I think this is a really simple question so please bear with me -- I just had my first class in regression and I'm a little confused about nomenclature/labeling.  Does anyone recommend some good weblinks that explain beginning linear regression really well?  There's a question I've been looking at for a while and I'm not sure how to do it (although I'm sure the solution is simple):  Show that the sample estimate $\hat{\mu} = \bar X = \frac{1}{n} \sum X_i$  is a least square estimator of $\mu$ for a variable $X$ given $X_1, \ldots, X_n$.  My first thought was,  $$SSE = \sum (\mu - \hat{\mu})^2,$$  but I'm not sure if that's right. I'm confused about what the $\beta$ is (is it $n$?) and I don't know if there are enough parameters to expand it.   Thanks so much for your patience and if this doesn't make sense, I can clarify more. Thanks!

I think this is a really simple question so please bear with me - I just had my first class in regression and I'm a little confused about nomenclature/labeling.  Does anyone recommend some good weblinks that explain beginning linear regression really well?  There's a question I've been looking at for a while and I'm not sure how to do it (although I'm sure the solution is simple):  Show that the sample estimate $\hat{\mu}(X) = \frac{1}{n} \sum X_i$ is a least square estimator of $\mu$ for a variable $X$ given $X_1, \ldots, X_n$.  My first thought was,  $\mathrm{SSE} = \sum (\mu - \hat{\mu})^2$  But I'm not sure if thats right. I'm confused about what the beta is (is it n?) and I don't know if there are enough parameters to expand it.  Thanks so much for your patience and if this doesn't make sense, I can clarify more. Thanks!


Are there any generators that help with drawing circuits?    More or less R2 is supposed to be a rhetostat but i really have no idea how to code a drawing.      edited to make circuit little better (drew it in illustrator), i am trying to include it as a pdf but coming out lousy figure the circuit drawing method would be pretty cool nevertheless.

What are some ways to draw electric circuits in TeX systems?  I'm making this community wiki since I haven't found a question related to this.  I was thinking along the lines of . What do you think of that? Other examples are more than welcome, of course.


I'm trying to compile a java file that uses multiple jar files as imports. the command that I have used to compile my code : javac -cp jackson-databind-2.12.1.jar:jackson-core-2.12.1.jar:jackson-annotations-2.12.1.jar TestRunner.java  as a result two .class files are created : TestRunner.class and TestRunner$1.class then I run the command : java TestRunner  but it throws an error that says: Error: Unable to initialize main class TestRunner Caused by: java.lang.NoClassDefFoundError: com/fasterxml/jackson/core/type/TypeReference  I have included all the required libraries in the javac command, tested it with the IDE and it works fine. I have tried other versions of the jackson library but I'm stuck with the same error.

I am getting a NoClassDefFoundError when I run my Java application.  What is typically the cause of this?


I want to add 8 values of the clicked buttons in an array.  When a user will press any button the id/value against that button stored in an array but my array only save 1st value in the array at array [0].  How to insert other values in an array?  Here is the code:    function reply_click(obj) {   var id = [obj.id];   for (i = 0; i <= id; i++) {     alert(id);   } }  var arr = [id];  alert(arr);  if (id[0] == "1") {   alert(6666666666); }  if (id[0] == "2") {   id[0] = 1;   id[1] = 2;   alert(777777777777); }   if (id[0] == "3") {   id[0] = 1;   id[1] = 2;   id[2] = 3;   alert('login'); }  alert(id);  $(document).on('click', '.btn', function() {    alert($(this).val());    var myvalues = $(this).val();   alert(myvalues);    var cars = [myvalues, "myvaluesv", "Toyota"];   alert(cars);   var x = cars.length;   alert(x); }); <script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script> <button id="1" onClick="reply_click(this)">1</button> <button id="2" onClick="reply_click(this)">2</button> <button id="3" onClick="reply_click(this)">3</button>  <button id="tahira" name="btn" class="btn" value="tahirahassan">hi tahira</button> <button id="sobia" name="btn" class="btn" value="sobia">hi sobia</button> <form action="testingjquery.php" method="post">   <input type="submit" id="btn1" class="btn111" name="val1" value=" i am tahira" />   <input type="submit" id="btn2" class="btn112" name="val1" value="hassan" /> </form>

How do I append an object (such as a string or number) to an array in JavaScript?


I am watching a series of lectures about General relativity by F. Schuller. In the Lecture 7 - Connections (  ) he gives the properties for a covariant derivative respect to a vector field. But instead of the Leibniz rule: $$\nabla_v(T\otimes S)=(\nabla_v T)\otimes S + S \otimes (\nabla_vS)$$ he gives this rule: $${ \nabla_v}(T(w,Y)) =        ({ \nabla_v}T)(w,Y)+T({ \nabla_v}w,Y)+T(w,{ \nabla_v}y)$$ And he claims is equivalent to the Leibniz rule,  but I cannot even derive this rule from the Leibniz rule. Some help please??

I recently came across a video by prof Fredrick Schuller on general relativity where he defines the leibniz rule to be,  $\nabla_X (T(\omega,Y))=\nabla_XT(\omega,Y)+T(\nabla_{X} \omega,Y)+T(\omega,\nabla_{X} Y)$  Where $X$ and $Y$ are vector fields, $\omega$ is a covector field and $T$ is a $(1,1)$ tensor. The rule can be generalised for $(p,q)$ tensors similarly.  I cannot find a way to show that it is equivalent to the leibniz rule expressed as $\nabla_X$ acting on tensor product of two tensor fields.  i.e. $\nabla_{X}(T \otimes S) = \nabla_XT\otimes S + T\otimes \nabla_XS$  How do I proceed to show the equivalence between the two?


Having $c\gt0$ $a, c \in \Bbb{R}$ $$(a+b)^2\le(1+c)a^2+(1+\frac{1}{c})b^2$$ I don't know how to solve this inequality, I tried with the AM-GM inequality and I reached this point so far. $$(a+b)^2\le a^2(c+\frac{1}{c})+b^2(c+\frac{1}{c})$$ I don't know how to continue, and I don't even know if this is the right path. If you have any hints, those would be much appreciated. Thanks

Can anyone point me to any reference on the following inequality: Let $c>0, a,b \in \Bbb{R}$ $$ \|a+b\|^2 \leq (1+c)\|a\|^2+(1+{\textstyle\frac{1}{c}})\|b\|^2 $$  I'm not even sure if "Bohr's Inequality" is this inequality's name, since I can't find it anywhere in the internet.  I'm having a bad day and I got stuck in this one, apparently. Any suggestions or hints on how to prove it will be appreciated.


I want to learn security testing. To be candid I have just heard this term and never tried it. Is it beneficial for the product if security testing is done? How can I start? Do organizations value security testing and would it be another asset if added to my skill set?

I'm on to an R & D task for testing the security vulnerabilities that can happen in a web application. I want to use an open source tool. There are many type of vulnerabilities like Cross Site Scripting, Denial of Service, File Access, Format Validation, Mass Assignment, SQL Injection, Session Setting, etc. So, I would like to have a best fit cross platform tool to do penetration testing in a best possible way. I've gone through  and , and I found it useful. But, as it was posted a year ago, I would like to have an updated answer.


The average or expected lifespan of Hobbits, Men and Dwarfs is easily found but I can find no definitive answer for the 'expected' lifespan of an Orc. All I can find so far is, 'unknown'.

Orcs were the most commonplace villains serving the Dark Powers in all of Tolkien's Legendarium, a race of sentient beings bred by the evil Vala Melkor (Morgoth) during the time of the Great Darkness.  If Orcs were made by Melkor (by breeding Elves he had captured and corrupted) then are they immortal?


I have to save credentials using a service account onto a remote machine and also should be able to access the credentials from remote machine using the service credentials.  I have tried using credman.ps1 script not able to do it.  Is there a way that I can do this using cmdkey exe I can execute the same script from my c# code

I have a Windows account that is used for running services (ie. it's not intended that any person should log in as that account). Turns out one of the services needs to access a remote network share that's on a machine in a different Windows domain, and so needs to supply remote credentials to get to that share.  Now if it was me needing to access the remote share, I would simply open Credential Manager, and save the required credentials.   But it's not me, and my understanding of credential manager is it only saves credentials to be used by the logged in user.  I can of course solve this problem. I temporarily elevate the privileges of the service account to allow interactive logins, then I login as that user and use credential manager to store the correct remote credentials. Then I remove the interactive login privileges.  But that feels very hacky and not the kind of thing I ought to be doing.  So my question is: Is there another way to save remote credentials for an account other than the one you're logged in as? Any better way to solve my problem.


I was drinking water while watching something and something funny happened and I spit water all over my monitor, which is one used for desktops. "Nothing" happened instantly but I quickly dried it with a towel and then I used paper towel to make sure it was (seemingly) dry. I used my fingernail with the paper towel to see if anything got into the casing at the bottom. It was a bit wet but now it seems dry (or at least the paper isn't wet anymore) It turns on and off and it seems okay. I've done it a few times and nothing seems wrong, at least in this first 1/2 hour. I know nothing will ease my paranoia, but am I okay? Or should I start saving up for a new monitor or repairs?

Alright so i spilt a bit of water on my keyboard while back. It was very little so i didn't really try to do anything. However a few minutes later i realised that some of the keys on my keyboard won't working very well. So I switched the laptop off and kept it upside down. I turned it on after half an hour and although things have improved, I'm very  concerned...  For example, the A key doesn't work. Pressing 1 or 2 types out both etc.   Rest everything seems to work as usual.   Do I need to do anything except wait this out?


Let $G$ be a group and (the center of $G$) $Z(G)=\{e\}$. Prove that $Z(\mathrm{Aut}(G))=Z(\mathrm{Inn}(G))=\{I_G\}$ Since  $\mathrm{Inn}(G)\leq \mathrm{Aut}(G)$, it seems that we only need to prove $Z(\mathrm{Inn}(G))=\{I_G\}$, but I do not know how to continue. Appreciate your help!

I am trying to show that if for a group $G$ we have $Z(G)=1$, then $Z(\operatorname{Aut}(G))=1$.  I have tried everything I can think of, but to no avail.  The first part of the problem was to show that $\operatorname{Inn}(G) \triangleleft  \operatorname{Aut}(G)$ - does this have any connection?  I couldn't find one.  I know that $\operatorname{Inn}(G) \cong G/Z(G)$, so in this case $\operatorname{Inn}(G) \cong G$ and $Z(\operatorname{Inn}(G))=1$.  Is there any way to get from this to $Z(\operatorname{Aut}(G))=1$?  How do we go about showing this?  Thanks.


I currently have 2 links enclosed within 2 spans however when a link is clicked an dis active, the link has a class"linkActive". I need to apply a border for the span containing the active link how can one do this in css styles       HTML
                           Link1                                      Link2
   I would like to apply border to span containing the anchor tag with link active class   i tried    span.sec a.linkActive{                  border-bottom: 3px solid black;              }   It does not seem to work. Any help will be appreciated

Is there a way to select a parent element based on the class of a child element in the class?  The example that is relevant to me relating to HTML output by a nice menu plugin for .  The output renders like this:

           Active Page

             Some Other Page

     My question is whether or not it is possible to apply a style to the list item that contains the anchor with the active class on it.  Obviously, I'd prefer that the list item be marked as active, but I don't have control of the code that gets produced.  I could perform this sort of thing using javascript (JQuery springs to mind), but I was wondering if there is a way to do this using CSS selectors.  Just to be clear, I want to apply a style to the list item, not the anchor.


