Ubuntu 15.10 freezes on viewing YouTube video on full screen using Google Chrome

The case:   Launch Google Chrome. Open YouTube video using the 720p resolution with 60 fps. Make it full screen. Use the "system volume up" hotkey.   After step 3 the video is frozen, but sound continues to play. I can only open console using "CTRL+F1" hotkey and reboot the PC.  Another unstable case, that brings the same result:   Launch Google Chrome. Open YouTube video using the 720p resolution with 60 fps. Make it full screen. Exit full screen.   I'm using Intell HD Graphics with new drivers, but the same case was when I used default Ubuntu's driver.  The Google Chrome version: 49.0.2623.87 (64-bit)  The same situation repeats on three different PCs. These cases do not repeat on Firefox.  Can someone confirm the same bug on his PC? Is there some way to resolve (or temporarily resolve) this problem?


What is the explanation for the use of 'transporter sites' in Star Trek?

In various episodes (such as ) 'transporter sites' appear to be used for transporting people to and from planets.   Is there any particular explanation for this? From other series, and other episodes of the same series, it appears as if site-to-site transport had been perfected by that point and was no longer a formal requirement.    Based on the linked question/answers, seems that the most likely relevant explanation is one of time efficiency?  Within the context of the specific episode, the (large) away team was not in immediate danger. Emergency transporting each individual would have led to a slower total transport time (since locking on each signal and performing the transport would be slower), probably be more energy-expensive, and also riskier (since all calculations for the designated transport site would have had time to be optimized in advance).   [Still seems rather a convenient plot device for the episode, but maybe not as terrible as it seemed on first pass]


Where does backtick and single quote come from when denoting commands e.g. `prog'?

When referring to commands in tutorials, man pages, and articles I see authors use the backtick and single quote in this way:  `./configure' `make'   I believe I have seen gcc denote points of failure during compilation with that sequence. Where does it come from and why do many people use it as a convention for commands to issue?


I have two classes named RA_Shortcode and WPBakeryShortCodesContainer  Now I need a third class RA_ShortcodeContainer inherit both classes..  Any idea how to achieve it.  Thanks in advance


I am trying to make a table with 10 columns.  For some reason, when I add an 11th column, the table no longer compiles.    Below is, I believe, a minimum working example.  Specifically, the table works with    \begin{tabular}{l*9{c}}   but it does not work with   \begin{tabular}{l*10{c}}   Note that the following ONLY compiles because it is the version with the 9 rather than the 10.  I would like for it to have the 10 so I can insert an extra column.  My tables begin as:  \documentclass{article} \usepackage{array} \begin{document}  \begin{tabular}{l*10{c}}  & (1) & (2) & (3) & (4) & (5) & (6) & (7) & (8) & (9) & (10) \\   \end{tabular}  \end{document}


I have this question for a test: A judge is 35% sure that Tim commited burglary. The witness would lie at a probability of 0.25 if Tim is guilty but would tell the truth if Tim is innocent What probability would the witness commit perjury?  Is P(witness commit perjury) = 0.35*0.25 = 0.0875 ?


How can I run command line programs with GUI in UBUNTU Desktop?

I recently installed ubuntu desktop and started its GUI with startx and now I want to run commands like tar lamp etc, how can i do that?


markdown link parsing bug for urls with underscore

compare auto-link:    with [url](url) workaround:    the sole underscore between slashes is enough to trigger this:    and also when you have trailing and leading low-dashes at the same time:    or when you mix them with dashes:    counter-examples:      sorry for abuse of h3 tags, but it was the only wayt to make the post readable.


How to submit an article (for example, on arXiv) without being affiliated to any institution?

The core of the problem is already in the title but I feel as i should add some more details.  I was doing some mathematics and, if there are no logical flaws or mistakes of any other nature (it seems that there are none) I managed to prove some result that, again, if it is proved with no errors, would, I believe, enrich the field in which it belongs.  Of course, I immediately started to think about arXiv.org and I decided that I want to submit an article there, but, when I was reading help section, there stands this, written:     Note: It is a violation of our policies to misrepresent your identity or institutional affiliation. Claimed affiliation should be current in the conventional sense: e.g., physical presence, funding, e-mail address, mention on institutional web pages, etc. Misrepresentation of identity or affiliation, for any reason, is possible grounds for immediate and permanent suspension.   But, as you are aware by now, I do not belong to any institution and as such, am not affiliated with any, I am just an amateur that among all fields thinks about mathematics the most. So, I have stumbled upon this cautious note quoted above and do not know what to do.  So, I decided to write to all of you here to see what can be done in this case of mine. I am not 100% sure that among all sites this is the one most suited for this problem of mine (for example, I could have written this on MO Meta or MSE Meta) but surely I will try to welcome opinions and help, even if they do not resolve this issue that I am faced with.  What should be done?  EDIT: This is not a complete duplicate of the question mentioned in such a way as this one is a duplicate of that one because the body of the question mentioned goes like this:  "Assume you have already completed your undergrad and have been working for a number of years. Does one need to be part of a university or a learning institution to publish papers?"  But, I did not complete my undergrad and I am working for a number of years (independently). so, there are some similiarites but the question is not exactly the same, although answers seem to fit well.


Find all integer solutions to $x^2+y^2+z^2=2xyz$

I am working on some of these types of problems for fun, just want to see a couple solved as examples.


I use Windows since ever, sometimes Linux, sometimes OSX.  Since Windows ME/2000 I have been having this major problem:  I install a fresh copy of Windows, it boots fast as hell, everything goes smoothly. 1 month later, and I have to wait between 10-15 minutes for it to boot up. This has happened to me 10 years ago, and still happens today, with different computers and different versions of the OS.  So I can only come up with this conclusion: or it is the OS which sucks, or it is me.  I really don't know what is going on, . Take a note that even after that video some programs were still booting up.  These are the specs of my current machine, but as I said, different machines, same problem:    My HDD status:      According to this defrag tool I have my HDD 30% fragger, however it spent all night defragging and the furthest it went was 2% complete!!    These are the apps I have installed:    These are my non-Microsoft services:    These are my startup apps:    (I always keep removing that Google Chrome from the startup but he insists going there, sucker... Also I cannot understand why I have two spotifies there, however no spotify opens at bootup as you can see from the video).  Disk performance tests    (repetition just in case)    My device manager showing unknown devices    With Driver Inspector I get this:      PCI-Z findings report      AutoRuns generated file:     Driver Identifier report:      I really dont know what to do... I hate windows for this. My other OS don't have these kind of trouble.


How to instal document class type for use in R studio.

I found a template on writeLaTex.com for optica style articles. I downloaded the optica.cls from the optical website so i could follow that format. Just fooling around to learn more and unfortunately can't get this one at all.         \documentclass[9pt,twocolumn,twoside]{optica}   no matter what the following code is, which should be okay because I'm working with a template that I downloaded with the optica.cls zip folder, the error i receive is "Latex error: file 'optical.cls' not found". but its just sitting in downloads.   You should also know that the file is still in my "downloads folder" and i don't know exactly where to place it  After hours of pain and reading i can't seem to figure this one out on my own.   you might also want to know that i am using RStudio on a Mac OS 10.10 as my PDF compiler if that changes anything.  Thanks in advanced for helping out and taking your time to read.


Space movie with alien probe that makes the crew turn homicidal

Made for TV movie about a spaceship on the edge of the solar system that becomes contaminated by an alien probe. The disease makes the crew try to kill each other. Some of the crew are in life support pods, and are transferred to another ship. I can't remember the title.


How to know if a game concept is "different enough"?

For the past year or so, I've been designing a top-down zombie shooter game. However, after playing a , it's given me inspiration to build a similar game. The graphics would be very similar, though there would be new things like building.  I'm trying to decide if this concept is different enough; there's another , though it has different graphics and some other key differences.  I'm wondering at what point two games become too similar, and how to avoid taking too many ideas from one game (a common problem for me).


Independence between a constant random variable and another random variable.

Intuitively, I understand that if $Y$ is a constant random variable and $X$ is another random variable, then $X$ and $Y$ are independent.   However, I can't make a formal proof because I can't show that their joint density function are the product of two functions that rely only on x's and y's respectively or using similar methods.   (What is the density function of a constant random variable for example?)  Can you give me a hint in order to make a proof?


Unable to book same price ticket as shown in matrix.itasoftware.com

How to book the tickets dispalyed by matrix.itasoftware.com When I search through any ticket booking site, the prices differs a lot. Even the airline website does not show the same.


I have a null pointer exception in this my code. What exactly is a null pointer?  How can I fix this? When I remove the if clauses the NPE will be gone. Why is that?  import java.io.BufferedReader; import java.io.FileReader; import java.io.IOException; import java.util.Scanner;  public class InToPost {    private Stack theStack;    private String input;    private String output = "";    public InToPost(String in) {       input = in;       int stackSize = input.length();       theStack = new Stack(stackSize);    }    public String doTrans() {       for (int j = 0; j < input.length(); j++) {          char ch = input.charAt(j);          switch (ch) {             case '+':              case '-':             gotOper(ch, 1);              break;              case '*':              case '/':             gotOper(ch, 2);              break;              case '(':              theStack.push(ch);             break;             case ')':              gotParen(ch);              break;             default:              output = output + ch;              break;          }       }       while (!theStack.isEmpty()) {          output = output + theStack.pop();       }       System.out.println(output);       return output;     }    public void gotOper(char opThis, int prec1) {       while (!theStack.isEmpty()) {          char opTop = theStack.pop();          if (opTop == '(') {             theStack.push(opTop);             break;          }          else {             int prec2;             if (opTop == '+' || opTop == '-')             prec2 = 1;             else             prec2 = 2;             if (prec2 < prec1) {                 theStack.push(opTop);                break;             }             else             output = output + opTop;          }       }       theStack.push(opThis);    }    public void gotParen(char ch){        while (!theStack.isEmpty()) {          char chx = theStack.pop();          if (chx == '(')           break;           else          output = output + chx;        }    }     class Stack {       private int maxSize;       private char[] stackArray;       private int top;       public Stack(int max) {          maxSize = max;          stackArray = new char[maxSize];          top = -1;       }       public void push(char j) {          stackArray[++top] = j;       }       public char pop() {          return stackArray[top--];       }       public char peek() {          return stackArray[top];       }       public boolean isEmpty() {          return (top == -1);      }    }       public static void main(String[] args)     throws IOException {        BufferedReader read = new BufferedReader (new FileReader("C:\\Users\\Josh\\Desktop\\test.txt"));        String str = "";         String s;         char  in;         int x=0;          stack b=new stack();         char[] store=new char[10];          Scanner insert=new Scanner(System.in);         while ((str=read.readLine())!= null)         {        if (str.contains("print"))        {            System.out.println(str);        }        else if (str.contains("read"))        {             in=insert.next().charAt(0);                 store[x]=in;                  x++;        }         else if (str.contains("="))        {String input = "";       String output;       input = read.readLine();       input = input.replace(";", "");       InToPost theTrans = new InToPost(input);       output = theTrans.doTrans();        System.out.println("Postfix is " + output + '\n');        }    } }}   It said that nullpointerexeption is at line 126. What should I do to my code to fix this?


