experiences"?
Comment: I know what the sentence means in the English-language sense, but what does it mean in a psychological sense?  The psychiatrist is alluding to some underlying psychological phenomenon, but the quote is too succinct to give a clear indication of what it is.
Comment: Although this is loosely related to Psychology, the question is more about English Language Usage. This belongs on https://english.stackexchange.com
Comment: I don't think this has any psychological basis.  He is just making a statement to try and back an opinion he has on the possible existence of the Blue Whale Challenge
Answer: I think there is nothing formal psychiatry or psychology related about the psychiatrist's use of language when saying 'people join narratives to explain their experiences'. What he is saying is that people tend to link causally various narratives/stories they have heard of to generate an explanation without much evidence of there being an actual causal link. The joined up narratives then make an appealing sense of things having been explained.
The reason why explanations are appealing is clear upon reading https://en.wikipedia.org/wiki/Blue_Whale_(game) - there is a very disturbing event - suicide by young people, then there is something of an explanation which seems to make some sense.
See also:
Causal relatedness and importance of story events; Tom Trabasso, Linda L Sperry
Journal of Memory and Language: Volume 24, Issue 5, October 1985, Pages 595-611
https://doi.org/10.1016/0749-596X(85)90048-8
Answer: I think it sits somewhere in between scapegoating (assigning the blame to another person or less often some other force) and "everything happens for a reason". It's a basic psychological need to find causality, especially for upsetting things in life. There is in fact no shortage of attribution theories in psychology, and covariation (same causes leading to same effects) sits fairly highly among them. So if one heard that X commited suicide because of the Blue Whale, and then Y commits suicide and someone else mentions Blue Whale... However, in this case it's probably more appropriate to quote another media article on the Blue Whale moral panic:

French anthropologist René Girard famously studied how moral panics ultimately derive in scapegoating. Whenever a society goes through difficult times, there is the tendency to unfairly blame an individual or a particular group for all the troubles. The collective animosity builds against these scapegoats, and very frequently, they are either killed or exiled, as an attempt to put an end to the crisis. This is the psychological mechanism at work in lynchings and purges.
[...] The Blue Whale designers, whoever they may be, are scapegoats.
The Blue Whale moral panic is far from being the first in its kind. The idea that some media product (a song, a movie or a videogame) has the power to drive mindless kids to kill themselves is quite ancient. The first version of this cultural trope goes back all the way to the 14th Century, with the famous Piper of Hamelin story. According to this legend, a piper was hired to rid a town of its rats; the piper played a melody that drove the rats away; the townspeople refused to pay, and as revenge, the piper played a melody that made the kids mindlessly walk into a river, thus being drowned. The Piper of Hamelin story is clearly fantasy, well suited for the credulous medieval mentality. The Blue Whale story seems to be along the same lines, and unfortunately, the same credulous and paranoid mentality is at work.
[...]
Listening to a song or playing an internet game will not make anybody commit suicide, unless that person already had previously strong suicidal ideation. In that case, alleged instigators such as Blue Whale or Judas Priest would be scapegoats.


C++ template that calls function with vector of arguments

Question: I'm currently working on making a benchmark test harness for functions that will let me compare average run times for multiple functions with the same prototype. This is mostly just an academic exercise to learn more about template meta programming.
So here is the problem. I'm trying to create a template function that will let me call another function that is passed in as an argument using the values cast to their appropriate type from a vector that is also passed in.
I know that the run function will need specialization for position = 0 so that the recursion will stop and the function will be called. however currently I get a compile error when I try to extract the argument type telling me

error: non-template 'arg' used as template

However it is clearly defined as being a template.
Also I'm using code from here for the function traits.
template<typename Args>
struct function_traits;

template<typename R, typename ...Args>
struct function_traits< R(*)(Args... ) >
{
    static const size_t nargs = sizeof...(Args);
    typedef R result_type;
    template <size_t i>
    class arg
    {
        typedef typename std::tuple_element<i, std::tuple<Args...>>::type type;
    };
};

struct Argument
{
    char * data;
    int size;
};

template<size_t position,typename Func,typename... arguments>
function_traits<Func>::result_type run(vector<Argument> arglist,
                                       Func f,
                                       arguments... args)
{
    //compile error on this statement.
    typedef typename function_traits<Func>::arg<position>::type argtype;

    return process<position-1>(arglist,f,(argtype)(*arglist[position].data) ,args...);
}

Answer: Adding the template keyword seems to work for me.
typedef typename function_traits<Func>::template arg<position>::type argtype;

See this question for more details.


Joomla router file with fragment(# parameter in URL) in a custom component

Question: How can I get & set the fragment(# parameter in URL) in the URL with the Joomla's existing build & parse method in the router file of the custom component?
Comment: You have a [joomla.se] Stack Exchange account; would you like Stack Overflow moderators to migrate this question to the purpose-built community?
Comment: Yes, please. I need the solution/suggestion ASAP
Comment: Can you please edit your question to include what you have tried so far and any relevant links that you found while researching? Please read [ask] and take our [tour].
Answer: Your question is not fully clear about using Fragments in Joomla Routers and it is because I do not really see  what you really want to do with the fragments in your component's router. Few things I'd like to clear about that though.
#Fragments are not handled by the Joomla Router class basically since #fragments do not require routing. It is handled by the Joomla Uri class however as a URI component (out of other defined uri components). But since uri #fragments - otherwise pointers to "html anchors" - show direction to an HTML element and the browser will scroll that element into view, thus you do not have to write a separate router for them in your Joomla component. It is processed without any router work on the page where your router sent you.

The fragment identifier functions differently to the rest of the URI: its processing is exclusively client-sided with no participation from the web server,...(from wikipedia)

In Joomla however you can set and get and "manipulate" the fragment part of the URL by the Joomla Uri class. This is the class you can build, parse or manipulate URLs with in Joomla.
So if you create an Html anchor element on any page in Joomla:
#This is my Fragment here

Then you can point to that HTML anchor by adding that anchor name (or id) as the fragment to the end of the URL of the page where that anchor is and you can of course use the Joomla Uri class for doing that. Thus in your PHP code where you handle URLs (and/or routing maybe) you can get and set and might "manipulate" that URL part. As an example, on the top of your PHP file include Joomla Uri class (you can try this code in any layout file):
<?php

use \Joomla\CMS\Uri\Uri;

// Returns the global JUri object, only creating it if it doesn't already exist.
$uriInst = Uri::getInstance();

// adding a fragment to the url object you got
$uriInst->setFragment('my_anchor');

echo "
this is the Uri instance's string url with the added fragment: " . $uriInst; // or
echo "
Uri instance plus fragment to string:" . $uriInst->toString() . "
";

// to get the fragment part from the Uri object
$myFragm = $uriInst->getFragment();

echo "
" . $myFragm;

?>

Now, if you dump the Uri object at this point: var_dump($uriInst);, then you will see something like this:
object(Joomla\CMS\Uri\Uri)[345]
  protected 'uri' => string 'http://mysite/index.php?option=com_mycomponent&layout=default_page_html' (length=76)
  protected 'scheme' => string 'http' (length=4)
  protected 'host' => string 'mysite' (length=7)
  protected 'port' => null
  protected 'user' => null
  protected 'pass' => null
  protected 'path' => string '/index.php' (length=10)
  protected 'query' => string 'option=com_mycomponent&layout=default_page_html' (length=51)
  protected 'fragment' => string 'my_anchor' (length=10)
  protected 'vars' =>
    array (size=2)
      'option' => string 'com_component' (length=19)
      'layout' => string 'default_page_html' (length=17)

You see, a perfect URI object with all of the uri components needed for the Router builder if you would like to use that there too. But it is important to note that the router builder/parser is expected to work with the 'query' part of the URI/URL. I hope that the above helps a bit to clear the subject more for you and you will be able to use it.
references: URI Fragments , URLs in Joomla , Joomla Uri class


Engineered hardwood repair help needed

Question: I have a piece of engineered hardwood that I am using to replace a damaged board.   The replacement piece has a slight bow in it.   Can I do a light cut on the back to reduce some of the bow pressure?
Comment: that would not do it, a steam roller will
Answer: If the tongue/groove are there and intact, the force of the neighbors might hold the bow down.
Otherwise, cutting kerfs in the underside, perpendicular to the bow, can help. Go shallow and numerous, rather than a small number of deep cuts.

