About 50% of my questions have had 0 answers on Stack Overflow. Many people are refraining from answering my questions.  Why?

The way the askers write questions is a factor in determining how good the answers we get are. Obviously, if you ask a clear, direct question it is easier for a someone to answer you.  But, sometimes I've done that and my questions have still been overlooked.  I've noticed some question-posting methods that aren't exactly obvious, but do help me get better answers.    Some tricks I've learned...   Even if my question is very complicated, I try to write a short question.  People get turned off by longer questions, probably because they think its not worth their time (relative to other questions with equal reputation potential).  After I get some traffic and votes on my question, and maybe some comments like "Can you post the code?" or "Clarify this..." I might post more, but by then I am already getting attention to my question.  So, in summary, even if I know the answer requires a long question, I don't make it long until I've already gotten people to look at it. I use more generic tags when possible.  People are more likely to have c# and linq as a favorite tag, than MethodCallExpression, and I tend to get more views if I use at least one or two general purpose tags along with my more specific tags. I've noticed that if I give my question the performance tag, then SO heavy-weights like Marc Gravell, Jon Skeet and Eric Lippert are more likely to answer my question (especially if I use it in conjunction with a C# tag).  Since having this realization, if I can think of a way to rephrase my question to sound like it is related to C# performance, I will word it as such and tag it accordingly.   "Be polite. SO Users HATE when people be impatient, rude or impolite." - Benny   So,  Does anyone else have any tips for getting better answers and question-recognition on SO?  I think it would be really helpful if everyone contributed their own observations and techniques here.  P.S. This question is probably too long.


I am trying to call a function using a variable with it's name.  Here's the code:  var selectedFunc = 'func2';  var myModule = {      func1: function() {        //something here       },      func1: function() {        //something here      }  };  myModule.selectedFunc();   I would normally do this:  myModule.func1();   which will work but I'm trying to use the variable to define it's name, which is not working.  How can I fix this issue?

I have the name of a function in JavaScript as a string. How do I convert that into a function pointer so I can call it later?  Depending on the circumstances, I may need to pass various arguments into the method too.  Some of the functions may take the form of namespace.namespace.function(args[...]).


How to calculate the determinant of $$ A=(a_{i,j})_{n \times n}=\left( \begin{array}{ccccc} a&b&b& \cdots & b\\ b& a& b& \cdots& b\\ \vdots& \vdots& \vdots& \ddots&\cdots\\ b&b&b & \cdots&a \end{array} \right)? $$

I have the following $n\times n$ matrix:  $$A=\begin{bmatrix} a & b & \ldots & b\\ b & a & \ldots & b\\ \vdots & \vdots & \ddots & \vdots\\ b & b & \ldots & a\end{bmatrix}$$  where $0 < b < a$.  I am interested in the expression for the determinant $\det[A]$ in terms of $a$, $b$ and $n$.  This seems like a trivial problem, as the matrix $A$ has such a nice structure, but my linear algebra skills are pretty rusty and I can't figure it out.  Any help would be appreciated.


today I've installed Windows 8.1 and everything is working as it should be but I'm stuck at installing the Graphic drivers, I have a Dell Inspiron 5537 with AMD Radeon HD 8670M, I've found a driver on Dell Support for my laptop graphic driver, but on AMD website I've found an Up-to-date driver for my Radeon HD 8670M, also Windows Update provides a driver.. So the question is     Should I download the driver from Dell website, or   AMD Website, or Windows Update?

Today I see that there's an update to my graphics card driver (NVidia GT 220) available on Windows Update. Should I install that, or stick to the drivers provided by the manufacturer?  (Re-asked here after asking on gaming.stackexchange).


Recently I have installed ubuntu 18.04 on my laptop and I have downloaded all the necessary packages which included scilab version 6.0.1, but I am unable to open neither the scilab console nor scilab advance. Only my scilab CLI seems to open when I click it. Can someone help me out please as I am new to this Ubuntu

I have installed clean Ubuntu MATE 18.04 LTS and installed Scilab from repository here with    sudo apt-get update sudo apt-get install scilab   After installation I tried to launch it from GUI (Applications → Other → Scilab) - it does not start. Then I tried to launch it from terminal with scilab command. Terminal output is as follows:  $ scilab /usr/bin/scilab-bin: error while loading shared libraries: libjava.so: cannot open shared object file: No such file or directory   so it can't find Java. I reported  about this problem.  I checked existence of libjava.so:  $ dpkg -S libjava.so   openjdk-11-jre-headless:amd64: /usr/lib/jvm/java-11-openjdk-amd64/lib/libjava.so   so it is in place.  What should I do to get Scilab 6.0.1 working on Ubuntu 18.04 LTS?


I am working in programming for last couples on years, but today I saw a new thing that I searched on net but can't find the perfect answer. There is a code which says  for(String string : mCha) // line 1 { // loop working }   I want to ask that what does the line 1 mean? As I have studied that there should be 3 parameters in for loop and if we don't want to give that than the following method should follow  for(;;) { }   Please explain me as I am totally new to this syntax and I searched on net but can't find any thing useful.

Consider:  List<String> someList = new ArrayList<String>(); // add "monkey", "donkey", "skeleton key" to someList     for (String item : someList) {     System.out.println(item); }   What would the equivalent for loop look like without using the for each syntax?


I've noticed that some people getting the  badge are being awarded it 4 times within a short time period.  Here are a few I found in around 2 minutes but there are countless others:         These all happened around the same time in the day (on the 14th)

I am just .   I checked  and  but can't figure out why. I also checked  and I think I understand that it can be awarded to multiple answers to the same question.   But the same answer? Why?


My input file is below INPUT FILE <ReconSummary> <entryName>Total Deep</entryName> 777 <License>L</License> <Tran>H20</Tran> <job>1234</job> </ReconSummary>   <ReconSummary> <entryName>Total Saurav</entryName> 666 <License>L</License> <Tran>H20</Tran> <job>1234</job> </ReconSummary>  I have code which looks like LineNum=`grep -n "Deep" deep.xml | cut -d: -f 1 | awk -F '[\t]' '{$NF = $NF -1;}1'` sed -i "/$LineNum/s/^/

I have an input xml file like below INPUT FILE <ReconSummary> <entryName>Total Deep</entryName> 777 <License>L</License> <Tran>H20</Tran> <job>1234</job> </ReconSummary>   <ReconSummary> <entryName>Total Saurav</entryName> 666 <License>L</License> <Tran>H20</Tran> <job>1234</job> </ReconSummary>   <ReconSummary> <entryName>Total Ankur</entryName> 555 <License>L</License> <Tran>H20</Tran> <job>1234</job> </ReconSummary>  I want to comment the tag if i find the pattern "Total Deep" so that the output file looks like below OUTPUT    <ReconSummary> <entryName>Total Saurav</entryName> 666 <License>L</License> <Tran>H20</Tran> <job>1234</job> </ReconSummary>   <ReconSummary> <entryName>Total Ankur</entryName> 555 <License>L</License> <Tran>H20</Tran> <job>1234</job> </ReconSummary>  Since i am new to shell scripting, can anyone help me out as to how i can apply this with the help of shell scripting?


Suppose $\mathbb{Z} \overset{1}\longrightarrow \mathbb{Z} \overset{2}\longrightarrow \mathbb{Z} \overset{3}\longrightarrow \mathbb{Z} \overset{4}\longrightarrow\mathbb{Z}\longrightarrow\cdots$.  How to compute the direct limit of above groups?Does there exist a general method to calculate the direct limit of groups?

How do I start computing easy direct limit of groups:  1) $\mathbb{Z} \overset{1}\longrightarrow \mathbb{Z} \overset{2}\longrightarrow \mathbb{Z} \overset{3}\longrightarrow \mathbb{Z} \overset{4}\longrightarrow\mathbb{Z}\longrightarrow\cdots$ where the maps are just multiplication by "above arrow" numbers.   2) $\mathbb{Z}\overset{2}\longrightarrow \mathbb{Z} \overset{2}\longrightarrow \mathbb{Z} \overset{2}\longrightarrow \mathbb{Z} \overset{2}\longrightarrow$$\mathbb{Z}\longrightarrow\cdots $ where the maps are just multiplication by 2.   How do I get intuition for the resulting direct limit?