Let $G$ be a finite group and let $Z(G)$ denote its center.  A simple result states that if $G/Z(G)$ a nontrivial cyclic group then $G$ is abelian.  Of course if $G$ is abelian then $Z(G)=G$ and consequently $G/Z(G)$ is the trivial group.  Hence we conclude that no non-trivial cyclic groups can result when we quotient a group by its center.  My question is whether there are any other restrictions as to what groups can occur as the quotient of some group by its center.

So if I'm given $H$, when I can conclude there is a group $G$ such that $H\cong G/Z(G)$? It's easy to show that non-trivial cyclic groups are not of this form. More generally, any group with the property that all finitely generated subgroups are cyclic (e.g. $\mathbb{Q},\mathbb{Q}/\mathbb{Z}$) cannot be of this form. Are there are any others?


I'm pretty familiar with regular expressions in various contexts, but bash substring matching just baffles me. Can someone please explain them to me, ideally with some examples? The examples I've found on google are very simple, and suggest pretty generic (if limited) regex matching, but when I try to use them in practical situations it never works.  From my understanding substring matching should work as follows:   result=${string##pattern}   will find the longest substring of 'string', starting from its beginning, that matches 'pattern'. It removes that match from 'string' and puts the remainder in 'result'. But consider:  temp=${myvar##[^0-9]*} && echo $temp   As far as I can tell, my pattern should match 'zero or more characters that are not digits' - the longest such match from the start of the string. Then take as example:  myvar=my_file_123_45.txt   I should expect the characters 'my_file_' to be matched: that is the longest combination of characters from the start of 'string' that aren't digits. Instead, the returned result is empty! Everything gets matched! What happened to excluding digits?!  In both gedit (using the search-and-replace regex engine), and in Labview's regex tools, the match pattern   pattern=^[^0-9]*   which i believe to be equivalent, results in my expected match - 'my_file_'. What's different about Bash?

I'm quite confused about the following regular expressions I found in a shell script:  ${0##*/} ${0%/*}   How do they work?


Imagine this javascript code is inside an already busy loop:  if (a==0) {      d=6; }else if (a==1) {      d=31; }else if (a==2) {      d=null; }   I thought of replacing it with:  var array=[6,31,null]; d=array[a];   Which would be faster? In case it is the array approach, is it faster to have this array as a global var? I am thinking "Yes, because if you make it local, the program becomes a bit slower because it has to declare the array every time". Thank you in advance.

CPU Cycles, Memory Usage, Execution Time, etc.?  Added: Is there a quantitative way of testing performance in JavaScript besides just perception of how fast the code runs?


I would like to implement an intelligent bot for Quake-3. I downloaded the and built the code successfully under Linux. My problem is that I couldn't find any complete tutorial telling me how to build an agent; telling which files to use( as there are many files in the source code).  Can you give me a website or piece of source code telling me how to start? Or something like an example source code for a bot.

Does anyone know source example source codes and tutorials to start writing an intelligent bot for Open Arena?


I want to render 2 object, in the rendered preview it looks fine   butwhen I press F12 the result is only a black screen like this   I have switched the little camera icon in the left on, btw I deliberately switch off camera in object 'Plane' that I don't want to render,   If you want to help me please download this blender file, thanks

This is meant to solve this problem once and for all. What is every reason an object isn't showing up in a render or viewport in when using the cycles render engine?


Why is it that the object b has the same variables as a and not unique ones? class FOO:        def __init__(self):          FOO.x = [3, 1]          self.y = [9, 4]        def g(self):          FOO.x[1] = FOO.x[1] + 7          self.y *= 2          return FOO.x + self.y    a, b = FOO(), FOO()  print(a.g())  print(a.g())  print(b.g())  Why do I get this output:  [3, 8, 9, 4, 9, 4] [3, 15, 9, 4, 9, 4, 9, 4, 9, 4] [3, 22, 9, 4, 9, 4]  and not this?  [3, 8, 9, 4, 9, 4] [3, 15, 9, 4, 9, 4, 9, 4, 9, 4] [3, 8, 9, 4, 9, 4]  Isn't each object unique?

Is there any meaningful distinction between:  class A(object):     foo = 5   # some default value   vs.  class B(object):     def __init__(self, foo=5):         self.foo = foo   If you're creating a lot of instances, is there any difference in performance or space requirements for the two styles? When you read the code, do you consider the meaning of the two styles to be significantly different?


I have 16gb Ram,but I need 48gb....so I should increase my swap space to 32. Can I?  I ve tried to use Gparted but it's sth such as lock (or mount)!!!! tnx

Previously, I have installed Windows 7 on my 320 GB laptop with three partitions 173, 84 and 63 GB each. The 63 GB partition was where the Windows was installed. The rest were for file containers.  Now I changed my OS to Ubuntu 12.04 LTS. I installed Ubuntu by replacing the entire Windows 7 on the 63 GB partition. The rest of the partitions remain as an NTFS Windows partition and I can still access them both (the 173 and 84 GB partitions).  Now I want to change the two partitions of Windows into an Ubuntu format partitions plus most importantly, I want to extend the 63 GB partition to more than a 100 GB because at the moment I am running out of disk space. Whenever I try to install any application, especially using wine, it always complains for a shortage of disk space.  How do I do the extending activity before I entirely format my laptop again and lose all the important files on my partitions?


What is actually being conserved? I've calculated it for the Wess-Zumino model but I still have no idea what is actually being conserved due to Noether's Theorem.  There is already a similar question,  But the answers don't actually say if there is anything physically conserved.   I have heard that the number of fermions is kept equal to the number of bosons, but is this not a fact that susy requires? I feel like it doesn't actually come from the charge itself.  In Qmechanic's answer it is said that "the experimental consequences of a conserved supercharge are extracted by other indirect means." What are these means?

According to , for every continuous symmetry there is a conserved quantity. What is the quantity that corresponds to Supersymmetry?


In Europe, travelers can buy a special rail pass that gives them unlimited train rides for a month. And some airlines offer tickets where a list of destinations is chosen in advance, but the flight dates are flexible and can be chosen on short notice.   Is there anything similar for traveling around the US by bus or train? Greyhound used to offer something like it, called the "Discovery Pass," but it seems to have been discontinued. And Amtrak only seems to offer unlimited passes on specific short routes, mainly targeting commuters.

I've heard mention of 'limitless' tickets in North America, either by bus or  train.  Do these exist? What are the conditions and prices?


I am a Linux user for 20 years and I know how to automatically mount Windows partitions in LINUX. But I am trapped in Kubuntu that too on a Lenovo laptop. How can I auto mount windows partitions on Kubuntu?

I have two NTFS partitions, and I don't want to mount them manually every-time I start Ubuntu.   How can I do this?  Is there a tool or a code to use?   If so, is it safe to automount? specially when they are being used by another OS?


So I am trying to establish a connection to my postgresql database in java but I keep getting this error: "java.sql.SQLException: No suitable driver found for jdbc:postgresql://localhost:5432/postgres"  I have seen that there are a lot of people having this issue but none of their solutions helped in my case.  Here is my program:  public class psql{      static String url = "jdbc:postgresql://localhost:5432/postgres";     static Properties props = new Properties();      public static void main(String[] args){         Connection connection = establishConnection();     }       private static Connection establishConnection(){          props.setProperty("user", "userName");         props.setProperty("password", "password");          Connection connection = null;          try {             connection = DriverManager.getConnection(url, props);         } catch (SQLException e){             System.err.println("Didnt establish connection");             e.printStackTrace();         }          return connection;     } }   I have installed the newest postgresql jdbc driver. I have it in the same folder as my java file. I run it in cmd like this:   javac -cp postgresql-42.2.12.jar:. psql.java java -cp postgresql-42.2.12.jar:. psql.java   I have also made sure that the username, password, etc are all spelled right and I simply dont have any idea what else to do. Can anyone tell if I am missing anything?  Edit: There is no need for help anymore. I have found the solution guys. As commented by Mark Rotteveel, I needed to use ; instead of : to sepparate items on the classpath. I cant really mark the comment as an answer so I chose to edit the question. Thank you for the assistance.

Note I'm running windows, the path just looks like it's linus because I typed it manually and thats how I think of paths.  I'm trying to run a java class That I have built to diagnose my connection to a databse, it references the oracle jdbc adaptor.  When I just run it without a class path:  %> java DBDiagnostics <connectionString>   I get an exception when it reaches the following line of code:  Class.forName("oracle.jdbc.pool.OracleDataSource").newInstance();   with the following exception:  java.lang.ClassNotFoundException: oracle.jdbc.pool.OracleDataSource         at java.net.URLClassLoader$1.run(URLClassLoader.java:200)         at java.security.AccessController.doPrivileged(Native Method)         at java.net.URLClassLoader.findClass(URLClassLoader.java:188)         at java.lang.ClassLoader.loadClass(ClassLoader.java:307)         at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)         at java.lang.ClassLoader.loadClass(ClassLoader.java:252)         at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:320)         at java.lang.Class.forName0(Native Method)         at java.lang.Class.forName(Class.java:169)         at DBDiagnostics.GetConnection(DBDiagnostics.java:43)         at DBDiagnostics.runDiagnostic(DBDiagnostics.java:29)         at DBDiagnostics.main(DBDiagnostics.java:18) Creating connection. java.sql.SQLException: No suitable driver found for lskd         at java.sql.DriverManager.getConnection(DriverManager.java:602)         at java.sql.DriverManager.getConnection(DriverManager.java:207)         at DBDiagnostics.GetConnection(DBDiagnostics.java:55)         at DBDiagnostics.runDiagnostic(DBDiagnostics.java:29)         at DBDiagnostics.main(DBDiagnostics.java:18) Veryfying connectivity to Database Exception in thread "main" java.lang.NullPointerException         at DBDiagnostics.verifyTable(DBDiagnostics.java:86)         at DBDiagnostics.verifyTable(DBDiagnostics.java:76)         at DBDiagnostics.verifyDatabseConnectivity(DBDiagnostics.java:68)         at DBDiagnostics.runDiagnostic(DBDiagnostics.java:36)         at DBDiagnostics.main(DBDiagnostics.java:18)   I assume that this is because I need to include it in the classpath.   So, I tried adding it to the classpath like this:  %> java -classpath .:ojdbc6.jar DBDiagnostics <connectionString>   The VM just says it cant find the class:   Exception in thread "main" java.lang.NoClassDefFoundError: DBDiagnostics Caused by: java.lang.ClassNotFoundException: DBDiagnostics         at java.net.URLClassLoader$1.run(URLClassLoader.java:200)         at java.security.AccessController.doPrivileged(Native Method)         at java.net.URLClassLoader.findClass(URLClassLoader.java:188)         at java.lang.ClassLoader.loadClass(ClassLoader.java:307)         at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)         at java.lang.ClassLoader.loadClass(ClassLoader.java:252)         at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:320) Could not find the main class: DBDiagnostics.  Program will exit.   I know this is a question I should just know the answer to, but what am I doing wrong?