Hot Questions suggestions showing question I am currently viewing

Okay so I was viewing  question when I noticed that the suggested hot network questions is still suggesting this page.. but I am currently viewing it already.   I mean no offense to anyone, I have the utmost respect for the Stack exchange dev team and it isn't really a big deal and it harms no one I guess.. but maybe redesign hot network questions to show a different question instead?   It's just a little teeny tiny suggestion though.. and if it's like that by design then it's cool. Still love the site. Just trying to be helpful in the smallest way I guess


Two different App centres appearing in Ubuntu 20.04

I just fresh installed Ubuntu 20.04 and during my initial start Ubuntu software centre was not working.  Hence I have reinstalled using the following command:   sudo apt install --reinstall ubuntu-software   But for some reason, there are two software centres are installed. So I have completed removed package and cleared cache and then reinstalled but still same issue.   I just want to get rid of duplicate one - please help me.


Finding the lists of connected indices associated with disjoint mesh elements

Is there a fast way (without looping over all edges/faces/verts) using ops.mesh or bmesh to get the lists of indices associated with mesh islands as shown below? These islands are part of one mesh but are disjoint from each other.    I know how to select the boundaries by running the operator Select boundary Loop or calling bpy.ops.mesh.region_to_loop() but can't find any API calls to return the vert/edge/face indices associated with the individual islands.


How do I install Tor Browser on Ubuntu 17.10?

Having a nightmare with this. Windows 10 laptop running Lubuntu 17.10 in VirtualBox.  I downloaded the file tor-browser-linux64-7.5.3_en-US.tar.xz from the website, it went into my Downloads folder.  I opened the terminal and ran the following command, but it failed:  tar -xvJf tor-browser-linux64-7.5.3_en-US.tar.xz   The error message was:  No such file or directory   So I right-clicked the file and extracted all contents to a folder on Desktop called 'tor. I open that folder and there's an icon called 'Tor Browser Setup', but nothing happens when I double click this.  I tried an alternative method using terminal to but it failed due to a known bug where there is no version file.  3 different ways to install Tor - none of them work!


What do physicists mean when they say "speed of light"?

Does it make sense to say, "The speed of light varies?"  Some may say right off the bat "Yes, it changes as a wave passes through a different medium."  However, I'd like to say no, because when I hear someone say the speed of light, I always think of the constant $c$ (unless the medium is specified to not be a vacuum, but then it isn't $c$ anymore), not the speed of a particular wave.  To me, it makes more sense to say something like, "The speed of a particular wave varies." What is the correct way to state this in the professional world? And in general, when professional physicists say "the speed of light," are they referring to the constant or the actual speed of the wave?


What will happen to Eren's titan powers?

Now that   Eren has died  will each of his three Titan powers randomly go to three different Eldian babies? And what happened the spine creature?


Angular momentum $L$ cannot be completely aligned with $z$-axis

In reading a postulate on angular-momentum coupling, the author made this statement:     In Q.M, the angular momentum cannot be complete aligned with the $z$-axis, otherwise its $x$ and $y$-components would be zero and be known simultaneously.   I don't fully understand this statement.  Is there a better way to gain insight into this statement?


What is azimuthal symmetry? When to use azimuthal symmetry and and how to know whether the problem has azimuthal symmetry or not?


What is better driver for GeForce Gt 220 M?

Are three times that I format my notebook, and I play on Nexuiz online. And I need what is the best driver for target device video GeForce Gt 220M. I use Lubuntu 64 bit:  uname -a Linux mrk 3.16.0-28-generic #38-Ubuntu SMP Fri Dec 12 17:37:40 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux   This is the image that there are 5 options:    I have the driver that is checked how in image and with this question, I want to know, which is the better driver for fast "reproduction video"?  Update: Ok I compile ubuntu-drivers devices and the result is:   ubuntu-drivers devices == /sys/devices/pci0000:00/0000:00:01.0/0000:01:00.0 == vendor   : NVIDIA Corporation modalias : pci:v000010DEd00000654sv00001043sd00002039bc03sc00i00 model    : G96M [GeForce GT 220M] driver   : nvidia-304-updates - distro non-free driver   : nvidia-331-updates - distro non-free driver   : nvidia-331 - distro non-free recommended driver   : xserver-xorg-video-nouveau - distro free builtin driver   : nvidia-304 - distro non-free   Then what is the better because I not understand distro or free or non-free


How can I remove launcher drive icons on 14.04?

Non of the solutions work from . Do someone have any solution for the new, 14.04 release?


Meaning of Conditional sentences with 'should' and 'happen to'

I'm a bit familarized with conditional sentences. But the following sentences with 'should' and 'happen to' are quite confusing too me. They are:   If it should rain, I will stay at home. 2.If it should happen to rain, I'll stay at home   If it happens to rain, I'll stay at home.    What are the meaings of those sentences ? Do they all mean the same ? Thank you a lot in Advance for your answer.


How do I make my PHP login script secure from SQL injection?

I have this PHP login code (that I borrowed from another question on here) - I am easily able to hack it with SQL injection and would like to make it more secure - bit of a newbie to development and would like some assistance! How do I stop these kind of attacks? Thank you!    $userinfo = array(                 'user1'=>'password1',                 'user2'=>'password2'                 );  if(isset($_GET['logout'])) {     $_SESSION['username'] = '';     header('Location:  ' . $_SERVER['PHP_SELF']); }  if(isset($_POST['username'])) {     if($userinfo[$_POST['username']] == $_POST['password']) {         $_SESSION['username'] = $_POST['username'];      }else {         //Invalid Login     } } ?> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"         "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">               <title>Login</title>                   <?php if($_SESSION['username']): ?>
You are logged in as <?=$_SESSION['username']?>

Logout
         <?php endif; ?>         <form name="login" action="" method="post">             Username:  <input type="text" name="username" value="" />
             Password:  <input type="password" name="password" value="" />
             <input type="submit" name="submit" value="Submit" />         </form>


Oracle: Sending query result through email?

I'm extremely new to oracle and I've been tasked to send the result of a certain SELECT query through email and have it regularly scheduled as well.  I've tried looking at other posts as well but I could not make sense of any of it. Can someone show me how to do it in a simple way?


Prove that if A and B are independent, then they are independent conditional to any event C.

So far I have:   P(AnB)=P(a)*P(B) because the two events are independent (given in statement). I know we need to show:  P(AnB|C)=P(A|C)*P(B|C).. Is this right?


Why does printf() not print anything before sleep()?

I'm just learning C with Kernighan and Ritchie's book; I'm in the basics of the fourth chapter (functions stuff). The other day I became curious about the sleep() function, so tried to use it like this:  #include <stdio.h> #include <unistd.h>  int main(void) {   printf(" I like cows.");   sleep(5);   return 0; }   The problem is the output of the program, it looks like it does the sleep() first and then the printf(), in other words, it waits five seconds and then prints the string. So I thought, maybe the program gets to sleep() so fast that it doesn't let printf() have his work done like I want, that is print the string and then sleep.  How can I show the string and then put the program to sleep? The compiler is GCC 3.3.5 (propolice) in OpenBSD 4.3.  PS I don't know how you put here the preprocessor lines correctly.


What happens to the acceleration of a body undergoing constant force?

Here's the problem I have, specifically relating to a rocket in deep space: A rocket burns fuel at a constant rate. Assuming its mass remains constant, what happens to its acceleration? I seem to get two different answers depending on how I solve it (using conservation of energy or conservation of momentum): Conservation of Energy $\frac12mv^2=E_{exhaust}$, where $E_{exhaust}$ varies with time. $v=\sqrt{\frac2mt}$, meaning that velocity varies with $\sqrt t$, meaning that acceleration decreases over time. This also means that depending on your frame of reference's velocity relative to the rocket, the ship's acceleration must change...which makes about 0 sense, Conservation of Momentum $P_{exhaust}=mv$ Meaning that as more fuel is consumed, the velocity of the ship increases too (as $P_{exhaust}$ increases linearly with time, $v$ must also increase linearly with time). I am assuming that the mass of the spaceship is constant. While not quite true, the effect would be negligible and the paradox I'm running into would remain true anyways. Can anyone tell me what I'm doing wrong? The acceleration cannot possibly change depending on where you observe it from, but the acceleration also cannot remain constant as that violates conservation of energy. Thanks in advance!


I got notification from one question. One guy replied to my comment. I clicked it and Stack Exchange app started loading. I clicked the notification in in-app notifications bar and it redirected me where it should: .   But, when I scrolled up, one answer (DourHighArch's) and its comments were blank. They looked like every text on them was just set to white color. It was tall enough, so its content would fit it. (I mean, it was looking like there was some content, but written in white)  Sorry if I made something wrong in this "question", it is first time I report an error and I wasn't sure how do I do that. Also, sorry if duplicate.  Screenshots:      PS: When I re-visited the linked page, everything was correct, like if this was random issue.   App Version: 1.0.85 Device Manufacturer: samsung Device Model: GT-I9305 OS Version: 4.4.4 (I9305XXUFNJ1)


Do the single quote (') and double quote (") work in jQuery like they do in PHP?

Does either the single quote (') or double quote (") have a function where they will parse through the string and replace variables with values? I remember that in PHP the parsing engine will parse through the string and automatically switch out any variables with their values (I don't remember which actually has that effect off the top of my head) so you don't have to type "somestring" + aVariableusing the concatenation  operator. in what I have read through so far on  I haven't been able to find anything about it. Also unless I missed it the post  does not directly cover this information.


I have what I think is a plain text .mp file made on notepad++, it chokes on the first line (whatever I put on the first line). Any ideas? This is MetaPost, version 1.999 (TeX Live 2015/W32TeX) (kpathsea version 6.2.1) (c:/texlive/2015/texmf-dist/metapost/base/mpost.mp (c:/texlive/2015/texmf-dist/metapost/base/plain.mp Preloading the plain mem file, version 1.005) ) (./hyperbola.mp ! Text line contains an invalid character. l.1 ´      ╗┐% Experiment


Cannot get current page ID with VF page in Community

I built a VF page that is used in a community and I am trying to grab the current page id using ApexPages.currentPage().getParameters().get('id'). For some reason, this always returns null. If I use a standard controller with extension, then I can see the value just fine on a page layout outside of the community, only issue is with user in the community pages. Could this be some type of profile setting that is off or is there a different way to grab this value in community? This is a custom object, the record id is shown in the url. I have tried using both a custom controller and an extension with the standard controller from the custom app object. Additional Details: The community walks the user through a series of screens which create the Application record. I am using a workaround right now where I query the last modified Application by the use since this will be the record that is created as the user is walked though the screens. This just seems like a less than optimal workaround.     public class OnlineAppController2{              public String getName(){         App__c app2 = [SELECT ID, Name FROM App__c WHERE ID=: ApexPages.currentPage().getParameters().get('id')];         return app2.Name;     }   }


How do I make default's monospace font smaller?