Engineered hardwood repair help needed


Is it safe to store SSN's in Azure Cloud?

Question: I'm doing due diligence on a company. They are entirely cloud based and need to collect lots of personal information from users (including SSN). Is this something I should be majorly concerned with? They say they are using encryption, and Azure is a secure platform. I'm unfamiliar with how securely reliable cloud storage is currently, and how complex it is to setup and maintain. If cloud storage is OK for this data with proper precautions, are there any questions I need to ask on this topic?
Comment: Before you can conclusively say that a cloud provider complies with the technical standards of "safe", you need to be aware what industry regulations and governmental regulations apply to your specific use case. For example, if you handle credit card numbers, then PCI-DSS may apply to you and you need to base your audit on those regulatory frameworks.
Comment: Unless the key is also uploaded to Azure, I don't see, a huge concern of its encrypted the correct way. what does the regulations for this company with regards to this type of information?
Answer: Given the current state of public cloud, I would argue that in many cases it is in fact more secure than on-premise storage.  Granted I work for Microsoft, but my opinion both pre-dates my employment, and extends to competitors like Amazon and Google as well.  Companies whose business models are built on data center operational expertise and excellence, are simply always going to be better and running and protecting their assets than companies who view IT and data as simply a cost to be tightly controlled.
That said, there are definitely a couple of things that I would take a careful look at.

How are they encrypting the data?  Encryption is easy to get wrong, and with data as structured as SSNs, and with such a small domain, getting it wrong could result in a significant breach of confidentiality.
How are they managing access?  For this you need to look not only at who has access via the application and to the machines, but from an Azure-specific perspective, who has access to the resource groups and the subscription?
Key management.  Azure offers HSM-based key-storage.  For significantly sensitive data, you should ensure they're using an HSM-protected Key Vault.
Comment: As a PaaS/SaaS geek I endorse @Xander's statements.  In fairness to your customers, also cross reference the Governmental Disclosure list for thier requests for private information.  It is part of Google's transparency project, and MSFT has a similar initiative. I don't know if Amazon, Rackspace, Telerik Cloud, Salesforce or the many other less known players have the same transparency.  (Dropbox, Box.com,O365, Intermedia, Proofpoint... not to omit any player, but "cloud" is so broad these days)
Comment: I would say this sweeping statement is true only for major cloud providers. There are more unknowns with smaller providers, which may not be under as much scrutiny.
Comment: One of the many things I would do when performing an architecture review of IaaS, PaaS, and SaaS providers is ask about multi-tenancy and shared environments. It also depends on company policy. A former employer went to the extreme (and, IMO, the right thing to do) of not allowing off-prem storage of PII, at least without architecture review and security testing.
Answer: To add to Xander's answer, there are a few things to consider:

Company policy
IaaS, PaaS, and SaaS multi-tenancy
Key management
Current internal security posture

Company policy
Some companies are okay with *aaS, some companies say a certain level of PII is okay to store off-prem without encryption, or require encryption for a certain level, and say above that level, no off-prem storage. If the company does not have those policies, encourage them to get those policies.
Multi-tenancy
Multi-tenancy, or hosting multiple customers in the platform or network space. This makes pivoting and sniffing of traffic easier.
Some providers will give you a dedicated instance if you are willing to pay a little (or a lot) extra.
Key management
As Xander mentioned, some providers (Amazon and Microsoft do this for sure, I don't know about Google, though I'd guess they do) offer an HSM for key management. Is the company trusting of the SEE code in the HSM? Is the company willing to give out the key to encrypting and decrypting identity significant data? Can the company control the SEE code?
Company security posture
Does this company have a mature vendor management process? Incident response process? What happens if one of these providers is breached? Does the company IR team have the ability to work with the provider? Will the provider be held to a contract to notify the company in the event of a detected breach? Will logs be forwarded to a company log monitoring solution? Is that log monitoring solution monitored and maintained? Does the company have a mature security testing and review program?
These are all questions that should be asked and answered beyond "is it safe?" because policies, security posture, and provider environment impact that "is it safe?" a lot.


How can you make it automatically invisible to render if its already invisible in viewport?

Question: The objects i make invisible in viewport i want them to automatically be invisible to render. Is there any cool way to have this option ?
Comment: I  do not know of a cool way, but you can click the camera icon in the outliner.
Comment: `bpy.data.objects["Cube"].hide_render = True`
Comment: Select every visible objects by pressing "A" then hit "W" and select "Restrict Render Unselected"
Comment: That i know, but when you have too many objects, you need to go through all.
Was wondering if there was some option or python script
Comment: @FFeller this doesnt seem to work on blender 2.8, nothing comes up after pressin W
Comment: @rob thats awesome, but only hides the one mesh with the name you put in the brackets... "cube" but not the other ones....
Answer: Handlers
Could set in a handler. bpy.app.handlers.depsgraph_update_[pre or post] are the v2.8x equivalent of scene update in versions prior.
Run this script once. Now every time the depsgraph updates ( a lot ) it will match the hide render attribute to the objects hide status.
import bpy

def hide(scene):
    for o in scene.objects:
        o.hide_render = o.hide_get()

    return None

# uncomment to clear all
#bpy.app.handlers.depsgraph_update_post.clear()
bpy.app.handlers.depsgraph_update_post.append(hide)

Comment: Great!  !!!!!
Answer: This code when run will hide all the selected objects from being rendered
import bpy

selection = bpy.context.selected_objects

for obj in selection:
    bpy.data.objects[obj.name].hide_render = True

It also make sense if you are doing this a lot to change the functionality to toggle.
This version will toggle the render visibility of all the selected objects
import bpy

selection = bpy.context.selected_objects

for obj in selection:
    obj.hide_render = not obj.hide_render

Comment: thanks @batFINGER, updated
Comment: In 2.79 version we could move the selected objects to some other layer and leave that layer hidden. Could it be a similar way to do it in 2.8? Unfortunately, I can't use the 2.8 version yet.


Xen Live Migration with Gluster

Question: Has anyone used or found a HOWTO on how to use Xen with Gluster? I'm working on a testbed of two servers, possibly three, that will be syncing a volume via IP and I'd like to work on finding a way to do live migration of the VM between (among) the servers but I don't see any howtos for setting that up or managing it.
Answer: I know a couple people who run DRDB. What that does is mirror each fs operation. Then move the IPs with heartbeat around and you got migration. Not sure if it's as robust as ESX' hot migration.
Answer: I know your question is now over a year old...
for the record: there is a posting about this on the opensharedroot.org list.
dom0 using shared root on gluster.

Xen Live Migration with Gluster


Why is my transaction dropped?

Question: I am trying to figure out why a user needs to approve a tx multiple times in order for it to finally go through. How could I potentially fix this?
Answer: Below is taken from Based Orion: https://twitter.com/BasedOrion_:
There's multiple sections of the lifetime of a tx where it can potentially get dropped:

At the scheduler: tx compute doesn't fit into block anymore; other txns have more prio fees; account is write locked too many times

At the validator network pipeline: too many txns coming thru, validator only accepts certain amount

Rpc: rpc too slow, doesn't forward fast enough or to the right leader etc

Priority fees help with 1. since it helps prioritize your tx once it actually reaches the runtime scheduler.
Spam-approving helps with 2. Since the more you spam, the likelier it is to be part of the network bunch that the validator accepts.
Having a fast, dedicated rpc helps with 3. since it's only under load from your requests and not a bajillion others.
Answer: If your txes do not get confirmed, and you are sending with skipPreflight: true, try disabling it.
Some frens and I have had some success with it:)

Why is my transaction dropped?