I have to find $gcd(x^{P-1}-1,x^2+1)$ in $\Bbb{Z}/p\Bbb{Z}[X]$ for some prime number p in order to show that $-1$ is a square $\pmod p$ iff $p\equiv1\pmod4$. I really have no idea where to start. I don't see how to get the gcd given that p is not a number. Any help would be appreciated.  Thanks

I am really having trouble working a problem in my course. I will post it and then add what I have thought etc.  Let p be an odd prime, then using the Euclidian Algorithm, calculated the GCD of of $x^{p-1}-1$ and $x^2+1$ in $\mathbb{Z} / p\mathbb{Z}[x]$  Also, how does $p=1 (mod4)$ tell us that  $-1$ is a square in $\mathbb{Z} / p\mathbb{Z}$, infact that $-1$ is a square here if and only if $p=1(mod4)$.  My thoughts:   I know that $$x^{p}-x=(x)(x-1)(x-2)…(x-(p-1))$$ and so that in this sense our roots will be the congruence classes of $1,2,…p-1$  and also that $$x^{p-1}-1=(x-1)(x-2)…(x-(p-1))$$  But I get lost when trying to apply the EA to these polynomials,  like how can I do it when p is arbitrary?  Preferably id like to be able to understand/see how to do the first part first i.e. using division with residue and then move on to the second part. Any insight/hint or solution to this would be great,  Thank you all  Update:  When I try to do division with residue, I just get  $$x^{p-1}-1=(x^2+1)(x^{p-3}-x^{p-5}+x^{p-7}-x^{p-9}...)$$  for example,  $p=7$  $$(x^{6}-1)=(x^2+1)(x^4-x^2+1)$$  for $p=11$  $$(x^{10}-1)=(x^2+1)(x^{8}-x^{6}+x^{4}-x^{2}+1)$$  which for specific cases tells me that 1 is the gcd, but I dont know how to generalize that for the case with arbitrary prime p.


I have two of the same objects. Now i moved object 2 lets say...how can i move it back to the same location and size of object 1  ? is there any way to copy this from object one to object 2  ?

I want an object to have the same Transforms (location, rotation, and scale) as another object. How can I copy the Transforms from one object to another?


Consider a vector $a \in R^n$. I want to know how I can find analytically the solution of the following optimization problem: $x^* = argmin_{x \in R^n} f(x)$, where $f(x) = ||x-a||_{2}^2 + \lambda ||x||_1$, $\lambda > 0$ and $||.||_p$ is the p-norm in $R^n$.  Thanks in advance.

In orthogonal design of lasso, we get  $\hat{\beta}_j^{\text{lasso}} = 0 \text{ if abs}(\hat{\beta}_j) \le \lambda /2$. WHY?   I've seen the answer and derived it myself, but don't know why.  We begin with definition of lasso, $$\hat{\beta}^{\text{lasso}} = \underset{x} {\arg\min}  \sum_{i=1}^{n} ( y_i - \sum_{j=1}^{p}\beta_{ij}x_{ij} )^2 + \lambda \sum_{j=1}^{p} |\beta_j|  $$  In orthogonal design case where $X^T X= I$, $\hat{\beta} = (X^TX)^{-1}X^{T}y = X^Ty$  \begin{align} L(\beta, \lambda) & = \sum_{i=1}^{n} ( y_i - \sum_{j=1}^{p}\beta_{ij}x_{ij} )^2 + \lambda \sum_{j=1}^{p} |\beta_j| \\  & = (Y - X \beta)^T(Y - X \beta) + \lambda \mathbf{I}_p \text{ abs}(\beta) \\  & = Y^TY -2\hat{\beta}^T\beta + \beta^T \beta+ \lambda \mathbf{I}_p \text{ abs}(\beta) \\  & = Y^TY + \sum_{j=1}^{p} L_j(\beta_j, \lambda) \end{align}  where $L_j(\beta_j, \lambda) = -2 \hat{\beta}_j \beta_j + 2\beta^2_j + \lambda \text{ abs}(\beta_j)$.  Leave aside $\beta_j=0$, take dereivative w.r.t. $\beta_j$ for abs$(\beta_j) > 0$, $$\frac{L_j(\beta_j, \lambda)}{\partial \beta_j}  = -2 \hat{\beta}_j + 2\beta_j + \lambda \text{ sign}(\beta_j)$$  and $\hat{\beta}^{\text{lasso}}$ is either zero or solve, $$\beta_j + \lambda \text{ sign}(\beta_j) / 2 = \hat{\beta}_j,$$  which is, $$ \hat{\beta}^{lasso}_j =  \begin{cases}     \hat{\beta}_j - \lambda/2, & \text{if } \hat{\beta}_j > \lambda/2\\     \hat{\beta}_j + \lambda/2, & \text{if } \hat{\beta}_j < -\lambda/2 \end{cases} $$  My question is the following derivation,  If abs$(\hat{\beta}_j) \le \lambda / 2$, we get $$L_j(\beta, \lambda)  = -2 \hat{\beta}_j \beta_j + 2\beta^2_j + \lambda \text{ abs}(\beta_j)  \ge -\lambda \text{ abs}(\beta_j) + \lambda \text{ abs}(\beta_j) \ge 0 = L_j(0, \lambda)$$ and, we can tell $\hat{\beta}_j^{\text{lasso}} = 0 \text{ if abs}(\hat{\beta}_j) \le \lambda /2$ (Why? How can you tell?)  Why $\mathbf{\hat{\beta}_j^{\text{lasso}} = 0}$? The explanation of $L_j(\beta_j, \lambda) \ge L_j(0, \lambda)$ does not seem to justify the reason.


I've created a horizontal navigation menu in HTML using
 and inline-block display styling. I'm wanting to set the background colour of the containing
, but it isn't working. It's as though the
 isn't wrapping around the
.  The first
 is supposed to set the background colour for the entire width of that part of the page. The second
 then sets the width of the navigation menu within that area, and centres the
 so that the unused space is evenly distributed either side.  Here's the code:

Design

Proofreading

   Also, how would I centre the
 within the second
, so that the
s appear in the centre?

Although elements like
s normally grow to fit their contents, using the float property can cause a startling problem for CSS newbies: If floated elements have non-floated parent elements, the parent will collapse. For example:

Div 1

Div 2

    The parent div in this example will not expand to contain its floated children - it will appear to have height: 0. How do you solve this problem? I would like to create an exhaustive list of solutions here. If you're aware of cross-browser compatibility issues, please point them out. Solution 1 Float the parent.

Div 1

Div 2

    Pros: Semantic code. Cons: You may not always want the parent floated. Even if you do, do you float the parents' parent, and so on? Must you float every ancestor element? Solution 2 Give the parent an explicit height.

Div 1

Div 2

    Pros: Semantic code. Cons: Not flexible - if the content changes or the browser is resized, the layout will break. Solution 3 Append a "spacer" element inside the parent element, like this:

Div 1

Div 2

    Pros: Straightforward to code. Cons: Not semantic; the spacer div exists only as a layout hack. Solution 4 Set parent to overflow: auto.

Div 1

Div 2

    Pros: Doesn't require extra div. Cons: Seems like a hack - that's not the overflow property's stated purpose. Comments? Other suggestions?


I was reading An Enquiry concerning Human Understanding by David Hume, and came across (a couple days ago) a part wherein Hume draws a counterexample towards his epistemological theory and drops it. The paragraph in question is as follows  "There is, however, one contradictory phenomenon, which may prove, that it is not absolutely impossible for ideas to arise, independent of their correspondent impressions. I believe it will readily be allowed, that the several distinct ideas of colour, which enter by the eye, or those of sound, which are conveyed by the ear, are really different from each other; though, at the same time, resembling. Now if this be true of different colours, it must be no less so of the different shades of the same colour; and each shade produces a distinct idea, independent of the rest. For if this should be denied, it is possible, by the continual gradation of shades, to run a colour insensibly into what is most remote from it; and if you will not allow any of the means to be different, you cannot, without absurdity, deny the extremes to be the same. Suppose, therefore, a person to have enjoyed his sight for thirty years, and to have become perfectly acquainted with colours of all kinds, except one particular shade of blue, for instance, which it never has been his fortune to meet with. Let all the different shades of that colour, except that single one, be placed before him, descending gradually from the deepest to the lightest; it is plain, that he will perceive a blank, where that shade is wanting, and will be sensible, that there is a greater distance in that place between the contiguous colours than in any other. Now I ask, whether it be possible for him, from his own imagination, to supply this deficiency, and raise up to himself the idea of that particular shade, though it had never been conveyed to him by his senses? I believe there are few but will be of opinion that he can: And this may serve as a proof, that the simple ideas are not always, in every instance, derived from the correspondent impressions; though this instance is so singular, that it is scarcely worth our observing, and does not merit, that for it alone we should alter our general maxim."  I was quite troubled by how Hume dismissed the example as inconsequential, considering that the event could further imply missing auditory or other sensory qualities which could be conceived without a corresponding impression. What then, is this counterexample dismissed? My idea was that perhaps the ideas derived from the impressions of the nearby colors could be combined, augmented and diminished (three of the four ways Hume states that ideas can be conjoined) to create the idea of the missing shade. Hence, perhaps the idea of the missing shade, rather than being a simple idea, would be a complex idea with no corresponding impression. But if this is the case, why then does Hume claim that the example is a counterexample? I myself am highly skeptical of my idea, so if there exists a better defense from a more experienced Hume scholar, it would be greatly appreciated.