I thought the task would be so easy I will be able find an answer in a second. As it turned out, I can't make my verb| | look smaller without changing the "global" settings (which isn't what I want). I want to set a scale factor or a font size a bit smaller for the default's (I guess it's CM) typewriter font. How can I do it? \documentclass[10pt]{article} % expect something like this \usepackage[scale=0.9]{monospacefont} \begin{document} Hello \verb|world| \end{document}


Compiler Error: '::main' must return 'int' C++

#include<iostream>  using namespace std; int hour(int h) {     int second;     //second=(h/3600);     if (h>3600)         second=h/3600;     else         second=(h/3600);     return (second); }  int minute(int m) {     int second2;     second2=(   );     return(second2); }  int second(int s) {     int second3;     second3=((s-3600)%60);     return (second3); }  void main() {     int convert;     cout<<"please enter seconed to convert it to hour\b";      cin>>convert;     cout<<"hr : min : sec \n";     cout<<hour(convert)<<":"<<minute(convert)<<":"<<second(convert)<<endl;     system("pause"); }   thanks for the help, this is supposed to convert seconds to minutes to hours but it doesnt seem to work properly.again, sorry if its super simple i just started learning c++ this year and a lot of stuff confuses me


How to fix " Ignoring file ***** as it has an invalid filename extension"

When I try to update my Ubuntu 20.04 LTS from terminal I get this error message, any help please? N: Ignoring file 'rethinkdb.list.save.1' in directory '/etc/apt/sources.list.d/' as it has an invalid filename extension N: Ignoring file 'rethinkdb.list.save.2' in directory '/etc/apt/sources.list.d/' as it has an invalid filename extension E: Type '“deb' is not known on line 1 in source list /etc/apt/sources.list.d/signal-xenial.list E: The list of sources could not be read.


If an orthogonal matrix has determinant -1 then it has -1 as an eigenvalue

I want to show that if a real orthogonal matrix $A$ has determinant $-1$ then $\lambda=-1$ must be an eigenvalue of $A$.  I have proven this in a long-winded way and I was wondering if these is a quick way of seeing it.


Is it possible to get the "intermediate" Java code (or the syntax tree) before having been generated to bytecode

Books about basics of Java told some compiler behaviors. For instance in the book - OCA Oracle Certified Associate Java SE 8 Programmer I Study Guide,   Chapter 1 Java Building Blocks > Creating Objects > Constructors: For most classes, you don’t have to code a constructor—the compiler will supply a do nothing" default constructor for you. Chapter 2 Operators and Statements > Understanding Java Statements > The for Statement > The for-each Statement > Real World Scenario - Comparing for and for-each Loops: Java actually converts the for-each loop into a standard for loop during compilation   ...   All the books only told this, but they never proved it practically with some special tools. So I would like to know is it possible to see such compiler behavior by means of some tools or just programmatically so that we can drill down the explanation from the books?  I tried the javap, which listed only the public instance members with the assembly instructions. I also tried the online decompile tool , which decompiles exactly the original source code other than the intermediate code as those books told.


What is the exact use of the symbols $\partial$, $\delta$ and $\mathrm{d}$ in derivatives in physics? How are they different and when are they used? It would be nice to get that settled once and for all.  $$\frac{\partial y}{\partial x}, \frac{\delta y}{\delta x}, \frac{\mathrm{d} y}{\mathrm{d} x}$$   For what I know, $\mathrm{d}$ is used as a small infinitisemal change (and I guess the straight-up letter $\mathrm{d}$ is usual notation instead of italic $d$, simply to tell the difference from a variable). Of course we also have the big delta $\Delta$ to describe a finite (non-negligible) difference. And I have some vague idea that $\partial$ is used for partial derivatives in case of e.g. three-dimensional variables. Same goes for $\delta$, which I would have sworn was the same as $\partial$ until reading this answer on Math.SE:    Then to make the confusion total I noticed an equation like $\delta Q=\mathrm{d}U+\delta W$ and read in a physics text book that:     The fact that the amount of heat [added between two states] is dependent on the path is indicated by the symbol $\delta$...   So it seems $\delta$ means something more? The text book continues and says that:     a function [like the change in internal energy] is called a state function and its change is indicated by the symbol $\mathrm{d}$...   Here I am unsure of exactly why a $\mathrm d$ refers to a state function.   So to sum it up: down to the bone of it, what is $\delta$, $\partial$ and $\mathrm{d}$ exactly, when we are talking derivatives in physics.  Addition  Especially when reading a mathematical process on a physical equation like this procedure:  $$\delta Q=\mathrm{d}U+p\mathrm{d}V \Rightarrow\\ Q=\Delta U+\int_1^2 p \mathrm{d}V$$  It appears that $\delta$ and $\mathrm{d}$ are the same thing. An integral operation handles it the same way apparently?


Suppose a particle with mass $m_1$ and speed $v_{1i}$ undergoes an elastic collision with stationary particle of mass $m_2$. After the collision, particle of mass $m_1$ moves with speed $v_{1f}$ in a direction of angle $\theta$ above the line it was moving previously. Particle with mass $m_2$ moves with speed $v_{2f}$ in a direction of angle $\phi$ below the line which particle with mass $m_1$ was moving previously. Using equations for conservation of momentum and kinetic energy, how can we prove these two equations  $\frac{v_{1f}}{v_{1i}}=\frac{m_1}{m_1+m_2}[\cos \theta \pm  \sqrt{\cos^2 \theta - \frac{m_1^2-m_2^2}{m_1^2}}]$  and  $\frac{\tan(\theta +\phi)}{\tan(\phi)}=\frac{m_1+m_2}{m_1-m_2}$ ?  EDIT. Here is what I've done:  For the first one, set the $xy$ coordinate system so that the positive direction of the $x$ axis points toward the original path of the particle with mass $m_1$. So we have three equations:  $m_1v_{1i}=m_1v_{1f}\cos \theta + m_2v_{2f} \cos \phi$  $0=m_1v_{1f}\sin \theta - m_2v_{2f}\sin \phi$  $m_1v_{1i}^2=m_1v_{1f}^2+m_2v_{2f}^2$.  From the second one, we get:  $v_{2f}=\frac{m_1v_{1f}\sin \theta}{m_2 \sin \phi}$  Plotting this into third equation, we get  $v_{1i}^2=v_{1f}^2(1+\frac{m_1 \sin^2 \theta}{m_2 \sin^2 \phi})$ (1)  From the first equation, we have  $\cos \phi =\frac{m_1(v_{1i}-v_{1f}\cos \theta)}{m_2v_{2f}}$  which after applying the equation we have for $v_2f$ becomes  $\sin^2 \phi = \frac{1}{1+\frac{(v_{1i}-v_{1f}\cos \theta)^2}{\sin^2 \theta \times v_1f^2}}$  Plotting this into equation (1), gives us an equation in terms of $m_1$, $m_2$, $v_{1f}$, $v_{1i}$ and $\theta$, but it is too far from what I expected.  For the second one, assigning the $xy$ coordinate in a way that the positive direction of the $x$ axis points toward the final path of the particle $m_2$, will give us three equations (two for conservation of linear momentum and one for conservation of kinetic energy), but I don't know what to do next.


I know I can test for an empty string in Bash with -z like so:  if [[ -z $myvar ]]; then do_stuff; fi   but I see a lot of code written like:  if [[ X"" = X"$myvar" ]]; then do_stuff; fi   Is that method more portable? Is it just historical cruft from before the days of -z? Is it for POSIX shells (even though I've seen it used in scripts targeting bash)? Ready for my history/portability lesson.    The same question was asked on Server Fault as  but no one offered an explanation as to why you see code with the X"" stuff.


Can a single spell be targeted by multiple sequential counterspells during the same turn?

Setup  Wizard NPC Zed casts a Fireball at 4th level. PC Alice casts Counterspell at 3rd level to prevent this. Unfortunately she fails the ability check to counter the spell. PC Bob is also within 60 feet of Zed, and has Counterspell prepared and a reaction available.  Question  Can Bob decide, after it's known Alice's Counterspell failed, to cast his own Counterspell?   Further, is the answer at all dependent on the casting time of Fireball (1 action)? e.g. would the answer be different for a 4th level Shield spell, due to the "shorter" casting time?  This question isn't:  "Can a casting of Fireball be targeted by multiple Counterspells?"   Clearly there is nothing to prevent that - the question is whether the multiple Counterspells have to be cast simultaneously, or can be cast one after the other.


Adding/Editing tags - CSS issue on meta.stackexchange.com

See the screen shot:        I guess it's not a feature but another minor bug.


Blender viewport shading render mode not working propperly

Im watching a blender tutorial and they said to select render mode but when I select render mode the model pretty much disappears and the lighting doesn't work and ends up looking like this.


Fake proof, symmetric and transitive relation is already reflexive

Let $R$ be a symmetric, transitive relation. If $(x, y) \in R$ then the symmetric property implies that $(y, x) \in R$. Using the the transitive property upon $(x, y)$ and $(y, x)$ we can conclude $(x, x) \in R$. Is this fair logic or is it flawed?


Why do many people say that virtual particles do not conserve energy?