If the gaseous molecules didn't have any kinetic energy would the surface of a filled balloon still be firm?

Question: The most of the ideal gas law equation is based on the fact that the gaseous molecules are moving around and cause collisions and thus have some pressure. If these molecules were to not have any kinetic energy, and thus consequently would not suffer any collisions would the surface of let's say a balloon, a filled balloon, which is firm only due to the pressure offered by the gas inside, still be firm? would the volume of the gad contribute to its firmness and give it shape? won't the volume be affected too
Comment: What about the gas around the balloon? What do you think it does?
Answer: If ideal gas molecules had had no kinetic energy, there would have been no gas pressure. Inside nor outside the balloon. The outer gas would have been laying on the ground, the inner gas on the bottom of the balloon.
In such a case, the only remaining force, aside of gravity, would have been the elastic forces of the balloon, pulling the balloon rubber together to its original shape and volume.
For real gases compressed to volume about equal to tight arrangement of molecules, a sudden repulsive force and therefore pressure would have progressively appeared, due repulsion of electrons.
Comment: Thanks a lot for answering! I still had a question though, given that the gas molecules aren't showing any kinetic energy, they'd probably have a fixed position over time, giving them a fixed shape, and as you said they'd be lying at the bottom. So what would cause to bring about an elastic force in the rubber balloon? Just this matter at the bottom?
Comment: Elastic rubber force is gas independent. If you stretch a piece of rubber then after  stretching is released, it contracts black again, regardless of if there is a gas around, or not.
Comment: You would not be able to blow up the balloon in the first place, at least now in the way how you are used to. You would be able to fill it by a densely packed gas, but the balloon would be heavy and hard.
Comment: That's right. So, the balloon obviously wouldn't hold structure as it would before when filled with a gas, and would instead behave like a deflated rubber balloon filled with a less fluid substance, almost like a solid in its physical properties due to the negligible kinetic energy of the gas molecules
Comment: Yes, like solid. And everything around such a gas would freeze solid as well. Rubber would break when you would touch it. Note that even at absolute zero 0 K, matter does have residual kinetic energy, related to zero point oscillations.


Does surface tension increase for a flowing fluid?

Question: When a fluid is moving with velocity V, what becomes of its surface tension, does it increase or decrease in value
Answer: Surface tension does not change with fluid velocity. Typically surface tension is only affected by solutes, surfactants, or temperature gradients. The subsequent effect of gradients in surface tension are referred to as Marangoni effects.
Answer: Surface tension is not influenced by velocity, but it may become negligible compared to inertial forces which arise due to velocity.
Inertial forces scale as $\rho V^2L^2$ and surface tension forces scale as $\sigma L$. The ratio of these is the Weber number $We$:
$$ We = \frac{\rho V^2 L}{\sigma}$$
When $We >> 1$, or when the velocity $V$ or length scale $L$ are very large, surface tension becomes less important compared to inertia; you will not see the effects of surface tension for high $We$ but they still exist. The velocity by itself, however, does not affect surface tension.


Can you derive new theories in physics by only looking at the math?

Question: Can you develop new theories in physics by only looking at the maths from past physics concepts? Or does observation of physical reality or converging of physical concepts ALWAYS come first before the math, and that the math's just there to further explain the theory?
Comment: I think there is no well-defined answer to such a question. Math is the language to express physics. The question is if there exists all vocabular and grammar before we develop a new theory or if we need new "words" or "grammar". In some cases in history of physics we needed a new kind of math in some the math existed allready.
Comment: I think [De Broglie's hypothesis](https://en.wikipedia.org/wiki/De_Broglie_hypothesis) on wave-matter duality did just that.
Comment: Related: http://physics.stackexchange.com/q/4849/2451 and links therein.
Answer: This is about theoretical physics and experimental physics working together.
The purpose of physics is to create a set of laws that allow us to predict the behavior of physical systems.

New, untested theories (i.e. maths) are hypothesized based on previous experiments.
These theories are used to predict behaviors in untested regimes (e.g. higher energies, larger velocities, smaller distances).
Experiments validate or invalidate those theories.
New theories are hypothesized from these new observations.
Rinse, repeat

A great example of the necessity of experiments is the Michelson-Morley experiment which disproved the existence of an aether and eventually led to Einstein's theory of special relativity. Before that experiment, no one knew that light traveled at the same speed in all frames.
A great example of the necessity of theory is the Dirac equation which predicted the existence of antimatter from a simple equation. Before this, antimatter was never considered, but it was later experimentally confirmed.
Comment: I agree, however, concerning  Michelson-Morley experiment, Einstein did not mention that experiment in his famous 1905 paper on SR. Apparently he did not know that crucial experimental result. He only based his construction  on the theoretical hypothesis that Maxwell's equations have the same form in every inertial reference frame, i.e., the inclusion of electromagnetism into the relativity principle.
Comment: @Valter I did not know that Einstein was not aware in 1905 of the Michelson-Morley experiment from 1887. Do you have a reference on that?
Comment: According to the GR book by Hobson et al it's unknown whether Einstein was aware of/motivated by the results of Michelson-Morley. But it's true that he didn't cite it in his 1905 paper, and so it's suspected that his motivation was to take Maxwell's equations at their word (they give a frame-invariant light speed).
Comment: @lemon  Thanks for that clarification. As an engineer who works with mostly classical EM, I might have overextended myself a bit in my knowledge of the history of physics. Nevertheless, it was a cool experiment and result :)
Comment: You might read Einstein's Mistakes (Ohanian), which is a nice review of his work, and what he was aware off , or not, during his working career. It's a real encouragement (for me at least)  to read about the many revisions of GR  and Einstein's various interpretations of what his own work actually physically represented.
Comment: @led23head: Even if Einstein was unaware of the experiment, I think it's safe to say that the experiment helped other physicists be more open to accepting Einstein's work.
Comment: [Einstein claims he didn't know](http://physics.stackexchange.com/a/89379/127229)
Comment: Also on the subject on the influence of the Michelson and Morley experiment is: https://arxiv.org/abs/0908.1545
Answer: It depends on what you mean by a new theory. If you mean a complete, self-contained and logical set of axioms/postulates and their theorems/predictions, then it is not possible. To build a physical theory one has to start with a set of laws. How would you enunciate physical laws without physical intuition? That is impossible.
If you mean a further knowledge and explanation of some phenomena based in a pre existent or larger theory, then it is possible that the math plays a sole role.
I recall three examples now:

The Dirac's antiparticles prediction based on mathematical rigour.
The Pontecorvo's neutrino oscillation which grew up as a didactic exercise on linear algebra and quantum mechanics and provided an answer to a problem that did not exist at that time, the missing neutrinos problem.
The General Relativity's idea that the gravitational interaction comes from a curvature of spacetime.

Note however that it is not true that the General Relativity Theory is a completely mathematically based theory. It is indeed based on principles of symmetry however those principles come from physical observation or intuitions which are then postulated to be valid (such as space homogeneity, isotropy, equivalence principle and so on).
Answer: You can. The Laser is a prime example. Short cersion: The effect was predicted 1917. Then 1951 the Maser was predicted from theory and the  theoretical work from 1917. Then experimentalist tried to build such a device and succeded in 1954.
Another example would be Maxwell completing the Maxwell equation from purely theoretical grounds. It took Hertz a few decades to show this to be true.


Lambda function with itertools count() and groupby()

Question: Can someone please explain the groupby operation and the lambda function being used on this SO post?
key=lambda k, line=count(): next(line) // chunk
import tempfile
from itertools import groupby, count

temp_dir = tempfile.mkdtemp()

def tempfile_split(filename, temp_dir, chunk=4000000):
    with open(filename, 'r') as datafile:

    # The itertools.groupby() function takes a sequence and a key function,
    # and returns an iterator that generates pairs.