From reading this  on Hume, having read the first seven sections of the Enquiry Concerning Human Understanding (which covers the relevant section), a further question hit me. Hume dismisses the occurrence as "singular ... scarcely worth our observing", yet he brings the counter example up instead of others. Why does he bring up a counterexample which he himself dismisses as trivial? Is it to bolster his argument by suggesting that the only counterexample so important as to be worth mentioned is itself highly trivial? Or is it merely because its the only concrete, simple counterexample Hume conceived of? Responses with links to Hume scholars would be appreciated.


My husband and I have applied for Belgium tourist visa on September 17th and we were highly confident that we provided all the necessary documents, especially proving the fact that we will leave the country on the scheduled date. Yesterday we received an email implying that our visa application was refused because the reasons and conditions were not well justified.      l'objet et les conditions du séjour envisagé n'ont pas été justifiés   We bought flight tickets in advance, but we booked hotel with free cancellation policy to not lose more money in the case of being rejected. The only doubt we had was, not providing any documents showing we are married since all the fund and bank accounts were for one of us (my husband) and I just filled out the application form stating that I am currently studying an MS in Computer Science (last semester) but I provided no evidence whatsoever. I also am a freelance translator and speak over 3 languages fluently, I know it might be unrelated but given that the translation company I work for is quite popular, will it help them understand it is only a tourist visa, being desperate to see Bruges (inspired by the movie,  (as silly as it sounds))?   I wonder if we could appeal and explain the situation more clearly for the consulate. I wouldn't risk reapplying again since the fee is quite high. As I searched their website, they provide no information on appealing, does it mean there is no such an option in their embassy in Iran? Would sending an email help?  Further information: I once applied for a schengen visa and traveled to Germany four years ago before getting married. My husband applied for a UK student visa 5 years ago (thrice) and was rejected. I wonder if we are rejected because of that.   Edit: I have read all the related questions, but I guess such questions must be answered individually, I might be wrong)   There is also another reason that could have made them skeptical. We bought our ticket online which was a fairly cheap flight, then we planned to set an appointment online via Belgium embassy website and found out the earliest available date is October 18th, two days before our planned departure date. We sent the embassy an email requesting for an appointment any time earlier than that with a print of our ticket attached. Then they set us another appointment on Sep 17th (they said the email is for urgent cases only)

Schengen refusal formulae can be difficult to understand sometimes.    When an applicant receives a refusal with "Justification for the purpose and conditions of the intended stay was not provided", what does it mean?


I'm reading the book Analysis 1 by Terence Tao. There is a concept of well-defined which is mentioned a lot of time in the book but I don't fully understand. For example, in the picture below, in order to define the $subtraction$ $operation$ of 2 integers, he firstly defined the $negation$ $operation$ of integers. After the definition, he stated that the definition is well-defined and we can prove that it is well-defined. Could you please explain me what well-defined means and how can we prove something is well-defined or not ? Is there any collection of criteria for something to be well-defined ? ("something" here can be a definition, an operation) Thank you very much for your help! [Image]

What does it mean for a function to be well-defined? I encountered with this term in an excersice asking to check if a linear transformation is well-defined.


Let us say we are adding several elements to the dom. What is the best way to make sure these elements also have a click handler added to them? For example, if I have a click handler on all elements with the class "canvas-section", and I keep adding "canvas-section" elements, what is the best way to make sure in Jquery that these new "canvas-section" elements also have that click handler added.   Before I used to use the "live" jquery function or "on" but those don't seem to work for elements that are dynamically added or added after the original click listener is added.

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


I'm using Ubuntu 15.10. I have noticed a weird problem.   When running a rsync command embedded in a shell script (as root) with --exclude={} options, rsync works and excludes paths as it's supposed to when I launch it as root via   ./rBackup.sh   However, when I run it as root via   sh rBackup.sh   the exclude directory options do not carry over, and it infinite loops when backing up the drive it's backing up to in /media/. Why?  Edit - this is not a sh / bash difference - or shouldn't be. I have #!/bin/bash as the first line, so when running via "sh *.sh" it should use the bash interpreter - at least, in theory.  Script is as follows:  #!/bin/bash  StandbyMount="/media/astump/sdb2" mount /dev/sdb2 $StandbyMount rsync -aAXv --exclude={/dev/*,/proc/*,/sys/*,/tmp/*,/run/*,/mnt/*,/media/*,/lost+found,/etc/fstab,/boot/grub/grub.cfg} --delete-before / $StandbyMount umount $StandbyMount rm -fr $StandbyMount

Have a look at the code:  #!/bin/bash read -p "Eneter 1 for UID and 2 for LOGNAME" choice if [ $choice -eq 1 ] then         read -p "Enter UID:  " uid         logname=`cat /etc/passwd | grep $uid | cut -f1 -d:` else         read -p "Enter Logname:  " logname fi not=`ps -au$logname | grep -c bash` echo  "The number of terminals opened by $logname are $not"   This code is used to find out the number of terminals opened by a user on the same PC. Now there are two users logged on, say x and y. I am currently logged in as y and there are 3 terminals open in user x. If I execute this code in y using different ways as mentioned above the results are :  $ ./file.sh The number of terminals opened by x are 3  $ bash file.sh The number of terminals opened by x are 5  $ sh file.sh The number of terminals opened by x are 3  $ source file.sh The number of terminals opened by x are 4  $ . ./file.sh The number of terminals opened by x are 4   Note: I passed 1 and uid 1000 to all these executables.  Now can you please explain the differences among all these?


What is the correct way to say?:  Her mother, her family and I or I, her mother and her family

I've always been taught to put myself last when referring to myself in the same sentence as others but the usage of "me and..." seems to be everywhere these days. The misuse of the word "me" instead of "I" aside, is there some new rule I haven't heard of? Shouldn't we put ourselves last regardless of the "me"/"I" usage?  Examples of "correct" usage:      My friends and I went for some ice   cream. Did you see my friends and me   at the ice cream stand?   Examples of "incorrect" usage:     Me and my friends went for some ice   cream. Did you see me and my friends   at the ice cream stand?   Note: I was also taught that the only person who could put themselves first was the queen.


I have got two 2 subdomains for the domain example.com. Which is remote.example.com and archive.example.com.  Apache is taking requests for all subdomains leading always to the same virtual host.  The Server is listening to port 8082.  This is my virtual hosts file /etc/apache2/sites-available. archive.example.com-conf:  NameVirtualHost archive.example.com:8082  <VirtualHost *:8082>     ServerAdmin webmaster@example.com     ServerName archive.example.com     DocumentRoot /var/www/archive </VirtualHost>   When I enter remote.example.com in the browsers address line it os being routed to the same virtual host as archive.example.com.  Output of apache2ctl -S:  AH00548: NameVirtualHost has no effect and will be removed in the next release /etc/apache2/sites-enabled/archive.example.com.conf:1 VirtualHost configuration: *:8082                 archive.example.com (/etc/apache2/sites-enabled/archive.example.com.conf:3) ServerRoot: "/etc/apache2" Main DocumentRoot: "/var/www/html" Main ErrorLog: "/var/log/apache2/error.log" Mutex default: dir="/var/run/apache2/" mechanism=default Mutex mpm-accept: using_defaults Mutex watchdog-callback: using_defaults PidFile: "/var/run/apache2/apache2.pid" Define: DUMP_VHOSTS Define: DUMP_RUN_CFG User: name="www-data" id=33 Group: name="www-data" id=33

It's the following part of a virtual host config that I need further clarification on:  <VirtualHost *:80>   # Admin email, Server Name (domain name), and any aliases   ServerAdmin example@example.com   ServerName  141.29.495.999   ServerAlias example.com ...   This is and example config, similar to what I currently have (I don't have a domain name at the moment).  <VirtualHost *:80> - Allow the following settings for all HTTP requests made on port 80 to IPs that this server can be contacted on. For instance, if the server could be accessed on more than one IP, you could restrict this directive to just one instead of both.  ServerName - If the host part of the HTTP request matches this name, then allow the request. Normally this would be a domain name that maps to an IP, but in this case the HTTP request host must match this IP.  ServerAlias - Alternate names accepted by the server.  The confusing part for me is, in the above scenario, if I set ServerAlias mytestname.com and then made an HTTP request to mytestname.com, there would have to be a DNS record pointing to the server's IP for this to work? In which case, is ServerAlias just basically EXTRA ServerName entries?  Say I had a DNS entry such that foobar.com = 141.29.495.999 but then I had ServerName = 141.29.495.999 and ServerAlias was empty, would that mean that although foobar.com gets resolved to the right IP, because there is no reference to accept foobar.com in ServerName or ServerAlias?  Or something. Man I'm confused.


