What is the statistical mathematical argument for the population standard deviation to be divided by N and the sample standard deviation to be divided by N-1? I have searched several places and they take it for granted, but do not offer a deeper explanation. That of accepting the formulas because that is the way it is done does not suit me.

I have an HP 50g graphing calculator and I am using it to calculate the standard deviation of some data. In the statistics calculation there is a type which can have two values:  Sample Population  I didn't change it, but I kept getting the wrong results for the standard deviation. When I changed it to "Population" type, I started getting correct results!  Why is that? As far as I know, there is only one type of standard deviation which is to calculate the root-mean-square of the values!  Did I miss something?


base.buffer.length in the main method throws an exception, whereas isFull method works, can someone please help me understand what is going on?  package chp14;  public class BaseBoundedBuffer<V> {     private final V[] buffer;     private int head, tail, count;      public BaseBoundedBuffer(int capacity) {         this.buffer = (V[]) new Object[capacity];     }      public boolean isFull() {         return buffer.length == count; // But this works     }      public boolean isEmpty() {         return count == 0;     }      public static void main(String[] args) {         BaseBoundedBuffer<String> base = new BaseBoundedBuffer<>(10);         System.out.println(base.isFull());         int count = base.buffer.length;         // This line throws an exception, but the method isFull works, why?         // Exception in thread "main" java.lang.ClassCastException:         //      java.base/[Ljava.lang.Object; cannot be cast to java.base/[Ljava.lang.String;         //          at chp14.BaseBoundedBuffer.main(BaseBoundedBuffer.java:21)      } }

Due to the implementation of Java generics, you can't have code like this:   public class GenSet<E> {     private E a[];      public GenSet() {         a = new E[INITIAL_ARRAY_LENGTH]; // error: generic array creation     } }   How can I implement this while maintaining type safety?  I saw a solution on the Java forums that goes like this:  import java.lang.reflect.Array;  class Stack<T> {     public Stack(Class<T> clazz, int capacity) {         array = (T[])Array.newInstance(clazz, capacity);     }      private final T[] array; }   But I really don't get what's going on.


When a Company was expected and then made a profit of X $ then      That X$ increased it's share price. or those the Sellers and Buyers?   Is it because Company A did a profit of X amount, so X is now Added to valuation of the company and since Company is valued by its share it thus increases the value of each share.    Is it just the buyers and sellers that decide the value or price of each share  Thanks in advance.

So a company decides to raise money by selling shares of its stock. The stock is offered at an initial price of their determination. The stock is then traded in a market where forces of supply and demand, as well as speculation, affect its price.  When a company performs well (or makes decisions that will likely increase the company's earnings in the future), more people want to buy that stock than do people wanting to sell it. This creates demand for that stock which causes its sell/bid prices rise. When a company performs poorly, the opposite occurs; more people want to sell the stock than want to buy. This creates a surplus that causes sell/bid prices to fall.  Understanding this, people speculate over company performance to determine the future behavior of a stock, and attempt to "buy low, sell high" or "borrow high, return low" in order to make a profit.  But my question is regarding the first part of that process. What is it about company performance that causes the perceived value of its stock to rise? This is especially perplexing since I would guess that most people don't exercise their voting rights, and many stocks don't pay dividends.  It's not like a shareholder has any direct financial gains from increased company earnings (speculative stock pricing notwithstanding).  What is the intrinsic value of the stock?  It seems to me that all participants in a stock market tacitly agree that stock price will have a direct correlation with company performance. So another way of asking the question is, would an opposite agreement hold? What financially (this isn't a question about logistics, communication, or feasibility) stops all participants in a market from agreeing to value a particular company's stock inversely with respect to the company's performance?  Since I feel like I can't quite nail down my question, another form of it would be, why is stock market behavior driven by company performance?


TestCase.h  class TestCase {   public:     template<size_t N> TestCase(int (&arr)[N]) {       // Constructor code here, I iterate over the array of values.     }     // etc   private:     int var1;     // etc }   This is my header file for a class. The class takes in an array of any size using a template. This works great but I hate having the constructor code in the .h file. How can I move the constructor code into the .cpp file with the rest of the member functions? I can't use vectors or anything. Thanks :)

Quote from :     The only portable way of using templates at the moment is to implement them in header files by using inline functions.   Why is this?  (Clarification: header files are not the only portable solution. But they are the most convenient portable solution.)


Is there a place on Stack Exchange that lists specific user privileges earned, such as question, answer, flag, vote, comment?  There's already a place to see user-earned badges.

Formerly Reputation requirements compared. What are the reputation requirements for privileges on the various sites in the network? Also, how do reputation requirements for various privileges compare on different Stack Exchange sites? Specifically, the following types of sites:  Designed sites e.g. Stack Overflow, Ask Ubuntu, Gaming, etc. Public beta and non-designed sites Private beta sites  ...as well as any site-specific differences.


I am writing a paper using the springer journal LaTeX template. For some references I want to use in-text citation like this:    but for some reason, when I try this in my document I get the following:    I can't seem to figure out where the problem lies.  I tried using \citeauthor and \citeyear, but that does not solve the problem unfortunately.  Below is a MWE:  \documentclass[]{article} \usepackage[numbers, sort, comma, square]{natbib}  \begin{document}   bla bla bla \citet{aaronson1998}.    \bibliographystyle{unsrt} \bibliography{bibfile}   \end{document}   BiBTeX entry:  @article{aaronson1998,   title={Translation, validation, and norming of the {D}utch language version of the  {SF}-36 Health Survey in community and chronic disease populations},   author={Aaronson, Neil K and Muller, Martin and Cohen, Peter DA and Essink-Bot,      Marie-Louise and Fekkes, Minne and Sanderman, Robbert and Sprangers, Mirjam AG and  te Velde, Adrienne and Verrips, Erik},   journal={Journal of Clinical Epidemiology},   volume={51},   pages={1055--1068},   year={1998},   publisher={Oxford; New York: Pergamon Press, c1988-}     }

I would like to show the author names using \citet but I get just the reference number. Here is a minimal code:  \documentclass{report} \usepackage[utf8]{inputenc} \usepackage[english]{babel} \usepackage{natbib}  \begin{document}   The author \citet{toschi09} has shown that ..  \bibliographystyle{plain} \bibliography{foo}  \end{document}   And here is foo.bib  @article{toschi09, author = {Toschi, F. and Bodenschatz, E.}, title = {Lagrangian Properties of Particles in Turbulence}, journal = {Annual Review of Fluid Mechanics}, volume = {41}, number = {1}, pages = {375-404}, year = {2009},  }   What I get is:     The author (author?) [1] has shown that ..   Any help will be more than welcome, thank you!


is a new TeX-to-web renderer that is supposed to be faster and more lightweight than MathJax.  Normally, I would just dismiss it as an interesting technology that might not be ready for production use yet.  However, the example at the bottom of that page…    … caught my eye as something that looked !  I think that compatibility might be a concern, though, both in terms of browser support and fidelity when rendering existing content.

Khan Academy released , a library that does essentially the same job as MathJax does today -- only . Part of that is probably because (the hard?) part of the layout can be preprocessed on the server. This may also enable mathematics typesetting in apps more easily.  As of now, it does not offer all the symbols and functions MathJax has -- so we don't want to switch now -- but eventually we should consider moving over. MathJax is nice but it is just painfully slow on pages with many formulae, which sites like (math|cs|cstheory).SE have plenty.  Using KaTeX as primary engine with MathJax as fallback ; this solution would already speed up many a page.  Some site metas have picked this up:


Let $G$ be a group such that $|G| \ge 3$ then $|AutG| \ge 2$.  How can I approach to this problem?  It is necessary to divide in cases? For G finite and infinite, or Abelian and non-Abelian?  The Lagrange theorem can help me?  Could you suggest some hints?

Well, this is an exercise problem from Herstein which sounds difficult:   How does one prove that if $|G|>2$, then $G$ has non-trivial automorphism?   The only thing I know which connects a group with its automorphism is the theorem, $$G/Z(G) \cong \mathcal{I}(G)$$ where $\mathcal{I}(G)$ denotes the Inner- Automorphism group of $G$. So for a group with $Z(G)=(e)$, we can conclude that it has a non-trivial automorphism, but what about groups with center?


Can anyone give me a good explanation of how to use Lambda and give a good example. I have seen it but I dont know what it is or does.

I have quickly read over the  documentation.  This kind of example has helped me to understand better, though:   delegate int del(int i); del myDelegate = x => x * x; int j = myDelegate(5); //j = 25   Still, I don't understand why it's such an innovation. It's just a method that dies when the "method variable" ends, right? Why should I use this instead of a real method?


Is it possible to rescale a beta prior to range from, say, $(0.5,1.0)$? For example, say that your likelihood function for some parameter $p$ is binomial and you know that $p \in (0.5,1.0)$ due to some physical constraint, is there a conjugate prior for this model?

What is the difference between standard beta and unstandard beta distributions? How to understand in an article if it is not described if it is standard or not?


I am trying to create a toggle action but with raw JS. So instead of using toggle class I must add and remove each part.  When the user clicks a radio button, one div gets class enabled and the other gets class disabled which controls my styling (to grey the area out)     I am using the following for this:  var d = document.getElementById('justfull'); d.className = d.className + " enabled";   and then giving the other div disabled  var other = document.getElementById('firstandlast'); other.className = other.className + " disabled";   But I am stuck when it comes to removing the class if it's previously been added. As obviously the user can toggle between the two radio buttons. I need to add the enabled class to my new div but I also need to check to see if there was previously a disabled class added to it and if so, remove it.  So I am using the following code:  var oldclass="disabled";  d.className=d.className.replace(oldclass,"");   But this doesn't seem to work as the classname just adds and adds until I have something like this:  <div id="justfull" class="  enabled  enabled  enabled disabled">   How would I properly both add the enabled class and check for a removal of the other? Essentially a toggle class but in raw JS.

How can I change the class of an HTML element in response to an onclick or any other events using JavaScript?


Screaming frog tells me that I have missing confirmation links in my hreflang, but I cannot seem to identify the problem. Here is a screenshot of the code on our Korean page:   Here is a screenshot of the code on our regular US page. Anyone have an idea of what I'm doing wrong? Thanks!

I am confused about hreflang="x-default".  I have a site in 2 languages. In each page I have a link to the page itself and a link to the same page in the other language. If I understand correctly, I have to put an x-default also. In my case it goes to the page "language". There the user can see two buttons to choose the language of the site.  The x-default link is the same on all pages and it is present in all of them.   <link rel="alternate" hreflang="en" href="http://example.com/about" />  <link rel="alternate" hreflang="fr" href="http://example.com/fr/about" /> <link rel="alternate" hreflang="x-default" href="http://example.com/language" />   I use Screaming Frog to detect possible errors. It says "Missing confirmation links in all the pages" when I see the details of the error. It makes reference only to the x-default link. I do not understand.  How to use the hreflang="x-default"?