    # Each pair contains the result of key_function(each item) and
    # another iterator containing all the items that shared that key result.

        groups = groupby(datafile, key=lambda k, line=count(): next(line) // chunk)
        for k, group in groups:

            print(key, list(group))

            output_name = os.path.normpath(os.path.join(temp_dir + os.sep, "tempfile_%s.tmp" % k))
            for line in group:
                with open(output_name, 'a') as outfile:
                    outfile.write(line)

Edit: It took me a while to wrap my head around the lambda function used with groupby. I don't think I understood either of them very well.
Martijn explained it really well, however I have a follow up question. Why is line=count() passed as an argument to the lambda function every time? I tried assigning the variable line to count() just once, outside the function.
    line = count()
    groups = groupby(datafile, key=lambda k, line: next(line) // chunk)

and it resulted in TypeError: <lambda>() missing 1 required positional argument: 'line'
Also, calling next on count() directly within the lambda expression, resulted in all the lines in the input file getting bunched together i.e a single key was generated by the groupby function.
groups = groupby(datafile, key=lambda k: next(count()) // chunk)

I'm learning Python on my own, so any help or pointers to reference materials /PyCon talks are much appreciated. Anything really!
Answer: itertools.count() is an infinite iterator of increasing integer numbers.
The lambda stores an instance as a keyword argument, so every time the lambda is called the local variable line references that object. next() advances an iterator, retrieving the next value:
>>> from itertools import count
>>> line = count()
>>> next(line)
0
>>> next(line)
1
>>> next(line)
2
>>> next(line)
3

So next(line) retrieves the next count in the sequence, and divides that value by chunk (taking only the integer portion of the division). The k argument is ignored.
Because integer division is used, the result of the lambda is going to be chunk repeats of an increasing integer; if chunk is 3, then you get 0 three times, then 1 three times, then 2 three times, etc:
>>> chunk = 3
>>> l = lambda k, line=count(): next(line) // chunk
>>> [l('ignored') for _ in range(10)]
[0, 0, 0, 1, 1, 1, 2, 2, 2, 3]
>>> chunk = 4
>>> l = lambda k, line=count(): next(line) // chunk
>>> [l('ignored') for _ in range(10)]
[0, 0, 0, 0, 1, 1, 1, 1, 2, 2]

It is this resulting value that groupby() groups the datafile iterable by, producing groups of chunk lines.
When looping over the groupby() results with for k, group in groups:, k is the number that the lambda produced and the results are grouped by; the for loop in the code ignores this. group is an iterable of lines from datafile, and will always contain chunk lines.
Comment: Thank You. Appreciate your help!
Answer: In response to the updated OP...
The itertools.groupby iterator offers ways to group items together, giving more control when a key function is defined.  See more on how itertools.groupby() works.
The lambda function, is a functional, shorthand way of writing a regular function.  For example:
>>> keyfunc = lambda k, line=count(): next(line)

Is equivalent to this regular function:
>>> def keyfunc(k, line=count()):
...     return next(line) // chunk

Keywords: iterator, functional programming, anonymous functions

Details

Why is line=count() passed as an argument to the lambda function every time?

The reason is the same for normal functions.  The line parameter by itself is a positional argument.  When a value is assigned, it becomes a default keyword argument.  See more on positional vs. keyword arguments.
You can still define line=count() outside the function by assigning the result to a keyword argument:
>>> chunk = 3
>>> line=count()
>>> keyfunc = lambda k, line=line: next(line) // chunk       # make `line` a keyword arg
>>> [keyfunc("") for _ in range(10)]
[0, 0, 0, 1, 1, 1, 2, 2, 2, 3]
>>> [keyfunc("") for _ in range(10)]
[3, 3, 4, 4, 4, 5, 5, 5, 6, 6]                               # note `count()` continues

... calling next on count() directly within the lambda expression, resulted in all the lines in the input file getting bunched together i.e a single key was generated by the groupby function ...

Try the following experiment with count():
>>> numbers = count()
>>> next(numbers)
0
>>> next(numbers)
1
>>> next(numbers)
2

As expected, you will notice next() is yielding the next item from the count() iterator.  (A similar function is called iterating an iterator with a for loop).  What is unique here is that generators do not reset - next() simply gives the next item in the line (as seen in the former example).
@Martijn Pieters pointed out next(line) // chunk computes a floored integer that is used by groupby to identify each line (bunching similar lines with similar ids together), which is also expected.  See the references for more on how groupby works.
References

Docs for itertools.count
Docs for itertools.groupby()
Beazley, D. and Jones, B.  "7.7 Capturing Variables in Anonymous Functions," Python Cookbook, 3rd ed. O'Reilly. 2013.
Comment: Thank you so much for the clarification!


Correspondence of representation theory between $\mathrm{GL}_n(\mathbb C)$ and $\mathrm U_n(\mathbb C)$

Question:
If I know something about the representation theory of the general linear group $\mathrm{GL}_n(\mathbb C)$, what can I say about the representation theory of the unitary group $\mathrm U_n(\mathbb C)$? E.g. branching rules
Similarly for the groups $\mathrm{SO}_n(\mathbb C) \subset \mathrm O_n(\mathbb C)$?
Is module over ${\mathbb C\mathrm{GL}_n(\mathbb C)}$ that is not semi-simple necessarily infinite-dimensional? How does it typically look like? See new Question here
If I have information about the restriction of representations of the general linear group, can I make any statements about the induction (by Frobenius reciprocity)? E.g. I know $$\mathrm{res}^{\mathrm{GL}_n}_{\mathrm{GL}_k\times \mathrm{GL}_{n-k}} V(\lambda)_n \cong \bigoplus_{\alpha, \beta} c_{\alpha, \beta}^\lambda V(\alpha)_k \otimes V(\beta)_{n-k}$$
where $V(\lambda)_n$ is the irreducible polynomial representations corresponding to a partition (or Young diagram) $\lambda$ of $\mathrm{GL}_n(\mathbb C)$ and $c^\lambda_{\alpha,\beta}$ are the Littlewood-Richardson numbers. Is it true that
$$ \mathrm{ind}_{\mathrm{GL}_k\times \mathrm{GL}_{n-k}}^{\mathrm{GL}_n} V(\alpha)_k \otimes V(\beta)_{n-k} \cong \bigoplus_\lambda c_{\alpha,\beta}^\lambda V(\lambda)_n ?$$
(I know it is not but true but it should be true up to being semi-simple.) See new question here
Comment: While these questions are certainly all about representation theory, they really aren't related (except 1 and 2), are they? I think these 3 and 4 should should each get their own question, and a more descriptive title would then be appropriate.
Answer: The "nice" representations of $GL_n(\mathbb{C})$ are equivalent to the "nice" representations of $U_n$; the question is just how you should define nice. Let $\rho: GL_n(\mathbb{C}) \to GL_N(\mathbb{C})$ be a map of groups. Then the following are equivalent:

The entries of the matrix $\rho(g)$ are complex analytic functions of the entries of the matrix $g$.
The entries of the matrix $\rho(g)$ are polynomials in the entries of the matrix $g$ and $\det(g)^{-1}$.

Let $\sigma: U_n \to GL_N(\mathbb{C})$ be a map of groups. The following are equivalent:

The entries of the matrix $\rho(g)$ are continuous functions of the entries of the matrix $g$.
The entries of the matrix $\rho(g)$ are smooth functions of the entries of the matrix $g$.
The entries of the matrix $\rho(g)$ are polynomials in the entries of the matrix $g$ and their complex conjugates.