I am not sure if I have seen this before:  $$\dbinom{n}{p}\equiv\big\lfloor{\dfrac{n}{p}}\big\rfloor\mod p$$  where $p$ is prime and $\lfloor x\rfloor$ is the floor function.  So, for example, $\dbinom{34}{7}\equiv\lfloor\dfrac{34}{7}\rfloor=4\mod 7$.

This is an exercise from Apostol, which i have been struggling for a while.  Given a prime $p$, how does one show that $${n \choose p} \equiv \biggl[\frac{n}{p}\biggr] \ (\text{mod} \ p)$$ Note that $\Bigl[\frac{n}{p}\Bigr]$ denotes the integral part of $\frac{n}{p}$.  I would also like to know as to how does one try to solve this problem. Well, what we need is to show is whenever one divides ${n \choose p}$ by a prime $p$ the remainder is the integral part of $\frac{n}{p}$.  Now, $${ n \choose p} = \frac{n!}{p! \cdot (n-p)!}$$ Now $n!$ can be written as $$n!= n \cdot (n-1) \cdot (n-2) \cdots (n-p) \cdots 2 \cdot 1$$  But i am really struggling in getting the integral part.


Is there a single word to mean the following:  'having more than one meanings'

Is there a better alternative to ambiguous for a word with a wide range of meanings, difficult to find, because they become different in connection with person's opinion.


well I need to write some text right next to my shape. But it's too complicated when making it all coordinate i and write it. How I make it easier?

How can I insert a line break in a TikZ node? Simply putting \\ where I want the break doesn't work (see MWE).  Is there a way to make lines break automatically at some specified width?  And can I control the alignment of the text (left, right, centered, justified)?  \documentclass{article} \usepackage{tikz} \begin{document} \begin{tikzpicture} \node {First line\\second line}; \end{tikzpicture} \end{document}


So, I'm having some trouble with pst-optexp lately. There seems to be some compilation problems with my sketch, since it doesn't show the elements properly. My current code is   \documentclass{standalone}     \usepackage{pstricks-add}     \usepackage{pst-optexp}         \let\clipbox\relax  \begin{document}     \begin{pspicture}[showgrid](0,-0.3)(9,2.3)         \pnode(1.8,1){A}\pnode(4.5,1){B}\pnode(7,1){C}\pnode(8,1){D}         \begin{optexp}             \optbox[position=start, labeloffset=0](A)(B){Fonte}             \lens[n=1.3, lensradius=-1 -1, lensheight=1](A)(B)             \lens[n=2, lensradius=2 2, lensheight=2](B)(C)             \pinhole[position=end, innerheight=0, outerheight=1.5](B)(D)             \drawwidebeam[beamwidth=0.3,fillstyle=solid, fillcolor=green!40](A){2-3}(D)         \end{optexp}     \end{pspicture} \end{document}   This code yields the following result (when compiled with XeLaTeX on Overleaf v2):   If I remove the optexp environment, i.e., use the following code:   \documentclass{standalone}     \usepackage{pstricks-add}     \usepackage{pst-optexp}         \let\clipbox\relax  \begin{document}     \begin{pspicture}[showgrid](0,-0.3)(9,2.3)         \pnode(1.8,1){A}\pnode(4.5,1){B}\pnode(7,1){C}\pnode(8,1){D}             \optbox[position=start, labeloffset=0](A)(B){Fonte}             \lens[n=1.3, lensradius=-1 -1, lensheight=1](A)(B)             \lens[n=2, lensradius=2 2, lensheight=2](B)(C)             \pinhole[position=end, innerheight=0, outerheight=1.5](B)(D)             \drawwidebeam[beamwidth=0.3,fillstyle=solid, fillcolor=green!40](A){2-3}(D)     \end{pspicture} \end{document}   Then I'll get this result:   I have dealed with similar issues on other PSTricks diagrams, which seemed to compiled when put in certain pages of the document, but were breaking in other places. How can I solve this?  I'm sorry if this is a known issue or something alike, I've been searching the web for quite sometime now and I just couldn't find a solution. Also, please let me know if there are bad style issues in this post, I have asked few questions over here so far.

I have troubles with optexp environment. There is a code  \documentclass[pstricks,margin=12pt]{standalone}  \usepackage{pst-optexp}  \begin{document} \begin{pspicture}(3.2,5) \pnodes(0,3){A}(1,3){BS}(3,3){M1}(1,5){M2}(1,1){PD} \psset{mirrortype=extended, mirrordepth=0.2}  \begin{optexp} \beamsplitter[bsstyle=plate, compname=BS](A)(BS)(PD) \mirror[compname=M1](BS)(M1)(BS) \mirror[compname=M2, variable](BS)(M2)(BS) \lens[compname=L](BS)(PD) \optdetector[compname=Det, dettype=diode](BS)(PD) \addtopsstyle{Beam}{beamwidth=0.2, fillstyle=solid,fillcolor=green!20!white} \drawwidebeam(A){BS}{M1}{BS}{M2}{BS}{L}{Det} \end{optexp} \end{pspicture}  \end{document}   and the result is this    and I get "MiKTeX GPL Ghostscript 9.19: Unrecoverable error, exit code 1" error. When I remove optexp environment, so  \documentclass[pstricks,margin=12pt]{standalone}  \usepackage{pst-optexp}  \begin{document} \begin{pspicture}(3.2,5) \pnodes(0,3){A}(1,3){BS}(3,3){M1}(1,5){M2}(1,1){PD} \psset{mirrortype=extended, mirrordepth=0.2}   \beamsplitter[bsstyle=plate, compname=BS](A)(BS)(PD) \mirror[compname=M1](BS)(M1)(BS) \mirror[compname=M2, variable](BS)(M2)(BS) \lens[compname=L](BS)(PD) \optdetector[compname=Det, dettype=diode](BS)(PD) \addtopsstyle{Beam}{beamwidth=0.2, fillstyle=solid,fillcolor=green!20!white} \drawwidebeam(A){BS}{M1}{BS}{M2}{BS}{L}{Det}  \end{pspicture}  \end{document}   the result is     which is correct but optical components are behind beam. I use XeLatex. What am I doing wrong? Which packages are missing? Thank you (example is from manual "Drawing optical experimental setups" where the code works correctly).


I am trying to dual boot two Linux distributions. My machine is running MintOs and I am trying to install kali Linux. I need to know whether I have to create a new swap area or can I use the old one.

In order to save disk space, I want to have two OS installations share a single swap partition (a dual-boot). Is this a good idea?


The function $f(x)$ is continuous on the interval $[0,1]$ and we have that   $$ \int_0^1f(x)x^ndx = 0, \quad\, n=0,1,2,\dots $$   Prove that $f(x)= 0$ on the interval $[0,1]$.   So I am thinking like this, I can expand $f(x)$ to an even function and for even $n$ I got this  $$\frac{1}{2}\int_{-1}^1f(x)x^ndx$$ and then $f(x)$ must be zero for all $x$ in this interval, is this right? What about odd $n$? Not even sure if this is the right way to attack this.  This is in my Fourier Analysis course and its in the chapter that contains orthogonal set of functions. So I need to prove this with tools within this area.

As the title says, I'm wondering if there is a continuous function such that $f$ is nonzero on $[0, 1]$, and for which $\int_0^1 f(x)x^n dx = 0$ for all $n \geq 1$. I am trying to solve a problem proving that if (on $C([0, 1])$) $\int_0^1 f(x)x^n dx = 0$ for all $n \geq 0$, then $f$ must be identically zero. I presume then we do require the $n=0$ case to hold too, otherwise it wouldn't be part of the statement. Is there ay function which is not identically zero which satisfies $\int_0^1 f(x)x^n dx = 0$ for all $n \geq 1$?  The statement I am attempting to prove is homework, but this is just idle curiosity (though I will tag it as homework anyway since it is related). Thank you!


According to Newton's third law, Action and Reaction are equal and in opposite direction. If both forces are equal and in opposite direction then why they don't make equilibrium and void the effect of force?

Given Newton's third law, why is there motion at all? Should not all forces even themselves out, so nothing moves at all? When I push a table using my finger, the table applies the same force onto my finger like my finger does on the table just with an opposing direction, nothing happens except that I feel the opposing force. But why can I push a box on a table by applying force ($F=ma$) on one side, obviously outbalancing the force the box has on my finger and at the same time outbalancing the friction the box has on the table? I obviously have the greater mass and acceleration as for example the matchbox on the table and thusly I can move it, but shouldn't the third law prevent that from even happening? Shouldn't the matchbox just accommodate to said force and applying the same force to me in opposing direction?


I dynamically created various images and other elements within various div elements and assigned a class to them, like: divOM = document.getElementById('omain'); kd = document.createElement('img'); kd.src = 'pics/k0.jpg'; kd.class = 'mww'; divOM.appendChild(kd);  This works well – the debugger shows the desired result (# children with class ‘mww’).  I have the (maybe naïve) hope that wlist = document.getElementsByClassName('mww')  gives me all elements which have class=’mww’, but unfortunately it doesn’t. The debugger shows length:0 for wlist!?? Is it possible that document.getElementsByClassName doesn’t work for dynamically created elements?

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


Often on meta sites I'll see questions asking about specific posts or users, which, for the most part, are fairly unbiased and fair. However, sometimes these posts can spiral out of control into personal attacks.   Should users that are the topic of these discussions be privately or publicly notified if they are the center of such debates? It would allow them a chance to explain actions or clarify things if need be.  I don't think all cases where a specific user is involved needs a notification back to the OP, but possibly things involving suspicious behavior on part of the person in question?

As I have been learning the ropes here on Meta, I have been reading and sometimes participating in discussions similar to  where other users have been mentioned by name and berated or mocked for some bad/gaming behaviour. Other times I've seen users simply just commented upon with "I've noticed that this user has a tendency to do link-only self-answers, what should I do?", and I have found myself thinking: "I wonder if they've ever said something similar about me?"  A couple of days ago, as part of  discussion, where a specific user is mentioned for supposedly poor reviewing another user made this comment to the OP:     -1. Exposing another user like this is not appropriate IMHO. You could just post the image without the link to his profile   The OP defended his position and I made a comment backing the OP, because the site favours substantiating claims with facts; especially on Meta those facts are frequently specific (sets of) questions and occasionally specific (sets of) users' behaviour. That is just how things are done, but I do think the objection is valid because when you are linking to a user profile you are targeting that specific user, and not some general behaviour.  So I suggest that one of the abilities that should come with perhaps 1000 or 1500 rep is that the "Responses" on your profile is expanded with "Links/Mentions" - and that this list is populated with mentions (in questions/answers/comments) where somebody have linked your profile.   The point being two-fold:   The community is no longer discussing/snickering behind said users backs, but are offering the criticism more directly. The user in question have a chance to know that something is not done right, and can act to improve (or defend) it, even when the behaviour is not bad enough to warrant intervention by system or mods. Also, when/if the behaviour improves, the user can flag the links to be removed as obsolete - and hence won't continue to be the laughing stock of everybody who happens to read the post.    The reason I think some reputation is required is from the assumption that more seasoned users will have thicker skin and hence handle the criticism better. I realise that some users will be beyond reach, but I think others would gain from it - and even without the gain, I do feel we all have a right to know when we are being discussed in the open.  Note that this suggestion is NOT for @-mentions in comments, but for links to user profiles.