I've seen this claim made all over the Internet.  It's on Wikipedia.  It's in John Baez's FAQ on virtual particles, it's in many popular books. I've even seen it mentioned offhand in academic papers.  So I assume there must be some truth to it.  And yet, whenever I have looked at textbooks describing how the math of Feynman diagrams works, I just can't see how this could be true.  Am I missing something?  I've spent years searching the internet for an explanation of in what sense energy conservation is violated and yet, I've never seen anything other than vague statements like "because they exist for a short period of time, they can borrow energy from the vacuum".  The rules of Feynman diagrams, as I am familiar with them, guarantee that energy and momentum are conserved at every vertex in the diagram.  As I understand it, this is not just true for external vertices, but for all internal vertices as well, no matter how many loops deep inside you are.  It's true, you integrate the loops over all possible energies and momenta independently, but there is always a delta function in momentum space that forces the sum of the energies of the virtual particles in the loops to add up to exactly the total energy of the incoming or outgoing particles.  So for example, in a photon propagator at 1-loop, you have an electron and a positron in the loop, and both can have any energy, but the sum of their energies must add up to the energy of the photon.  Right??  Or am I missing something?  I have a couple guesses as to what people might mean when they say they think energy is not conserved by virtual particles...  My first guess is that they are ignoring the actual energy of the particle and instead calculating what effective energy it would have if you looked at the mass and momentum of the particle, and then imposed the classical equations of motion on it.  But this is not the energy it has, right?  Because the particle is off-shell!  It's mass is irrelevant, because there is no mass-conservation rule, only an energy-conservation rule.  My second guess is that perhaps they are talking only about vacuum energy diagrams, where you add together loops of virtual particles which have no incoming or outgoing particles at all.  Here there is no delta function that makes the total energy of the virtual particles match the total energy of any incoming or outgoing particles.  But then what do they mean by energy conservation if not "total energy in intermediate states matches total energy in incoming and outgoing states"?  My third guess is that maybe they're talking about configuration-space Feynman diagrams instead of momentum-space diagrams.  Because now the states we're talking about are not energy-eigenstates, you are effectively adding together a sum of diagrams each with a different total energy.  But first, the expected value of energy is conserved at all times.  As is guaranteed by quantum mechanics.  It's only because you're asking about the energy of part of the superposition instead of the whole thing that you get an impartial answer (that's not summed up yet).  And second... isn't the whole idea of a particle (whether real or virtual) a plane wave (or wave packet) that's an energy and momentum eigenstate?  So in what sense is this a sensible way to think about the question at all?  Because I've seen this claim repeated so many times, I am very curious if there is something real behind it, and I'm sure there must be.  But somehow, I have never seen an explanation of where this idea comes from.


I'm totally not an expert, but do you think it could be possible to sell an answer or question on any Stack Exchange in ? There are a lot of question around this: how could it harm Stack Exchange in term of quality, is that in alignment with SE values, etc.


Mail is marked as spam by gmail - no idea, why

I'm using my DSL-Business-connection for a small office. I just installed a Mac Mini Server with mail-support and try to send an email to googlemmil, but this mail is getting marked as spam. This is the header of my mail.  The IP is static and I set up the PTR and SPF.  What else can I do?  Delivered-To: testmailadresse12345-456789-1012345@gmail.com Received: by 10.202.7.193 with SMTP id 184csp174199oih;         Fri, 31 Oct 2014 03:42:56 -0700 (PDT) X-Received: by 10.112.97.135 with SMTP id ea7mr25452495lbb.46.1414752175877;         Fri, 31 Oct 2014 03:42:55 -0700 (PDT) Return-Path: <ich@meinedomain.de> Received: from buero.meinedomain.de (buero.meinedomain.de. [80.147.xx.xxx])         by mx.google.com with ESMTPS id ri5si15978175lbb.115.2014.10.31.03.42.55         for <testmailadresse12345-456789-10@gmail.com>         (version=TLSv1 cipher=RC4-SHA bits=128/128);         Fri, 31 Oct 2014 03:42:55 -0700 (PDT) Received-SPF: pass (google.com: domain of ich@meinedomain.de designates 80.147.xx.xxx as permitted sender) client-ip=80.147.xx.xxx; Authentication-Results: mx.google.com;        spf=pass (google.com: domain of ich@meinedomain.de designates 80.147.xx.xxx as permitted sender) smtp.mail=ich@meinedomain.de Received: from localhost (localhost [127.0.0.1])     by buero.meinedomain.de (Postfix) with ESMTP id C17275486E9     for <testmailadresse12345-456789-10@googlemail.com>; Fri, 31 Oct 2014 11:42:53 +0100 (CET) X-Virus-Scanned: amavisd-new at meinedomain.de Received: from buero.meinedomain.de ([127.0.0.1])     by localhost (buero.meinedomain.de [127.0.0.1]) (amavisd-new, port 10024)     with ESMTP id GUEFHVd811Ma for <testmailadresse12345-456789-10@googlemail.com>;     Fri, 31 Oct 2014 11:42:53 +0100 (CET) Received: from [192.168.2.30] (unknown [192.168.2.30])     by buero.meinedomain.de (Postfix) with ESMTPSA id 9DAF75486DB     for <testmailadresse12345-456789-10@googlemail.com>; Fri, 31 Oct 2014 11:42:53 +0100 (CET) From: =?utf-8?Q?Mein_Name9Fler?= <ich@meinedomain.de> Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Subject: Eine Testemail Message-Id: <F7485894-1928-4091-B857-1E554F4F1FFF@meinedomain.de> Date: Fri, 31 Oct 2014 11:42:52 +0100 To: testmailadresse12345-456789-10@googlemail.com Mime-Version: 1.0 (Mac OS X Mail 8.0 \(1990.1\)) X-Mailer: Apple Mail (2.1990.1)  Hallo,  dies ist eine Testemail. Bitte vergesse den Termin am Sonntag nicht.  Danke Dir!`


I take screenshots very often. I have a dedicated folder for screenshots, but I have to select it each time I take a snapshot with Ubuntu's default screenshots tool. How can I set the default folder to save them to?


I'm writing on a large document with many tables. Rules require me to provide every table as a standalone PDF file as well, so I do this:  In main.tex:  \documentclass{article} \usepackage{standalone} \begin{document} \section{Hello}\label{sec:hello} \input{table} \end{document}   In table.tex  \documentclass[float=true,preview=true]{standalone} \begin{document} \begin{table} \begin{tabular}{c}    A table in section \ref{sec:hello} \end{tabular} \caption{A Table} \end{table} \end{document}   Now, at first glance, this works nicely. However, in the standalone version of the table, the section reference is broken for obvious reasons, since LaTeX doesn't know about the section in the standalone file.   I suppose there is some hack to make this work by making LaTeX use the main.aux when compiling table.tex, but I can't really think of a nice way to handle this. Any suggestions?


Hi I'm a new at Blender can anyone help me?  I'm practicing to create an anime character, I clicked Ctrl + R to make a line to connect on the hand (as picture) but doesn't work, it doesn't go through on the back.  Does anyone know what should I do ? Please help me  I am sorry for my English


How can I check if my computer's powerful enough to run a certain game?

Is there a service that I can use to check if my machine will be able to run a certain game?


As a new user and therefore perhaps "fresh eyed" to the site, I found the following a bit confusing:  In the main menu Questions you find a sub entry called Unanswered.  But in main menu one also find "Unanswered" as it's own entry (and sub-menu "no answers").  Have a look at the image,     Trying a little forth and back I now realize the difference, but perhaps an improvement can be made here simply by choosing some other title (ie. Non-responded or unsolved... ).  Besides from that, excellent pages and site!


Why is the power of $T$ to the fourth in Stefan's law? Any particular reason?

Someone posed a question in front of me that why is the power of t 4 in Stefan's law? please help


How to extend partition with unallocated space?

I have currently cloned my old SSD to a bigger SSD which resulted in that the exact size of the partition table cloned to it, instead of using the full space. I've tried with gparted to extend it but can't seem to do it. I am currently running it on a live Ubuntu usb.     how do I extend?


Why does Jiji not talk at the end of the movie?

In the film, Kiki's Delivery Service, the small black cat that Kiki keeps with her a sort-of familiar is Jiji. Jiji can talk, and is quite incisive, really.  In the middle portion of the film, Kiki loses touch with her powers and Jiji goes silent. Yet, by the end of the film, Kiki's powers are restored, but Jiji remains silent. Why?


c++ Iterate through vector with variable direction

I was wondering if anyone had any thoughts on how to iterate through the elements of a vector (or container) when the direction of the iteration is input.   This was the first thing I could come up with:      std::vector<int> vec = {1, 2, 3, 4};     int direction = 1 // or -1;     int start = direction == 1 ?  0 : (int)arrs.size()-1;     for (int i=start; i<(int)vec.size() && 0<=i; i+=direction) {       // do your stuff     }   Does anyone know any better or nicer way to do this?


How do I make vim highlight math properly in the align environment?

Sorry if this is the wrong place to ask this, I'm new to the site :/  My issue is this: when editing in vim, my syntax file highlights underscores and carets when found in non-math text, which is fine, except vim doesn't recognize that "align" is a math environment. What do I need to do to fix this?


Does anybody here know how magnifying power is defined for a concave mirror? I see these labels "5×" or "3×" on mirrors being sold as shaving mirrors or make-up mirrors. How is this defined?  I know the definition for magnifying glasses, how this is the ratio of the subtended angle in relation to what one can see with the naked eye at a standardised near point of 25 cm.  Is there an industry definition/advertising regulation for mirrors?


District 9: Is there an official explanation why the prawns' mother-ship landed on Earth?

The movie shows the majority of the aliens as unintelligent and seemingly incapable of operating, let alone inventing, a space ship. However, the exosuit/mech was clearly created in their image, weapons are hardcoded to work only with their DNA, and Christopher seems to know exactly how to operate the mother-ship and where their planet is located. Why then were conditions inside the ship so terrible and why did it stop to hover above Earth?    All that seemed to be required to start the ship again was the black fluid that Christopher, his friend, and his son collect. They obtain this from various pieces of alien technology scattered throughout the slums. Of course this technology must have been located inside the ship, so why didn't they simply collect it during the few weeks between the ship's arrival and the hull being cut open by humans? It took them years to collect this small amount, but I imagine it would have been much easier to locate on the ship, and the process would have been much quicker with the other prawns' assistance.    If help was what they hoped to gain on Earth, why didn't they send an emissary instead of just letting the ship hover over Johannesburg? Clearly, it would have been possible since we see the smaller ship detach from the mother-ship.


Where are all my downvotes gone? long time passing

I have an authority problem with my smartphone. It has this thing about downvoting users without asking for my opinion. So I have to check my downvotes.  But there is a discrepancy on my activity page. It says that I have n downvotes, but when I ask for the actual downvotes, to see what was downvoted, and possibly undo my smartphone initiatives, I find out that there are only m actual downvotes where m < n.  So, where have all the n-m downvotes gone. Is it downvotes of questions that were deleted, and thus disappeared, while remaining on my total count?  The fact is that the same is true for upvotes.


My father wants to sell his pc.  Before he does this he wants to delete personal data.  What is the best way to do this without a windows cd? He has a windows cd but it is scratched and does not work.


Is it common to use "where" after "a time" as a relative?

I heard the following comment of Mr. Marco Rubio about Mr. Donald Trump on CBS’s “Face the Nation” in a clip in February 29th AP Radio News:  “There is never gonna be a time where the Republican Party rallies around and says you have to get out or anyone has to get out for purposes of rallying around Donald Trump. Donald Trump is not Republican Conservative. Donald Trump is trying to pull off the biggest scam in American political history.”  I thought I misheard “There is never gonna be a time where –“ for “There is never gonna be a time when –“ at first, because I was in understanding that time should be trailed by “when” as a relative noun or adverb. An English Japanese dictionary at hand (Readers English Japanese Dictionary published by Kenkyusha) provides “where” singly as a relative to refer the ‘place.’ However, my lookup of the following two sources endorsed that I heard it right:  Here is what is never going to happen in this race. There's never going to be a time where the Republican Party rallies around and says you have to get out or anyone has to get out for purposes of rallying around Donald..  “Here is what is never going to happen,” Rubio continued. “There's never going to be a time where the Republican Party rallies around and says you have to get out or anyone has to ...   Is it common, at least not uncommon to use “where” after “time” as a relative?