If we use any of the conditions in these lists to define "nice" representations, the restriction from $GL_n(\mathbb{C})$ to $U_n$ is a functor from nice $GL_N$ representations to nice $U_n$ representations.
Theorem This functor is an equivalence of categories. In particular, every $U_n$ representation lifts to a $GL_N$ representation, $\dim Hom_{GL_N}(V,W) = \dim Hom_{U_n}(V|_{U_n}, W|_{U_n})$ and $V$ is irreducible if and only if $V|_{GL_n}$ is irreducible.
The easy parts of this are that  $\dim Hom_{GL_N}(V,W) = \dim Hom_{U_n}(V|_{U_n}, W|_{U_n})$ and $V$ is irreducible if and only if $V|_{GL_n}$ is irreducible. I don't know an easy way to see that every nice $U_n$ representation extends to a nice $GL_n$ representation. I covered this material on October 10 of my representation theory course. See Chapter 5 of Joel Kamnitzer's lecture notes for a more general discussion.
I don't know of any good results about non-nice representations of $U_n$. Non-nice representations of $GL_n$, however, are interesting for two reasons. First of all, you might want to study $GL_n(\mathbb{C})$ as a topological group, ignoring its complex structure. For example, $SL_2(\mathbb{C})$ is a double cover of $SO(3,1)$. Physicists are very interested in the representation theory of $SO(3,1)$, but they don't particularly care that the representations be analytic.
Second, there are interesting infinite dimensional representations of $GL_n$. In contrast, by the Peter-Weyl theorem, any continuous Hilbert space representation of $U_n$ is a direct sum of finite dimensional representations, so passing to infinite dimensions doesn't make the $U_n$ theory deeper.
Comment: Nice answer, David (+1). Personally, I think the infinite dimensional representations are "nicer". But I admit that it's a matter of taste. As for how to prove that every continuous irreducible $U_n$-rep lifts to $GL_n(\mathbb{C})$, one possible strategy is to observe that they are classified by highest weights and that you actually obtain all possible highest weights by restriction. Then by semisimplicity every continuous rep lifts. In fact, although I have never studied the proof I always imagined this was how it went for arbitrary maximal compacts in reductive groups.
Comment: Thanks. I tend to over use judgmental adjectives. How about this: The fact that infinite dimensional irreps exist at all is fascinating, and the basic theory of their classification is deeper. At the same time, they don't have as many convenient theorems, and as a result people tend to get less far into intricate combinatorial formulas than they do in the finite dimensional case.
Comment: As for proving $K$-reps lift to $G$-reps ($G$ is an affine algebraic group, $K$ is a maximal compact with $\mathfrak{g} =\mathfrak{k} \otimes \mathbb{C}$, I think there are two routes. One way is to do roughly what you suggest with weight theory. If you look at my lecture notes that I linked, you'll see that argument paired down to what I think is the minimum prerequisites.
Comment: The other way is to start with $K$ and define $\mathcal{O}(K)$ to be the set of continuous functions $f: K \to \mathbb{C}$ such that the vector space $\mathrm{span}_{k \in K} (x \mapsto f(kx))$ is finite dimensional. (In terms of the Peter-Weyl decomposition, these are the functions with finitely many Fourier terms.) It isn't too hard to show that $\mathcal{O}(K)$ is a commutative $\mathbb{C}$ algebra. One can define $G$ as $\mathrm{Hom}_{\mathrm{algebra}}(\mathcal{O}(K), \mathbb{C})$ and define the complex structure and group structure on $G$ from that. The troubles are:
Comment: (1) There is an obvious map $K \to G$: Send $k$ to evaluation at $k$. But, to prove that it is injective seems to need something roughly as strong as Peter-Weyl. This isn't a problem for a concrete choice of $K$ like $U_n$, where you can concretely write down lots of elements of $\mathcal{O}(K)$.
Comment: (2) It isn't obvious that the $G$ you get is the same as some concrete $G$ you started with.
Comment: Nice notes! Thanks for pointing them out. Best
Answer: The representations theory of $U_n$ is simpler than that of $GL_n(\mathbb{C})$: every continuous representation of $U_n$ is semisimple, and every continuous irreducible representation is finite dimensional and is the restriction of an irreducible algebraic representation of $GL_n(\mathbb{C})$. In fact, restriction from finite dimensional algebraic representations of $GL_n(\mathbb{C})$ to $U_n$ is a $\mathbb{C}$-linear equivalence of tensor categories. The basic idea of the proof is to observe that $U_n$ is Zariski dense in $GL_n$ and therefore irreducible algebraic representations remain irreducible upon restriction (this sometimes goes by the name Weyl's unitary trick and can be used to prove his eponymous character formula). Of course, the representation theory of the non-compact Lie group $GL_n(\mathbb{C})$ is much more complicated than this!
The relation between $SO_n$ and $O_n$ is even simpler: since every matrix in $O_n$ has determinant $\pm 1$, $SO_n$ is an index $2$ normal subgroup of $O_n$. Clifford theory then completely describes the relationship between their irreducible representations: each irreducible $O_n$-module either remains irreducible or splits into two irreducibles upon restriction, and which of these happens is determined by the behavior of representations upon tensoring with the determinant representation.


PdfLatex and UTF-16LE

Question: Is there an option to process UTF-16LE file directly by pdflatex, without the conversion to UTF-8? And does xelatex have such an option?
Answer: No.  You should convert to UTF-8.  It's the easiest solution by far.
The available input encodings for PDFTeX are documented in the inputenc manual.  You can also use these encodings, through luainputenc, with LuaLaTeX or (despite the name) XeLaTeX.

PdfLatex and UTF-16LE


Using the same mac address on the same network at different times on two devices

Question: If I was to use the same mac address as another device on the same network (wifi), at different times (one after the other). Would the devices for the network experience any problems, glitches or failure, while or after using the same mac address? I would be cloning the mac address from one of the devices.
Comment: The MAC address table on your switches might prove problematic as well, dependent upon whether or not the two devices are connected to the same switch port or to different switch ports.
Comment: ARP caching might be problematic, depending on how long that lasts and how closely the two different hosts reuse the same MAC.
Comment: Entirely depends on the network and how it is configured, especially with regards to security. For instance, if there is any sort of policy based decisions based on the platform (newer BYOD type setup where laptop may be treated one way and your smart phone anohter), this may create all sorts issues and get one or both devices flagged.
Answer: As long as the two devices are not active at the same time, then it won't be a problem. How quickly the network realizes that the MAC address has moved from one device to the other depends on the specific implementation of the switches used in the network as well as on the traffic patterns.
In principle what you describe would look the same to the network as if you unplugged the device from one location in your network and plugged it in another location.
If you are using WiFi you need to be aware that many WiFi drivers don't support changing the MAC address like you describe. Most drivers for wired Ethernet do support it.
After the MAC address was moved from one device to the other, the device which just got the MAC address should send a single broadcast packet to the network in order to ensure that all switches on the network have updated their CAM table.
Neighbor caches on various devices on the network map from IP address to MAC address. This means that all packets to the IP addresses assigned to the network interface where you have been using the MAC address will now be send to the device which took over the MAC address.
You better ensure that the device which took over the MAC address is prepared to handle traffic to all IP addresses which the previous device mapped to the MAC address. If you are implementing a failover solution, then this behavior would be considered a useful feature. If you are not implementing a failover solution, then it is most likely a mistake to use the same MAC address on two devices.


My BCH is marked 'unspendable' in my Blockchain Wallet

Question: My BCH is marked 'unspendable' in my blockchain wallet. I entered my public address instead of my private address by mistake when I exported the BCH from my paperwallet. Is that the problem and how do I correct this?
Answer: Exactly! Just reset your wallet and then import your private key. It'll work like magic.


Что такое десериализация в polymer?

Question: То ли слабый английский, то ли что. Объясните, что такое десереализация?

If a property is configured in the properties object, an attribute on
  the instance matching the property name will be deserialized according
  to the type specified and assigned to a property of the same name on
  the element instance.
If no other properties options are specified for a property, the type
  (specified using the type constructor, e.g. Object, String, etc.) can
  be set directly as the value of the property in the properties object;
  otherwise it should be provided as the value to the type key in the
  properties configuration object.
The type system includes support for Boolean and Number values, Object
  and Array values expressed as JSON, or Date objects expressed as any
  Date-parsable string representation.
Boolean properties are set based on the presence of the attribute: if
  the attribute exists at all, the property is set to true, regardless
  of the attribute value. If the attribute is absent, the property gets
  its default value.
Answer: Сериализация - это когда объект(как программная сущность) переводится в текстовый/бинарный формат, для удобства его хранения (например в БД) и/или передачи (например в виде json по http)
Десериализация - наоборот, восстановление из сериализованной сущности (текста/бинарного формата) исходного объекта.