I have a LED lamp (it already HAS a power adapter), all I'm trying to do is turn it on using a NPN transistor (2N3904):    Someone told me that I will burn my transistor or controller attached to the base if I don't know how much current the device (the LED lamp) is using.   I can only understand that I need to know this, so I can be sure that the transistor can handle that much current, but I don't understand what does it has to do with base and burning down the controller or whatever is attached to the base? Do I need to know the current of the device because extra current might come into the base? I'm completely lost..  My question: "Under what conditions can extra current come into the base?"  UPDATE: I measured the current for the LED, and it uses 150mA, does that mean I can safely use 2n3904?

Before I ask my question, I should say that I am very new to working with electronics and I may not quite know how to describe my problem.  I am trying to use a pin on my msp430 microcontroller I have as a replacement for a pushbutton on a device. The msp430 is 3.3v and the device I am switching is 5 volts. I was under the impression I could use a 2n3904 transistor in place of the button by applying current by turning on the pin on the msp430 which would let current go from the collector to the emmiter, and hopefully "push" the button.  This is my current setup    However, turning the pin on does not activate the circuit. When I connect the jumper for the onboard LED, I can verify the pin is working. also, when I connect the 5v from the collector to the base using a wire, I can activate the transistor.  What other information am I missing to solve this? Thanks in advance  EDIT: After reading the comments, adding a 4.6k resistor between the base and IO pin and connecting my 3v ground and 5v ground allowed me to control the transistor without any noticeable problems. Thank you!


Here I faced challenge for fixing line number style as like the attached image could any one help how to fix this.  Note: Required style as indicated in green color  MWE:  \documentclass{book}  \usepackage{multicols}enter image description here  \begin{document}  \section{Overview}  Numerous videos \textbf{xxx} $\textbf{Xx}\quad {\boldsymbol{Xx}}$ and interactivities are embedded just where you need them, at the point of learning, in your learnON title at www.jacplus.com.au. They will help you to learn the content and concepts covered in this topic. SOURCE 1 The rapid growth of towns during the Industrial Revolution resulted in most workers and their families living in slum conditions.  \subsection{Links with our times}  When a new suburb is established today, roads and footpaths are built, services such as water and electricity are connected, and underground pipes are installed to take away sewage and stormwater. All these facilities are usually in place before any homes are built, and even the construction of the houses is governed by strict building regulations. The situation was very different two hundred years ago.  \begin{multicols}{2}  As we learned in topic 2, the population increased dramatically in Britain during the Industrial Revolution. Changes in agricultural practices, as well as job opportunities in the newly established factories, brought large numbers of people into rapidly growing towns and cities. This influx of people was not matched by the provision of the types of server  As we learned in topic 2, the population increased dramatically in Britain during the Industrial Revolution. Changes in agricultural practices, as well as job opportunities in the newly established factories, brought large numbers of people into rapidly growing towns and cities. This influx of people was not matched by the provision of the types of server  \end{multicols}  \end{document}

Here I faced challenge for fixing line number style as like the attached image could any one help how to fix this.  Note: Required style as indicated in green color    MWE  \documentclass{book} \usepackage{multicol} \begin{document} \section{Overview} Numerous videos  and interactivities are embedded just  where you need them, at the point of   \subsection{Links with our times} When a new suburb is established today, roads and footpaths are built, services such as water and electricity are connected, and underground  pipes are installed to take away sewage and  stormwater. All these facilities are  usually in place before any homes are built,  and even the construction of the  houses is governed by strict building regulations.  The situation was very  different two hundred years ago.  \begin{multicols}{2} As we learned in topic 2, the population increased dramatically in  Britain during the Industrial Revolution. Changes in agricultural  practices,  as well as job opportunities in the  newly established factories, brought  large numbers of people into rapidly growing towns and cities. This  influx of people was not matched by the provision  of the types of server   As we learned in topic 2, the population increased dramatically in  Britain during the Industrial Revolution. Changes in agricultural     practices, as well as job opportunities in the newly established  factories, brought large numbers of people into rapidly  growing towns and cities. This  influx of people was not matched by the provision  of the types of server  \end{multicols} \end{document}


My laptop has Intel 6700HQ CPU and Nvidia 960M as graphics card. I have nvidia-361 driver installed.   I can use the nvidia program provided with the driver to switch between Intel GPU and Nvidia GPU. Nvidia GPU works fine actually, and gives me no problems most of the time. But it heats a lot and drains/heats up the battery too. So it is not practical to use.  While switching from nvidia GPU to intel GPU, I'm not having any problems. When nvidia is on, I can easily reboot, suspend, sleep, poweroff. But when I'm on intel GPU, I can do none of those. It always freezes and I have to hold on the power button to force close it. If it sleeps, it won't wake up and so on. Same problem occurs if I use terminal commands (such as sudo reboot) to do these too.  It stays like one of these. And nothing happens:   The cursor doesn't blink. Screen is completely frozen.  I've removed "quiet splash" from grub to see what's wrong in more details, but it gave something like

I have installed Ubuntu MATE 16.04 on a new Alienware 13 machine. My problem is that shutdown/reboot/logout stopped working properly and the system freezes one I try to do shutdown. The problem started after I tried to suspend the system and it lead to a freeze too. After extensive searching I found that this freeze on shutdown only happens when the system is switched to Intel card (it shuts down fine when Nvidia is on). Does anybody know the fix for this?


I am learning photography. I am really interested in night landscapes, moon, star trails. I need a cheap tripod, but not a useless one. Is the  worth getting? It's 60 inches. I'm 73.5 inches tall.

I am a novice in photography and my current camera (Sony alpha 230 kit) which I recently have bought is the first DSLR of mine. Soon I'd like to buy a tripod for it.  Please advise me what should I take into consideration when choosing a tripod? At present all the tripods seem similar to me and I feel that I need some help in choosing the right one.  From what I tend to shoot now, I think that the primary usage of the tripod will be landscape and portrait (outdoor) photography.


Is CO2 the only type of gas you could use to carbonate the beer in your keg. (Okay know carbonate means to use CO2). Something like say Nitrogen or Helium or whatever. If so what would that taste like and or change the flavor of the beer.

Obviously, most beers are carbonated with carbon dioxide, while some stouts/porters are "carbonated" with nitrogen.  I was curious if there has been any notable experimentation with other gasses to "carbonate" beer. If nitrogen can introduce a "creamy" texture to a beer, I would think that other gasses would also be able to introduce their own characteristics on beer. If any of these experiments have done, what characteristics do these other gases impart?  I'm sure cost would be an issue for certain gasses that would prohibit its use in beer, but for purposes of this question, cost is irrelevant.  As an aside, what is the correct term to use, as opposed to "carbonate", for a question of this nature?


Does anyone know how to create an effect like this in Illustrator? I need to understand how to create this angled wave/fold effect in a line pattern from scratch so that I can create my own styled one for a logo purpose Please help!   Thanks!


I need some help with this problem, I try to prove that all vertices of $G$ is in a cycle by I can't prove it. Can you help me?     Let $G$ be a connected and bipartite graph and $G$ is regular of grade $k>1$, prove that $G$ is a biconnected graph.

I've been struggling with this exercise; all ideas have been unfruitful, leading to dead ends. It is from Balakrishnan's A Textbook of Graph Theory, in the connectivity chapter:     Prove that a connected k-regular bipartite graph is 2-connected.   (That is, deletion of one vertex alone is not enough to disconnect the graph).  I think the objective is to make use of Whitney's theorem according to which a graph (with at least 3 vertices) is 2-connected iff any two of its vertices are connected by at least two internally disjoint paths. But I'll welcome any ideas or solutions.  Thank you!


I want to limit input field to one letter only(with JS),after one I want to get an error. How to do it?

How do you impose a character limit on a text input in HTML?


I have the mean and standard deviation for Male and Female groups in a study, I'm trying to get the combined mean and standard deviation. The two groups have different N's. I can get the weighted average of the two means, but I don't know how to get the new standard deviation, given that the N's are different. Is there a modified version of Var(x+y)=Var(x)+Var(y) that takes into account the sample sizes too that I can use?

I'm calculating the covariance of a distribution in parallel and I need to combine the distributed results into on singular Gaussian. How do I combine the two?  Linearly interpolating between the two almost works, if they are similarly distributed and sized.   provides a forumla at the bottom for combination but it doesn't seem right; two identically distributed distributions should have the same covariance, but the formula at the bottom of the page doubles the covariance.  Is there a way to combine two matrices?


This particular question was asked in my Quiz yesterday . It is not clear whether the quiz would be discussed or not , so I am asking it here .  Let $f:\mathbb{C} \to \mathbb{C}$ be an entire function such that $f(z+1)=f(z+i)=f(z)$ for every $z$ belonging to $\mathbb{C}$ . Then prove that $f$ is constant .  I will not be able to show an attempt for this as I could not think of anything concise . Kindly shed some light on how to approach this problem .

Let $f: \Bbb C \to \Bbb C$ be an entire (analytic on the whole plane) function such that exists $\omega_1,\omega_2 \in \mathbb{S}^1$, linearly independent over $\Bbb R$ such that: $$f(z+\omega_1)=f(z)=f(z+\omega_2), \quad \forall\,z\in \Bbb C.$$Prove that $f$ is constant.   The intuition seems clear to me, we have the three vertices of a triangle given by $0$, $\omega_1$ and $\omega_2$. All points in the plane are one of the vertices of that triangle under a suitable parallel translation. The constant value will be $f(0)$, fine. Throwing values for $z$ there, I have found that $$f(n\omega_1) = f(\omega_1) = f(0)=f(\omega_2) = f(n\omega_2), \quad \forall\, n \in \Bbb Z.$$  I don't know how to improve the above for, say, rationals (at least). Some another ideas would be:   Checking that $f' \equiv 0$. I don't have a clue of how to do that. Write $w = a\omega_1+b\omega_2$, with $a,b \in \Bbb R$, do stuff and conclude that $f(w) = f(0)$. This approach doesn't seem good, because I only have a weak result with integers above. Finding that $f$ coincides with $f(0)$ on a set with an accumulation point. This seems also bad: the set on with $f$ coincides with $f(0)$ by which I found above is discrete.    Nothing works and this is getting annoying... And I don't see how analyticity comes in there. I'll be very thankful if someone can give me an idea.  (On a side note.. I know that this title is not informative at all. Feel free to edit if you come up with something better.)


I am a newb to linux. I want to build a network server/file share. I have an Intel G3258 processor, 4gb ram and want to take advantage of the 64-bit processing abilities. It doesn't look like the latest stable release for Ubuntu server is for an Intel chip. Am I wrong? If not, which previous Ubuntu server release works for the 64-bit Intel chips?