We listen to songs, and sometimes we forget them because they are boring.  And when we listen to a catchy song, we hum it or sing it whole the day. Is it okay to consider such songs as memorable? If not, is there any specific word for this?

Is there a term for a catchy tune that stays in your head after you hear it? The Germans call it an earworm.


I have already installed Apache OpenOffice 4.0.0 and would like to update it to the newer version which is Apache OpenOffice 4.0.1.    I have already downloaded the _deb.tar.cz files that were required but I can't seem to access the download through the terminal to install it.    What I tried was to open the Home/ directory but it can't seem to find it using the command:   cd /home/downloads/apache    What did I do wrong?

How do I change directories to downloads, from the home folder, in the latest version Ubuntu 12.10? I tried cd /downloads, but it gave an error saying that there is no such directory.


When I boot my Ubuntu 16.04 system, the screen shows:  /dev/sda1: clean, 914558/6250496 files, 10712202/24999680 blocks ... [OK] Started udev Coldplug all Devices.      Starting Show Plymouth Boot Screen...   Detailed information is .  How to fix it? Can anyone give some advice?

I am trying to boot Ubuntu on my computer.  When I boot Ubuntu, it boots to a black screen.  How can I fix this? Table of Contents:


I am developing with Flask, and am trying to create a page to create pages (as a sort of custom CMS). So the page will need to create its own @app.route decorator for a function that renders the page template when called in the app.py file. What I have come up with is to create three functions: remove_last_two_lines and create_rendering_func and add_back_last_lines (named for what they do). The remove_last_two_lines function and the add_back_last_lines function do exactly what I want. What I'm having trouble with is the create_rendering_func. It simply doesn't do anything, and doesn't raise an error. So I think the code is valid (and I am passing valid arguments), I just don't understand why it isn't working. The lines being overwritten are empty (that's why there is multiple newlines after the last line of the function). Thanks in advance!  def add_new_url(route, func_name, title, filename):     lines = open(__file__, 'r').readlines()     lines[-6] = '@app.route(\'%s\')' % route     lines[-5] = '\ndef %s' % func_name     lines[-4] = '\n\trender_template(\'filename\', the_title=%s)\n\n\n\n\n' % title    (This method sucks. Any tips on better methods appreciated)

I want to loop over the contents of a text file and do a search and replace on some lines and write the result back to the file. I could first load the whole file in memory and then write it back, but that probably is not the best way to do it.  What is the best way to do this, within the following code?  f = open(file) for line in f:     if line.contains('foo'):         newline = line.replace('foo', 'bar')         # how to write this newline back to the file


I can paste images from clipboard into SE posts from within Chrome, but can't do that from within Firefox.  When Add Image dialog appears, it says supplementary "(or paste or drag-and-drop)" in Chrome and "(or drag-and-drop)".  Can this feature be enabled in Firefox?  What this feature depends on?

Since , Stack Exchange has been offering . This is awesome, but it doesn't work the same on all browsers.   Google Chrome (28.0.1500.71 m) provides both paste & drag-and-drop (this feature seems to have been removed in 35.0.1916.114 m):    Firefox (22.0) only provides drag-and-drop:    Internet Explorer (9.0.8112.16421) provides none:    Why is there a deficiency in certain browsers and/or what can be done?


The problem goes : Solve the following limit without using l'hopital's rule : $$\lim\limits_{x\to 0} \frac{x-\sin(x)}{x^3}.$$ I've tried multiplying with conjugate "$x+\sin(x)$", I've tried extracting $x$ from the numerator, and I always end up in a dead end. Pleas help.

I was given a task to find  $$\lim_{x\to0}\frac{x-\sin{x}}{x^3}$$ at my school today. I thought it was an easy problem and started differentiating denominator and numerator to calculate the limit but the teacher then said we aren't allowed to use  L'Hopital's rule, but to "play around" with known limits and limit definition. I got stuck here since I can't really think of a way to do this, and according to my teacher, there are at least 4 ways. A subtle hint would be enough. Thanks.


This question is extremely basic but I can't find any information online and it has never been mentioned at university:  Is the use of equal signs within comparisons allowed/mathematically correct?  Example A: $$3^2+1^2=10 < 16=(3+1)^2.$$  Example B: $$\DeclareMathOperator{fib}{fib}\fib(2)=1 < \fib(3)=2 < \fib(4)=3,$$ where $\fib(n)$ denotes the $n$-th Fibonacci number.

Is this considered bad style  $$2 = \sqrt{4} < \sqrt{16} = 4?$$  It seems as though this is not strictly correct, since $2 = \sqrt{4}$ is a logical proposition which represents boolean value (true or false). A boolean value cannot be less than $\sqrt{16}$.  On the other hand, I am sure that most people will correctly interpret this as shorthand for $2 = \sqrt{4},$ $\sqrt{4} < \sqrt{16},$ and $\sqrt{16} = 4$


This is something I came up with a day. I tried a procedure but later I found it was incorrect. So here it is:  $$2^s = 2s + 2 $$

A certain physics problem I have been working on has turned into a math problem. Particularly, I want to find the solutions of some equation of the form   $$f(x)=ae^{bx}+cx+d = 0$$  where $a, b, c,$ and $d$ are constant, real numbers that come from the physics problem and $x$ will be a real number. I do not know how to find the solutions of an equation of this form. In the special case where $c=0$, the solution is simply  $$x = \frac{\ln(\frac{-d}{a})}{b}$$  but for other values of $c$, I am stumped. If there is no exact form for the roots, is there a relatively simple way to estimate the roots?


I've been reminded several times that a question on a SE site should be able to help future visitors. Indeed, it's very common for a question to be closed for being too specific.  At the same time, we all know that duplicate questions are of the devil, and should be closed immediately.  Both of these lend themselves to the notion that an answerer should maintain their answers: They should be applicable to as many people as possible, and prevent the need for the question being asked again.  This works great for me, as I'm the type of person who returns to his old questions to tweak and improve them as I learn more. I enjoy having that control, and crafting my answers -- and it's not uncommon for me to tweak minor things like layout and wording.  Unfortunately, I've recently discovered that my passive tweaking bumps the entire question to the top of the active questions list. I've been told that this is done to help the community flag spam. This doesn't bother me at all, but I've found myself being scolded by certain community members for "deliberately bumping posts" (which is simply not true).  If some people don't like people editing their posts, and it irks them, is there a better system that would encourage the maintenance of answers, that wouldn't annoy these people?  Proposal: There be a "minor edit" button like Wikipedia has? These minor edits would check for formatting changes by the original author only, so they wouldn't get bumped to the top of the Active Posts list.

It would be nice to allow users to mark a change in an answer (or question) as minor (e.g. for a simple spelling or grammar correction). A change marked as minor wouldn't push the question on top of the list of questions on the home page or in the feeds. It wouldn't trigger any notification. This could be implemented with a "Minor change" checkbox when editing an entry (a la Confluence). What do you think?


How can one build a subset $A\subset [0,1]\times[0,1]$ containing at the most one point from each horizontal and each vertical section and whose boundary (frontier) is $[0,1]\times[0,1]$?  I don't know how to build this set. I know that if $A$ contains points in each quarter of the square it's enough.

Given a subset $A$ of $\mathbb{R}^{n}$, a point $x \in \mathbb{R}^{n}$ is said to be in the boundary of A if and only if for every open rectangle $B\subseteq\mathbb{R}^{n}$ with $x\in B$, $B$ contains both a point of $A$ and a point of $\mathbb{R}^{n}\setminus A$.  My question is from Spivak's Calculus on Manifolds: Construct a set $A \subseteq [0,1]\times [0,1]$ such that $A$ contains at most one point on each horizontal and vertical line but has boundary equal to $[0,1]\times[0,1]$.