The new Aether Revolt card  reads:     Enchanted land has "{T}: Add one mana of any color to your mana pool."   Does this mean the enchanted land provides two mana?

Let's say i enchant a land with . Would i be able to tap said land for mana, and use the ability of Underworld Connections concurrently?


I am looking for advice from the experienced community about the right direction for a CMS (content management system) based project I have upcoming, but I'm unsure of the right site to post this on. It's definitely not Stack Overflow, as requests for advice get eaten alive there. Thoughts?

Where do I ask opinion based questions on Stack Exchange? Why can't we have a stack-exchange that works like Quora? There has been a lot of research based on people's opinion. I think it is really not bad to have a SE on Opinions.  If there is already one please let me know  P.S This question is different from  ,  and  please don't mark as duplicate by linking to those questions!!  P.S.S : My question is completely different that . The question sounds same but the description and the answers are totally different. I have anyway received a reasonbly good answer. So it doesn't matter


Strongly related:   It appears that all the submitted content on Stack Overflow is licensed under the  (CC) license .  What I read from that, Stack Overflow owns all the content on the site. Everybody can use any code on SO as long as Stack Overflow is attributed.   This worries me for developing proprietary software, because now the app is not fully owned by my company anymore (and pieces are just licensed off SO). Our legal guys are probably not going to be happy with that.  If I were to ask questions about my open source project, this also implies I now need to put all my OS projects under the same license. I like BSD, and these two are not exactly compatible.  I'd like to see all the questions and answers be placed under the public domain. I feel most people on SO already treat it as such, especially the ones developing proprietary software. I think it's in everybodies interest to also make this very clear on the site.

I was wondering about the copyright of code snippets from answers. Let's say you ask a question and the solution consists of ten lines of code, which are given in an answer. Are there any restrictions about the use of that code?   It seems that the content of this page is under the . So does one have to attribute the author if code is used in an open source project? Can it be legally used in closed source projects at all?  I guess ten lines of code are not really problematic, but is there a critical number of lines?


Let $K$ be an extension of the field $F$ of degree $n$, $K = \{c_0 b0 + c_1 b_1 + \dots + c_{n-1} b_{n-1} : c_i \in F \}$. Then for any $a \in K$, $\phi_a : K \to K : x \mapsto ax$ is an $F$-linear transformation of $K$, so the matrix for $\phi_a$ would be $A_a = \begin{pmatrix} \phi_a(b_0) & \phi_a(b_1) & \dots & \phi_a(b_{n-1})\end{pmatrix}$ where $\phi_a(b_k)$ is understood to be the column vector at the basis vector $b_k$.  I've shown that $\Phi : a \to A_a$ is additive, but how do you show that it is multiplicative?  The purpose is to show that $K$ is isomorphic to a subfield of the ring $F^{n\times n}$.  My attempt: $\Phi(ad) = \begin{pmatrix} ad b_0 & ad b_1 &\dots & ad b_{n-1}\end{pmatrix}$.  I've also tried working with a $2\times 2$ example and don't see where to take it.  Thanks.  EDIT:  The answers in the comments don't answer my general question, they only give an example. Therfore, this question is NOT a duplicate!  In fact, I was already aware of the content of those answers!  (See above!)

Suppose $K \subset L$ is a finite field extension of degree $m$. Is it true that there exists some natural $n$ such that $L$ is isomorphic to a subfield of $M^{n\times n}(K)$, the ring of $n\times n$ matrices with entries in $K$? What is the smallest dimension (as a function of $m$) for which an isomorphism exists?  The example I had in mind was the 2-dimensional extension $\mathbb{R} \subset \mathbb{C}$ with $\mathbb{C}$ being isomorphic to $\{ \begin{pmatrix}a&-b\\b&a\end{pmatrix} : a, b \in \mathbb{R}\}$.


I want to move a S3 bucket from Tokyo to Seoul, and I don't want to re-create it. Is there any way doing this? (Move region without deleting and recreating) If not, what should I keep in mind?  I don't want to make another bucket to dump it temporarilly, syncing it, and then deleting/recreating in another region, and sync it again.

We use S3 for storing millions of entries in our webapp, now we move the whole thing to EC2, EU servers, and we also want to move that S3 data to EU. But the bucket we use is in US, and there seem to be no tool to move whole bucket content to different bucket.  There is also problem on how to synchronize the data later on when we switch to EU bucket, the data that will be created meanwhile while the migration was running.


You know, that word that's on the tip of your tongue. It's that elusive word that escapes the brain but you know it's there. I can't exactly place it. But if you mention it, I'll recognize it immediately.  I tried searching the web for it but I don't know the search terms for that word.   I'd find a use for it to describe in the following sentence:     I was going to say foo, but it doesn't fit. What is the ________ that should fit in the blank?

I vaguely remember seeing this word years ago, it started with "log-". I want to know what this word is because I have this problem all the time (as many others do), where the word I am thinking of is right at the tip of my tongue but I just can't remember it.   It's a bit fitting for this situation, isn't it?


How to install PHP 7 via apt-get ?  /etc/apt/sources.list  deb http://packages.dotdeb.org jessie all deb-src http://packages.dotdeb.org jessie all   command line  wget https://www.dotdeb.org/dotdeb.gpg apt-key add dotdeb.gpg apt-get install php7   install  # apt-get install php7 Reading package lists... Done Building dependency tree Reading state information... Done E: Unable to locate package php7

I'd like to try PHP7.0 on Debian Jessie and am trying to install it from sid. However,  depends on  which depends on php-common > 18 while  in sid is at 17. Does this mean it's simply impossible to install php7.0 from this distribution at the moment? Why is that?  I know that it is possible to install from source as explained e.g. , I'm just asking about the official packages.    Note: the packages in sid have been fixed and it is now (Jan 6, 2016) possible to install from there.


i have a keyframe with the size of the smoke domain at the very beginning of my animation and a keyframe at the middle. I want the smoke domain to enlarge at the second keyframe and not to grow between them is this somehow possible? Cant find the right option.  There must be a option to make the values not to rise  between keyframes.  thanks in advance Ben SuperSpamTube

I animated a bunch of blinking LED lights, and put key frames on the spots where I want the LED on and off. The LED lights have an f curve to them, currently it's on the more logarithmic curve. I am aware of how to turn the f curves into linear slopes, or how to manually edit an individual curve into a shape I want. What I want is to have the curves non-existent - once it hits the key frame that says "on" it holds this level until it reaches the key frame that says "off". For onstance:  Frame 100: on 106: off 112: on  I have twenty LED lights, almost two hundred frames and key frame changes every quarter second. Please tell me there is an easy way to do this:(  Also, is there a way to copy key frames and paste them later on in the dope sheet? Every 48 frames my animation resets, so copying 48 frames four times is easier than doing 192 frames.


I'm trying to read floats from a text file into a 2d array. The file has the following structure:  1.1 3.3 2.4576 0.2432 1.3 235.234   I wish to read these lines into a 2d list, and end up with the following.  data = [[1.1, 3.3]         [2.4576, 0.2432]         ...         [1.3, 235.234]]   My code so far:  f = [] with open(str(i)) as fl:     for line in fl:         f.append(float(line))   Is there an easy and "nice" way to do it, without using a lot of help variables?  (Both the length of the file and the size of the array(x*x) are known)

I have a list of arbitrary length, and I need to split it up into equal size chunks and operate on it. There are some obvious ways to do this, like keeping a counter and two lists, and when the second list fills up, add it to the first list and empty the second list for the next round of data, but this is potentially extremely expensive.  I was wondering if anyone had a good solution to this for lists of any length, e.g. using generators.  I was looking for something useful in itertools but I couldn't find anything obviously useful. Might've missed it, though.  Related question:


I would like to invoke my chrome or firefox browser when a file that I specify is modified. How could I "watch" that file to do something when it gets modified?  Programmatically it seems the steps are.. basically set a never ending interval every second or so and cache the initial modification date, then compare the date every second, when it changes invoke X.

I have a log file being written by another process which I want to watch for changes. Each time a change occurs I'd like to read the new data in to do some processing on it.  What's the best way to do this? I was hoping there'd be some sort of hook from the PyWin32 library. I've found the win32file.FindNextChangeNotification function but have no idea how to ask it to watch a specific file.  If anyone's done anything like this I'd be really grateful to hear how...  [Edit] I should have mentioned that I was after a solution that doesn't require polling.  [Edit] Curses! It seems this doesn't work over a mapped network drive. I'm guessing windows doesn't 'hear' any updates to the file the way it does on a local disk.


Give an example of a function $f : R \rightarrow R$ which is continuous at all irrationals points and discontinuous at all rational points of $R$.

Consider the function:  $f(x)= \begin{cases}  1/n \quad &\text{if $x= m/n$ in simplest form} \\ 0 \quad &\text{if $x \in \mathbb{R}\setminus\mathbb{Q}$}  \end{cases} $  Prove that the function is continuous at every irrational point and also that the function is not continuous at every rational point.  Also, we can say that the function is continuous at some point $k$ if $\displaystyle\lim_{x \to k} f(x)=f(k)$.  I was thinking of doing an epsilon delta proof backwards using the fact that $\mathbb{Q}$ is dense in $\mathbb{R}$ for rational points and irrational points.  Any ways on how to expand on this are welcome.


While trying to solve a problem my friend asked me, "is $(2^{50})-1$ prime?", I found a pattern where if $n$ is composite, $(2^n)-1$ is also composite, and in many cases if $n$ is prime, the term is also prime. However this fails at a few prime numbers, the first of which is $11$. I was able to check for composite results up to $80$ before having to work on other things. I am wondering if anybody can prove or disprove the assertion above. While playing around with the pattern, I also found that for composite $n$, $(a^n)-(a-1)$ is also composite. I am less sure about this one, but it is much more exciting if true.

Are there any solutions to $x^{n}-1=p$ with p prime, integers $x,n>1$ and $x$ not a power of $2$?  $x$ must be even. $n$ is odd since if $n=2m$ then $p=x^{n}-1=(x^{m}+1)(x^{m}-1)$ hence $p=x^{m}+1$ and $1=x^{m}-1$, which has solution $p=3$ given by $x=2^{2}$.   This generalises; for any solution to $x^{n}-c^{2}=p$, $n$ must be odd. And for any solution to $x^{n}-c=p$, $x$ is odd iff $c$ is odd unless $p=2$ and, if $a$ divides $c$ and $p$ does not divide $c$ then $x$ divides $c$.