Travel to Cuba as Dual Citizen (Dutch born-Dutch/US Citizen)

This is actually a question a friend of mine had that I couldn't answer directly and really don't know the laws specifically.  If a person already has dual citizenship (specifically American and Dutch) but was born Dutch are they still required to follow travel restrictions to Cuba?  It is unlawful for an American citizen to travel to Cuba since the trade embargo without being granted permission. Most countries do not require a visa up front when traveling as an American citizen and a visa can easily be obtained upon arrival.  Of course there are ways around this rule but without bending or breaking the law of the US.  Would such a travel under a Dutch passport be detrimental to a US citizenship? Or traveling with the US passport even not a native citizen?


How do you express the common phrases "by an abuse of notation", "abusing the notation", etc. in German without invoking negative connotations? (Without this addendum, I'd have asked at german.se.) "Durch/Unter Missbrauch der Schreibweise/Notation" looks horrible to me, in particular, due to sexual allegations of the word "Missbrauch". How do they (e.g., folks such as Harro Heuser, or, from the further past, Edmund Landau, David Hilbert, Emmy Noether, von Neumann, etc.) typically write it in German books on mathematical subjects?  An example of the original sentence:     Abusing the notation, we write $ℚ⊂ℝ$, viewing the rational numbers as particular real numbers.   Related:


how to identify if raid1 or raid mirror configure on OS disk

we want to verify if raid1 is configured on out linux machine  so we found the answer on -   but from the output -  how we can be sure that raid1 is configured?  and how to understand it from the command: dmesg | grep raid  when non raid , and when raid1 is configured ?


How to take a screw out of my laptop casing that has no head?

I was trying to take apart my laptop to replace the DC jack for it, and the screw inside of the casing was very hard to remove, so after messing with it for about 15 minutes, the plus sign (or the head) was erased and became more of a circular square. Is there any way to take it out without breaking anything?


How to use exception handling with initializer-list with constructor?

I used to use initialization list through Constructor and everything went well. But now I need some exception handling in my class.  So here is some sample code:  1- Without exception handling  class CVector{     public:         CVector(const int);     protected:         int* pInt;         int size; };  CVector::CVector(const int sz) :     pInt{ new int[sz]}, size{ sz}{  }   The constructor above doesn't check whether an invalid sized is passed, or new failed...  Now I edited the constructor to handle exceptions:  2- With exception handling:  CVector::CVector(const int sz){     size = sz;     if(size <=0 )         throw; // some exception object      pInt = new int[sz];     if(nullptr == pInt)         throw; // some memory exception }    The problem now: Are they exclusive? - I mean How to mix exception handling with initialization-list through Constructor?


How to integrate a paper where I am third author, but did a lot of work, into my master's thesis?

I am writing my thesis currently and I want to include papers that I am included on as an author.  I will have a couple papers where I am 1st author, but there is one where I am third but did a lot of the work.  How do I go about integrating it into my thesis?  Can I copy/paste most of the text still or do I need to rewrite it?  I don't want to plagiarize but don't want to rewrite it if I don't have to.


Members must use their own cards ,or, members must use their own card?

Which is correct? Members must use their own cards, or, members must use their own card?


How to resize tikzcd figure to fit in beamer frame?

I am preparing my slides using beamer. My working code is as follows: \documentclass{beamer}  \usepackage{pgf,tikz,tikz-cd}  \usetikzlibrary{calc, arrows, backgrounds, fit, positioning, quotes, shapes, shapes.geometric, intersections, decorations.pathreplacing}  \begin{document}     \begin{frame}[fragile]         \frametitle{Introduction}         \framesubtitle{Background and motivation}         \begin{figure}[h!]             \label{figure:maptoR}             \begin{center}                 \[                 \begin{tikzcd}[cells={nodes={circle,align=center,inner sep=1pt,                             text width={width("$\mathrm{Row}_i\times\mathrm{Row}_i$")},draw,                             path picture={\path[ball color=gray!60,fill opacity=0.4]                                 (path picture bounding box.center)                                  circle[radius={width("$\mathrm{Row}_i\times\mathrm{Row}_i$")*1pt}];                     }}},                     bend angle=50,every arrow/.append style={-stealth,bend left},                     every label/.append style={font=\normalsize},                     sep=small]                     M_n\times M_n \arrow[r,"R_i"]                     \arrow[rrrr,bend right=25,"\succ",start anchor=-60,end anchor=-120]                     &  \mathrm{Row}_i\times \mathrm{Row}_i \arrow[r,"\omega_{ij}"]                     & M_n \arrow[r,"\omega_{ij}'"]                     & M_{1\times n} \arrow[r,"\omega^*"l]                     & \mathbb{R}\\                 \end{tikzcd}                 \]\caption{Composition of function $\succ$.}             \end{center}         \end{figure}     \end{frame} \end{document}  which produces:  What do I need to do so that the figure fit in the frame nicely? Please help.


GPT partition table warning message during install of ubuntu

/dev/sda contains GPT signatures indicating that it has a GPT table. However, it has a fake msdos partition table as it should. Perhaps it was corrupted? Is this a GPT partition table?  So, that's the error message and this is during my first OS install of Ubuntu. Can close the message box. Can't click yes and can't click no. What do I do?


Can I use Ctrl+Shift for changing languages? I can't set this hotkey for changing keyboard languages.  At this moment Alt+Shift switch languages, but I can't see this hotkey in keyboard hotkeys list or in   gsettings list-recursively  org.gnome.desktop.wm.keybindings | sort | more   output.


Set of commuting Matrices $\Rightarrow $ Common Eigenvector

I am trying to prove that if we have an arbitrary set of commuting matrices in $M_n(\mathbb C)$ then they have a common eigenvector.  Well, if we have only 2 matrices, the answer is easy and it has been already answered here:  (acutally in this case we find a common eigenbasis, in case they are diagonalizable)  For the general case of an arbitrary set I am trying to find a subspace of $M_n(\mathbb C) $ which contains that arbitrary set of commuting matrices. Then Prove the statement for the basis ( is going to have  $\leq n^2$ elements) by induction.   So if $Y $ is that arbitary set, take $span(Y)$ which has dimension $\leq n^2$ so find a basis $Y_1 ,Y_2,\dots Y_k,k\leq n^2$  Then prove by induction that we can find a common eigenvector $v\neq 0 $ for the vectors of the basis. So, if $A\in Y\Rightarrow $ $$A=\sum_{m=1}^k a_mY_m\Rightarrow Av=\sum_{m=1}^k a_mY_mv\Rightarrow$$ $$Av=\sum_{m=1}^k \left( a_m\lambda_m\right) v$$ i.e. $v$ is an eigenvector for $A$.  What do you think about that solution?  P.S. I asked if you could check my solution. I have already seen the post which is supposed to answer my question but I am not satisfied ( see comment).


Using the "start" command with parameters passed to the started program

I have a Virtual Machine in Virtual PC 2007.  To start it from the desktop, I have the following command in a batch file:  "c:\program files\Microsoft Virtual PC\Virtual PC.exe" -pc "MY-PC" -launch   But that leaves a dos prompt on the host machine until the virtual machine shuts down, and I exit out of the Virtual PC console.  That's annoying.  So I changed my command to use the START command, instead:  start "c:\program files\Microsoft Virtual PC\Virtual PC.exe" -pc MY-PC -launch   But it chokes on the parameters passed into Virtual PC.  START /? indicates that parameters do indeed go in that location.  Has anyone used START to launch a program with multiple command-line arguments?


I was looking for a book to complement the lecture notes of the course for a more intuitive approach to the subject and full of examples (mathematical), because the handouts seem only a bunch of mathematical definitions. I've read the suggested books in the question , but that's not what I'm looking for. In fact, they either deal with a few subjects, or have too physical examples. I was looking for more geometric examples. The program of our course (the third year physics study) is this:   Groups and axioms:   Axioms of the group. Finished and infinite group. Examples. SN groups. Continuous and discreet group.  Abelian and non-Abelian group. Unchanged subgroups and subgroups.  Isomorphism and homomorphism between groups. Simple and semi-simple groups.   Lie groups and Lie algebra:   Lie groups and Lie algebra. Structure constant. Examples.   Representation theory:   Representation of the group. Irreducible representations. Schur's lemma. Characters.   Basic group / groups of homotopies:   Fundamental group and groups of general homotopies. Exact succession.   SU Group (2), SO (3) and SU (3):   Groups and algebra of SU (2), SO (3) and SU (3). Isospin. Spin and rotations in R3. Wigner-Eckart theorem.  Tableaux of Young   Representations of the SO group (4), of the Lorentz SO group (3.1)   and Poincaré: Group and algebra of SO (4). Vectors of Lenz and hydrogen atom. Lorentz Group.   Roots and weights; Dynkin diagrams:   Vectors of roots and weights. Dynkin diagrams and the classification of compact groups.


We have a 3 hour layover in Frankfurt, on the way to Rome. My husband wants to leave to get a bite to eat and see a small part of the city. Will we have enough time? Is this a smart idea?


Where does the component of the centripetal force in circular motion come from?

If a man is standing on the equator of a non-rotating planet then the normal force is equal and opposite to the weight force.   If the planet now starts rotating then there would be a net (centripetal) force directed towards the centre equal to $mg-N$. If the planet continued to increase its rotational speed then eventually the centripetal force would equal the weight force and the man would be in orbit (on the surface of the planet). My question is where does this net force stem from? Is the centripetal force a part of the weight force or is the centripetal force opposing and reducing the normal force? If it is opposing and reducing the normal force then wouldn't this require an actual force to do so?