Why those hexagons appears in sculpting mode?

I'm currently making a donut using blender gurus tutorial. I have no idea why, but there are holes in my icing. Does anyone know what could be causing it? Thanks for any help.


I did a small table thats ask for product name and product # my question how can I alert the user that he is leaving the page without saving the information.  <form action="index.php" method="post"> <input type="text" name="pnumber" value="" placeholder="Product Number...."/>  <input type="text" name="pname"   placeholder="Product Name...." /> <br> <button id="save">save</button> </form>

I have a requirement to implement an "Unsaved Changes" prompt in an ASP .Net application.  If a user modifies controls on a web form, and attempts to navigate away before saving, a prompt should appear warning them that they have unsaved changes, and give them the option to cancel and stay on the current page.  The prompt should not display if the user hasn't touched any of the controls.  Ideally I'd like to implement this in JavaScript, but before I go down the path of rolling my own code, are there any existing frameworks or recommended design patterns for achieving this?  Ideally I'd like something that can easily be reused across multiple pages with minimal changes.


I've tried to change my prompt by editing .bashrc:  export PS1="\e[0;32m[\u@\h \W]\$ \e[m"   This seems to work, but ctrl-r to access reverse history ends up with my typing not appearing in the same place as it will be interpreted (like ). It is fine when using the up or down arrows to select previous commands though.  I've had a look at that question, but can't seem to work out where to apply the escape characters in my prompt. I've tried a few combinations but then I break normal text typing functionality or simple back/forwards through history.  If you could include an explanation of which instances of characters need escaping and why, that would help me (and hopefully others) learn.

I have an issue where if I type in very long commands in bash the terminal will not render what I'm typing correctly. I'd expect that if I had a command like the following:  username@someserver ~/somepath $ ssh -i /path/to/private/key myusername@something.someserver.com  The command should render on two lines. Instead it will often wrap around and start writing over the top of my prompt, somewhat like this:  myreallylongusername@something.somelongserver.comh -i /path/to/private/key  If I decide to go back and change some argument there's no telling where the cursor will show up, sometimes in the middle of the prompt, but usually on the line above where I'm typing.   Additional fun happens when when I Up to a previous command. I've tried this in both gnome-terminal and terminator and on i3 and Cinnamon. Someone suggested it was my prompt, so here that is:  \[\033[01;32m\]\u:\[\033[01;34m\] \W\033[01;34m \$\[\033[00m\]  Ctrll, reset, and clear all do what they say, but when I type the command back in or Up the same things happens.  I checked and checkwinsize is enabled in bash. This happens on 80x24 and other window sizes.  Is this just something I learn to live with? Is there some piece of magic which I should know? I've settled for just using a really short prompt, but that doesn't fix the issue.


My credit card due date is May 4th and the closing date is May 7th. I have paid statement balance in full today, so it's early than the due date. But I would like to continue purchase through this credit card.  Do I still need to pay this part of statement balance before the due date and if not will I be charged interest fees?

First of all, I am a resident of Canada.  I am  new to credit cards, so I hope my question makes sense. I've had my card for a few months ago and I've always paid the balance in full by the time the due date rolls around. Just out of curiosity, say the day after tomorrow was my due date. If I made a purchase tomorrow and didn't pay it off by the day after tomorrow, would I be charged any interest on it? Is there any negative ramifications at all for doing this?  Thanks.


Consider this piece of snippet :     char *str = "hellow Ghost";   str[0] = 'z';   printf("%s", str);   It is a segmentation fault. Also does it come under run time memory error ?  What I understood by segmentation fault is : Segmentation fault when you are accessing a memory that doesn't belong to you. It is basically a utility created for you to ease your work without letting you corrupt the memory.   How much and what kind of memory errors Segmentation fault covers and what invokes it to check out that a pointer or reference is wrong dealing with memory.  Run time error also occurs due to improper logic. Apart from that, are there any differences between run time error and segmentation fault regarding memory.

The following code receives seg fault on line 2:  char *str = "string"; str[0] = 'z';  // could be also written as *str = 'z' printf("%s\n", str);   While this works perfectly well:  char str[] = "string"; str[0] = 'z'; printf("%s\n", str);   Tested with MSVC and GCC.


So I move stuff around to my liking. Change the theme to my preferred look.  I Go to User Preferences>File> uncheck:(Load UI). Hit [Save user preferences] Hit the + next to default and rename my own layout. Close and reopen, the theme stays but the layout is back to default and my own custom layout is deleted from the list.  BUG or I am doing something wrong?

I'm currently working on a very small screen, and I'd like to have all the panels closed by default and only open the ones I need manually, or if possible even just remember my last open panels when I save a project. Is it possible?    (open (1) and closed (2) panels in the editor)  I know I can use Ctrl+LMB to open a panel singularly, and that alone is a great help, but this would be even better.


So, I spawned sea turtles on a beach. I bred them. The pregnant one just jumped into the ocean, not even going to the original beach, and started to turn in circles everywhere. I did not breed them on the same beach as the one that they were spawned on, but I had a clear path. Would holding the female captive work? This is in Minecraft P.E. by the way.

I recently made a turtle breeding farm in Minecraft survival mode and when ever I bred the pair of turtles all I got was experience points and that’s it, they did not lay eggs and yes the farm was next to the ocean and there was sand for the turtles to lay their eggs.


I have a MySQL DB. I created a table with below definition which supports multiple languages (Hindi, Thai, etc.).  CREATE TABLE test_multi_lang (    language_name varchar(500) CHARACTER SET utf8 COLLATE utf8_unicode_ci )  INSERT INTO test_multi_lang (language_name ) VALUES ('ตัวอย่าง')  INSERT INTO test_multi_lang (language_name ) VALUES ('नमूना')    But when I select the data. It is showing all the data as ??????.  SELECT * FROM test_multi_lang   Sample Image   How can I solve this problem?  Thanks in advance.

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.


To manually initially an N x N list of 0 values, you can do the following  mylist = [[0 for x in range(n)] for y in range(n)]   Printing a 3x3 version you'd see:  >>> mylist = [[0 for x in range(3)] for y in range(3)] >>> print(mylist) [[0, 0, 0], [0, 0, 0], [0, 0, 0]]   Change any value, all good:  >>> mylist[0][1] = 1 >>> print(mylist) [[0, 1, 0], [0, 0, 0], [0, 0, 0]]    Now, I know you can initialize a size N list with:   mylist = [0] * n   And to create an  NxN the following appears to work (same 3x3 example)  >>> mylist = [[0] * 3] * 3 >>> print(mylist) [[0, 0, 0], [0, 0, 0], [0, 0, 0]]   However, modifying this list produces unexpected results  >>> mylist[0][1] = 1 >>> print(mylist) [[0, 1, 0], [0, 1, 0], [0, 1, 0]]    Can someone explain why the second way of initializing the NxN list acts in this manner?

I needed to create a list of lists in Python, so I typed the following: my_list = [[1] * 4] * 3  The list looked like this: [[1, 1, 1, 1], [1, 1, 1, 1], [1, 1, 1, 1]]    Then I changed one of the innermost values: my_list[0][0] = 5  Now my list looks like this: [[5, 1, 1, 1], [5, 1, 1, 1], [5, 1, 1, 1]]    which is not what I wanted or expected. Can someone please explain what's going on, and how to get around it?


I'm solving this equation in integers: $6 \, x + 10 \, y + 15 \, z = 1$. I can find many solutions, by combining two two-variable equations into $x = u \, p$, $y = v \, p$, $z = q$, where $u = 2 + 5 \, t$, $v = -1 - 3 \, t$, and $p = 8 + 15 \, s$, $q = -1 - 2 \, s$, with $s$ and $t$ integers. (see ) But I'm obviously missing some solutions. How does Mathematica arrive at this elegant general solution?

$$ 3x+6y+5z=7 $$ The general solution to this linear Diophantine equation is as described    $$ x = 5k+2l+14 $$ $$ y = -l $$ $$ z = -7-k $$ $$ k,l \in \mathbb{Z} $$  If I plug the original equation into  the solution is: $$ y = 5n+2x+2  $$ $$ z =-6n-3x-1 $$ $$ n \in \mathbb{Z} $$  I can rewrite this as:  $$ x = l $$ $$ y = 5k+2l+2 $$ $$ z = -6k-3l-1 $$ $$ k,l \in \mathbb{Z} $$  However now two equations depend on two variables ($k,l$) and one on one variable $l$. In the first solution one equation depends on two variables and two on one variable.  Questions:  How can I come from a representation like the one from wolfram alpha for the general solution to one where all equations depend on one distinct variable except one equation.  Is there always such a representation?