My Account disappeared yesterday from math and chem stack exchange.  I am very confused what happened was that I was told something strange happened to my account and I logged in and sure enough I have 1 reputation point on chem stack exchange and my math stack exchange got deleted.   Can someone explain what is happening?

So in Chemistry and Math Stack Exchange I got suspended for six days and got my votes reversed. I believe that is because the moderators thought that I voted for myself.  So basically what was happening was that this account, John Rawls, had this other account Nick Bostrom voting for John Rawls. But rather I know Nick Bostrom so I kept on facebooking him the links to my questions so that I can get an answer.  I was wondering whether I am going to get my points back for Math.SE and Chem.SE after six days. If not, I was wondering if I could get it reversed because I don't understand why this is happening and I believe that this is unfair.  This question is specific and should not be marked as duplicate because this is a scenario where someone is voting for me


I have an iOS app that uses 2FA for certain account related features. I'd like to create some UI automation tests for those features, but they require receiving either SMS messages or email. On a simulator, there is no such way to access SMS. I think it might be possible to access the email instead, but that would involve opening up Mobile Safari and logging into an email account- do iOS automation frameworks even support that level of granularity for accessing UIWebViews?.  Is it even possible to have automated tests for 2FA? One presumes that if there's a way to access the test account's SMS or email accounts- so on a device, not in the simulator- it might be feasible.

Are there methods for testing 2FA signup or login? I would assume judicious use of dummy phone numbers and/or emails would be involved.


I once read about a story in which, by a series of unlikely manoeuvres of time travel and a sex change operation, one person (originally a girl) managed to be her own mother and father. IIRC, she was brought up in an orphanage, travelled back in time to father a child (herself) with a near-stranger in a bar, then later became a man and travelled back in time to impregnate a near-stranger (him/herself) in a bar.  Unfortunately, because I only heard about the story and never actually read it, I have no idea whether it's a novel or short story, when and in what language it was written, what it looked like, etc. Hopefully the plotline will be distinctive enough to enable someone to find it!

I remember having read a short story in which the main character, thanks to a series of happenings also involving time travel, grew up, changed sex, made sex with himself and had a son... who of course was himself. The story ended with the main character saying something like "I know where I come from: but what about you?"  As you may guess, I don't have enough data to search for the title, so I am asking knowledgeable people :-)


I am trying to have a click event on
 tag of my table that's dynamically generated.  While registering event for 1st time, there is no exception. But Function is not being called if I click on tablerow.  I tried getElementById also, which is even giving extra exception while registering on click event.  Please help.  Below is part of my code:  Script:  $("#empName").on("click", function(){         alert("Hi");     });   HTML:  $(obj).find('#abc tr:last').after("
"+emp+"
"+eventName+"
"+ind+"
"+loc +"
");

I have a bit of code where I am looping through all the select boxes on a page and binding a .hover event to them to do a bit of twiddling with their width on mouse on/off.  This happens on page ready and works just fine.  The problem I have is that any select boxes I add via Ajax or DOM after the initial loop won't have the event bound.  I have found this plugin (), but before I add another 5k to my pages with a plugin, I want to see if anyone knows a way to do this, either with jQuery directly or by another option.


When I compile with LaTeX (emacs+AUCTeX), I get the following warning:  LaTeX: there were unresolved references, {52} pages   I know that I have some \ref{somefuturething} here and there, and I would like to control them every now and then.   How do I browse through the unresolved cross references in a big document (several files) in emacs AUCTeX?

How do I find unresolved references? Does LaTeX tell me this somewhere? Is it in a log file? The LaTeX output just says I have unresolved references, but it doesn't tell me what they are, or does it? thanks


I plan on making a device that the user can control with their phone via a WiFi connection to an ESP8266 or ESP32. If I end up selling this device, will I need to get it certified?  The ESP32/8266 has an FCC ID written on it. Does this count, or do I need an FCC ID for my device? I don't plan on selling more than 100 of them, so it would be too expensive for me to get it tested.   Does the answer to this question depend on whether I: Use an external antenna? Use a readily available ESP breakout board? Design the ESP directly into my board?

The manufacturer of this radio module I bought claims that it's FCC certified, but  there's no FCC ID on it (though there is the FCC logo). If the final product is to be FCC tested, would it then be tested as an intentional radiator since there's no FCC ID on the radio module (rendering the certification invalid)? AFAIK, that costs a lot more than an unintentional radiator test.  Their website has the FCC ID - could I just print it on a sticker and stick it on the module?  Thanks


When I compile my .tex file, it generates a lot of different files (with extensions such as .aux, .log), but all I want is the .tex and .pdf files. Those files just fill my hard drive for nothing. Is there any trick to make LaTeX retain only the .pdf and .tex files and delete everything else after compilation?

Is there a way to make TeX delete files?   In my document a lot of auxiliary files are created and it would be wonderful to have them removed after their content has been used.


The  states that a feedforward neural network (NN) with a single hidden layer can approximate any function over some compact set, provided that it has enough neurons on that layer.   This suggests that the number of neurons is more important than the number of layers.  But in practice deep learning is obviously very successful at various prediction tasks. Why is that? Shouldn't all deep NNs be equivalent to single layered NNs with enough neurons? Why do we need depth?

I haven't seen the question stated precisely in these terms, and this is why I make a new question.  What I am interested in knowing is not the definition of a neural network, but understanding the actual difference with a deep neural network.  For more context: I know what a neural network is and how backpropagation works. I know that a DNN must have multiple hidden layers. However, 10 years ago in class I learned that having several layers or one layer (not counting the input and output layers) was equivalent in terms of the functions a neural network is able to represent (see Cybenko's ), and that having more layers made it more complex to analyse without gain in performance. Obviously, that is not the case anymore.  I suppose, maybe wrongly, that the differences are in terms of training algorithm and properties rather than structure, and therefore I would really appreciate if the answer could underline the reasons that made the move to DNN possible (e.g. mathematical proof or randomly playing with networks?) and desirable (e.g. speed of convergence?)


I have been trying to solve the recurrence   $T(n) = \sqrt{n} T \left(\sqrt n \right) + n$  for some time now. I only know substitution, recursion trees, and the master method (though it doesn't apply here, so i'd prefer help in those forms. I also attempted to change variables but got nowhere.  My plan was to use a recursion tree, but I seem to be stuck, as this recurrence isn't in the usual form $T(n)= aT(n/b)+f(n)$. However, I do know that the first level of the tree has the cost of $cn$, and that the next level down has $\sqrt n$ nodes. My main concern is how I can express the next level's recurrence, which I got to be $T(\sqrt n)=\sqrt nT(\sqrt(\sqrt n))+\sqrt n$, though I feel like that is wrong.

$$T(n) = \sqrt{n} T \left(\sqrt n \right) + n$$  Master method does not apply here. Recursion tree goes a long way. Iteration method would be preferable.  The answer is $Θ (n \log \log n)$.  Can anyone arrive at the solution.


I was doing a  the other day, and the task was to match 'u' at the end of the string without using $. The goal was to match "fu", "tofu" and "snafu" but not "futz", "fusillade", "functional" or "discombobulated".   I came up with fu[^tsn], which worked on ; however, it does not pass the test as it does not match any of "fu", "tofu" and "snafu" for some reason. I'd like to know why it is not working, and if there is a smarter way to work around this (bonus: is there any real-life situation where not using $ would be better).

I don't really understand regular expressions.  Can you explain them to me in an easy-to-follow manner?  If there are any online tools or books, could you also link to them?


If $A+B+C=\pi$, prove that $\cos (A-B) \cos (B-C) \cos (C-A)\ge 8\cos A \cos B \cos C$  I know this is true for acute angle triangle.   I want to know whether it is true for every real $A,B,C$ such that $A+B+C=\pi.$

In acute angle triangle, prove that    $$\cos (A-B) \cos (B-C) \cos (C-A)\ge 8\cos A \cos B \cos C$$   My progress:  $$\cos(A-B)=2\cos A\cos B+\cos C\ge 2\sqrt{2\cos A\cos B\cos C}$$  $$\implies \prod\cos(A-B)\ge 8\left (2\prod \cos A\right )^{\frac 32}$$


When I import a model from ROBLOX, it offsets the model from the tool if the model was not built in the center in ROBLOX. It is very frustrating to work with parts when the move/rotate tool is somewhere super distant in the world.    I haven't been able to find a solution to make it so that the tool is on the object like so:    What can I do so that I have the move/rotate tool centered to my model?

I have a sword that currently rotates around a pivot point thats off of the actual object. Im new to blender and im not sure how i would go about changing it so that the sword rotates around the handle. Any help would be appreciated!


I have a email server (iRedmail on Ubuntu) where I host my personal domain, and several other domains. Despite the fact that non of the domains spam, somehow, MXtoolbox tells me my server is on the Spamhaus ZEN blacklist. This server is a VERY low traffic mailhost, the only domain that actually "sends" any quantity of email from the server is my personal domain, with me and my wife having our email accounts there. The remainder of the domains hosted are one small local startup non-profit that has one email address hosted for incoming email (currently ONLY incoming), another is a domain for a small business some friends and I are trying to start, and another is my ebay business. Anyway enough background.. I'm trying to tighten up the server, MXToolbox already shows its ok as to "open-relay".. But since everywhere I look, says doing an spf record on the dns host is a good thing, I'm trying to set one up. What I'm seriously UNclear about, is how I add the other domains that this server is supposed to send/receive mail for in the spf record (I'm trying to use the spf wizard at www.spfwizard.net)..  Do I need an spf record on each domain referring to my personal domain (which is the domain the server "lives" in). I have successfully (according to the MXToolbox spf record checker) added a spf record to my personal domain as follows   frandin.org.  IN TXT "v=spf1 mx a ip4:23.94.39.114/32 ?all"   I guess my main question is do I need an spf record in each domain?

This is a  about setting up .     I have an office with many computers that share a single external ip (I'm unsure if the address is static or dynamic). Each computer connects to our mail server via IMAP using outlook. Email is sent and received by those computers, and some users send and receive email on their mobile phones as well.  I am using  to generate an SPF record and I'm unsure about some of the fields in the wizard, specifically:   Enter any other domains who may send or relay mail for this domain Enter any IP addresses in CIDR format for netblocks that originate or relay mail for this domain Enter any other hosts which can send or relay mail for this domain How stringent should SPF-aware MTA's treat this?   the first few questions i'm fairly certain about... hope i have given enough info.