Что такое десериализация в polymer?


Repeated answer. Should I complain?

Question: My answer got repeated on this question. Almost exactly. Should/can I complain?
Comment: @RomanB. I find it very annoying that you claim I am copying your answer, our answers were only two minutes apart. Initializing an array in C with that syntax isn't anything novel or unique to you, it is perfectly reasonable for two people to reach the same solution, in fact several people in that thread came up with the same solution.
Comment: Note that, if the answers happened within two minutes of each other, it is possible that some cutting and pasting occurred, but it's also possible that Hunter was composing his answer the same time that you were composing yours, and he didn't even see your answer until his was posted.
Comment: That answer is substantially different from yours, and comes to a different conclusion than your answer does.  It uses some of the same code yours does, but that code logically follows from the OP's question and variable names.
Comment: @Michael: It's not even a copy.  Some of the code is similar, but the language is different.  It's an original answer.
Comment: @RobertHarvey Your opinion is very clear; I'm asking what the OP is posting about
Comment: Just to make sure. You are saying that: "However I would initialize the array just as it is created.

float user_queue[24] = {0.0};"

is not equal to "For this you don't even need a loop:

/* Array of 24 users */
float user_queue[24] = { 0.0 };

this will initialize the array to all zeros without the for loop.
"

Am I right?
Comment: Anyway, Mystical beat both of you, with a better answer.  I see what you are saying, but with two upvotes, the community apparently liked the way Hunter phrased his answer better than yours.  It happens.
Comment: @RobertHarvey That's not a point. It has nothing to do with Mystical. Hunter McMillen answered 2 min after me.
Comment: ok. no discussion anymore. thanks.
Comment: It's unclear; are you saying you think somebody copied your answer, or just that they posted the same answer a little after you?
Comment: Related: [Answer stealers](http://meta.stackexchange.com/questions/27724/answer-stealers)
Comment: @MichaelMrozek I do not know what happened at the other side. All I see is the paraphrased part of my answer that came 2 min afterwards. anyway, don't mind.
Comment: @Hunter, I very much agree this was not about copying. That said: there's nothing wrong with deleting one's answer when seeing someone else posted the same just before you did. I'm not saying that should be done in this example; maybe your answer is better. But in general the "two minutes apart" is no reason for me to not delete my duplicates. (And maybe edit some more info into an existing answer.)
Answer: When talking about very basic questions such as this one, it's going to happen quite a bit. There's two very low hanging apples there to pick:

The OP is having off by one and scope / declaration issues
The OP doesn't need a loop in the first place

What happens isn't that people copy your answer, they don't need to copy it on such a basic question. People know the same answer that you did, and naturally they want to post it. They may (or may not) have seen your answer posted prior to adding their own. They may have skipped right from the question to the answer field and started typing away in all of the excitement we used to feel in History class when we actually knew the answer the teacher wanted. Back then, we threw our hand high up in the air and trampled over our fellow class mates, chanting the all familiar war cry ... ooooooh!!! ooooooh!!! PICK MEEEEEE!
One of the biggest reasons why I don't have 3x the rep that I do is because I read the existing answers before adding one. This results, 8/10 times in me not answering a question that I could because someone else did a fine job of answering. However, when working on unlocking reputation based privileges, people don't always show such restraint.
Wherever there's low hanging fruit, there's bound to be a feeding frenzy. This almost always means that several terse and nearly identical answers will compete. If you notice a blatant pattern of a specific user copying other answers nearly byte by byte, that's probably something we'd want to look into. Barring that, it's just part of using the site.
For a final bit of irony, I see @Shog9 has done a fine job of answering this :) But, I worked on my answer too, so I'm posting it anyway.
Comment: You bastard! You copied my answer word for word! And then added insult to injury by *changing all of the words!*
Comment: @Shog9 The best comment ^
Comment: +1 to give you some well-earned Unicorn dollars.
Answer:
Should/can I complain?

You... can... And really, you sorta are...
But should you? Well, what good does it do? If he copied at all, he didn't copy your answer verbatim... so you can't exactly claim plagiarism. Both answers are fairly trivial, so it's hardly surprising if multiple people came up with the same thing independently. Heck, someone just posted another answer that's also very similar to yorus...
But more importantly, if his answer disappeared, it wouldn't improve yours. There's no real value to the community in removing it apart from a little less noise - but then, removing yours would have the exact same advantage there, and you can achieve that without saying a word...
In short, complaining accomplishes nothing. So don't bother, unless you're doing it purely for catharsis.
What should you do? How about improving your answer to make it more unique / interesting / informative? Maybe a bit of background on how and why initializers work that way. Cite the spec for extra credit. Be creative. That way, everyone wins...
See also: What's the appropriate etiquette when two people correctly answer a question at the same time?

Repeated answer. Should I complain?


Wordpress and Mybb

Question: Yes I know that there is a plug in to bridge the two, but I want to keep them separate. Basically I want the nav menu in wordpress to point to a sub domain or a folder with the mybb forums. Everyone keeps telling me to use the plug in. Also if you add folders to wordpress, will it not just give you errors that those pages do not exist? So is a subdomain the best choice?
Answer: It's completely fine to keep the two separate without using the bridge.  If you want a link to MyBB from a Wordpress menu, you can add it in the Admin Panel -> Appearance -> Menus, add a Custom Link to your forum URL.
By default, the .htaccess file in Wordpress will not rewrite URLs any folders/files that exist on the server.  So it is possible to have MyBB as a subfolder in your Wordpress installation.  However, it may be cleaner and easier to maintain if you have it on a separate subdomain.

Wordpress and Mybb


Geodesics on a Grassmannian

Question: Where can I find the most direct and simplest presentation of what geodesics on a (complex) Grassmannian look like? I know how to do it from scratch, but, if I want to provide a reference to, say, a graduate student in EE who doesn't want to deal with any unnecessary abstract mathematical machinery, what should I point him to?
Comment: How are complex Grassmannians being used in EE?
Answer: Grassmanians are symmetric spaces, and symmetric spaces are "geodesic orbit spaces", that is, their geodesics are orbits of their group of isometries. Your Grassmanians, in particular, are of the form $SU(p+q)/SU(p)\times SU(q)$. If $g$ is the Lie algebra of the big group and $h\subseteq g$ the Lie algebra of the subgroup, then there is a $SU(p)\times SU(q)$-invariant complement $p$ to $h$ in $g$. The geodesics are the orbits of the $1$-parameter subgroups of $SU(p+q)$ whose tangent vectors are in $p$.
So to compute the geodesics, you need only find that complement $p$ and compute exponentials...
Comment: Yes, that's right. I'm writing up some notes to explain why this holds in the specific setting in a simple concrete way. I was wondering if maybe anybody else had ever tried to do this.
Answer: This answer is a little bit redundant with the other two answers given so far, but here goes anyway.
It is easier to describe the real Grassmannian case. We can look at the Grassmannian $\text{Gr}(n,k)$, and suppose that $2k \le n$; if not then you can pass to the opposite Grassmannian.  If $V$ and $W$ are two $k$-planes in $\mathbb{R}^n$, then there a set of $k$ 2-dimensional planes that are each perpendicular to each other and each intersect $V$ and $W$ in a line.  Call the angles between these lines $\theta_1,\ldots,\theta_k$.  Then in the connecting geodesic $V_t$ with $V_0 = W$ and $V_1 = V$, the angles are instead $t\theta_1,\ldots,t\theta_k$.  This is an explicit description that is basically equivalent to Mariano's remark about invariant complements.
The complex version has the same system of angles, but complexified lines, 2-planes, and $k$-planes.  The "angle" between two lines in a 2-plane can be defined as the geometric angle between their slopes plotted on the Riemann sphere.  Actually these angles are twice as large as the angles in the real case in the previous paragraph, but that makes no difference.