I am trying to limit the user from overfeeding a virtual cat by making it only if health level is less than 60 they can feed it.Also if user attempts to feed cat when health is over 60 then happiness decreases by 2 for option 1. I tried health < 60; but it gives me an error.This is different because it is limiting not comparing strings. different question not even sure why it's marked.  int food = 20; int health = 30; int happiness = 80; String option; System.out.println("pick an option "); System.out.println(" Option 1 feed cat "); System.out.println(" Option 2 play with cat"); System.out.println(" Option 3 give cat bath"); option = input.nextLine(); if(option == 1) {     food += 10;     happiness -= 15     health < 60;     happiness -=2; } else if (option == 2) {     happiness += 12;     health += 25; }

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


This is a question that has come up many times but I do not seem to be able to get this to work using any of the suggestions that have been made so I would REALLY appreciate any help.   I am trying to get LaTeX to find my style files in Windows 7. I am using TeXMaker.   I create a new folder, for example C:\localtexmf\tex\latex\Macros  This then satisfies the TDS compliant directory requirements.   I go into MikTeX settings -> Roots and add this folder.  I then click Refresh FNDB in the General settings.  However, when I try to compile I still receive the error that the cls files cannot be found. It seems that this procedure has worked for many other people but I just cannot find what I could be doing wrong here.

I know how to define a package or a class, but how do I make it available (to myself) at all times?  Say I have the package file commonstuff.sty (or myprettyclass.cls), that I want to be able to include in any .tex file I create on my computer. Where do I put it? Do I need to run some installer on it, or is it enough to keep it in a certain folder?  Note: I know I can just place it in the same folder as the .tex file, but that's not what I'm after here. I'm looking for a way to "install" the package centrally on my computer.


I was trying to find the value of x in the following equation.  $$x=\sum _{ i=0 }^{ \infty  } \left( i+1 \right) \cdot \left( \frac { 5 }{ 6 }  \right) ^{ i }$$  In a computer simulation, I found that $x=6^2$  I believe the following is also true, I just do not know how to prove it. $$p^2=\sum_{i=0}^{ \infty } (i+1)\dot\ (\frac{p-1}{p})^i$$  Could anyone tell me what theory I should look into to for this problem?

How can I evaluate $$\sum_{n=1}^\infty\frac{2n}{3^{n+1}}$$? I know the answer thanks to , but I'm more concerned with how I can derive that answer. It cites tests to prove that it is convergent, but my class has never learned these before. So I feel that there must be a simpler method.  In general, how can I evaluate $$\sum_{n=0}^\infty (n+1)x^n?$$


Hi all What would the best way/method be to approach this, any advice would be appreciated


Can someone provide me rules to detect following attack :   hping3 -S -p 80 --flood --rand-source [target]   I'm having problem with rules since packet comes from random source.  My current rules is :   alert tcp !$HOME_NET any -> $HOME_NET 80 (flags: S; msg:"Possible TCP DoS"; flow: stateless; threshold: type both, track by_src, count 70, seconds 10; sid:10001;rev:1;)   this rules only can detect from one source ip only.

This is a  about DoS and DDoS mitigation.   I found a massive traffic spike on a website that I host today; I am getting thousands of connections a second and I see I'm using all 100Mbps of my available bandwidth.  Nobody can access my site because all the requests time out, and I can't even log into the server because SSH times out too!  This has happened a couple times before, and each time it's lasted a couple hours and gone away on its own.  Occasionally, my website has another distinct but related problem: my server's load average (which is usually around .25) rockets up to 20 or more and nobody can access my site just the same as the other case.  It also goes away after a few hours.  Restarting my server doesn't help; what can I do to make my site accessible again, and what is happening?  Relatedly, I found once that for a day or two, every time I started my service, it got a connection from a particular IP address and then crashed.  As soon as I started it up again, this happened again and it crashed again.  How is that similar, and what can I do about it?


The best way to explain this is to show you:  :        As you can see, the logo is not right. Also, the font is orange, and all the logos on the chat rooms are one of Stack Overflow.  :        The difference is that below "Rooms", the SE chat says it is about the SE network, while in the SO chat, it states events coming soon about programming.  I do not remember the SE chat page being like that, so something must have happened, unless I am wrong.

Generally chat.<site>.com redirects to chat.stackexchange.com/?tab=site&host=<site>.com and go for same thing but here you can check your self:       Both are Different!  If one visits  and select site: StackOverflow, then it outputs  and they miss rooms that are only listed by .  So, why does this happen? Is this a bug?  Note: I found this while  for general chat-room at StackOverflow; see chat-discussion


I have read that there is and electrical current, but why and how?    How big can this current (and voltage) be (does an amount of foil, saliva, tooth filling have any influence on this)? Can it "dry out" after some time? Can it be harmful if occurs for longer period?

Possible Duplicate:          Today we were in our Literature class talking about the Renaissance and the Enlightement and our teacher also said that scientific experiments were being conducted, and she gave as an example the experiment in which they dropped objects with different mass from a tower to see which object would land first. She then said that she herself didn't know the outcome and since I'm known in my class as the #1, they asked me and I said that they landed at the same time (to my shock many classmates even disagreed with me about this fact). The teacher asked me to explain why and we haven't had anything about inertia in our physics class, so I was forced to use my own self-thought knowledge of physics: I said gravity does pull harder on heavier objects, but heavier objects have more resistance to move, in other words, they have more inertia. The entire class except for the teacher disagreed with me even though they usually don't. One fairly annoying kid asked me to explain why a feather falls way slower than a bowling ball, and I explained why and I also made the claim that in a vacuum they would fall at the same rate. Was I right or my class? Of course I know my explanation is lacking, but it has truth to it, right?


I am trying the following exercise : Let $f\in C^\infty(\mathbb{R}^2, \mathbb{R}^2)$ and $\forall x\in\mathbb{R}^2$ $f(kx)=k^2f(x)$ for $k\in\mathbb{R}$  Show that any periodic solution of $y'=f(y)$ is constant.  Thank you in advance

Let $f\in C^\infty(\mathbb R^2,\mathbb R^2)$ and $\forall x \in \mathbb R^2$ $f(kx)=k^2f(x)$ for $k\in \mathbb R$ Show that any periodic solution of $y′=f(y)$ is constant.  My attempt : Let $\lambda \in \mathbb{R}$. Let $g$ a periodic solution defined by $g_{\lambda}(t) = \lambda g(\lambda t)$. With Cauchy-Lipshitz theorem $g_{\lambda}$ and $g$ do not intersect for $\lambda \neq 1$ and for $\lambda >1$, if $g(0)>0$ we have $g_{\lambda} > g.$ but I do not see how to continue.


See screenshot:    I imagine this happens with the other types of review tasks as well.

Now that I've reached 2k on Stack Overflow, I get access to the "Suggested Edits" review queue.  Although I only have 20 edits per day, the "suggested edit awaiting" icon in the top bar is always there and it bothers me a lot!  My suggestion is to apply one of three solutions:   Remove the suggested edits icon when we reach the maximum (50) edits Remove the Highlight (orange) on the suggested edits Remove the suggested edits part when we click on it   What do you think?


I found out, that if you have a field defined as INT(8) without ZEROFILL it will behave exactly as INT(5)  in both cases the maximum value is  −2,147,483,648 to 2,147,483,647, from −(2^31) to 2^31 − 1   or do i miss something?  I found this Question:      The (5) represents the display width of the field. From the   , it states:           The display width does not constrain the range of values that can be stored in the column. Nor does it prevent values wider than the column     display width from being displayed correctly. For example, a column     specified as SMALLINT(3) has the usual SMALLINT range of -32768 to     32767, and values outside the range permitted by three digits are     displayed in full using more than three digits.         The display width, from what I can tell, can be used to left-pad   numbers that are less than the defined width. So 00322, instead of   322. TBH, I've never used it.       But it doesn't affect the storage size of the column. An int will take   up more space than a smallint.   so there seems to be no difference then.

In MySQL table definitions is there a different between INT(5) and SMALLINT(5)?  Or do they both represent the same size?


Check this   within blockquote  I checked the  for mouse over effect but no luck on it. how to do it? I'm not sure this is a bug.