I am trying to assign a static pointer in a class so I can access it by class functions.   Basically, the typeDef is defined in a third party header file.  typedef struct {   CAN_TypeDef                 *Instance;  /*!< Register base address          */    CAN_InitTypeDef             Init;       /*!< CAN required parameters        */    CanTxMsgTypeDef*            pTxMsg;     /*!< Pointer to transmit structure  */    CanRxMsgTypeDef*            pRxMsg;     /*!< Pointer to reception structure */    __IO HAL_CAN_StateTypeDef   State;      /*!< CAN communication state        */    HAL_LockTypeDef             Lock;       /*!< CAN locking object             */    __IO uint32_t               ErrorCode;  /*!< CAN Error code                 */  }CAN_HandleTypeDef;   Here is my Test class header file "Test.hpp"  #pragma once #include <stm32f4xx_hal.h> class Test { public:     static CAN_HandleTypeDef* hcan1;  };   Here is the Test class code "Test.cpp"  #include "Test.h"   void DoSomething() {            HAL_CAN_Receive(Test::hcan1, CAN_FIFO0, 100); }   Here is the main function where I try to assign it a value  int main(void) {    CAN_HandleTypeDef hcan1;   <-- Code is here that uses and populates hcan1 -->   // Initialize libraries     Test::hcan1 = &hcan1; }   When I try to compile I get the "error : undefined reference to `Test::hcan1'"  I am new to cpp, but I know when you declare you have to also define. However, when I try to define it tells me I have multiple declarations.  What's the solution here?

Can anyone explain why following code won't compile? At least on g++ 4.2.4.  And more interesting, why it will compile when I cast MEMBER to int?  #include <vector>  class Foo {   public:       static const int MEMBER = 1;   };  int main(){       vector<int> v;       v.push_back( Foo::MEMBER );       // undefined reference to `Foo::MEMBER'     v.push_back( (int) Foo::MEMBER ); // OK       return 0; }


How do I prove that $GL(n,\mathbb R)$, with the relative topology from $\mathbb R^{n^2}$, is not connected?

let $n\gt1$  be a fixed natural number, $S:=${$A $: $M_n (\mathbb{R})$ be all real matrix,define this meter for all $A=[a_{ij}]$ $B=[b_{ij}]$   $d(A,B)$:=max{|$a_{ij}-b_{ij}$|:i,j=1,2,2...,n} and $GL(n,\mathbb R)$ is set of all $n\times n$ non singular matrix how to prove that $GL(n,\mathbb R)$ is  not connected and open subset of $S$ ?  thanks in advance


In Excel 2013 or 2010, if you put this value in column B1:  2014022701000400   And then this formula in column C1:  =COUNTIF(B1,"2014022701000409")   The formula will evaluate to 1. But the numbers are different: the one in the formula ends with a 9, the one in the cell ends with a zero.  Why does countif match a value it shouldn't?  Is there a workaround available?

I want to add more than 20 digits in an Excel cell.  The current format of the cell is general, it converts the number to an exponential format. I tried with a number format and accounting, but when I enter more than 15 digits it gets converted to 0's.  What are the recommended steps for stopping Excel from converting data to exponential Format for 20 digits when in the general format?     Example: 12345678901234567890   Excel converts it to 1.23457E+19 in general format.  Without using ' before the value, is there any other way to keep value same?


I have read that the  is a psuedo force in a rotating system. But what is the origin and direction  of this force? I searched in Wikipedia but it didn't help me much. So I need a intuition about what causes this force.  Please discuss with examples and with images.

From the  article on Wikipedia, the following with regard to the Coriolis Effect on a rotating sphere:     By setting vn = 0, it can be seen immediately that (for positive φ and ω) a movement due east results in an acceleration due south. Similarly, setting ve = 0, it is seen that a movement due north results in an acceleration due east. In general, observed horizontally, looking along the direction of the movement causing the acceleration, the acceleration always is turned 90° to the right and of the same size regardless of the horizontal orientation.   My intuitive (but possibly incorrect) understanding is that if there are two points, Point A and Point B, at different latitudes in the Northern hemisphere, the Eastward velocities of these points are different because they are at different distances from the Earth's axis of rotation, and this causes the Coriolis effect for a rotating sphere.  If a projectile is fired due North from Point A near the Equator towards Point B near the North Pole, the projectile will start off with the higher Eastward velocity of Point A, and will land to the East of Point B, which is moving East at a slower velocity than the projectile.  Firstly, is that correct?  If that IS correct, that brings me to the quote off Wikipedia. The quote implies that, if a projectile is fired due East, it will experience a Coriolis force to the South. My intuitive explanation based on differences in velocities between origin and destination does not account for a Southwards movement at all, since the Point A and Point B velocities are identical if the points are on the same latitude.  What am I missing? Would a projectile fired due East or due West experience any North or South drift caused by the Coriolis effect (or anything else for that matter)?  Why?


I have a form section that deals with text inputs named options.  By default i'm providing two options. I want to add one more option field when last one is clicked.  <input type='text' name='options[]' class='options'>

 <input type='text' name='options[]' class='options'>   i tried   $(".options:last").click(function(){     $("#options").append("

<input type='text' name='options[]' class='options'>"); })   It does work the first time. But doesn't work after that. It doesn't considers the input that were added by jquery. So it works only when i'm clicking the 2nd option. Not the last one added by jquery. How to do that?

I have a bit of code where I am looping through all the select boxes on a page and binding a .hover event to them to do a bit of twiddling with their width on mouse on/off.  This happens on page ready and works just fine.  The problem I have is that any select boxes I add via Ajax or DOM after the initial loop won't have the event bound.  I have found this plugin (), but before I add another 5k to my pages with a plugin, I want to see if anyone knows a way to do this, either with jQuery directly or by another option.


I have three harddisks. 1. Laptop harddisk ( 720gb ) 2. Two External harddisk ( 1TB each )    These two external hard disk mainly contain movies, songs, games etc. Now, the point is I can't remember which movie is in which external hdd. For that I have to connect the hdd on by one and search.  ( Infact I know there exists duplicate copies of same files as well ).  Is there any software which can index the data in external hdd and later on it can use this data to search? That way I will be able to search in all my hdd without connecting these.      I am using Windows 7.

I have quite a few external hard drives that I want to store off-line, and possibly off-site.  The contents is not saved in a structured manner, however; basically  there's lots of project data for lots of projects.  Is there any software for Windows XP that will catalog all the hard drives, so I can search the catalog, find the files, and get the ID of the disk that has the content?


Say I have the question "How do I solve A". I do a search, and I find that Bob has already posted this exact question. He has also posted an answer, in which he says "I figured out I could avoid the issue by doing X", and marked correct.  However, I can't work around the problem. I need an actual solution to A. I can't post a new question, because then it will be immediately closed as a duplicate. But the old question is not going to get any more answers, because it already has an accepted one.  What am I supposed to do?

It's possible to offer and award bounties of reputation on questions.   What is a bounty? How can I find questions that have a bounty attached? How do I start a bounty? When can I start a bounty? Why is the system requiring me to choose a bounty amount that's higher than the minimum? Can I use Markdown formatting in the bounty remarks? Can I edit the remark? How long is the bounty period? How do I award a bounty? Can I award a bounty to my own answer? Can I award a bounty to an old answer? If I offer a bounty on someone else's question, can I award the bounty to their answer? After awarding the bounty, can I remove it or move it to another answer at a later time? What happens if there's no answer after the bounty period? What happens if I feel my question is still unanswered? What is automatic awarding? Are bounty awards exempt from the 200 points/day reputation limit? How does Community Wiki mode affect bounties? How does user deletion or post dissociation affect bounties? Can I award a bounty to an answer from a deleted user or one where the author was dissociated? Can I offer a second bounty after the first one has expired? Can I raise my bounty? What happens if a bounty question is closed or deleted? Why can't I vote to close or migrate a bounty question? What happens if I delete my account while I have an active bounty? Do I keep an awarded bounty when I delete my answer? What happens if a question where I awarded a bounty later gets deleted or migrated? Can I cancel my bounty? Can I affect / divide / share part of my bounty to two (or more) users? How many outstanding bounties can a single user have?      See also:  in the Help Center


Is there are LaTeX editor which supports camelcase navigation. Jetbrains Webstorm allows camelcase navigation such that a longCamelCaseWrittenWord could be navigated in several steps.  Is such a thing available for any LaTeX/xelatex editors? Or any editor for that matter.  I currently use texstudio with texlive  Edit:  This question is not a duplicate, none of the answers mention anything about navigating through camelcase words.  EDIT:  To elaborate on the problem further... It will go like follows (underscore _ represents the actual cursor position):  _LongCamelCaseWrittenWord -> CTRL+RIGHT_ARROW -> Long_CamelCaseWrittenWord -> CTRL+RIGHT_ARROW -> LongCamel_CaseWrittenWord -> CTRL+RIGHT_ARROW -> LongCamelCase_WrittenWord -> CTRL+RIGHT_ARROW -> LongCamelCaseWritten_Word -> CTRL+RIGHT_ARROW -> LongCamelCaseWrittenWord_   If longCamelCaseWrittenWord is one word, holding Ctrl and tapping → key does not take the cursor to the end of the word; rather, it takes the cursor through, one word at a time.  Hope I make sense.

What editors/IDEs are available for easing the process of writing TeX/LaTeX documents? Please state some useful features like code completion, spell checking, building final DVI or PDF files, etc.  This question is undergoing a systematic refurbishment, see  on Meta. If you’d like to see another editor feature covered here or to take care of an editor that’s not covered yet, share your ideas in that meta question.  List of editors Links to answers.


I have a cylinder (imported from Creo, in .obj), to which I've added a material, steel and rendered it. It looks great.  I've now cut it in half, and want to see a different texture on the cut face, how do I do that in Cycles?  I tried diffent tutorials from that site but doesn't work with Cycles and imported .obj.  Here is an outside view:    Then, when cut, the blueish part should show the cutting tool path leaving marks in the metal.    Marks or scratches could be like .

I have build a basic house but I would like to use different textures for the roof and walls. Here is what I have now.     The brick texture is on the roof when i want it to be a different texture


i have this so far:   public form = [         { val: 'monday', isChecked: false},         { val: 'sunday', isChecked: false } ];   and i want to achieve this:   public form = [         { val: 'monday'},         { val: 'sunday'} ];   how to remove only the 'isChecked' property? i did google it but couldn't find anything.. only how to remove the entire line how to do this?