I was told that computers with more than 2 gig's memory need a 64 bit operating system to utilize all RAM.  Is the 64bit Ubuntu download really JUST for AMD processors? I am asking because the disk image I downloaded says AMD64.  So will my new Intel 2.3Ghz Core i3 Dual Core processor work with 64 bit Ubuntu?  It runs the 64bit version of Windows without any qualm.


I'm trying to create a large random file on a ramdisk, in order to do some tests. I've created the ramdisk and my starting file (from /dev/urandom) without much trouble, but I'm having trouble increasing it's size (I was hoping I could just cat it into itself to double it up until the disk was full), and I'm unsure why. I'm hoping someone can tell me what I'm overlooking.  First, the file is definitely there:  $ ls -la /mnt/ramdisk/ramfile -rw-r--r-- 1 root root 163840 Nov 22 11:07 /mnt/ramdisk/ramfile   Second, I try to use cat to double it's size, which fails:  $ sudo -s "cat /mnt/ramdisk/ramfile >> /mnt/ramdisk/ramfile" /bin/bash: cat /mnt/ramdisk/ramfile >> /mnt/ramdisk/ramfile: No such file or directory   So I guess I'm misunderstanding something here, because I would expect that to work. I also tried catting the starting file twice to another file, but I got a similar error.  In case it's relevent, I created the file as follows:  sudo dd if=/dev/urandom of=/mnt/ramdisk/ramfile bs=16384 count=10   The reason I want to do this, I found urandom to be quite slow to read from (even on a massively overpowered server) and I want to ensure that the read speed from this random file isn't a bottleneck.  EDIT:  Versions-  GNU bash, version 4.3.11(1)-release (x86_64-pc-linux-gnu) cat (GNU coreutils) 8.21 Ubuntu 14.04 x86_64

I'm trying to execute the following command on my CentOS 6.3 x64 server:  nohup "/usr/local/bin/php -v"   The result is:  nohup: ignoring input and appending output to `nohup.out' nohup: failed to run command `/usr/local/bin/php -v': No such file or directory   This works on CentOS 5 no problem. Any idea what I'm doing wrong?


I brought a canon pixma G 2000 printer.I can't install it. Please help me to solve the issue.

I tried to install the MP190 drivers, but appeared a message show me that requires to have libcupsys2. I understand that libcup2 is an update of libcupsys2.   How do I solve this? Are there proprietary drivers for my Canon printer or scanner?


I am trying to achieve a text where an over-brace is followed by an under-brace with a last digit overlapping, but couldn't able to do it, anyone help me to fix it, the example code is given.  \documentclass[12]{article} \usepackage{amsmath}  \begin{document}  $$ . . . \overbrace{\times \times \times }^{\lbrace\pm 2x, \pm x, 0\rbrace} \underbrace{\times \times \times}_{\lbrace\pm 2x, \pm x, 0\rbrace} \overbrace{\times \times 0}^{\lbrace\pm 2x, \pm x, 0\rbrace}$$  \end{document}

Sometimes I want to describe portions of an equation using \underbrace and \overbrace in such a way that the portions are not completely distinct, for example:          /-------\ x = A + B + C + D + E     \-------/   \---/      What is the best way to do this?


I have a module with a bundleable content entity that has been deployed to an existing site.  On the site, a bundle was created and a date field was manually added to it via the UI. Now the date field needs to be automatically added to each new bundle created but I'm not sure how to go about doing this.  So far, I have exported the field storage YML file to 'config/install/field.storage.mymodule.field_date.yml' and created a 'hook_entity_bundle_create' function but am not sure how to load the field and add it to each new bundle created or even if this is the right approach.

My module provides a configuration form which allows to select a content type and on submit 2 new fields will be added to the selected content types.  I want to add these fields to the content types programmatically and I tried this using hook_entity_bundle_field_info but the fields don't get saved.  How can I save the fields? And how can I delete the fields (if the user changes the content type in the configuration form)?


I like to setup a website for a software to share it or sell it, the domain with .com already has been registered but .net and .org are available,  I have seen some products in .org, should I use this affix for my website?  Are there any advantage or disadvantage to use it over a .com website?

I've noticed .com is the standard top-level domain, but when should I not use .com? What are the most common alternatives? If someone has foo.com registered, should I choose a different domain or register foo.somethingelse?


My issue is as simple as it sounds, but can't find why it happens. I don't understand everything with encoding but here, on the same page, when I hit F5 to reload it, the accent only show up half the time. Which is very strange..  The string comes from a database where a table stores it as a VARCHAR encoded in latin1_swedish_ci. The accents in the database are correctly displayed.  I think nothing is wrong with that as with an other table and the same encoding, the accents don't have any problem.  Any idea on where it could mess up?

I'm setting up a new server and want to support UTF-8 fully in my web application. I have tried this in the past on existing servers and always seem to end up having to fall back to ISO-8859-1.  Where exactly do I need to set the encoding/charsets? I'm aware that I need to configure Apache, MySQL, and PHP to do this — is there some standard checklist I can follow, or perhaps troubleshoot where the mismatches occur?  This is for a new Linux server, running MySQL 5, PHP, 5 and Apache 2.


Give an epsilon-delta proof that the limit for x→0 of x³sin(x) exists.  What I can derive from this question is   lim = ?= 0  x=0  so, with an epsilon delta proof, i have to proof that at point x=0 there is a limit. So x³ isn't possible for x<0.   Because of de sin(x) I get that it is not possible to have a negative x, but I don;t know how to use the epsilon delta proof with this.   Please help

Give an epsilon-delta proof that the limit for $x\to 0$ of $x^3\sin(x)$ exists.  If I take a really big number for $x$ it doesn't seem to have a limit...


In Ubuntu GRUB how to set a password for editing options (e key), but not for regular booting a menu item?

I set up the GRUB password protection on my Ubuntu LTS 14 64bits. To do that I generated a hash of the password with grub-mkpasswd-pbkdf2. Then I edited /etc/grub.d/40_custom to add those 2 lines:  set superusers="admin" password_pbkdf2 admin grub.pbkdf2.sha512.10000.EC81D.............   After updating the Grub and rebooting, the password is present BUT everywhere. If I want to boot on Ubuntu, I have to enter my password. I'd like to set up the password only for 'e' editing GRUB menu. (to avoid single user mode)  Any Ideas ?  Thanks


I'm trying to partition my SD card with a ~31gb FAT32 partition and a 1024mb ext3 partition for A2SD. I've tried making the partitions with CMW-Alpharev Recovery v2.5.1.8 and with gParted (on a bootable live USB stick) and neither works. Basically, whenever I try to create a second partition on the card, the second (or later) partition doesn't work anywhere. It's not recognized by my phone, Windows or gParted (even right after parttitioning). The first partition does work, though. So if the ext3 is first, the FAT32 doesn't work and vice versa.  I have no clue as to what could be causing this or how to fix it, any suggestions?

I am going to install cm7 and it seems to me that is 'good' to partition my SD card.  I did some reading but I am not sure if ext partition will become accessible as mass storage when an Android phone is connected to the computer.   I still want to transfer files from / to my SD card via computer. How can I backup files if they are on an ext partition?  How big ext partition is good if my sd card is 16GB?    HTC Desire on Android 2.1


I have a query in which I am updating a table and have used IN keyword in the query. The query is something like this:   UPDATE q  SET b_id = 123      WHERE id IN (SELECT id FROM q WHERE b_id IS NULL LIMIT 1)   There is another query in which I am inserting data in table. The query is:   INSERT INTO q (id, item) VALUES (@id, @item)   The queries are executing on different threads. While executing the second (INSERT) query I am getting database is locked error.  What is the reason?  id is not primary key.

I've written an API for a client that accepts orders from clients and converts them into print jobs that go to an HTTP bridge into the company's RIP software. On the backend, the bridge is reading and writing job data to an SQLite database. It stores the job in SQLite and then sends it to the RIP. The RIP communicates back to the bridge when the status changes. It updates the record in SQLite, and through a series of subscriptions and webhooks sends the status update back to the API.  Neither the bridge nor the RIP automatically cleans up after itself, and the bridge imposes a limit of 5,000 tracked jobs at a time. So if we try to send job #5001 while it's storing 5,000 additional jobs, it will fail.  So the solution, at least in theory, would be to clean up jobs as they complete. Which is what we're doing.  When jobs complete my API enqueues a cleanup task, which is run from a separate process and requests the bridge remove that job.  The problem arises here. When we request cleanups the bridge starts failing job submissions due to DB lock errors. We're not deleting active jobs so there should be zero conflict between what is currently being INSERTed or UPDATed and what is being DELETEd as a result of our removal request.  I can only assume SQLite is locking the entire database for the duration of the delete instead of locking only the rows in use.  Would this make sense?  From the outside of the black box that is this software, is there anything I can do to affect this locking behavior in SQLite?  If not I essentially have to work around it by putting a buffer between everything our API does and the bridge that switches between a print mode and a cleanup mode but never does both synchronously. This will work but will slow production, and ultimately requires me to build a hack around a limitation in a $200,000 software product that just can't handle our volume.


So I've bought a Win10 laptop and I find myself using the command prompt frequently - in different folders. At first, I just put 1-line batch scripts everywhere to start the Prompt in that folder, but it was repetetive and not really worth it too much.  I remember (perhaps falsely) that I could right-click on a folder and an option "Open Command Prompt in This Folder" would appear. Is there a way to have that available in Windows 10?

When I'm working in a folder in Windows Explorer, sometimes I have a need to run some CMD command in this folder.  How do I open the command line from a current folder, so the console opens in the current directory?  Example:  I work in D:\Apps\Test. I would like to have a possibility to open a command prompt with the same context (meaning: D:\Apps\Test), so I don't have to navigate to this folder again within a console, ie. so it opens cd'd to the current location.  EDIT: The solutions from  do not work for me, what's why I asked a separate question.


Why is it necessary "to make holes" when a Pâte Brisée, Pâte Sucrée or Pâte Sablée or go to the oven if they are not made with baking powder?

When making a pie, you almost always have to make holes in the dough with a fork. This is called docking.  What is the exact reason for doing this? Are there kinds of pastry (puff, short crust, flaky) where this isn't necessary? Do you only need to do it when blind-baking? When you're using baking weights, does it still make a difference?


How does application (any) make its shortcut for launch in installation? For example c:\>start calc will launch windows calculator, but I have no idea where is located the executable calc.exe and how did the application make a shortcut for it (so it could be used as a argument to start command). Another example c:\>start gcc foo.c will trigger the gcc compiler (installed from mingw), but how does start command know where to find its executable? I know the cmd.exe will look in %PATH%, which in my case is C:\WINDOWS\system32;C:\WINDOWS;C:\WINDOWS\System32\Wbem;C:\WINDOWS\System32\WindowsPowerShell\v1.0\;C:\WINDOWS\System32\OpenSSH\;C:\Program Files\dotnet\;C:\Strawberry\c\bin;C:\Strawberry\perl\site\bin;C:\Strawberry\perl\bin;C:\Users\ppast\AppData\Local\Microsoft\WindowsApps;C:\Users\ppast\.dotnet\tools;C:\Users\ppast\OneDrive\Plocha\scripts; But for example - if I trigger c:\windows\system32> cl foo.c gives: 'cl' is not recognized as an internal or external command, operable program or batch file.  gives error. But I know I have the windows compiler installed (since I have visual studio c++ installed). So how does application makes shortcuts (and how to find out, which shortcut/name should I use as argument for start when I know application name) ? And how to make custom shortcut for my own exe files?