Calculate $Pr(X \ge 0, Y \ge 0)$ where $X, Y \sim N(0,1)$ and their correlation is 1/2

I've been working on this problem and got stuck.  Assume that X and Y have joint normal distribution, that each $X, Y \sim N(0,1)$, and that their correlation is $\frac{1}{2}$. Calculate $Pr(X \ge 0, Y \ge 0)$.  I know that I can rewrite (X,Y) in terms of independent normal variables (W,T) as follows  $$    \begin{bmatrix}    X\\    Y\\    \end{bmatrix} =    \begin{bmatrix}    1 & 0\\    \rho & \sqrt{1-\rho^2}\\    \end{bmatrix}    \begin{bmatrix}    X\\    Z\\    \end{bmatrix}    $$ where $\rho$ is the correlation. This has left me with $$ X=X\\ Y=\frac{1}{2}X + Z\sqrt{\frac{3}{4}} $$ And so I have $$ Pr(X \ge 0, Y \ge 0) = Pr(X \ge 0, \frac{1}{2}X + Z\sqrt{\frac{3}{4}} \ge 0) $$ So I just realized that the T variable I had before was superfluous, so I removed it. I am wondering from here if it would make sense to put this: $$ Pr(X \ge 0, \frac{1}{2}X + Z\sqrt{\frac{3}{4}} \ge 0)=Pr(X \ge 0, Z\sqrt{\frac{3}{4}} \ge -\frac{1}{2}X) $$ Still not sure how to proceed from here. Maybe simplify to $$ Pr(X \ge 0, \frac{1}{2}X + Z\sqrt{\frac{3}{4}} \ge 0)=Pr(X \ge 0,  Z\sqrt{\frac{3}{4}} \ge 0) $$ Since we are looking for $Pr(X \ge 0)$ anyway?


How to secure Monit web interface with SSL?

I have an Ubuntu 20.04 server and I installed Monit. I want to secure the web interface. I followed the following instructions :  $ cd /var/certs $ sudo openssl req -new -x509 -days 365 -nodes -config ./monit.cnf -out /var/certs/monit.pem -keyout /var/certs/monit.pem $ sudo openssl gendh 512 >> /var/certs/monit.pem $ sudo openssl x509 -subject -dates -fingerprint -noout -in /var/certs/monit.pem $ sudo chmod 700 /var/certs/monit.pem  1) When I run the following command I got an error. Yet I do it with "sudo". Why is it not working ? ubuntu@myserver /var/certs $ sudo openssl gendh 512 >> /var/certs/monit.pem -bash: /var/certs/monit.pem: Permission denied  2) It says in the address bar "not secure", yet I am using HTTPS. Is this normal ?  I would also like to know what these 2 command lines are for : $ sudo openssl gendh 512 >> /var/certs/monit.pem $ sudo openssl x509 -subject -dates -fingerprint -noout -in /var/certs/monit.pem


Since Enter posts a comment, it would be nice to be able to hit Esc to abandon a comment or editing it.


let's see an example:  let object = {     a: {         b: 1     } };   Now I want to modify the object.a from x:  s.1)  let x = object.a; x = 2;  console.log(object);   result:   [object Object] {   a: [object Object] {     b: 1   } }   s.2   let x = object.a; x = { b: 2 };  console.log(object);   result:  [object Object] {   a: [object Object] {     b: 1   } }   s.3  let x = object.a; x.b = 2; x.c = 2;  console.log(object);   result:  [object Object] {   a: [object Object] {     b: 2,     c: 2   } }   Why s.1 and s.2 fail?


What is the meaning of "int(a[::-1])" in Python?

I cannot understand this. I have seen this in people's code. But cannot figure out what it does. This is in Python.  str(int(a[::-1]))


Can citizens from the trusted districts move to live in the Capitol?

I understand the other districts can't, because during the dark wars the Capitol thinks those districts were the rebels (and yes, even Districts 1 and 2 had rebels). But would citizens of District 1 and 2, who the Capitol citizens or particularly Snow knows quite well, be not allowed to move to the Capitol and/or participate in Snow's rebel punishment known as "the Hunger Games"?


New mac user here (Linux background). I'm running macOS Catalina (Beta5). I've noticed there are 5 volumes in my main disk container. One is mounted at /, that I understand, it's the system, another is /System/Volumes/Data, which I tough it would be the Linux /home, but it's not, so what it it?  Also what are the other two unmounted volumes? One might be the recovery one, but the other? Thanks!


How can I only show three digists of the double value

I have double values like 0.0345333 or 1.0897777 and I want to convert them to 0.034 and 1.089 in Java?  How can I do it?  I want to convert the values, not print them since I need it for calculation.  I find the following way but I am looking for simple way. double score=(tff* idf); DecimalFormat df = new DecimalFormat("#.###"); p.score=Double.parseDouble(df.format(score));


Normally a professor is paid for eight to nine months each academic year for teaching several courses in the period. However, if a professor gets a research grant, he can support himself by the grant in the summer months, or teach fewer courses.  I'd like to know how it works exactly. Let's say, if a professor only teaches half of the normal load of courses, then he will receive half of his normal salary from the department and the rest is covered by the grant, right? If the grant is large enough, can he choose not to teach any course without loss of pay?


How are votes by users with less than 15 rep. recorded?

When I try to upvote a question, it says that "votes from users with less than 15 reputation are recorded, but do not change the publicly displayed score." How are they recorded? Do they actually do anything?


Travel to USA with visa in expiring passport

I am Egyptian but living in Taiwan. I am travelling to USA for two weeks only and returning back to Taiwan. I am using two passports: Passport 1 has less than six months left to expiry but contains the valid USA visa, Passport 2 is a new one.  Does it pose any problem for me?


computer science student here, haven't done much in GIS, just trying to finish a project for a class.  What I have is a CSV of origin/destination points as co-ordinates (longitude and latitude)  what I want to do is to create a heatmap of the routes, similar to a traffic heatmap that you see on google maps.   ie. I want more frequented pieces of road to be red, and less frequented to be green. not just the more frequented origins/destinations, thats trivial.  what's the easiest way to do this? I have experience with python, java and matlab.   I was wondering if there is a free software that could do it straight from the CSV? or maybe a python module?  edit: since im using just a CSV of origin/destination points, I believe it is not a duplicate, since the referenced post used GPS tracks, which is quite different information.


How do I repair armor with similar armor in fallout new vegas?

I searched everywhere for methods on repairing armor and people said that you could ask people to repair armor for you but it's too expensive. Then I saw people saying you could "cannibalize" armor, and by that I mean using similar armor to repair the primary armor set. But I don't see the option to do so. I went to my workbench but it didn't say anything about repairing my armor.


I'm trying to compile my bib references with natbib and \bibliographystyle{nature}. To my uttermost surprise BibTeX reports that some of the entries have an empty title, while IMHO the title is not empty, e.g., on the following bibliographic entries:  @INPROCEEDINGS{WuWangZhaoMa, author={Wu Kehe and Wang Zhuo and Zhao Xing and Ma Gang}, booktitle={Advanced Computer Theory and Engineering (ICACTE), 2010 3rd International Conference on}, title={Design and implementation of the monitoring system for EJB applications based on interceptors}, year={2010}, month=aug, volume={4}, pages={V4-5--V4-9}, ISSN={2154-7491}, location = {Chengdu, China} }   and  @inproceedings{DBLP:conf/sigdoc/TilleyH03,   author    = {Scott R. Tilley and                Shihong Huang},   title     = "A qualitative assessment of the efficacy of {UML} diagrams                as a form of graphical documentation in aiding program understanding",   booktitle = {SIGDOC},   year      = {2003},   pages     = {184--191},   ee        = {http://doi.acm.org/10.1145/944868.944908},   crossref  = {DBLP:conf/sigdoc/2003},   bibsource = {DBLP, http://dblp.uni-trier.de} } @proceedings{DBLP:conf/sigdoc/2003,   editor    = {Susan B. Jones and                David G. Novick},   title     = {Proceedings of the 21st annual international conference                on Documentation, SIGDOC 2003, San Francisco, CA, USA, October                12-15, 2003},   booktitle = {SIGDOC},   publisher = {ACM},   year      = {2003},   isbn      = {1-58113-696-X},   bibsource = {DBLP, http://dblp.uni-trier.de} }


an error with defining a template class constructor in cpp file

I defined a constructor of Bag class, but compiler gave me an error for the definition. I'm using CLion on Mac. I have no idea what is wrong. I'm thinking it's probably about CLion or compiler problem. Any help would be appreciated!  Here's the error message from compiler  /Users/username/Desktop/projects/bag/Bag.cpp:8:1: error: 'Bag' is not a class, namespace, or enumeration Bag::Bag() : data{new T[CAPACITY]}, size{0} {} ^ /Users/username/Desktop/projects/bag/Bag.h:15:7: note: 'Bag' declared here class Bag{   Here's declaration of Bag class which is in 'Bag.h' file.  #ifndef BAG_BAG_H #define BAG_BAG_H  #include <vector> #include <cstdlib> using namespace std;  static const size_t CAPACITY = 100;  template <class T> class Bag{ public:     Bag();      size_t size() const;     bool empty();     bool check(const T& item);      void resize(size_t new_size);     void clear();     void remove(const T& item);     void add(T item);     void print();  private:     T* data;     size_t _size; };   #endif //BAG_BAG_H    Here's the definitions of Bag class which is in 'Bag.cpp' file.   #include "Bag.h"  template <class T> Bag::Bag() : data{new T[CAPACITY]}, size{0} {}   ... other definitions   Here's main.cpp  #include <iostream> #include "Bag.h"  int main() {     Bag<int> temp();     temp().add(1);     temp().print();      cout << endl;      return 0; }


Is it OK to close an on-topic question from a bad user?

Imagine the following scenario. A user gets suspended (fairly) on some site, then creates a new account and asks an on-topic question (the new account asks the question and does nothing else). The IP address, writing style or some other information allow to identify the new account as a sockpuppet beyond reasonable doubt. Is it OK for the moderators to delete or close the on-topic question then, purely because of the past actions of the person who asked it?  Since MSE is not about discussion, I am looking for a generally agreed upon policy. My personal opinion is that it is not OK because Stack Exchange is about content, not about people, and on-topic questions should be welcomed from any source.


Why is the moment of inertia the integral of the "second moment"? What is the derivation for the formula?

In my dynamics textbook, the introduction to the  reads:      "Moment of inertia is the integral of the "second moment" about an axis of all the elements of mass dm which compose the body. For instance, the body's moment of inertia about the z axis is:"    $$I=\int_{m} r^2  \mathrm{d}m$$   Where does this formula come from and what is the derivation for it?


By the side of / by / beside / next to / close to

I was sitting **next to / by / by the side of / beside / close to ** my friend.  As a learner all of the preparations means near or close to to me.


Should SMOTE oversampling be done before or after holdout validation's training/testing split?

Originally, without SMOTE, my ML learning steps go like this:   Feature vectorization  split data into X_train, X_test, y_train, and y_test  use X_train and y_train for machine learning  predict/test on X_test and y_test   I think there are two spots I could inject my SMOTE codes. One is I can inject it before the train/test data split, so that oversampling of minority class takes place in both training and testing data. Like so:   Feature vectorization  SMOTE oversampling  split data into X_train, X_test, y_train, and y_test  use X_train and y_train for machine learning  predict/test on X_test and y_test   I got very good results using the above steps, but I wonder if SMOTE should only be done in the training data, but test on the original testing data set since the latter reflects the real-world distribution of majority and minority class samples. Like so:   Feature vectorization  split data into X_train, X_test, y_train, and y_test  SMOTE done only on X_train and y_train  use X_train_SMOTE and y_train_SMOTE for machine learning  predict/test on X_test and y_test   Which is a better implementation of SMOTE?