Say I create an object as follows: let myObject = {   "ircEvent": "PRIVMSG",   "method": "newURI",   "regex": "^http://.*" };  How should I remove the property regex to end up with new myObject as follows? let myObject = {   "ircEvent": "PRIVMSG",   "method": "newURI" };


We have a small office with 9 PCs and a Windows Server. Today one PC, Cypher shows this when trying to log in:     The security database on the server does not have a computer account for this workstation trust relationship.   I tried logging in with the username Cypher from a different PC, its working fine. Please help me in troubleshooting this.

I have a Server 2008 machine called OTTO I recently, by mistake, booted up an old machine, also called OTTO (the hardware was unstable, so the new one was set up to take it's place)  I shut down the old machine, turned it off, and recycled it (it won't ever be back on)  Now, whenever i try to log in to the real OTTO with the domain account (mydomain\Administrator) i get the following error:     The security database on the server does not have a computer account for this workstation   What can I do to fix this?  It doesn't appear in active directory any more I've added it, but I'm guessing this had no effect, due to a different SID  I can log in as the local administrator however


I recently bought D5300, initially I was happy, but after attending some photo walk sessions. I realized most people are using either D7000 or D7100 and some D90.   Now I'm confused whether I did big mistake choosing D5300 as D90 is same price as D5300. D90 seems more professional and better than D5300. I'm feeling bad about my decision.  Am I wrong?

So I decided to start photography. My aim is simple: take photos of my future travels around the world. I want to take good photos.  Well, I made the mistake of buying the gears before even learning about it. I bought a Nikon D5100 camera, and I think it's not good but maybe it's just my skills.  So here it goes my questions:   Where can I learn about gear? Things like a lens, protection and cleaning stuff... Is the Nikon D5100 a good camera? The lens is "18-55mm" What are the good software for editing photos and where to learn how to use them?   Also any estimates of how much time this should take?


I am trying to make a method called Baller(String str, char chr) which should return a boolean if the word contains the character. In the main method I have:   public static void main(String[] args) {     Balling ball= new Balling ();     System.out.println( ball.contains("Baller", 'a'));     System.out.println( ball.contains("Baller", 'A')); }   What I did was this but it did not work:   public boolean contains(String str, char chr ) {     if(str.length() == chr) {         return true;     }     else {         return false;     }        }   What could be the problem?  ANSWER  public boolean contains(String str, char chr ) {          for(int i = 0; i < str.length(); i++)             if(str.charAt(i) == chr)                 return true;         return false;     } }

In Java is there a way to check the condition:  "Does this single character appear at all in string x"  without using a loop?


I currently have a copy of Boccob's Blessed Book, which is fantastic, but I fear that if I lose it somehow (it gets stolen, sucked into the Astral Plane, etc.) I won't be useful as a wizard. I'd like to keep a backup somewhere, but manually copying out the current spellbook is expensive and time consuming.  Is there a spell that can quickly (and hopefully relatively cheaply) create a back-up copy of my spellbook in case things in my party go TPK?

At 1 page per spell level and 100gp ink per page scribing spells gets extremely expensive, and I have to spend money on spells instead of magical items. Assuming aggressive spell research, what's the cheapest way for a Wizard to scribe all of the spells they learn during their career into a spellbook?


I need help with this proof:  $f: X\rightarrow Y$  $C,D\subseteq Y$  $f^{-1}(C \cap D) = f^{-1}(C) \cap f^{-1}(D)$  Thanks.

$f^{-1}(S \cap T) = f^{-1}(S) \cap f^{-1}(T)$  I think I have to show that the LHS is a subset of the RHS and the RHS is a subset of the LHS, but I don't know how to do this exactly.


backport-iwlwifi-dkms v  8324-0ubuntu1 driver seems to work intermittently, freezing every few seconds for up to 30 seconds at a time.  boggles the mind how nobody bothered to test the wifi driver from the world's largest hardware company, on the world's most popular pre-installed with ubuntu computer. Any solutions?

I just upgraded from Ubuntu 18.04 to 20.04 on one of the  machines, and the network performance is abhorrent. Internet speed is very fast from a google speed test (>300Mb/s for both upload and download).     However, whenever I try to browse a website or even run sudo apt update the connection will often time out. My internet is very fast on all other devices and I really don't know how to debug this problem.  sudo lshw -class network -short && nmcli device status    shows  H/W path           Device           Class          Description ============================================================== /0/100/1c.6/0      wlp2s0           network        Wi-Fi 6 AX200 /3                 br-96f5b790e29e  network        Ethernet interface /4                 br-15e76fb81c05  network        Ethernet interface /5                 docker0          network        Ethernet interface  DEVICE           TYPE      STATE         CONNECTION       wlp2s0           wifi      connected     CSA HQ           br-15e76fb81c05  bridge    connected     br-15e76fb81c05  br-96f5b790e29e  bridge    connected     br-96f5b790e29e  docker0          bridge    connected     docker0          p2p-dev-wlp2s0   wifi-p2p  disconnected  --               lo               loopback  unmanaged     --               gpd0             tun       unmanaged     --                Solution:  It seems like this is a pretty common problem, and one without a definitive cause. For me, it was because Ubuntu resets the TLP configuration, and the power management went back to "on". I disabled Wi-Fi power management directly by editing:  sudo nano /etc/NetworkManager/conf.d/default-wifi-powersave-on.conf   Then changed the value from 3 to 2, saved changes and rebooted.  I actually got this solution from Reddit and this worked for my case specifically but it seems like it could be caused by a bunch of other things. Read all the proposed solutions below!


I use the following page as my 'home page' for Stack Exchange  I believe this is the user profile page - but in any case, it seems to be a good page for people to link to when they want to know about my over SE "creds." My question is this - is the new topbar scheduled to go to that page, or is this profile page heading towards deprecation?  If it is scheduled to go, what is the ETA? (Not pushing the schedule, just curious what it would be.)


package javaapplication1;  import java.io.BufferedReader; import java.io.IOException; import java.io.InputStreamReader; import java.util.ArrayList; public class arrrrr {     public static void main(String[] args) throws IOException {         String n,m;        BufferedReader br=new BufferedReader(new InputStreamReader(System.in));         ArrayList l1=new ArrayList();         l1.add("india");         l1.add("chennai");         l1.add("tamilnadu");         l1.add("mumbai");          n=br.readLine();         for(int j=0;j<4;j++)         {             if(n==l1.get(j))             {                 System.out.println("The array location  :"+"l1["+j+"]");             }         }     } }   I want to find a array location. When given input, the program exits automatically. If I assign the value to n, it works perfect. I want to know why the programs exits after giving input.

I've been using the == operator in my program to compare all my strings so far. However, I ran into a bug, changed one of them into .equals() instead, and it fixed the bug.  Is == bad? When should it and should it not be used? What's the difference?


For example if you divide 56 to 14 result is 4 56 / 14 = 4 But when you have 56 and 14 in separate numbers, the sum of their quotients is not same as the above one. 14 / 2 = 7 16 / 2 = 8 8 / 4 = 2 9 / 3 = 3 9 / 3 = 3 Sum of dividends -> (14 + 16 + 8 + 9 +9) = 56 Sum of dividers -> (2 + 2 + 4 + 3 + 3) = 14 Sum of quotients -> (7 + 8 + 2 + 3 + 3) = 23 Here the sum of quotients is 23, NOT 4 Even after divide 23 to count of operation (5 in our case) the result is 4.6 not 4 I am sorry for my bad explanation

I have a fraction I am trying to solve. I know the answer already, as Wolfram says it is $\frac{143}{300}$. The fraction is: $$\frac{5}{12} + \frac{3}{50} = \space ?$$ Please explain why and how your method works.


When taking a flight from Belfast to London do you need to present a photo ID (driving license/passport) and do you go through passport control?  Does this change if you are not a British or Irish national?

Can you travel from Northern Ireland to Britain without a passport or driver's license? In theory there are no border checks but ferries seem to demand photo ID.


I am struggling to set up a static IP address in Ubuntu server 18.04 server LTS. The OS is running in a VirtualBox machine.  What I have done so far:   Created a VM. Added a "NAT and a "Host-only" adapter to the network settings in VirtualBox. Installed Ubuntu Server 18.04 LTS. Configured netplan with static IP settings matching IP of "Host-only adapter. Ran netplan apply Ran netplan --debug generate to check syntax accuracy. (Passed) Rebooted server   My current netplan configuration as described by the netplan documentation:     Ping results in an error message: Temporary failure in name resolution.    Gateway and nameserver addresses are set to the IP of the NAT  adapter in VirtualBox's "Host Network Manager" as per screenshot:    The "Host-only" adapter is added to the VM under adapter 2:    This is configured in netplan as enp0s8.  Changing the configuration back to DHCP using eth0s3 allows name resolution, but the moment I switch back to eth0s8 with a static configuration I am unable to resolve to any domains.  Update: See the result of "route -n"    Please assist.

I'm running VirtualBox with 2 network adapters: standard NAT (enp0s3) and a Host-only Adapter (enp0s8). I use the NAT to access the internet and the Host-only Adapter to SSH in from my local machine.  The box boots up with both adapters enabled, both have IP addresses, everything looking good.    I can SSH into this box over the host-only adapter, no issues there. But I can't get on the internet with it. However, if I disable the host-only adapter, then I can access the internet (but obviously I can no longer SSH into it over the local tunnel).    And finally, here is my netplan yaml config:  # This file describes the network interfaces available on your system # For more information, see netplan(5). network:   version: 2   renderer: networkd ethernets:   enp0s3:     dhcp4: yes     dhcp6: yes   enp0s8:       dhcp4: no     dhcp6: no     addresses: [192.168.52.101/24]     gateway4: 192.168.52.101   Any ideas? It seems like maybe all my outbound traffic is routing through the host-only adapter somehow.  Edit: attaching the output of ip route list in case it helps.  default via 192.168.52.101 dev enp0s8 proto static default via 10.0.2.2 dev enp0s3 proto dhcp src 10.0.2.15 metric 100 10.0.2.0/24 dev enp0s3 proto kernel scope link src 10.0.2.15 10.0.2.2 dev enp0s3 proto dhcp scope link src 10.0.2.15 metric 100 192.168.52.0/24 dev enp0s8 proto kernel scope link src 192.168.52.101


I downloaded the 2.70 release of blender from the blender website (blender.org) and extracted the file to /home. The instructions in the readme say that I need to simply run the executable binary. However when I attempt to open the file nothing happens. I opened a bash and made the file executable, still no dice.  what am I doing wrong here? the terminal just tells me that it cannot execute the binary file...  I do not want the build available from the software center as it is v2.62. I already have this installed and am trying to install the 2.7 build available from the website  Output from the console   cromwell@Terminal:~$ sudo chmod +x /home/cromwell/blender-2.70-linux-glibc211-x86_64/blender [sudo] password for cromwell:  cromwell@Terminal:~$ sudo /home/cromwell/blender-2.70-linux-glibc211-x86_64/blender /home/cromwell/blender-2.70-linux-glibc211-x86_64/blender: 2: /home/cromwell/blender-2.70-linux-glibc211-x86_64/blender: Syntax error: Unterminated quoted string cromwell@Terminal:~$      cromwell@Terminal:/$ ls /home/cromwell/blender-2.70-linux-glibc211-x86_64 2.70                    GPL3-license.txt       LICENSE-bmonofont-i18n.ttf.txt blender                 GPL-license.txt        LICENSE-droidsans.ttf.txt blenderplayer           icons                  Python-license.txt blender-softwaregl      jemalloc-license.txt   readme.html blender-thumbnailer.py  lib copyright.txt           LICENSE-bfont.ttf.txt

is a perfect piece of software with many brilliant changes in each minor release. But often the most recent versions of Ubuntu does not have the latest versions of Blender.