Questions about    setting environment variables the PATH   are very common here, and in most cases the answers are very similar to each other. In the future it would be nice to have a good Q/A for this.  So the question is: What are environment variables, like the executable PATH, and how can I change and use them on major operating systems?  A good answer would include a simple explanation of what environment variables and especially PATH mean to the OS, as well as simple guidelines on how to set and read them accordingly.


On giving the command  sudo apt-get update   I am getting the following error:  E: Syntax error /etc/apt/apt.conf.d/01autoremove-kernels:1: Extra junk at end of file.   Also a red circle with negative sign is present on the upper right corner of the desktop and I am unable to access update manager.

I'm trying to configure some proxies for a guest virtual machine and now I'm getting:  sudo apt-get update E: Syntax error /etc/apt/apt.conf.d/95proxy:4: Extra junk at end of file   The content of the file is:  cat /etc/apt/apt.conf.d/95proxy   Acquire::http::proxy  "http://10.0.0.60:3128/" Acquire::ftp::proxy "http://10.0.0.60:3128/" Acquire::https::proxy "http://10.0.0.60:3128/"


Find all integer values of $x$ where $x^2+3x+24$ is a perfect square. By guessing I found one solution that $x=5$.I found the problem in the exercise of a book in the chapter of polynomials. So please help me.

Find all integers $x$ such that $x^2+3x+24$ is a perfect square.    My attempt:    $x^2+3x+24=k^2$ $3(x+8)=(k+x)(k-x)$    Now, do I find solution treating cases? But that doesn't seem very easy. Please help.


I was deleting all previous Eclipse versions , so I used sudo apt-get autoremove eclipse*. It said it would be about 40 Mb of files to uninstall, so I agreed believing it would work on the intended scope.  The expected behavior is that it removes the application itself and also its dependencies. In my case, it's begun to delete some linux-headers, python packages, etc. which I don't think are related to Eclipse, and it's got me worried. Help?

I was compiling a tool called Rejoystick so I installed a few packages and dependencies. But now I don't need it any more so I removed those packages. Running apt-get shows that I have some packages that are automatically installed and are no longer needed.   But I have a bad experience with apt-get autoremove. It broke my desktop environment when I uninstalled wine some time ago. Luckily, I had a clonezilla partition backup then, but this time, I don't have a backup. So I'm cautious. Running apt-get shows these packages are orphaned     gir1.2-gtk-2.0 libasound2-dev libavahi-client-dev libavahi-common-dev   libcaca-dev libcairo-script-interpreter2 libdbus-1-dev libdrm-dev   libexpat1-dev libfontconfig1-dev libfreetype6-dev libgl1-mesa-dev   libglu1-mesa-dev libharfbuzz-dev libharfbuzz-gobject0 libice-dev   libpcre3-dev libpcrecpp0 libpixman-1-dev libpng12-dev libpthread-stubs0-dev   libslang2-dev libsm-dev libx11-dev libx11-doc libx11-xcb-dev libxau-dev   libxcb-dri2-0-dev libxcb-dri3-dev libxcb-glx0-dev libxcb-present-dev   libxcb-randr0-dev libxcb-render0-dev libxcb-shape0-dev libxcb-shm0-dev   libxcb-sync-dev libxcb-xfixes0-dev libxcb1-dev libxcomposite-dev   libxcursor-dev libxdamage-dev libxdmcp-dev libxext-dev libxfixes-dev   libxft-dev libxi-dev libxinerama-dev libxrandr-dev libxrender-dev   libxshmfence-dev libxxf86vm-dev mesa-common-dev x11proto-composite-dev   x11proto-core-dev x11proto-damage-dev x11proto-dri2-dev x11proto-fixes-dev   x11proto-gl-dev x11proto-input-dev x11proto-kb-dev x11proto-randr-dev   x11proto-record-dev x11proto-render-dev x11proto-xext-dev   x11proto-xf86vidmode-dev x11proto-xinerama-dev xorg-sgml-doctools xtrans-dev   zlib1g-dev   I'm not sure if I should run apt-get autoremove. I was searching details related to each of these packages so that I can understand which ones are needed but they all seem important e.g.     gir1.2-gtk-2.0    I have Cinnamon, GNOME and Unity installed, I think apt-get autoremove will break something. Any help will be appreciated.   Thanks for reading.


I'm supposed to use Fermat's Little Theorem $($ If $p$ is a prime and $p$ doesn't divide $a$, then $a^{p-1} \equiv1 \mod p)$    and  to find the least residue of the following:  $24^{(54n + 1)} +11 \mod 19$, where $n  \in \mathbb{Z}^+.$  The 11 is trivial, so I'm just concerned with reducing the term with  $24^{(54n + 1)}$.  (24, 19) = 1, so the Theorem applies.  $24\equiv 5\mod19$, so   $24^{(54n + 1)} \equiv 24^{54n}(5)\mod19$  At this point, I'm not really sure what to do next because I can't really see how to bring the theorem into play!

How do I efficiently compute $a^b\bmod c$:  When $b$ is huge, for instance $5^{844325}\bmod 21$? When $b$ is less than $c$ but it would still be a lot of work to multiply $a$ by itself $b$ times, for instance $5^{69}\bmod 101$? When $(a,c)\ne1$, for instance $6^{103}\bmod 14$?  Are there any other tricks for evaluating exponents in modular arithmetic?  This is being asked in an effort to cut down on duplicates, see  and .


Mostly due to bathing or washing clothes our finger become wrinkled what was the reason behind it??

I found an explanation for my question here , which suggests that water washes out sebum (special oil, which covers our skin) and water gets into outer layer of now unprotected skin by osmosis. This article also suggests that fingers are not really shriveled - they are water-logged. But is this right? I think I observed many times my wrinkly fingers after swimming, but I never felt that they are water-logged. Any thought on this matter would be highly appreciated.


My B1/B2 visa expires on August 14, and I have to stay in the US from August 14 to 17. I want to apply for a new visa for these dates. Will the embassy give me a new visa or they will ask me to travel with the same visa?

I'm a bit surprised from my US Visa. I plan to go to a conference on 3rd of April. Amazingly though, the visa expiration date is written as April 3rd.  So what does that mean. Can I enter the US on April 3rd? or should I enter one day earlier?


What the wrong in the code, it is just show Array memory address instead of value in first index info[0][0].     car camry = new car();     car[][]info;     info = new car[2][3];     info[0][0] = camry;             int i = 0;     while( i < info.length)     {         int j = 0;       do        {                             System.out.println( info[i][j]);         j++;       }       while(j < info[0].length);       i++;     }

In Java, arrays don't override toString(), so if you try to print one directly, you get the className + '@' + the hex of the  of the array, as defined by Object.toString():  int[] intArray = new int[] {1, 2, 3, 4, 5}; System.out.println(intArray);     // prints something like '[I@3343c8b3'   But usually, we'd actually want something more like [1, 2, 3, 4, 5]. What's the simplest way of doing that? Here are some example inputs and outputs:  // Array of primitives: int[] intArray = new int[] {1, 2, 3, 4, 5}; //output: [1, 2, 3, 4, 5]  // Array of object references: String[] strArray = new String[] {"John", "Mary", "Bob"}; //output: [John, Mary, Bob]


Here is the sentence:     "General Martin Dempsey, the Joint Chiefs of Staff chairman who just   wrapped up a visit to Afghanistan, was asked whether he foresees North   Korea taking military action soon.”   Source()   Here is the revised sentence     “General Martin Dempsey, the Joint Chiefs of Staff chairman, who just wrapped up a visit to Afghanistan, was asked whether he foresees North Korea taking military action soon.”   The explanation is by combining the general’s title with the reference to his recent visit to Afghanistan, the sentence implies that more than one Joint Chiefs of Staff chairman exists; Dempsey is the one who had just returned from Afghanistan. The phrase “the Joint Chiefs of Staff chairman” must be bracketed by a pair of commas to show that it is the first of two parenthetical phrases dividing the subject from the object: “General Martin Dempsey, the Joint Chiefs of Staff chairman, who just wrapped up a visit to Afghanistan, was asked whether he foresees North Korea taking military action soon.”  Can someone explain to me the explanation? I just don't get it because there is only one chairman so even without a comma the sentence still makes sense to me.

A friend of mine, George, called the other day. The poem "The Road Not Taken" is one of Robert Frost's most famous works.   How come sentence 1 requires commas and sentence 2 does not? Both phrases ("George" and "The Road Not Taken") both specify the subject.


How can I loop an ocean animation with the ocean modifier? I really need this for a game. I want to do this so I have nice looking water!

Is there a way animate the ocean modifier so it loops continuously?  I would like to make an animation where the last frame seamlessly goes into the first without the ocean "jumping":    How can I achieve this?


Minor mistake in the text when clicking Recommend close on the low quality review-queue:

As you can see, the off-topic page isn't quite right...    Could this (minor) issue be fixed?


I am running Ubuntu on a Chromebook via Crouton.  As my keyboard does not have a Print Screen key, and I would like to take A screenshot, I am unsure of what to do.  I am using the Xfce interface, and I would like to take a screenshot of a LibreOffice drawing so as to change my background.

I am a new Xubuntu user. Earlier when using Gnome, I was able to configure several desktop shortcuts, particularly for navigation between workspaces.  But, now in Xubuntu, I cannot find those options.  Where can I find those options.


I'm making a hotel and a room key system, I'm trying to make the keys only be able to be placed on certain types of wool.   Example of what I'm doing:  /give @p minecraft:lever 1 0 {CanPlaceOn:["minecraft:wool"]}   I want the wool to have data like when in a /give command. The second number is the data example:  /give @p wool 1 5

I'm currently in the process of making a custom map and I want to add blocks that can only be placed on a certain colour clay.  This is the command I tried using.  /give @p cobblestone 1 0 {CanPlaceOn:["hardened_stained_clay"],Damage:3}   However, even with this command the cobblestone can be placed on any colour of stained clay. What command can I use for placing only on a certain block?


A little while ago I turned on my gaming computer and noticed the following window on my taskbar.     When I click it, I get the following window.    If I had my update settings turned off. Would they still be able to push the upgrade notification?

This icon showed up in my taskbar notification area today and I cannot seem to get rid of it:    Clicking on it displays the following screen:    So how do I disable or remove the "Get Windows 10" icon?


I have a bash script and sometimes happened that, even my script was scheduled, it was executed two times. So I added few code lines to check if the script is already in execution. Initially I hadn't a problem, but in the last three days I had got it again  PID=`echo $$` PROCESS=${SL_ROOT_FOLDER}/xxx/xxx/xxx_xxx_$PID.txt      ps auxww | grep $scriptToVerify | grep -v $$ | grep -v grep > $PROCESS num_proc=`awk -v RS='\n' 'END{print NR}' $PROCESS` if [ $num_proc -gt 1 ]; then   sl_log "---------------------------Warning---------------------------"   sl_log "$scriptToVerify already executed"   sl_log "num proc $num_proc"   sl_log "--------"   sl_log $PROCESS   sl_log "--------"   exit 0; fi   In this way I check how many rows I've got into my log and if the result is more than one, then I have two process in execution and one will be stopped.  This method doesn't work correctly, though. How can I fix my code to check how many scripts in execution I have?