I was vague on the positions of the planes.  The orthogonal projection of $V$ onto $W$ has a singular value decomposition, and the singular values are $\cos \theta_1,\ldots,\cos \theta_n$.  The orthogonal projection the other way is the transpose, or Hermitian transpose in the complex case, so it has the same singular values.  The corresponding singular vectors are the lines $V \cap P_k$ and $W \cap P_k$.  So the actual explicit work of finding the geodesic comes from solving a singular value problem, or equivalently an eigenvalue problem.
Comment: You have to work harder than that to find the planes.  They come from the singular value decomposition of the projection from $V$ to $W$ (or vice-versa).
Comment: Indeed. And looking at it this way it is easy to construct the geodesics: you need only construct the 2-planes $P_1$, ..., $P_k$. You do this as follows: pick a non-zero vector $v_1$ in $V$, and one $w_1$ in $W$, and let $P_1=\langle v_1,w_1\rangle$; next pick $v_2$ in $V$ and $w_2$ in $W$ orthogonal to $P_1$, and put $P_2=\langle v_2,w_2\rangle$, and and so on.
Comment: Urgh. Yes, you are right, of course.
Answer: This is a variation on the 1st answer, but I find it more straightforward and have explained it
to EE students.  Consider the map  $U(n) \to Gr(k,n)$  from the unitary group to
the Grassmannian by $g \mapsto gx_0$, with $x_0$ a chosen `base point'. Put the bi-invariant metric on the unitary group $U(n)$.   The metric
on $Gr(k,n)$ is defined so that this map is a Riemannian submersion: the orthogonal complement to the fiber is linearly isometric to the base tangent space.  As such, geodesics in $U(n)$
which are ORTHOGONAL TO THE FIBER project onto geodesics in the Grassmannian.  And all geodesics in the Grassmannian arise this way.  Now use that geodesics in the Unitary group
are all of the form  $g_0 exp(t \xi)$ -- translates of one-parameter subgroups, and work
out what it means , relative to $\xi$ for the geodesic to be tangent to the fiber in the
case $g_0 = Id.$
Comment: Thanks! This is exactly how I have explained to the EE student in question.
Answer: The complex Grassmannian SU(n)/S(U(k) * SU(n-k)) being a Hermitian symmetric space enjoys the property that its geodesics (in the standard Kaehler metric) are homogeneous, i.e., generated by action of a one parameter subgroup of SU(n). In the following reference there is an explicit construction of this map in the affine coordinates.
http://www.emis.de/journals/BBMS/Bulletin/bul972/berceanu1.pdf
Update:
Another method for the computation of the geodesics on symmetric spaces is through the solution of the radial part of the Hamilton-Jacobi equation. In the case of the complex Grassmannian, it depends on min(k, n-k) coordinates and depends only on the restricted roots of the symmetric space and their multiplicity (see, Helgason: Groups and geometric analysis for the definitions of the radial coordinates and the radial differential operators).
Answer: Have a look at the paper:

Y.~A. Neretin: On Jordan angles and the triangle inequality in
Grassmann manifold}, Geometriae Dedicata, 86 (2001).

There are explicit formulas for geodesics and even for the geodesic distance on real Grassmannians. This ties in with Greg Kuperberg's answer.
Comment: Thanks for the answer, even though it's 3.5 years later and alas I don't remember why I asked this.
Answer: Here are some references for Greg Kuperberg's answer:
"1996 Conway, Hardin, Sloane - Packing lines, planes, etc - packings in Grassmannian spaces" is a beautiful paper that gets into this territory. They cite [Golub and Van Loan 1989, p. 584] ("Matrix Computations"), which in turn cites "1973 Bjorck, Golub - Numerical methods for computing angles between linear subspaces", a paper with 90 MathSciNet references as of now.
This is a beautiful description of a geodesic interval in the Grassmanian. I would love to see a similar description for higher dimensional geodesic simplices.

Geodesics on a Grassmannian


Could Jesus Christ hate something or someone?

Question: Love and hatred are often described as polar feelings, therefore one cannot exist without the other. Just like magnet poles. Jesus is known as a person who could love all the people. Does it emphasize his uniqueness (he couldn't hate anyone or anything) or maybe there is a chance that hatred was familiar to him.
Comment: The word hate used in modern translations has many differing meanings, so in order to get an answer with any true meaning it is going to be necessary that you define more precisely what you mean by hate.
Comment: Hi and welcome. Even though there may be more latitude than at BH.SE for your question (we don't require a specific text as a starting point like they do), we're still looking for questions that are objectively answerable from a particular perspective. With that in mind, *who* (ie. which specific Christian perspective) are you wanting an answer from?
Answer: It is impossible to love without hating. They are opposites in a sense--in the same sense that every coin has two sides, and without one side the other cannot exist.

If you love your child, you have anything which harms your child: illness, a kidnapper, a vengeful ex-boyfriend
If you love cleanliness, you hate dirtiness
If you love quiet, you hate noise
If you love every person in the world, you hate anything which might harm them: Sin, the devil, foolish choices

So yes, absolutely, Jesus (and God the Father) is capable of hate. It's impossible to have love without also having hate.
The strongest direct Biblical support for God hating is not in the context of Jesus, but there is some for that as well.

Luke 14:26, Jesus instructing us to hate:

"If anyone comes to me and does not hate father and mother, wife and children, brothers and sisters—yes, even their own life—such a person cannot be my disciple.

Romans 9:13:

Just as it is written: "Jacob I loved, but Esau I hated."

Deuteronomy 32:19:

The Lord saw this and rejected them
because he was angered by his sons and daughters.

And here is a more exhaustive list of other such verses.
Comment: The word hate used in modern translations has many differing meanings, so in order to get an answer with any true meaning it is going to be necessary that you define more precisely what you mean by hate.
Comment: @Bye: I would say that's a deficiency of the question, not of the answer.
Comment: You're right sorry for putting my comment in the wrong place. please accept my apology.
Comment: @Bye: No apology necessary. No harm done. :)
Answer: Could Jesus Christ hate something or someone?
Yes. Since Jesus is God, he would hate the same things God hates.

John 10:30  I and my Father are one.
Proverbs 6:16-19  These six things doth the LORD hate: yea, seven are
  an abomination unto him:   A proud look, a lying tongue, and hands
  that shed innocent blood,   An heart that deviseth wicked
  imaginations, feet that be swift in running to mischief,   A false
  witness that speaketh lies, and he that soweth discord among brethren.


Stop Dataguard configuration to test standby database

Question: I would like to know how it would be the correct way in which I should proceed to stop the Dataguard configuration in order to perform a series of tests on the standby database.
It turns out that I have an environment with two Oracle 11gR2 databases, one primary and the other physical standby in a remote location (DR), the fact is that I have to perform some stress tests, modifications in some logical structures and above all, apply TDE to column level and measure the performance after applying it, all these actions I would like to do in the physical standby since it is impossible to stop the production database as it is very critical. So, as I was saying, the idea is to momentarily stop Dataguard, perform all operations on standby, and then return everything to the way it was before. What steps should I take to carry out the task in question?
Comment: You should have a dedicated test environment for this. The alterations - especially logical ones like encrypting columns; anything that affects the logical model of the database - must be made in the primary database and replicated to the alternate database. You won't be able to resync if you make changes to the standby.
Comment: I was thinking about the possibility of converting the physical standby into a standby snapshot, running the tests and putting it back in its initial state (physical standby), but I don't know if it would be a good idea, I am particularly concerned about how it would work with TDE. Any ideas? any suggestions? Someone who has been through something similar?
Comment: you have no test environment to do this in? you shouldn't have to change your production configuration to perform these kinds of tests. If something doesn't go as planned you will have compromised your DR capability, which could seriously affect your business. It is possible you might even need downtime to correct the problem, and you still wouldn't have your answers.
Answer: As suggested you should convert the physical standby database into a snapshot standby database. You can do almost all changes on the snapshot standby database, except for TDE operations.
To do TDE stuff you must have a keystone and a TDE master key. This you create on the primary database, and copy it to the standby database.
Part of the TDE configuration goes into the control file, so you can't undo that with Flashback Database (which is used by snapshot standby database).