This is a quote that I got from one of our customers: "I'm proud to be part of an elite group of individuals that genuinely loves going to work on a Monday morning!"


Let R=End(V) be the ring of all linear endomorphisms of an infinite dimension complex vector space V with countable basis $\{e_{1},e_{2},...\}$ . Prove that R and RxR are isomorphic as left R-modules.


Why does null objects cause NullPointerException

I'm currently working on making a basic TextEditor in Java FX but I'm having a bit of difficulty. I am trying to incorporate the MVC development style and using any object of type Document in the model when working with the editor although when I try to save the area of the contents I get a NullPointException when I try set any variables in the when the Document is initialised to null. It works fine with it set to a new document will null parameters though...  Any information on the reasoning for this would be really appreciated!  Edit:   Sorry for the ambiguity, I was meaning in terms of initialising an object that I am trying to then set variables for. I had it initialised to simply null:   Document workingDocument = null    When I changed this to:   Document workingDocument = new Document(null, null);   I understand what creating a new Documents does in terms of memory but not what simply initialising it to null does...


What is proportion of variance explained in PCA?

Can anyone explain about the proportion of variance explained in PCA and why it is important in the analysis of PCA?


Is there anything like Nanny that's still being developed?

Just installed Ubuntu 12.04 LTS for my kids to use. I am concerned about how long they use the PC each day.  Is anyone aware of any parental time-limit apps, like Gnome Nanny or timekpr, that are still active and will work with Precise?  I've found SelfControl but I'm looking for more than just internet access restriction.  For now, I am acting as the 'time keeper' until I find a software solution but thanks for any ideas.   Thank you.


for i in {1..40} do     echo $i done   I got  {1..40}   and I would like to have something like  1 2 3 and so on   so I can use the variable i inside a command's parameter.


The plural form of physical units are always confusing me. I asked some senior students, some of them said we need to use plural form of units but some said units are always singular.   For example, 1 meter is 1 meter. But it is 3 times, should it be 3 meters? I know that if we use the abbreviation form, no plural form, i.e. 3m. But if we use 'meter', for the case like 0.04 meter, should it be 0.04 meter or 0.04 meters? I think we should use 0.04 meter because it is less than or equal to 1.  The last question I have is about foot and feet, when the magnitude is less than or equal to 1, I should use foot, otherwise, use feet instead, is that right?


What happens if Uzumaki and Uchiha married each other? Will their offspring have Rinnegan?

Ok, I'm wondering . If Uchiha and Uzumaki have a child together, there are possibility that the child inherited Sharingan right? Since Uzumaki have ties with Senju then, can the child awaken Rinnegan?


I use vim and vim plugins for visual studio when writing C++. Often, I find myself wanting to search for a string within a function, for example every call to object->public_member.memberfunc().   I know vim offers a convenient way to search for a single word, by pressing * and #, and it can also search for typed strings using the ubiquitous slash / command. When trying to search for all the instances of a longer string like the one above, it takes a while to re-type after /.   Is there a way to search for selection? For example, highlight with v, then copy with y, is there a way to paste after /? Is there an easier shortcut?


How to remove uninstalled snaps from cache?

When I install a snap with snap install <SNAPNAME> then it is being downloaded and mounted. When I remove it with snap remove <SNAPNAME> then 'everything' is being deleted like the snap, user settings dependecies and so on. But when I re-install the snap after removing it, it has no download time so the snap must be stored somewhere. How can I clear the cache of snapd with all uninstalled snaps?


Answers that doesn't provide more help than existing ones

For example, a user asked a question.   Before long, an answer comes up, attempting to answer the question. Now, i've seen a lot of times that later, after about 15, 30 minutes, other answers popped out and basically, proposing the same solution as the first answer.   For example, take a look at   The first answer proposed the use of collections.Counter. In the next minutes, another 3 pops up and propose the same thing. And after half of an hour, two similar answers were added.  Although my annoyance to this problem is a bit subjective, since i also attempted to answer that question, i feel that something should be done.  What should i do in cases like this? Should i downvote the later ones, or just let them be?


Can't find boot-repair package for the newest version of Ubuntu

After upgrading Ubuntu 13.10 to 14.04, grub failed to load Ubuntu and threw the error symbol 'grub_term_highlight_color' not found. I followed the solution offered in the  but this failed for me, throwing the error failed to get canonical path of /cow.   Now, I'm trying to install Boot-Repair to fix this problem on a live pen-drive, using these commands.   sudo add-apt-repository ppa:yannubuntu/boot-repair sudo apt-get update sudo apt-get install -y boot-repair && (boot-repair &)   But after adding and updating the repositories, it shows ppa:yannubuntu/boot-repair 404 Not Found error.  W: Failed to fetch http://ppa.launchpad.net/yannubuntu/boot-repair/ubuntu/dists/trusty/main/binary-amd64/Packages  404  Not Found   Is this problem solvable or is there an alternative PPA for Boot-Repair?


Stopping the default Operating System from Booting

I use Linux 16.04 and Windows 10 in Dual Boot mode. I have Grub customizer installed and reordered my boot list. But I want to stop the default operating system to boot after the initial 10 seconds passed. I want it to halt as long as I do not choose any operating system to boot. I am badly in need of this. But do not know how to do this.


I recently came to know that banana produces antimatter. How does this happen and why doesn't the antimatter annihilate  as our Earth has matter. I looked for a relevant answer but could not find it.


(How) can I store and cook leftover rice so it isn't soggy?

My wife and I like Asian meals (Curry, Niku Jaga, et cetera) and without fail we tend to make more rice than we need.   I would encourage her to cook less rice, but a preferable solution would be to use the rice with the meal - since we tend to have leftovers anyway, and it would be more convenient to cook the amount of rice needed to go with the meal and leftovers.   However, rice in the microwave always comes out either soggy, grainy, or both at once.  This is hardly appetizing, and I suspect the reason for it is an improper method of storing leftover rice.   Normally we simply put the rice in a plastic Tupperware container in our refrigerator and then microwave it when we want to use it.  Is there a better way to store or cook our leftover rice so that we don't wind up with soggy, unappetizing rice leftovers?


Automatically stretch table to evenly fill horizontal space?

I want to have my tables fill the entire width of the page (i.e., \textwidth). So far, the only thing I've managed to come up with is:  \renewcommand{\tabcolsep}{4.4pt}   By manually trying different values, I can eventually get the table to spread out and fill the space. However, this is tedious as I have a lot of tables.  I tried the tabularx package:  \begin{tabularx}{\columnwidth}{ r r r r r r r } \toprule & $z_{6}$ & $z_{8}$ & $z_{9}$ & $z_{11}$ & $z_{13}$ & $z_{14}$ \\ \midrule fileA & 0.00 & 0.00 & 0.00 & 0.08 & 0.79 & 0.08  \\ fileB & 0.01 & 0.00 & 0.13 & 0.00 & 0.84 & 0.00  \\ fileC & 0.00 & 0.39 & 0.02 & 0.49 & 0.00 & 0.00  \\ fileD & 0.75 & 0.08 & 0.00 & 0.00 & 0.00 & 0.00  \\ \bottomrule                              \end{tabularx}   However, this still relies on the \tabcolsep value. (If the value is small, all the columns will still be close; if it's large, the columns will be more spread out.) What I'm looking for is an automatic solution for two things:   the table to take the entire width of the page; and each column to be evenly spaced along the horizontal.   tabularx only does (1). How can I get (2)?


Modifying columns of very large mysql tables with little or no downtime

I periodically need to make changes to tables in mysql 5.1, mostly adding columns.  Very simple with the alter table command.  But my tables have up to 40 million rows now and they are growing fast...  So those alter table commands take several hours.  In a couple months they'll take days I'm guessing.  Since I'm using amazon RDS, I can't have slave servers to play with and then promote to master.  So my question is if there's a way to do this with minimal downtime?  I don't mind an operation taking hours or even days if users can still use the db of course...  Can they at least read while columns are being added?  What happens if my app tries to write?  Insert or update?  If it fails immediately that's actually not so bad, if it just hangs and causes problems for the db server that's a big problem..  This must be a fairly common scaling issue, everyone needs to add columns..  What's typically done to a production db?  Slave -> master migration?  Update - I forgot to mention I'm using the innodb storage engine


Is it possible to explicitly tell Stack Overflow the language of the code block you are including?

Possible Duplicates:             Stack Overflow awesomely detects what language a code block is and syntax highlights it accordingly. But sometimes it fails. Is it possible to explicitly tell it what the language is?  php:  if ( force_ssl_admin() && !is_ssl() ) {     if ( 0 === strpos($_SERVER['REQUEST_URI'], 'http') ) {         wp_redirect(preg_replace('|^http://|', 'https://', $_SERVER['REQUEST_URI']));         exit();     } else {         wp_redirect('https://' . $_SERVER['HTTP_HOST'] . $_SERVER['REQUEST_URI']);         exit();     } }   ruby:  def destroy   @payment = Payment.find(params[:id])   @payment.destroy    redirect_to :back end   yaml (FAIL)  foo: this is foo! bar: this is bar! id: 5


Is it permissible to use somebody else's words (without quotations) to describe a concept once their work is cited?

Quite often one comes across a really succinct and precise explanation of a concept. I'm wondering if it is permissible to use this explanation verbatim, if the source work is cited in your paper (next to the explanation)? What's in question here is at most 3 sentences.


How to make deep copy of a dictionary within Dictionary in c#?

I have four Dictionary , two are (dictionary within Dictionary), declaration shown below      Dictionary<string, Dictionary<string, string>> dict_set = new Dictionary<string, Dictionary<string, string>>();     Dictionary<string, Dictionary<string, string>> dict_Reset = new Dictionary<string, Dictionary<string, string>>();     Dictionary<string, string> set_value = new Dictionary<string, string>();     Dictionary<string, string> Reset_value = new Dictionary<string, string>();   I want to first add elements in dictionary set_vlaue and Reset_value. once the values are added then i am adding these dictionaries to other two dictionaries as shown below.  dict_set.Add(condiName, set_value); dict_Reset.Add(condiName, Reset_value);  set_value.Clear();  Reset_value.Clear();   the values are getting added , but after adding set_value and reset_value dictionaries  , i want to clear these two dictionaries set_value and reset_value,but problem occurs that when set_value and reset_value are cleared the data from dict_set and dict_reset is also cleared..  can any one help me , to how to create deep copy of dictionaries in this case...


I don't understand philosophy very well, and so I am wondering whether you can "prove" anything in philosophy. It always seems you can go a layer down, and find another question, almost endlessly until you get to the question of "why/how/are we here?"  Can you prove, absolutely, and 100% that something is true, in the field of philosophy?