What's a quick-and-dirty way to make sure that only one instance of a shell script is running at a given time?


The pass by reference mechanism provided by c++ internally again uses pointers and is just pass by value or is it something different ?

I know references are syntactic sugar, so code is easier to read and write. But what is the difference between a pointer variable and a reference variable?


I was taking photos last night at a formal function and two of my photos came out like this one in the attachment? Can anyone tell me what would cause this to happen? Thanx

I have a number of raw images which were restored after deletion, when I open them in image viewer they seem to be fine, but if I open them in Photoshop image seem to be corrupted. How is it possible and is there a way to extract this uncorrupted image?


I Installed the 1.8.0v on Win7 profesional SP1 system (as administrator) and I take this message: "The procedure entry point sqlite3_open_v2 could not be lovated in the dynamic library sqlite3.dll". QGIS 1.7 was working. Help

Translation: Hello, I have a problem installing version 1.0.8. The following error message appears:  The entry point for the procedure sqlite3_open_v2 cannot be found in the dynamic link library sqlite3.dll  [The next sentence is ungrammatical in the original and therefore its translation is in doubt.] Previously I had version 1.7 Wroclaw, which I uninstalled before installing the new one. Thank you for your help. Original Bonjour, J'ai un problème pour installer la version 1.0.8, le message d'erreur suivant apparait:  Le point d'entrée de procédure sqlite3_open_v2 est introuvable dans la bibliothèque de liens dynamiques sqlite3.dll  J'avais avant d'installer la version 1.7 Wroclaw que j'ai désinstaller pour installer la nouvelle. Merci pour votre aide.


I encountered this problem that I do not fully understand. Find the multiplicative inverse of $[45]$ in $Z_{101}$ . Then determine the integer x between 1 and 100 such that $45^{99} \equiv x$ (mod 101) Using the Euclidean algorithm the multiplicative inverse of $[45]$ can be found as [9]. However finding $x$ is where my effort halts. Lets denote $a=45$, $e = 99$ and $p = 101$. Since $p$ is a prime and $a \nmid p$ Fermat's little theorem gives $a^{p-1} \equiv 1$ (mod p) = $45^{101-1} \equiv 1$ (mod 101) in a case where $e > (p-1)$ we could simply evaluate $a^e$ as follows $a^e = a^{k \cdot (p-1) + r} \equiv a^r$ (mod p) where $k$ and $r$ are integers. Finally $a^r$ could be envaulted in mod p and x would be found. However, in this problem, $e < (p-1)$ = $(99 < 100)$ and the evaluation described above is not possible. I.e. we can not evalute $45^{99}$ as $45^{k \cdot 100 + r}$. In summary, how can $x$ be found in the equation $a^e \equiv x$ (mod p) when $e < (p-1)$?

Why is $a^{-1}$ mod $p$ equal to $a^{p-2}$ mod $p$ in modular arithmetic?


Hie. My operating system won't play any other audio format except .flac so whenever i try playing playing an mp3 or wma file etc it says could not find required plugin. In need of a solution.  Thanks

I would like to install the restricted extras package, which I didn't select during the install. How can I do that?        is a meta-package that installs:         Support for MP3 and unencrypted DVD playback   Microsoft TrueType core fonts   Flash plugin   codecs for common audio and video files


I wanna round after decimal point. I know that the function round does it but when the number has only zeros after decimal point I also wanna keep the amount of zeros that I want, becouse python leaves only 1 zero. round(54.983839,2) == 54.98 round(54.0, 2) == 54.0    # and here I want 54.00

I want a to be rounded to 13.95.  >>> a 13.949999999999999 >>> round(a, 2) 13.949999999999999   The  function does not work the way I expected.


Problem I recently made a post that was deleted by the moderators for being only a link (still learning what's acceptable). My post:   I received 2 downvotes on the answer before it was deleted. I received -4 rep for the downvotes, but then +4 for the deletion (even though I was not the one to delete the answer). Later, I edited my answer and requested an undelete. Upon undelete the - 4 rep hit my account again even though this answer is entirely different from the first, and shows a 0 for the upvote/downvote interface.   Current Votes:      Current Rep for Answer:   Questions     Why do I receive positive rep when another user deletes my answer? Why does the negative rep from downvotes on the previous answer show in my feed (and affect my current standing), but not on the interface feature upon undelete? Is this a bug or just the way the site functions?   Explanation I do not think that this post is effectively explained by the post:   It does not explain why the negative rep persists and why the UI is unchanged.

On Stack Exchange, users may gain a certain level of reputation.  What does reputation do? How can a user gain or lose reputation?   See also   in the Help Center  - Maximum amount of votes a user can use in a day and reputation requirements to vote.  - How to get an exact overview of the actions that got you your reputation.  - A full list of all privileges granted at each reputation level on all sites.


Let's say I'm narrating a past incident in which a sentence goes like --  There was a rumor that Citibank is in debt.  Is the above sentence correct or do I need to replace 'is' with 'was' ?

A few days back, I asked a question - why in reported speech is the present perfect tense sometimes not back shifted to the past perfect tense ? For example:     He said that he has painted the door.   Someone said - "if the situation is still relevant and the results of it can be seen, heard or felt then the present perfect tenses are not back shifted to past perfect tenses." And this was all about indirect speech, and I totally agree with what was said.  Now let's take a case which is not indirect speech. For example:     1) He noticed that he has finished painting the house.   My question is, is this sentence correct under the condition that finishing the painting has some present relevance ?     2) The president learned that the earthquake has caused havoc across   the country.   My question is, is this sentence correct under the condition that the earthquake has recently come and the effects of it can still be seen ?     3) I realized that he has left his wallet.      4) It was unclear that she has painted the door.   Are these 4 sentences correct or do I need to use 'had' in place of 'has' ?


I'm trying to justify using of GLM model in my project instead of a simple linear regression. A lot of sources that I've seen contain the statement that "GLM allow us to build regression models for response variables that are not normally distributed". I can't understand what that is supposed to mean since we don't make any assumptions about variable distribution. Could you, please, explain  why it's often more appropriate (theoretically)  to use GLM if your response variable is,  say, count.

I understand that for certain datasets such as voting it performs better. Why is Poisson regression used over ordinary linear regression or logistic regression? What is the mathematical motivation for it?


Given three positive numbers a,b,c satisfying $$a^2+b^2+c^2=1$$ Prove that: $$\frac{bc}{a^2+1}+\frac{ac}{b^2+1}+\frac{ab}{c^2+1}\leq \frac{3}{4}$$ The things I have done so far: $$\sum \limits_{cyc}\frac{bc}{a^2+1}=\sum \limits_{cyc}\frac{bc}{2a^2+b^2+c^2}\leq \sum \limits_{cyc}\frac{bc}{2ab+2ac}$$ $$=\sum \limits_{cyc}\frac{bc}{2a(b+c)}\leq \frac{1}{4}\sum \limits_{cyc}\frac{(b+c)^2}{2a(b+c)}=\frac{1}{4}\sum \limits_{cyc}\frac{b+c}{2a}$$ $$=\frac{1}{8}.\frac{\sum \limits_{cyc}bc(b+c)}{abc}=\frac{1}{8}.\frac{\sum \limits_{cyc}bc(b+c)+3abc}{abc}-\frac{3}{8}$$ $$=\frac{1}{8}.\frac{(a+b+c)(ab+bc+ca)}{abc}-\frac{3}{8}$$ $$\leq \frac{1}{8}.\frac{\sqrt{3(a^2+b^2+c^2)}(a^2+b^2+c^2)}{abc}-\frac{3}{8}$$ $$=\frac{\sqrt{3}}{8abc}-\frac{3}{8}$$ I don't know what to do anymore.

Ff $a,b,c$ are positive real numbers that $a^2+b^2+c^2=1$ ,Prove: $$\frac{ab}{1+c^2}+\frac{bc}{1+a^2}+\frac{ca}{1+b^2}\le\frac{3}{4}$$   Additional info: I'm looking for solutions and hint that using Cauchy-Schwarz and AM-GM because I have background in them.   Things I have done: I tried to  change LHS to something more easy to work but I was not successful. For example $$\frac{ab}{1+c^2}=\frac{1}{2}\left(\frac{a^2+b^2+2ab}{1+c^2}-\frac{a^2+b^2}{1+c^2}\right)$$    that was not useful. Any hint for starting step is appreciated.


I'd like a different color for the inside. I want to make a pumpkin with a uv shell on the outside and just orange on the inside. it is possible?

How could a one-sided material be achieved with the Cycles renderer?  I would like to create a plane that is completely transparent from one side, and a mirror from the other side.  It would be cool if Cycles/Blender simple supported backface culling like the game engine. But I guess it doesn't?  How could something like that done with nodes?


I have started studying free groups but cannot get motivation behind it. I know that a free group $F_A$ over the set $A$ consisting of all combinations or expressions that can be built from the members of $A$.  But why would one want to do such a construction? What is the motivation behind it

In , one learns two definitions of free groups associating with sets.        Let $A$ be a set, the free group of $A$, $F(A)$ is the initial object in the category $\mathcal{C}$, where \begin{equation} \operatorname{Obj}(\mathcal{C})=\{A\xrightarrow{g}G\}, \end{equation}where the codomain $G$ are groups, and \begin{equation} \operatorname{Hom}(\mathcal{C})=\{\text{Commutative Diagrams } A\xrightarrow{g_1}G_1\xrightarrow{\phi}G_2\xleftarrow{g_2}A\}  \end{equation} where $\phi$ are group homomorphisms.   Also $F(A)$ has the concrete construction with elements being non-redundant words with alphabet $A$, and the group multiplication being juxtaposition and reduction.      But what good are free groups? Why are they useful?  says they are useful in topology, but does not explain why explicity.   Can someone give some examples that an undergraduate can understand? I am asking about examples that can show the usefulness of this abstract construction. So I guess the identification of $\mathbb{Z}=F({a})$ does not really count.


I have a survey that includes questions where you can choose one option from a list. For example: "How often do you go to the supermarket?" A. Every day B. 2-6 times per week C. Once per week or less D. Never  Say 1000 people respond to the survey and 100 people choose option A, 400 option B, 400 option C and 100 option D. How do you calculate the confidence intervals of these proportions? Are they simply binomial confidence intervals (i.e. just normal proportions)? Or is it something more complicated, because the proportions are related to each other?

I know what margin of error means in a poll with two choices. For example, if a poll estimates two candidates are to have 45% and 55% of the vote respectively and the margin of error is 4%, then we can say with 95% certainty that the first candidate will receive between 41% and 49% of the vote. This means that the second candidate will have between 51% and 59% of the vote. We can say this because there are only two choices and the total must add up to 100%.  However, some polls sometimes measure the percentage expected votes for 3 or 4 candidates. In this case, if you have variance for the measurement of one candidate, how is that variance for one candidate's estimate distributed among two or more candidates?