Use cases:   Programming puzzles. This way the answer can be posted the same time as the question, eliminating doubt that no answer is possible for hard questions and proving that the question is not a homework exercise (since the author already has the answer) The socratic method. In your answer you can ask a leading question, and then once the reader has a guess they can click to reveal the answer.     EDIT: now that several new websites have been created through SE 2.0, this became much more important.  Websites such as  really need it.


Light is considered as combination of electric and magnetic fields. So does a charged particle experience electric force in the presence of light?

Suppose there is an electromagnetic wave moving forward in the $\mathbf{\hat{k}}$ direction.  Its electric/magnetic field components are given by: $$\mathbf{E} = E_0 \sin(kz - \omega t) \mathbf{\hat{i}}$$ $$\mathbf{B} = B_0 \sin(kz - \omega t) \mathbf{\hat{j}}$$ If a particle of charge $q$ was lying on the wave's trajectory, the Lorentz force law says that the force is given $\mathbf{F} = q(\mathbf{E} + \mathbf{v} \times \mathbf{B})$. However, is an electromagnetic wave a combination of both E and B fields, requiring both fields to be plugged into the equation, or does the force on the electron only depend on one of the fields, and is  an EM wave only either an electric field or a magnetic field at one instant? Edit: changed x to z in expression for EM wave.


I am curious as to what the phrase "Winter is coming" might mean in Game of Thrones.   I know about the thing with the White Walker. Is there anything I am missing? What actually is going to happen when the winter comes? Does the winter signify the season or is it something different?

It's my understanding that the phrase "Winter is Coming" is the motto of the Stark house, when the story first reaches the wall it's implied that the winter is not a periodic season like it is in our world.  Does the winter refer to a particularly severe season or does a winter only occur every few years?


What is the intuition behind the fact that if every element in a group is of order $2$, we have that the group is abelian? I can prove it, but I do not know the intuition behind it.

If the order of all nontrivial elements in a group is 2, then the group is Abelian. I know of a proof that is just from calculations (see below). I'm wondering if there is any theory or motivation behind this fact. Perhaps to do with commutators?    Proof: $a \cdot b = (b \cdot b)  \cdot (a \cdot b) \cdot (a \cdot a) = b \cdot (b \cdot a) \cdot (b\cdot a) \cdot a = b \cdot a$.


Clarification: Does $\lim\limits_{x \to \infty}f'(x)=0$ as $x$ approaches infinity  mean $\lim\limits_{x \to \infty} f(x)$ exists in the extended real numbers $[-\infty,\infty]$?  I was thinking a lot about this problem and I couldn't  prove it; I would appreciate any help!  This isn't a duplicate! In that problem you have to prove that the limit of f(x) exists in the extended real numbers, you don't assume it does.

I've been trying to solve the following problem:  Suppose that $f$ and $f'$ are continuous functions on $\mathbb{R}$, and that $\displaystyle\lim_{x\to\infty}f(x)$ and $\displaystyle\lim_{x\to\infty}f'(x)$ exist. Show that $\displaystyle\lim_{x\to\infty}f'(x) = 0$.  I'm not entirely sure what to do. Since there's not a lot of information given, I guess there isn't very much one can do. I tried using the definition of the derivative and showing that it went to $0$ as $x$ went to $\infty$ but that didn't really work out. Now I'm thinking I should assume $\displaystyle\lim_{x\to\infty}f'(x) = L \neq 0$ and try to get a contradiction, but I'm not sure where the contradiction would come from.   Could somebody point me in the right direction (e.g. a certain theorem or property I have to use?) Thanks


A test has probability $P_f$ of failure where it is expected that $.0001 <P_f < .01$.   Given $N$ test samples where all tests succeed and there were no failures (thus $\sigma=0$), what is the best way to estimate the approximate value of $P_f$  assuming that is nonzero? What would be the most appropriate method to calculate error bars for this test?

I was wondering if there is a way to tell the probability of something failing (a product) if we have 100,000 products in the field for 1 year and with no failures? What is the probability that one of the next 10,000 products sold fail?


How do I make this script search through all users' home folders and then rm -f the files matching EXT? Right now it's only deleting the files matching EXT in the current folder where I am executing the script.   #!/bin/bash EXT=jpg for i in *; do   if [ "${i}" != "${i%.${EXT}}" ];then     echo "I do something with the file $i"     rm -f $i   fi done

I want to delete all *.o files in a directory and its sub-directories. However, I get an error: sashoalm@aspire:~/.Workspace.OLD$ rm -r *.o rm: cannot remove `*.o': No such file or directory  On the other hand, rm *.o works, but it's not recursive.


The basic principles of Stack Overflow are to:   ask and get answers, and  read and answer questions.   I'm good at asking, but when it comes to answering questions I feel like a fool because I lack the skills and/or knowledge.  Unfortunately I feel constrained to answer questions because otherwise I feel as if I am cheating on the principles of the site.  To make a long story short, I feel like a dumbass and get proven to be one by not being able to answer questions.  There must be a way out of that psychological struggle.

I have used the websites of SO a lot the past few months because I am busy with a large scale web project. I feel I get better answers here on SO than when I just do a Google search, maybe because I can be more specific here with my problem, and the responses are really fast.  Occasionally when I am not working I try to answer some questions, but the question almost always has an answer which is 'as good as' or 'better' than the answer I would supply.  So my question/answer ratio is about 20/1 something, if not more. When I look at my profile page I see a bucket-load of questions and almost nothing I answered myself.  Is this considered bad behaviour? I can see that this looks a little egoistic.  : One devoted to one's own interests and advancement.


We can cure many diseases nowadays, and thus the natural selection is very limited. Plus, mankind spent the whole beginning of its existence in almost the same hostile environment, and that's where he evolved the most, whereas our environment is changing very quickly. So, can we say that mankind froze, if not stopped, its own evolution ?

The theory of natural selection has it that individuals with better genes tend to survive and reproduce, passing their genes to their offspring. This gradual process results in a population more adapted at survival. However, due to the advancement in medical science, humans with poorer genes tend to survive and reproduce just as well.  For example, in the past, many people, excluding those with natural immunity due to some genetic mutations, would have succumbed to illnesses such as malaria and typhoid. But with better hygiene and medical treatment, these patients tend to survive.  Now, imagine a future where all illnesses including cancer can be treated. How would it impact the survival of the human race? Would we become more and more vulnerable such that our survival hinges heavily on medical technology, analogous to how an astronaut's survival is dependent on his spacesuit?


I always get confused between deciding whether to use present perfect or past simple with expressions like these. So how can I use them correctly?

When is the present perfect tense used instead of the past tense?    I know that the present perfect tense is used when some adverbs (e.g., never, ever) are present in the sentence; the same is true for sentences like the following one.     When you returned, I have been at home since 3:00 PM.   In which other cases should I use the present perfect? Do the following sentences require it?     I have walked downtown everyday for a year.        I have been at home since 3:00 PM.


I am new here & trying to ask a question about C++ on Stack Overflow.   The question contains a long code & I don't know how to add it in short time. I tried to use code sample tool provided there but it added only a line at a time. So, please help me with this.

How do I post text so that it is formatted as code?  What do I need to do so that my code shows up properly — not escaped or removed — when posted? And how to get the correct syntax highlighting?     For more information, see "" in the .


There seem to be plenty of similar questions, for example:    However the answer given is to prepare the program beforehand by making its stdin a pipe.  There's also:    Which is answered by commanding a terminal multiplexer under which the program in question is running. That means it also needs prior preparation.  This question is about how to do this without having done any preparation beforehand.  At first I thought it might be as simple as:  echo foo > /proc/$p/fd/0   but that just writes to the terminal. So then I tried:  echo foo > /proc/$terminal_emulator/fd/$ptmx_fd   but that also fails because it just opens up a new terminal device slave for echo.  I already have an answer using gdb (sigh) which I'll be posting below, but I wonder if anyone knows of a simpler and better alternative.

I have this setup where I have computer with ssh and a display where I have a user logged in to terminal. What I want to do is send commands like I was using that local session with keyboard. I tried to echo to /dev/tty1 but it just shows what I typed instead executing it. Which makes sense. The system only has bash so no GUI or anything like that.


I'm trying to comprehend the following: If I choose any starting value (e.g. 1) and keep clicking on cosine on the calculator (in radian mode), it gives me a result of about 0.739085...(I believe it's the result of cos(x) = x), but when I repeat the same procedure using sin and tan, I get something completely different (looks like for sin it's converging to 0 while for tan I get very wild results).  Thanks for your help.