I've been asked to estimate the power consumption of the servers I run for my laboratory. I thought that I'd ask if there was some handy Linux commandline to get the power consumption of the server. It looks like powertop is useful for minimizing power consumption but it does not seem to show information that server A is using B watts.  Is there something buried in the /proc system that would help me out?

Is there a way to return the current watt consumption on the command line? I have found about the powertop program, but have not seen a way to return the Watt consumption as a value to the command line. I'm thinking of some file that I can cat or grep.


I just read about the First and Second Isomorphism Theorems in the book Abstract Algebra by Dummit and Foote. After proving the Second Isomorphism Theorem, they said:        Proposition 13 isn't really important for my question (I guess) but anyway it is the one that states that if $H$ and $K$ are two finite subgroups of $G$ then $|HK|=\dfrac{|H||K|}{|H\cap K|}$.  I didn't understand why $|AB:A|=|B:A\cap B|$. It is obvious if $AB$ is finite because using the Second Isomorphism theorem we have $|AB:B|=|A:A\cap B|$ because $AB/ B \cong A/ A\cap B$. Then $$ |AB:B|=\dfrac{|AB|}{|B|}\quad\textsf{and}\quad|A:A\cap B|=\dfrac{|A|}{|A\cap B|}\\[0.3in] \implies\dfrac{|AB|}{|B|}=\dfrac{|A|}{|A\cap B|}\\[0.3in] \implies\dfrac{|AB|}{|A|}=\dfrac{|B|}{|A\cap B|} $$ which proves that $|AB:A|=|B:A\cap B|$, but this doesn't prove it if $A$ or $B$ is infinite and I believe there's a simple general proof that under the asssumptions in Theorem 18 we get $|AB:A|=|B:A\cap B|$. Could anyone please help me? If the proof is easy (and I guess so because they stated the relation in the book like if it was obvious) then could you give me hints?  Thank you in advance!

Let $H$, $K$ be subgroups of $G$. Prove that $o(HK) = \frac{o(H)o(K)}{o(H \cap K)}$.  I need this theorem to prove something.


While trying to set up some services (OS X 10.10 Yosemite), I accidentally did a sudo launchctl unload -w /System/Library/LaunchDaemons/ and the screen was frozen immediately. Now my Mac doesn't boot any more. The loading bar is half full, and nothing happens.  Is there a way to restore the daemons with some kind of rescue console? Unfortunately, I don't have a working time machine backup, my external hard drive crashed some days ago.  I can still boot into recovery mode, using Cmd+R while booting. I can also access the terminal. I tried a launchctl load -w /System/Library/LaunchDaemons/ but it said ‘Operation already in progress’ for every process.  When trying to load the LaunchDaemons files, I was on the rescue partition. After switching to /Volumes/Macintosh HD/System/Library/LaunchDaemons/ and doing a launchctl load -w /Volumes/Macintosh HD/System/Library/LaunchDaemons/ I got some errors with File already exists, but some other Daemons seem to load.  But I suspect, that they are loaded into the rescue system. So I also tried to use the launchctl file of /Volumes/Macintosh HD/bin/launchctl. But unfortantely, same result, the screen stucks with a half progress bar during startup.  I had a look into the verbose startup (pressing Cmd+V at startup). The last lines, where everything stops are  hfs: mounted Macintosh HD on device root_device XCPM: registered VM Swap Subsystem is ON Darwin Bootstrapper Version 2.0.2: Mon Mar.... boot-args = -v ** /dev/rdisk1 (NO WRITE) ** Root file system    Executing fsck_hfs (versoin hfs-285) Warning: couldn't block sleep during cache update Warning: proceeding w/o DiskArb /dev/disk1 on / (hfs, local, journaled) BootCacheControl: Unable to open /var/db/BootCache.playlist: 2 No such file or directory Bash: /etc/rc.server: No such file or directory USBMSC Identifier (non-unique): 0000000... bash: /etc/rc.installer_cleanup: No such file or directory AppleUSBMiltitouchDriver::checkStatus - received Status Packet, Payload 2: device was reinitialized   I also tried to reinstall Yosemite over my old system (without deleting the filesystem, so my data is still there). Unfortunately, the problem stays the same.  Now I can log in in single-user mode (I had to press an additional Enter). After that, I set the filesystem to read with mount -uw /. Then I load all the daemons with launchctl load -w /System/Library/LaunchDaemons. And then, surprise it loads my Mac's login screen, and I can login.  But when I try to restart, I have to repeat that step to login (which is kinda annoying…). I also tried to load all daemons with launchctl load -w /System/Library/LaunchDaemons when I'm logged in.  Here I get ‘Operation already in progress’. I read something in the single-user mode that the loading of services is not supported. Does this affect the fully loaded OS X too? I'm not sure if I'm still in single-user mode or not. How can I tell OS X to load all the LaunchDaemons on startup?

I ran:  sudo launchctl unload -w /System/Library/LaunchDaemons/   by mistake, now my Mac does not boot... Any idea how to fix that?  OS version: Yosemite.


I have kept a listview in the activity_main_one and the list is filled by an array. Now i have kept a searchview in activity_main_page to search that list. But instead i am getting an error :   Attempt to invoke virtual method 'void com.example.abc.hotelomania.MainActivity1.initList()' on a null object reference  The code of activity_main_one is in MainActivity1.class  MainActivity1.class  public class MainActivity1 extends ActionBarActivity {  String[] items; ArrayList<String> listItems; ArrayAdapter<String> adapter; ListView listView; EditText editText;  protected void onCreate(Bundle savedInstanceState) {     super.onCreate(savedInstanceState);     setContentView(R.layout.activity_main_one);     initList();     items=new String[]{"Canada","China","Japan","USA"};         listItems=new ArrayList<>(Arrays.asList(items)); }  public void initList(){     adapter=new ArrayAdapter<String>(this,             R.layout.list_item, R.id.txtitem, listItems);     listView.setAdapter(adapter); } }   MainPage.class     public class MainPage extends Activity {    MainActivity1 mn;    String[] items;    ArrayList<String> listItems;    ArrayAdapter<String> adapter;    ListView listView;    EditText editText;     @Override    protected void onCreate(Bundle savedInstanceState) {       super.onCreate(savedInstanceState);       setContentView(R.layout.activity_main_page);       items=new String[]{"Canada","China","Japan","USA"};        listItems=new ArrayList<>(Arrays.asList(items));       listView=(ListView)findViewById(R.id.listview);     editText=(EditText)findViewById(R.id.txtsearch);     mn.initList();     editText.addTextChangedListener(new TextWatcher() {     @Override     public void beforeTextChanged(CharSequence s, int start, int count, int after) {     }      @Override     public void onTextChanged(CharSequence s, int start, int before, int count) {        if(s.toString().equals("")){                 // reset listview                 mn.initList();        }        else {                 // perform search                 searchItem(s.toString());        }      }      @Override      public void afterTextChanged(Editable s) {      }   }); }   public void searchItem(String textToSearch){     for(String item:items){         if(!item.contains(textToSearch)){             listItems.remove(item);         }     }     adapter.notifyDataSetChanged();     }

What are Null Pointer Exceptions (java.lang.NullPointerException) and what causes them?  What methods/tools can be used to determine the cause so that you stop the exception from causing the program to terminate prematurely?


I think that it has something to do with Brewster's Angle, but not really sure

Why do polarized sunglasses remove (most) reflections on car windows?  I know that both lenses of polarized sunglasses are polarized in the same direction and I can see that reflections in my own windshield and the windows of other cars appear, disappear, or change depending on how I tilt my head, but why?  Why is the light in those reflections polarized?  edit: And why is most of the light in the various reflections on the interior of my own windshield and various windows/windshields at what seem like a variety of angles all polarized in a sufficiently narrow set of ways as to make polarized sunglasses work?


I was reading the book  and came across the section that tried to interpret ridge regression using singular value decomposition (SVD) of the design matrix, $X$. Specifically, I found the following:  $X=UDV^{T}$, where matrix $U$ is $N\times p$, $V$ is a $p\times p$ orthogonal matrix, and $D$ is a $p\times p$ diagonal matrix.   I am confused because from Wikipedia, the orthogonal matrix has to be a square matrix. In this case matrix $U$ does not qualify. Later I tend to believe that $U$ contains orthogonal columns only, and that results in $U^{T}U=I$, but $UU^{T}\ne I$. This seems to make sense because I found in the book   $X \hat{\beta}=X(X^{T}X)^{-1}X^{T}Y=UU^{T}Y$, and $UU^{T}Y$ should not be equal to $Y$  So my question becomes: are there two versions of SVD I can do? One results in both $U$ and $V$ being orthogonal and square matrix, and the other like this? Or is there anything wrong with my argument?  Any guidance is appreciated.  Update after receiving initial answer:  After reading @BabakP 's answer, I thought testing the algorithm using software is a good idea. So I tried svd function in Matlab. The result shows a square U matrix in dimension NxN, a diagonal matrix D in dimension Nxp, and a square V matrix in dimension pxp. Example below:  A=[ones(10,1) randn(10,1)]; [U,S,V]=svd(A); >> size(U)  ans =  10    10  >> size(S)  ans =  10     2  >> size(V)  ans =   2     2    So does this mean R and Matlab give two different versions?