My friend and I were working through old preliminary exams. This problem is the fifth one on  list, but we were unable to come up with a solution.  Let $(A,\mathfrak{m})$ and $(B,\mathfrak{n})$ be local Noetherian rings. Suppose that $\phi:A\to B$ is a map such that $\phi(\mathfrak{m})\subset\mathfrak{n}$, and suppose that  $A/\mathfrak{m}\to B/\mathfrak{n}$ is an isomorphism. $\mathfrak{m}\to\mathfrak{n}/\mathfrak{n}^2$ is surjective. $B$ is finitely generated as an $A$-module.  Prove that $\phi$ is surjective.  Does anyone have an idea on how to proceed, or possibly a solution to this?

Let $(A,\mathfrak{m})$ and $(B,\mathfrak{n})$ be local Noetherian rings. Suppose that $\phi : A\rightarrow B$ is a map such that $\phi(\mathfrak{m}) \subset \mathfrak{n}$ and suppose    $A/\mathfrak{m} \cong B/\mathfrak{n}$; $\mathfrak{m} \rightarrow \mathfrak{n/n^2}$ is surjective; $B$ is a finitely generated $A$ module.   Show that $\phi$ is surjective.  Here is my approach so far: Consider $0\rightarrow \mathfrak{m} \rightarrow A \rightarrow A/\mathfrak{m}\rightarrow 0$ and the exact sequence for $B$. Then we can establish an commutative diagram of the two exact sequences. (Sorry i do not know how to type that.) Then apply the snake's lemma, the isomorphism in condition 1 yields an isomophism $\mathfrak{n}/\phi(\mathfrak{m})\cong B/\phi(A)$. To see $\phi$ is surjective, it suffices to show $\phi(\mathfrak{m})=\mathfrak n$. Since $\mathfrak{n}$ is the maximal ideal of $B$, if $\phi(\mathfrak{m})+\mathfrak{n}^2 = \mathfrak{n}$, Nakayama will give the desired result. Now somehow I want to conclude $\phi(\mathfrak{m})+\mathfrak{n}^2 = \mathfrak{n}$ from conditions 2) and 3), which seems to be true but cannot really proceed.


Microsoft Word wants to change this "whom" to "who" -- but wouldn't that be wrong!?   She previously saw another physician in the practice whom she describes as a “terrible doctor.”

Is this correct?     The person with whom I'm doing the project should be here soon.   If it is, is with always a dative preposition (like mit in German)?


How can I install Skype on Ubuntu 14.04 with synaptic? I don't want to download from the site

I want to install Skype, but I can't locate it in Software Center or by using Synaptic Package Manager. Can anyone help me?


Nine distinct positive integers are arranged in a circle such that the product of any two non-adjacent numbers in the circle is a multiple of n and the product of any two adjacent numbers in the circle is not a multiple of n, where n is a fixed positive integer. Find the smallest possible value for n.

Given: A circle with nine distinct positive integers. n is a fixed positive integer.  So these positive integers are arranged in the circle in such a way that the product of any selected two NON-ADJACENT numbers in the circle is a multiple of n. The product of two ADJACENT numbers in the circle is NOT a multiple of n. What is the smallest posible value for n.


Edit:  This question is actually a duplicate of . It's solution worked for me.    Basically, I want to do what  is doing, but using bibtex instead of biblatex.   To summarize what it's doing there, I want a single .bib files to store the bibliography entries for an entire document. When I run a section file (ie. not the main.tex), it cannot find the Sources.bib and so fails to make the reference. If I run main.tex though, the reference that is inside the section file resolves perfectly fine.  For a minimum working example (it doesn't run correctly, but it gives you the idea), see below.  So I have the following file structure:  project_dir |    main.tex |    background.tex |    Sources.bib   Inside main.tex, I have:  %%%% main.tex %%% \documentclass[10pt]{ClemsonThesis} \usepackage{amsmath} \usepackage{subfiles}  \begin{document} % blah blah blah  \subfile{background.tex}  \bibliographystyle{plain} \bibliography{Sources} \end{document}     %%% background.tex %%% \documentclass[main.tex]{subfiles}  \begin{document}  %blah blah blah Here's some random text I have in a few paragraphs. Here's a citation for referencing an external resource: \cite{McCormack2012}.  \end{document}     %%% Sources.bib %%% @Inbook{McCormack2012, author="McCormack, Percival", title="The Vortex", bookTitle="Vortex, Molecular Spin and Nanovorticity: An Introduction", year="2012", publisher="Springer New York", address="New York, NY", pages="1--65", abstract="The first notable works on fluid motions appeared in the early seventeenth century. Descartes in his ``Principia Philosophiae'' (1644) considered that space was filled with frictional vortices, so that the planets are carried along by the vortex motions. Vortices had fascinated mankind for many centuries before Descartes. It was considered that life had started in the water of the primeval vortex -- in whirlwinds and whirlpools.", isbn="978-1-4614-0257-2", doi="10.1007/978-1-4614-0257-2_1", url="https://doi.org/10.1007/978-1-4614-0257-2_1" }   Using the files below, if I compile background.tex, the bibtex reference fails. If I run main.tex, the bibtex reference that is in background.tex resolves perfectly fine.  I've tried adding \bibliography{Sources} to the end of the background.tex file, but got nothing.

I have a problem very similar to the question being asked in  . My .bib is references in main.tex. When compiling main, everything works like a charm. Working on the subfiles, I have two issues though (which are most likely related):   I can't access the bib with auto-completion When compiling the subfile, it doesn't insert the citations.   I tried including  \bibliographystyle{plainnat} \bibliography{mybib}   in the subfiles, which also worked smoothly. Obviously, the bibs are included in every chapter of the document when compiling main.tex, then. I tried setting a global boolean in main.tex:  \newboolean{printBibInSubfiles} \setboolean{printBibInSubfiles}{false}    and in the subfiles:  \ifthenelse{\boolean{printBibInSubfiles}}    {}    {\bibliographystyle{plainnat}     \bibliography{../betterbib.bib}}    For some reason, then setting the boolean to false, the "bibliography"-header was printed in the subfiles as well as for the main file, but there was no output of citations under any of the "bibliography"-headers. Furthermore, compiling only the subfiles didn't work correctly.  My document structure is the following:  main.tex:  \begin[document] ... \subfile{sub/dataprocessing} ... \bibliographystyle{plainnat} \bibliography{mybib} \end{document}   the subfiles:  \documentclass[../main.tex]{subfiles} \begin{document} ... \cite{Random2014} ... \end{document}   After all this explanation: the only thing I want is to access the .bib from the subfiles without having to manually uncommenting something when compiling the main file. Any takers?  PS: Obviously, I also tried the solution provided in "" but couldn't get it to work. I don't know whether that would solve my problem anyway, since I don't have the \printbibliography-issue of the thread opener.


I am reading in a text file containing several lists with each on its own line. The elements in a given list are non-integer x,y co-ordinates that need to be placed into an array such that:  [x1, y1, x2, y2, x3, y3,....xn, yn]  becomes:  x1 x2 x3....xn y1 y2 y3....yn  but in the same 2d array. I'm very new to coding and have tried various methods but to no avail. Right now I am looping over the number of co-ordinate pairs and trying to append the values within the loop but am unsure how to do this. This is how I have started it: with open('textfile.txt', 'r') as infile:     for line in infile:         array=[]         number=(line.count(" ")+1)/2 #number of x,y pairs in list         for i in range(0, number-1):               Now I don't know where to go from here so any help would be greatly appreciated! Thanks

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


I've set the / volume for 30gb and it's getting full now. I want packages and programs to be installed in /home partition and I don't know how.  I want to install things into my /home partition!!

I do not want packages to be installed under /. (sudo apt-get install ...).   The reason why I need to do this is that:  My '/' is mounted with my SSD(16GB) and my hard disk(500GB) is mounted at '/home'.   I have already installed my Ubuntu 12.04 on that SSD. There is not much free space under '/' now.


I have some phone numbers diplayed from database. When i click on that number i have to call that number using skype.I am using a php code.   Call the Skype Echo / Sound Test Service   It works only if the system have skype installation. If computer does not have skype i need a skype installation procedure.  Anyone help me.

Is it possible for some Javascript to detect whether Skype is installed or not?  The reason I ask is that I'd like to change a link's href based on that: if Skype isn't installed, show a popup explaining what Skype is and how to install it, if it is installed, change the link to skype:my.contact.name?call so the click will start a call. Real estate issues means that I'd prefer to only have one link shown.


drwxrwxr-x 2 xyz xyz 176128 Jul 29 02:03 20170429   drwxrwxr-x 2 xyz xyz 110592 Jul 31 01:22 20170430  cd 20170429   ls -lart   total 196   drwxrwxr-x   2 xyz xyz 176128 Jul 29 02:03 .   drwxrwxr-x 253 xyz xyz 20480 Aug  4 00:00 ..     du -sh 20170429 176K    20170429  du -sh 20170430 124K    20170430   Referring to the above information, I wanted to know for the empty directories 20170429, 20170429 , why is it still showing having memory space of 176128 and 176128 while we do ls -lrt. Where from do these information comes from? Is it from inode? Also note that even by du -sh they still shows 176k and 124k respectively for the empty directory.

What does size of a directory mean in output of ls -l command?


I am looking for a complete list of bash commands as well as what the command does. Everything i find is some long drawn out article.

I often see things like     read man xyz   For more information read xyz's man page.   see info xyz    so I wonder:   How can I get help on terminal commands generally? What exactly are these man and info pages?   How can I find and view them?


I would like to upgrade to the latest 3.17 Linux Kernel because it has support for the Xbox One Controller and I really want to test it out.   I am running Ubuntu 14.10 64bit with the latest pre-release updates.  I have looked around the internet but most of the tutorials seem outdated, I don't want to follow them, have something mess up and have to reinstall everything

Currently I'm running Linux-3.0 and I want to update it to Linux-3.3.1 the latest stable kernel release as mentioned at . Can I update to 3.3.1 in Ubuntu without any risk of crashes? I'm updating my kernel regularly as provided by the Update Manager..Currently I have Linux-3.0.0.17..Can I update?  NOTE:  The latest kernel version any user is supposed to use in Ubuntu is updated automatically via the Update Manager, so no action is normally required by user regarding kernel upgrades. What the question author is referring to is mainline kernel, see:


I have a field that is varchar(8), holding date values that I converted from float to varchar.    Some records have eight characters, and some have seven.  I would like to make them all the same length by adding a leading zero to the ones that have 7.    8 char example: 12162003 7 char example: 5072004 (needs a leading zero)   The query:     select birthdate_new from table_name

As compared to say:  REPLICATE(@padchar, @len - LEN(@str)) + @str


Is there any kind of documentation about how a Stack Exchange site that has left beta is being customized? Is this done by the people starting the new site, or by Stack Exchange itself?

I'm asking this because the  site has been in public beta for 838 days and is still using the default beta-site theme which seems quite inappropriate for a site full of graphical designers.