Is it possible to express $0.999...$, a repeating number, as a fraction? Or as a ratio of two numbers?  Basically all (my) attempts at the problem cancels all the terms and returns $1$. Is it even possible? Or has it been proven to be an exercise of futility?


What does the number next to a hot question in the supercollider mean?

Its a pretty self contained question.  I know its not the votes for a question, and not the total views. Is it views in a certain time period?  The number I'm talking about is circled in the below image.


In the book "Elements of Statistical Learning", early on the author is discussing linear regression, and naturally discusses the residual sum of squares (RSS) based on the parameter space $\boldsymbol{\beta}$. In the general formulation, $\text{RSS}(\beta) = (\boldsymbol{y} - \boldsymbol{X}\beta)^T(\boldsymbol{y} - \boldsymbol{X}\beta)$ where $\boldsymbol{X}$ is an $N \times p$ matrix and $\beta$ is a $p \times K$ matrix. The author then says to minimize RSS, you differentiate with respect to $\beta$ and get $\boldsymbol{X}^T(\boldsymbol{y} - \boldsymbol{X}\beta) = 0$  My question is, what are the mechanics of differentiating with respect to the matrix $\beta$? I have a B.S. in physics, so I have a reasonably sophisticated math background, but I never covered this in my undergraduate education. I tried looking a bit into "Matrix calculus", but it wasn't much help. Is that the correct term? If this is the language used in the remainder of the textbook, what are some good resources somewhat familiar with vector calc and linear algebra to learn "matrix calc"?


Evaluate $\lim_{x\to \infty} \cos (\sqrt {x+1})-\cos (\sqrt x)$

Evaluate $$\lim_{x\to \infty} \cos (\sqrt {x+1})-\cos (\sqrt x)$$   For this question I have tried using the squeeze theorem and some trigonometric manipulations such as using $$2\sin A\sin B=\cos (A-B) -\cos (A+B)$$.  But they were of no use. I also tried using the substitutions like $$x=1/y$$ Hence as $x\to \infty$ , $y\to 0$ but still no success.  I could've also tried using L'Hospital rule but I am not able to convert the function in appropriate indeterminate form. Any help would be greatly appreciated


How often do the S&P 500 components change?

And do index funds such as SPY and VOO usually rebalance immediately to reflect the change?


Using series of LM 78XX for power supply

I'm new in electronics. I want provide 9V (VVD9) and 5V (VCC) for my electronic board including power mosfets (IRF 3205), high power LED (14V-3.5A), micro-controller (at-mega16), and etc. I use this strategy to provide those voltages for aforementioned elements as depicted below:    For more details I provide the main part of circuit as shown below. The circuit provides strobe (5Hz-2%duty cycle) for LEDs and a Camera:    I have two questions:   Is using that strategy (shown in first image) good? As depicted in first image, input voltage is 24V. I Also use it for high power LEDs (in second image). Is there any side effect? (for example, voltage drops when LEDs are pulsing).   Any help or suggestion will be appreciated.


Normally we access an array element in this manner: arrayName[elementID]. But even we use like elementID[arrayName] it compiles and does not cause any errors in runtime. Isn't it logically wrong? Can anyone explain me this. I'm new to C++. Thank you in advance for any help!  #include<iostream> using namespace std;  int main() {     int arr[4] = {2, 4, 5, 7};     cout << arr[2] << endl; //this is the correct way to use it      cout << 2[arr] << endl; //this gives the same result and does not cause any errors     return 0; }


Pass by value-doesn't execute as I want it

I do not understand the concept of pass by value in C. Here is my function:   void add(int x){    x = x+1; }   and when I call the function:  int y=3;   add(y);   but when I compile, I still get 3. I've been told it has something to do with pass-by-value but I still do not understand? Can anyone explain why?


Prove that the multiplicative inverse of $a$ modulo $m$ exists if and only if $a$ and $m$ are coprime.  Can someone help me with this?


In what order should I watch the films in the Marvel Cinematic Universe?

What films make up the Marvel Cinematic Universe, and what order should they be watched in?


What really happened to Voldemort's nose?

The nose of Tom Riddle (as a student) was fine, as I have seen in the movies. But, Voldemort's nose doesn't look like a normal human nose. What really happened?


I don't mean to be cheeky with the question, but it reflects the myriad of often seemingly conflicting answers I've seen around this. And that's not surprising of course given the dual nature of light and the multiple possible interpretations of what's actually happening at the quantum scale. As a quick summary of what I understand of the particle perspective, glass is clear because the photons that aren't reflected based on the angle of incidence, aren't absorbed either and so just go straight through. A similar explanation I've heard is that the question itself is flawed, as the real question should be why things are opaque since most of matter is just empty space, leaving one having to explain why all photons don't just go through all matter. And this of course can be explained by electron energy levels and photons carrying enough energy to lift an electron to a higher energy level, absorbing the photon, and later emitting it back. And then there are some quantum mechanical explanations for how the photon maintains its direction and frequency between absorption and emission. That said, here's where I get stuck: I know that light travels "more slowly" through denser materials like glass and water (while of course traveling at c between molecules), and this slowdown causes refraction; yet glass is clear because photons don't get absorbed by glass. I'm not getting how both these statements can be true: how can photons both travel through glass because of not being absorbed, and be refracted which ostensibly requires photon-molecule interaction (absorption/emission). Funny thing is, as I wrote this long question, I feel like I answered my own question. Is it basically that whereas the molecules in opaque materials generally convert photons to heat after absorption, those in transparent materials such as glass/water are unable to do so and so must re-emit them?


What is the highest obtainable resolution of FREE elevation data in the UK?

I am seeking closure with this question guys.  I am aware of various sources of free elevation data ~30+ m, and I have been searching for higher resolution FREE data for a while now. This already exists somewhat (), but may have changed since a year.  I'm afraid I may know the answer already, but to put an end to my misery and false hope:  What is the highest resolution, freely available (outside of academic institutions), elevation data covering the ENTIRE UK? - is 10 m available?


Some time ago I built a website using mysqli to access a database with user info. This database contains some text in cyrillic.  Yesteday I replaced the mysqli with PDO. Now all the cyrillic looks like this:  Ð’Ð¸ÐºÑ‚Ð¾Ñ€Ð¸Ñ Ð‘ÐµÐ»Ð¾Ñ‡ÐºÐ¸Ð½Ð°  I have UTF8 encoding everywhere. Here is my code:  $pdo = new PDO('mysql:host=mysql.host.com;dbname=db;charset=utf8',  'database', 'password'); $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION); $pdo->exec("set names utf8"); return $pdo;   and on the page  <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />   What could be the reason?  I googled a lot but couldn't find a solution.


Why did Windows Update 'forget' about the updates I did?

Until now I've kept my Windows installation offline as I've just used it for gaming offline (I have Ubuntu on a separate disk as my main OS). I recently (last week) decided to download Unreal Engine as I'm beginning to learn C++.   To install Unreal I needed to download SP1, so for the first time, I connected my PC to the internet and began updating; this is where the problem begins.  First, SP1 didn't appear in the list of updates, so I installed all of the other updates hoping it would appear, and after many failures in the optional updates, they eventually finished and SP1 appeared.  Again, many failures in trying to install SP1, approximately 6 days later (around 2-3 hours ago), Windows came out of the blue boot-up screen after finalizing updates. I thought I was finally ready to install Unreal. Open it (Unreal) up and begin installing, it throws out an error that it needs SP1, even though I just finished installing it. I opened Windows Update to make sure I hadn't missed anything, and I hadn't. I figured one more reboot and it should have applied itself.  Following the reboot, I open Unreal to see the same error (No SP1). I open Windows update, and sure enough: all the updates I'd been working at the past 6 days where in a list in front of me, "ready to install".   TL;DR: wanted to use Unreal Engine, needed Windows SP1, spent 6 days installing Windows Updates and pulling out my hair at all the errors. Finally "finish" the updates. They've reverted. The past 6 days and dozens of restarts, failures and error codes; wasted.  Why won't Windows take the damn updates? I would have posted this on the Microsoft forums but looking at other people's posts, Microsoft aren't massively helpful.


Is audio and video slightly out of sync when iPhone is used with a Bluetooth earphone?

Because wireless audio through Bluetooth is usually slightly delayed, so when a Bluetooth earphone is used, is the audio and video slightly out of sync for:   YouTube videos Videos in general, such as Facebook videos, and movies on iTunes What if Apple's own Airpods is used, is it optimized for (1) and (2) above?


Syntax error near unexpected token `{workingDir=$(pwd)'

Here is the problematic line in question.  function gradeUpdate() {workingDir=$(pwd); cd $GRADE_DIR; rm -Rf gradingScript/; git clone https://github.com/[redacted]/gradingScript/; cd $workingDir}   Of course, [redacted] in this case is the username of the repository owner. I can guarantee that $GRADE_DIR is a valid directory, and if I execute cd $GRADE_DIR in the Terminal, it works fine.  Also, if I enter all of the contents of the function (not the function itself) into the Terminal, then it works fine.


A robot moves on 2-Dimensional grid. It starts out at (0,0) and is allowed to move in any of these four ways: 1. (+2,-1) 2. (-2,+1) 3. (+1,+3) 4. (-1,-3) Prove that this robot can never reach position (1,1)


passive Vs active or omission of 'which is'

What is the part of speech of 'regarded' in the following?     "a quality of beauty and intensity of emotion regarded as characteristic of poems"    Why isn't it "... [which is] regarded ..."?  And in another case:      "a small lizard with wide feet, found especially in warm countries"     And also:      "Words used to describe writing or speech style"    In all these examples, why shouldn't the verbs be in their passive form (e.g. which is found, words that are used)?   I am a ESL learner and I am very confused by these usages!


How to find unique multisets of n naturals of a given domain and their numbers?

Let's say I have numbers each taken in a set $A$ of $n$ consecutive naturals, I ask myself : how can I found what are all the unique multisets, which could be created with $k$ elements of this set $A$?  For example I've got $A=[1,2,\dots,499]$. If I wanted to create unique multiset of 3 elements, I would search all the multisets $\{a,b,c\}$ such as $a\leq b\leq c$ and then have all the unique multisets. As such for each elements $a$ there is $499-(a-1)=500-a$ possibilities for $b$ and $500-b$ possibilities for $c$. Unfortunately I'm stumped here and can't find the number of possible combination, as I didn't do any maths for years. I know that I should have some kind of product, but I don't know how to find the product anymore.  So first, I would like to know if I am right in my original assumption, or if I am looking in the wrong direction. Second I would like to approach that as if I were doing an homework, as I would like to understand the logic behind it: What would be the formula to give the numbers of multisets of $k$ elements from a set $A$ of $n$ consecutive naturals?  P.S. I'm totally new to math.SE, as such, I'm not sure I tagged the post appropriately.