I am reading the book Elements of Statistical Learning and trying to understand singular value decomposition (SVD). In particular, what is an orthogonal matrix as it relates to SVD?  According to Wikipedia, an orthogonal matrix is a square matrix, the transpose of an which is equal to its inverse.   As this CrossValidated question points out however, in the SVD example discussed in Elements of Statistical Learning, this does not hold.   What am I missing?


If I flip 10 dice, what's the probability I get an Odd sum?? I couldn't do anything with this any help would be really appreciated...

Question:     6 unbiased dice are tossed together. What is the probability that the sum of all the dice is an even number?   I think the answer would be 50%, purely by intuition. However, not sure if this is correct. How should I go about solving such a problem?


Prove for any integer $a$, one of the integers $a$, $a+2$, $a+4$ is divisible by $3$.   I know I would use the division algorithm but I am really confused how to go about this. Step by step explanation please? thank you so much!

Intuitively it's true, but I just can't think of how to say it "properly".  Take for example, my answer to the following question:     Let $p$ denote an odd prime. It is conjectured that there are infinitely many twin primes $p$, $p+2$. Prove that the only prime triple $p$, $p+2$, $p+4$ is the triple $3,\ 5,\ 7$.   And my solution:     Given an odd integer $n$, between the three integers $n$, $n+2$ and $n+4$, one of them must be divisible by $3$... Three possible cases are $n=3k$, $n+2=3k$, and $n+4=3k$. The only such possible $k$ that makes $n$ prime is $k=1$. In this case, given an odd prime $p$, either $p=3$, $p+2=3$, or $p+4=3$. This would imply that $p=3$, $p=1$, or $p=-1$. The only of these three that is prime is $p=3$, therefore the only three evenly distributed primes are $3$, $5$, and $7$.   Is there a "better" way that I can assert that one of the integers is divisible by 3? This feels too weak.


I'm wondering if it's possible to recover files from the Google Chrome cache from an Android phone, specifically, an HTC One S running Android 4.0.2.  I'm trying to recover the stylesheet from a site whose data has been partially lost, and of course this phone is the only device to have accessed it today before the crash.

I am using a Samsung Note 2 (N7100) running on root. I want to know where Chrome for Android saves its cache files. Like on Windows, the cache is located on ..\AppData\Local\Google\Chrome\User Data\Profile 1\Cache. Where is the location for Chrome for Android's cache?


I haven't found anyway to upload a text file when I am asking a question. How can I do so?

I posted a question and a couple of respondents asked for the source code. I could only post portions of the code.  If attachments were allowed I could have uploaded a .zip file with the whole application.  Will this be a feature in SO?


\documentclass{article}  \newcommand*{\DefineRealCommand}[1] {     {The real command name is: #1}     \newcommand*{\#1}{I am the real command.} }  \DefineRealCommand{HelloCommand}  \begin{document} \HelloCommand \end{document}   My purpose is obvious. However, the simplest tex file cannot be compiled.  How should I implement it correctly?

I want to define a macro \create that accept a single mandatory argument from which another new macro is created and named.   The following code snippet may speak clearer what I want to achieve. But the following code cannot be compiled because it is wrong. :-)  \documentclass{article}  \newcommand\create[1]{% \newcommand\#1{My name is #1}}  \begin{document} \create{test} \test \end{document}   How to define a macro to create a new macro with a name passed as its argument?


This question is not about removing a virus. I tried removing the virus using all of the methods recommended by various websites for several hours.  This is about how to uninstall/reinstall IE 11 because I cannot find this virus and have already uninstalled every part of IE11 I can and cannot reinstall it because MS is telling me it is still there.  My internet explorer 11 got hijacked by some sort of malware that made it open up with what looked like a google search for "remove+everything+else". I couldn't find any information about this problem, and the terms make searching difficult.  IE also disappeared from my list of programs in the "uninstall programs" list, and from the programs folder, but appeared as a separate folder at the same level as the programs folder.  I deleted all of the files in the folder except the "en-US" folder that contains .mui language files. I can't figure out how to get rid of this.  I downloaded IE from the MS site and have been trying to install it again, but am being told it is still there. I tried turning IE off using "windows features" and that didn't work. Turning it back on didn't work either.  I also tried the MS advice here:   Nothing about IE appears in the "installed updates"  I've asked for help at the MS support website and the advice I've been given is that I can't uninstall IE from my computer.  I'm pretty sure I did this in the past on the same computer because I didn't use it, and then installed it again when I needed it for work. This also seems like the "automatic bundling" that MS got the antitrust investigation for.  Can I uninstall IE and reinstall it, and if so how?

What should I do if my Windows computer seems to be infected with a virus or malware?  What are the symptoms of an infection? What should I do after noticing an infection? What can I do to get rid of it? how to prevent from infection by malware?   This question comes up frequently, and the suggested solutions are usually the same. This community wiki is an attempt to serve as the definitive, most comprehensive answer possible. Feel free to add your contributions via edits.


I would like to count instances of numbers from a number in a cell. For expample we have the number 78812557839. I need a formula or function to count how many instances of 7,8,1,2,5,3,9 this long number consist of, i.e. 8-3 instances, 5-2,7-2,9-1 etc. Thanks for a tip in this regard.

Feel silly asking this question, but I need some help!   I want to count how many * appear in a range of 5 cells.  The cells will range from 0-7 * each.   I was thinking of using the =COUNTIF(A2:A:6,"*") function, but if the cell has more than one *, it doesn't work. Any idea what function I should use or how I can modify my COUNTIF function to make it work?  Thanks in advance.


I want to write a simple HTML file containing 10 buttons, each button with text from 0 to 9, and when a button is clicked it shows on the console the number corresponding to it. The buttons have to be dynamically created in a javascript file.  Here is my code:  HTML file:  <!DOCTYPE HTML>

     Javascript (test.js) file:  $(document).ready(function () {     DOM_ready(); });  function DOM_ready() {     var maindiv = document.getElementById("maindiv");     var button_create_aux;     for (var i = 0; i < 10; i++) {         button_create_aux = document.createElement('button');         button_create_aux.innerHTML = i; // sets the button text corresponding to its iteration value.          $(button_create_aux).click(function () {             clicked(i);         });          maindiv.appendChild(button_create_aux);     } }  function clicked(num) {     console.log(num); }   The problem is that when I click the buttons in the HTML page, it shows always on the console the last value given to the variable i used in the for loop (in this case, 10).  It looks like that in the line clicked(i); the argument passed is the reference to the variable i, not its value, so I want a way to pass the value that i has at each iteration of the loop.

How would you explain JavaScript closures to someone with a knowledge of the concepts they consist of (for example functions, variables and the like), but does not understand closures themselves?  I have seen  given on Wikipedia, but unfortunately it did not help.


I want to type Arabic text in Photoshop, but the text appears disjointed and the letters do not connect at all. For example محمد appears as م ح م د.  I'm using Photoshop CC 2014 on Windows 8.1 64 bit.

I want to type Arabic text in Photoshop, but the text appears disjointed and the letters do not connect at all. For example محمد appears as م ح م د.   I'm using Photoshop CS6 on OSX Mountain Lion.


I remember reading a book about a teenage girl's father marrying a woman with a son and daughter. The teenage girl soon finds out that something was weird about this new family. And what's fishy is that the woman and her children never age. They were immortal. The son and daughter try to kill the girl in a secret lake during the book sometime. And the book ends with her living with the daughter as she ages and dies like a normal human. Thank you

I read a group of books in 2009. They were all dark, scifi thrillers by the same author - can't remember the name but I'm almost sure it was a woman. It only took me a few hours to read each so they were pretty short.  I read about 5 of them but I can only really remember one. A girl visits somewhere in the south (pretty sure its Louisiana) and there is this family that doesn't age (not vampires) that lives on a swamp. One of the sons is supposed to kill her but they end up falling in love and he helps her escape.  I'm pretty sure one of the other books is about time travel. The only thing I really remember about that one is a picture of an hourglass on the cover.  I know this is a long shot but I really want to find these books.


Player's Handbook page 195:     Two-weapon fighting   When you take the Attack action and attack with a light   melee weapon that you're holding in one hand, you can   use a bonus action to attack with a different light melee   weapon that you're holding in the other hand. You don't   add your ability modifier to the damage of the bonus   attack, unless that modifier is negative.   If either weapon has the thrown property, you   can throw the weapon, instead of making a melee   attack with it.   What if a character:   holds a light weapon in one hand, and nothing in the other hand fights with bare fists (not being a monk)   Can they use the bonus action for a second attack?

I want to make a fighter whose primary weapons are his unarmed attacks using the Tavern Brawler feat. If I take the Two Weapon Fighting style would that work with 2 unarmed strikes? In the weapons table it doesn't have the light property generally required for fighting with two weapons, but they're fists.


What is the difference between running the echo command with argument passed in quotes v/s without quotes? echo -e hi\n    # Output = hin echo -e "hi\n"  # output = hi  (with extra new line) echo -e hi\\n   # output = hi  (with extra new line)  I want to understand the difference between the above 3 commands and how the bash interprets them? P.S - I am trying to explore the echo command with the option -e

If yes, when? Can anyone explain this? echo -e \tr\t\e\\re\e #eete  echo \tr\t\e\\re\e #trte\ree


I’m trying to find records on my grandfather, his name was Adolf Schwartz and he was a Luftwaffe pilot in world war 2. I only have a picture of him. Does anyone know where I could find his records? He was born is 1913 in Rostock, Germany.

Where can I find information on German soldiers from World War I and World War II?   I am curious to find out about my ancestors' role in the wars, i.e. what rank they had, where they where fighting, with whom and anything else.


So I'm guessing I'm missing something fairly simple here but I am trying to read a file line by line, tokenizing the buffer as I go. I have pasted the basics of what I'm trying to do with my code. I have never had issue with strtok, so I'm guessing it has to do with the buffer that I'm using. Any nudges in the right direction? I read that strtok isn't a great option, but it's the only thing I'm familiar with (I suppose I could write my own function) It reads the first token as it's supposed to every time. It doesn't seg fault until I try to find the second token with "strtok(NULL," ");"  I don't know why this was downvoted as a duplicate. Yes, there are answers out there that tell the basics of what I'm trying to do, but I want to understand the problem, not just cut and paste." I'd prefer to know WHY there is a seg fault and why my code is behaving as it does. No need to downvote when I'm asking specific questions not pointed out directly in other posts.  const char *file = "path/to/file/file.txt"; void tokenize();  //Eventually file will be command line opt FILE *open_file(const char *file);  int main(int argc, char *argv[]) {     tokenize(); }  void tokenize() {     FILE *fp;     fp = open_file(file);     char buffer[BUFSIZ];      while(fgets(buffer,BUFSIZ,fp) != NULL)     {         //puts("========================================");         //puts(buffer);         //puts("========================================");          char *data = strdup(buffer);         char *token;         token = strtok(data, " ");         //puts(token);         while(token != NULL)         {             token = strtok(NULL, " ");              puts("++++++++++++++++++++++++++++++++++++++++++++++");             puts(token);             puts("++++++++++++++++++++++++++++++++++++++++++++++");         }     } fclose(fp) }  FILE *open_file(const char *file) {     FILE *fp;     fp = fopen(file, "r");      if(fp == NULL)     {         perror("Error opening file");     }     return fp; }

Java has a convenient split method:  String str = "The quick brown fox"; String[] results = str.split(" ");   Is there an easy way to do this in C++?