Help identify a fern

Question: I bought this fern from the super market, but they don't have any identification on it. Can you please help identify it so that I know how to take care of it.
Comment: pnuts: the shape of the leaves looks very different from Boston Fern. Boston Fern looks long, sword like, this is more rounded.
Answer: This is definitely not a Boston, but this is from the fern family. The care is about the same as any fern. Keep it moist not wet. The temperatures should be 50°F-55°F at night, and up to 72°F in the day. Give it indirect light, not full sun. I love ferns but personally they're a little fussy for me.

Help identify a fern


Bash script to toggle wifi in lion

Question: Is it possible to have a bash script that toggle my wifi on and off? I am using lion (10.7.2).
Answer: Assuming your hardware is somewhat similar to mine:
networksetup -setairportpower en1 on
networksetup -setairportpower en1 off

You can run networksetup -listallhardwareports to find the device (en1) of your Wi-Fi in case it's different.
To toggle put something like the following lines into a script or shell function:
[[ "$(networksetup -getairportpower en1)" == *On ]] && v=off || v=on
networksetup -setairportpower en1 $v

Answer: #!/bin/bash

device=$(networksetup -listallhardwareports |
grep -E '(Wi-Fi|AirPort)' -A 1 | grep -o en.)
[[ "$(networksetup -getairportpower $device)" == *On ]] && v=off || v=on
networksetup -setairportpower $device $v

The port name is Wi-Fi on 10.7 and AirPort on 10.6. The device name can be at least en0, en1, or en2 depending on your setup.
Answer: Head over to this page. A guy by the name of heatxsink made a pretty handy script that will toggle your wifi on or off depending on the status of your ethernet connection.
You can add your own growl notifications pretty easily if you want. Also make sure to follow every step precisely as the script relies on filenames and locations of the files.
Other options:
You can try out ControlPlane. It seems promising to fill your need for automation.

Bash script to toggle wifi in lion


How does Apple know whom an inactive iPhone belongs to?

Question: I tried to log into my daughter's iMessage on an inactive iPhone. She called Apple because she got an email. They told her it was an iPhone 5c black. How did they know that? Do they know who the owner is? Is there a way to block my old iPhone so Apple can't trace it?
Answer: They store device information thats linked to the UDID of the device. As far as I know, they can't tell who the owner is for sure. Moreover, I also doubt you can block the old phone.
Comment: Thank you for the info! You guys are great so full of knowledge
Comment: when we lived in Indiana, my son sold the iPhone I had given him.  Years later, I was living in Oklahoma, and I got a phone call from a repair shop in Seattle saying my iPhone was ready for pick-up.
Answer: The serial number has the device information included. Their database just pulls up the record according to the serial number. You can try and see it for yourself with any Apple device by using the support page. There, click on "Browse by Product" and type in your serial number. While this search does not necessarily give you the color or size, the type of device (e.g. iPhone 5c) will show up as first search result.
Another of their pages will show some more information and allows you to even get what support you have left by entering the serial number: Check Your Service and Support Coverage
So, nothing fancy or ill-meant really.
The owner gets registered when the iPhone is used with the iTunes Store or iCloud the first time.  With both also being Apple services, it is simply tying this information together.


Apply Expand only to parts of expression

Question: I have the following term:
term = (x AngleBracket[x (-x+Sum[v'[y[j]],j])])/AngleBracket[x^2]+Sum[v'[y[j]],j];
term //TeXForm

$\frac{x \left\langle x \left(\sum _j v'(y(j))-x\right)\right\rangle }{\left\langle
   x^2\right\rangle }+\sum _j v'(y(j))$

and want to apply Expand only to the part within the AngleBrackets. How can I do that?
The result for this simple example is supposed to be
(x AngleBracket[-x^2 + x Sum[v'[y[j]],j]])/AngleBracket[x^2] + Sum[v'[y[j]],j] //TeXForm

$\frac{x \left\langle x \sum _j v'(y(j))-x^2\right\rangle }{\left\langle x^2\right\rangle
   }+\sum _j v'(y(j))$

It is important to me that a solution should work for any example, no matter the depth of the expression etc.
Comment: does `Replace[expr,  AngleBracket[a_] :> AngleBracket[Expand[a]],All]` give what you need?
Answer: I like using Composition (@*) for this kind of thing:
term /. AngleBracket -> AngleBracket @* Expand //TeXForm

$\frac{x \left\langle x \sum _j v'(y(j))-x^2\right\rangle }{\left\langle x^2\right\rangle
   }+\sum _j v'(y(j))$


Moving several Emails at the same time with Google Mail

Question: I typically use a Mac and in MAC Mail I can sort my emails by subject and move many of them at the same time to saved folders with client subjects to appropriate folders. Is there a way to do that with Gmail?
Answer: Of course there is. However, Gmail orders messages (conversations) by date; you cannot change the sort order to be by subject.
What you'll want to do is filter your messages. You can specifically target the subject by using the subject: search operator.
subject:"You're a winner"

That search will find all messages with "You're a winner" in the subject line. You can then easily select all or some of them and change the labels as you need. (Note that Gmail uses labels, not folders. Messages/conversations can have multiple different labels.)
If you know what the subject (or part of it) is going to be ahead of time, you can set up filters to do a number of things on the messages as they come in, including applying labels. The basic way to create a filter is to search for your criteria, then "create a filter" right from the search drop-down. Choose your actions and you're done.
More information on this and much more can be found at https://support.google.com/mail/


Atmospheric Humidity Effects on Non-water Evaporation

Question: Does evaporation of non-water liquids into the atmosphere vary with atmospheric humidity?
Answer: Yes, because though the liquid phase initially contains no water, water molecules may enter the liquid phase from the gas phase.  The more hygroscopic the liquid is, the more the evaporation rate will be affected by humidity.  If the liquid is very hygroscopic and has a low vapor pressure, the initial evaporation rate may even be negative in humid conditions, as water enters the liquid phase at a rate greater than liquid enters the gas phase.


How to identify Non-Negative Operators?

Question: Given a finite dimensional vector space $E$, let us consider a non-negative operator $P:E\rightarrow E$. The question is: besides its standard characterization, where $P$ is self-adjoint and $\langle Pv,v\rangle \geq 0$, is there any other criteria to identify them? It is worth mentioning here it is also supposed to be known that such condition is equivalent to: $P$ self-adjoint and $\lambda\geq 0$, for every eigenvalue. Thanks in advance.
Answer: Any factorization of the form $P=M^{T}M$ is sufficient to show that $P$ is positive semidefinite.
If $P$ is given to you in matrix form and you're interested in a numerical computation then you can check for positive definiteness by computing the eigenvalues of $P$ or by computing a Cholesky factorization.  For positive semidefiniteness, you'd have to use some kind of tolerance since any floating point computation of the eigenvalues or the Cholesky factorization would be subject to round-off errors.
Answer: I will presume that $E$ is a complex vector space, or at least that $P$ is self-adjoint.
To determine that $P$ is positive definite, it suffices to apply Sylvester's criterion.
Now, let $P$ be a self-adjoint operator, and let $X$ be a matrix whose columns form an orthonormal basis for the image of $P$ (that is, the image of $X$ is the image of $P$ and $X^*X = I$).  Then $P$ is positive (non-negative definite) if and only if the matrix $X^*PX$ is positive definite.
Comment: A little nuance: @Brian Borchers asks for condition of **semi**definiteness, connected to **semi**definite positiveness.
Comment: @JeanMarie see the entire last paragraph of my post

How to identify Non-Negative Operators?