I have a SSH Login to a dev computer (used for hosting PHP and Python files). It has vim installed, but a stripped down version of it - it has syntax and whole lot of other stuff disabled .  So, my question is - can I install my own "local" vim without a superuser account?

I've got some troubles when I try to install Vim on Linux while I don't have a root account. The error information is shown below:    How can I solve this? Can I install it in another directory other than /usr/local/bin/vim?


Suppose X and Y are independent and follow uniform distribution (-a,a). How do we find the distribution of X-Y? I tried finding the area with the help of a diagram for cases when x-y>0 and x-y<0. I want to know what is the right way to do it.

I've been wondering about this one for a while; I find it a little weird how abruptly it happens. Basically, why do we need just three uniforms for $Z_n$ to smooth out like it does? And why does the smoothing-out happen so relatively quickly?  $Z_2$:     $Z_3$:    (images shamelessly stolen from John D. Cook's blog: )  Why doesn't it take, say, four uniforms? Or five? Or...?


I attempted this by assuming that a/b + c/d is an integer and coming to a contradiction, but I got stuck. Any hints?

Prove for positive integers $a,b,c$ and $d$  (where $b  \neq 0$ , $d \neq 0$ and $b \neq d$), if $\gcd(a,b) = \gcd(c,d) = 1$, then $\frac{a}{b} + \frac {c}{d}$ is not an integer.  I understand that if $\gcd(a,b)$ and $\gcd(c,d) = 1$, at least one number in each pair is a prime or is $1$. As for after that, I'm totally stumped, could I get some tips, clues, help?


Which of the following is correct? 1.  The center of the small-town called Islip will develop compared to how it is in the present.      The center of small-town called Islip will develop compare to how it is in the present.

The sentence below:     Our method cannot achieve 100 percent accuracy as compared to DART method due to the imprecise modeling.    Why does the sentence above use as compared to? Can we use as compare to instead?


I've just chowned all the computer. I wanted to chown a folder completely so I used the option -R. I forgot that I had used su root before and I was in the folder where everything is (/ isn't it ?)  So, I chowned everything. When I did, there was no problem, I thought mine fixed (my folder was chowned... since everything was..) but when I restarted, ubuntu is dead.  Now that I want to reinstall it, I couldn't install it because when I went to something else (so I could change the partitions), I was unable to delete the partition of the old Ubuntu because it was mounted and being used (or being busy I don't know). It was mounted on /cdrom.  Did I kill my computer? How can I reinstall Ubuntu or Fedora or anything...

I ran this command on my ubuntu 12.04 by mistake:  chown someuser / -R   On RHEL it would be fixed by this command:  rpm --setugids -a   Is there anyway to fix it in ubuntu server?


I have searched to see if there was any post about this but the only thing I could find was  explaining what Meta is, and it still suggests that Meta is supposed to be used for asking questions, not advertising new features or announcing new community managers.  For example, how is  a question?  Why should someone get 1460 (292*5) points for "asking" it?  We then have people getting 530 (53*10) points just for saying congratulations and nothing else:         Furthermore, and perhaps of most importance, why do we only let these free points for people saying things like "congratulations" go to people that already have 10 points reputation (see image below)?

Meta Stack Exchange seems to have different rules and user behavior than the "regular" Stack Exchange sites.  How is it different?    Individual questions answered below:                Related


How do I calculate the determinant of the following $n\times n$ matrices  $$\begin {bmatrix} 0 & 1 & \ldots & 1 \\ 1 & 0 & \ldots & 1 \\ \vdots & \vdots & \ddots & \vdots \\ 1 & 1 & ... & 0 \end {bmatrix}$$  and the same matrix but one of columns replaced only with $1$s?  In the  above matrix all off-diagonal elements are $1$ and diagonal elements are $0$.

This question aims to create an ""  of numerous questions that ask about determinants of specific matrices (I may have missed a few):              The general question of this type is  Let $A$ be a square matrix of rank$~1$, let $I$ the identity matrix of the same size, and $\lambda$ a scalar. What is the determinant of $A+\lambda I$?  A clearly very closely related question is  What is the characteristic polynomial of a matrix $A$ of rank$~1$?


I changed my e-mail from hotmail to gmail during 2013.  I want my Apple id to follow that.  The old email account is still there when I configured my iPhone 5s and tryied to install my icloud and phone settings.  The new phone wants both apple ids. Why?    Question : How do I remove my old Apple-id from my phone?

Recently, I've changed my Apple ID because my old E-mail has been hacked. Now that I set the new one as my apple ID, the old Apple account still appears when I open almost all my apps on my Ipod Touch (4th Gen.), asking for the password to my old Apple ID. When I put in the old password to my old Apple ID, it'll keep asking for it no matter how many times I type it in. How do I fix this while keeping my account secure? Any suggestions would help!


I feel like this is a lot easier than I'm making it, but for some reason I just can't wrap my head around it.  Let's say I'm sampling a voltage, for argument's sake. I want to know the average voltage over a period of time. If I know the number of samples - it's simply:  $$\frac{\sum_0^n s_n}{n}$$  But, what if I'm trying to do it live? It becomes:  $$\frac{1}{T}\int_0^T s(x) dx$$  But in that case, since $T$ is changing, the first sample will be weighted  most heavily, with weight decreasing over time.  Is there an easy way to get the average when I don't know how many samples I have ($n$ or $T$ in this case)? What if the number of samples is significantly large?

Is there a way to incrementally calculate (or estimate) the average of a vector (a set of numbers) without knowing their count in advance?    For example you have a = [4 6 3 9 4 12 4 18] and you want to get an estimate of the average but you don't have all the values at hand so you want to have a running average without keeping all the previous values available.


I'm referring here to situations in which people are seeking to enter or re-enter the US. Here I mean border to include airports. I'm interested not just in what powers the authorities technically have but how these powers are generally applied. Related question about the UK .  By search I mean access the contents of the devices by requiring the owners to turn them on and log in to facebook (etc) accounts.  Presumably also the answer would be different for US citizens vs non-US citizens. I assume that non-US citizens are free to decline access to electronic devices (including social media accounts), but in return border authorities are free to decline entry. In practice how commonly do such situations occur? Is it very rare for tourists to be asked to provide access to electronic devices? What has happened when they refuse to do so?  With regard to US citizens, what happens if they just flat out refuse to unlock any device or to comply in any way?  What about green card holders and any US non-citizens with some residency rights?

I'm travelling to LAX and from some anecdotal horror stories I've seen online and in real life, I worry that customs officers may ask to search my laptop, seize it indefinitely and/or possibly clone the hard drive seeing as I've read that they have power to inspect you and every item when entering/leaving the United States.  I have a significant amount of pornography (all legal) on my laptop which I wonder would I have to declare to the officers as other countries such as Australia make travellers declare on arrival.


I don't understand why the below code doesn't work in c# (.NET Core 1.1).  public interface IChild { }  public interface IParent {     IEnumerable<IChild> Children { get; set; } }  public abstract class ParentBase<TChild> : IParent     where TChild : IChild {     public IEnumerable<TChild> Children {get; set; } }   The error message is      Error CS0738  'ParentBase< TChild>' does not implement interface member 'IParent.Children'. 'ParentBase< TChild>.Children' cannot implement 'IParent.Children' because it does not have the matching return type of 'IEnumerable< IChild>'.   The error message says the IEnumerable< TChild> is not of type IEnumerable< IChild> while I constrain TChild to IChild.  I found two 'easy' ways out of this, but both require rather bad changes in the client code.  I load an entire object tree of these types using ConfigurationSection.Bind() in the client code.  Unwanted solution 1 : Make the parent interface generic  public interface IChild { }  public interface IParent<TChild>     where TChild : IChild {     IEnumerable<TChild> Children { get; set; } }  public abstract class ParentBas<TChild> : IParent<TChild>     where TChild : IChild {     public IEnumerable<TChild> Children {get; set; } }   Unwanted solution 2 :   public interface IChild { }  public interface IParent {     IEnumerable<IChild> Children { get; set; } }  public abstract class ParentBas<TChild> : IParent     where TChild : IChild {     public IEnumerable<IChild> Children {get; set; } }

It seems that a List object cannot be stored in a List variable in C#, and can't even be explicitly cast that way.  List<string> sl = new List<string>(); List<object> ol; ol = sl;   results in Cannot implicitly convert type System.Collections.Generic.List<string> to System.Collections.Generic.List<object>  And then...  List<string> sl = new List<string>(); List<object> ol; ol = (List<object>)sl;   results in Cannot convert type System.Collections.Generic.List<string> to System.Collections.Generic.List<object>  Of course, you can do it by pulling everything out of the string list and putting it back in one at a time, but it is a rather convoluted solution.


I have following symlink in my home directory.  lrwxrwxrwx 1 mtk mtk   43 Aug  8 20:35 tripple-bit -> /media/mtk/study/Collage/docs   I use the symlink to navigate to the docs folder directly. But now, while being in docs folder, I want to move to it's parent directory i.e. /media/mtk/study/Collage in this case.   How can I achieve this?  On giving cd .., it comes back to the home directory and not the parent directory.

When I cd a link, my current path is prefixed with the link's path, rather than the path of the directory the link links to.  E.g.  ~/dirlinks/maths$ ls -l logic lrwxrwxrwx 1 tim tim 71 Jul 27 10:24 logic -> /windows-d/academic discipline/study objects/areas/formal systems/logic  ~/dirlinks/maths$ cd logic ~/dirlinks/maths/logic$ pwd /home/tim/dirlinks/maths/logic  ~/dirlinks/maths/logic$ cd .. ~/dirlinks/maths$   I would like to have my current path changed to the path of the linked dir, so that I can work with the parent dirs of the linked dir as well. Besides ls the link to find out the linked dir, and then cd into it, what are some simpler ways to accomplish that? For example, after cd into a link, how do you change your current path to the path of the linked dir?