In Radian mode, continually pressing the $\cos$ function of a number causes the result to converge to $x=0.739085133$, a fixed point of $\cos(x)$. Repeating this behavior with the $\sin$ function causes the result to converge to $x=0$, a fixed point of $\sin(x)$.   What happens if this is done using the tan function? It seems that $x=0$ is a repelling fixed point with no convergence in this case.  What would be the best way to explain these results mathematically?


I am studying for my complex analysis exam and this question popped up few years ago on the "mini quiz":  Find all $f \in H(\mathbb{C})$ such that for all $|z| \geq 1$ we have $|f(z)| \leq \frac{1}{|z|}$.  The hint was to use some theorem about entire functions. Could anyone give me a hand? I have no idea how to tackle this and this seems like one or two liner.

Does there exists an entire function $f$ such that $f(0)=1$ and $|f(z)|\leq \frac{1}{|z|} $ for all $|z|\geq 5$?


I've always been doing research on how to download a firmware for a different device. What i'm trying to say is: What will happen if I download a firmware that is not meant for my device? I downloaded the iPhone 4s iOS 6 IPSW to for my iPhone 6s. Will it not work? Will it brick the device? Will it still work anyway but will the display be stretched? No, i'm not trying to make a duplicate question, I just want to know is going to happen.

I'm trying to downgrade my iPhone from the current iOS to an older one, as per .  But every time I try, I always receive this error:     The iPhone could not be restored. This device isn't eligible for the requested build.     I have tried many times with and without DFU mode. Any ideas regarding this?


In RSA, is deducing the public key from the (message, signed message) pair possible? If so, how can it be done?

Given enough RSA signature values, is it possible to determine which public key is required to verify the values?  Could there be enough information to establish which key is required? Is there anything in the RSA scheme to retrieve the modulus, assuming the public exponent can be guessed?  Only padded RSA for signature generation with PKCS#1 v1.5 padding or PSS padding may be considered, not raw/textbook RSA.    This question is related to  asking about the same question for RSA encryption.


Given that $1,w,w^2,w^3,w^4.....w^{n-1}$ are nth roots of unity. find the sum of $$\sum_{i=1}^{n-1}\frac{1}{2-w^i}$$ The method I used was to write the equation of $w\;\text{as}\,z^n-1=0$ and further are writing this as $$z^n-1=(z-1)(z-w)(z-w^2)(z-w^3)....(z-w^{n-1})$$ and then replacing z here by 2. From this I was able to find out the denominator of the series in question but I couldn't figure out a way to simplify the numerator

The question asks to compute:   $$\sum_{k=0}^{n-1}\dfrac{\alpha_k}{2-\alpha_k}$$   where $\alpha_0, \alpha_1, \ldots, \alpha_{n-1}$ are the $n$-th roots of unity.   I started off by simplifiyng and got it as:  $$=-n+2\left(\sum_{k=0}^{n-1} \dfrac{1}{2-\alpha_k}\right)$$  Now I was stuck. I can rationalise the denominator, but we know $\alpha_k$ has both real and complex components, so it can't be simplified by rationalising. What else can be done?


Its the only thing I'm missing, and I'm going crazy

No matter where I look, I just can't find gnome number [insert number here]. Where can I find every gnome in the game?


I have a proposition on the book  which states the following:  Let $x_n$ be a sequence in $\Bbb R$ and let x $\in \Bbb R$. Then $x_n \to x$ iff every subsequence of $x_n$ converges to $x$.  Could you please help me on the proof of this? I can't see any way to approach it.

In Rudin textbook, there are lines, "$(P_n)$ converges to p if and only if every subsequence of $(P_n)$ converges to p. We leave the details to the reader."  I'm confused because I thought there can exist several different subsequential limits?


ActiveSupport extends Object with an instance method blank?:  class Object   def blank?     respond_to?(:empty?) ? !!empty? : !self   end end   Could !!empty? be written as empty? instead? Is this a stylistic choice so that it reads easily as a method returning a boolean? Or is there something else?


When I create a new script, I always have to manually add executable permissions with chmod +x foo.sh. My default permissions are set to 644, and but I'd like any file with extensions like .sh .py to automatically be set to as soon as they're saved so that I don't have to chmod them every time. I've seen several articles relating to how to change default permissions for all files in a folder or directory, but none discussing differentiating by file extension.  I use Vim. I would accept an explanation of what to put in my .vimrc to accomplish this as an answer.

Is there any way to set +x bit on script while creating?  For example I run:  vim -some_option_to_make_file_executable script.sh   and after saving I can run file without any additional movings.  ps. I can run chmod from vim or even from console itself, but this is a little annoying, cause vim suggests to reload file. Also it's annoying to type chmod command every time. pps. It would be great to make it depending on file extension (I don't need executable .txt :-) )


I was listening to a lecture by leonard susskind and one of the analogies he used was a coin having two states and he "broke" time into intervals. He continued to say that at each interval of time, if the coin has a state of heads or tails, it remains heads or tails. Is this truly how the universe works? Or could it be that time is just an idea we use to describe the changing of configuration of a system ie our universe? This probably doesn't have an answer but is there any way to test this? I know in computer programs we use a refresh rate not sure if that is measurable if you were within the program.

I was coding a physics simulation, and noticed that I was using discrete time. That is, there was an update mechanism advancing the simulation for a fixed amount of time repeatedly, emulating a changing system.  I though that was interesting, and now believe the real world must behave just like my program does. It is actually advancing forward in tiny but discrete time intervals?


My desktop experienced hardware failure and black out, after changing the hardware, the system works, however, it fails to connect to the internet (ethernet), so I want to reinstall the internet module through dpkg, does any know which packages should I install via dpkg? I tried: $sudo lshw -C network *-network UNCLAIMED  I also triedifconfig -a and basically it only returns info of inet 127.0.0.1 Edit: The output of lspci -knn | grep Eth -A3 (sorry for the picture cuz there is no internet)

So I did a fresh install of Ubuntu 20.04 on a computer with the new RTL8125B Realtek network card and I cannot get the network to work. I was very suprised since this is supposed to be the new feature of the 5.4 kernel (I have 5.4.0-26-generic installed). Does anyone have any idea on how to get it working? Thank you. $ lspci -knn | grep Eth -A3 06:00.0 Ethernet controller [0200]: Realtek Semiconductor Co., Ltd. RTL8125 2.5GbE Controller [10ec:8125] (rev 04) Subsystem: ASUSTeK Computer Inc. RTL8125 2.5GbE Controller [1043:87d7] Kernel modules: r8169 07:00.0 VGA compatible controller [0300]: Advanced Micro Devices, Inc. [AMD/ATI] Ellesmere [Radeon RX 470/480/570/570X/580/580X/590] [1002:67df] (rev e7)  $ dmesg | grep -i r8169 [    0.911236] r8169 0000:06:00.0: unknown chip XID 641


Let $(C[0, 1], d_∞)$ be the metric space of continuous functions on $[0, 1]$ , where the distance function is defined by   $$d_∞(f,g)=  \sup_{x\in [0,1]}|f(x)-g(x)|$$ Consider the function $T:(C[0, 1], d_∞)\rightarrow (C[0, 1], d_∞)$ defined by $$(Tf)(x):=\int_{0}^{x}f(t)dt$$ Prove that $T$ is not a contraction, i.e. there does not exist $0 < K  < 1$ such that $$d_∞(Tf,Tg)\leq K\cdot d_∞(f,g)$$ holds for any $f, g ∈ C[0, 1]$ .  Well, this problem asks to prove it, but I could disprove it (in a wrong way, but I don't know what is wrong). My solution  $d_∞(Tf,Tg)= \sup_{x\in [0,1]}|Tf(x)-Tg(x)|= \sup_{x\in    [0,1]}|\int_{0}^{x}f(t)dt-\int_{0}^{x}g(t)dt|= \sup _{x\in    [0,1]}\left | \int_{0}^{x}\left \{ f(t)-g(t) \right \}dt \right |$  Then, for some $a\in [0,1]$, $\sup _{x\in [0,1]}\left | \int_{0}^{x}\left \{ f(t)-g(t) \right \}dt \right |=\left | \int_{0}^{a}\left \{ f(t)-g(t) \right \}dt \right |$  $d_∞(f,g)= \sup_{x\in [0,1]}|f(x)-g(x)|$  Then, for some $b\in [0,1]$, $\sup_{x\in [0,1]}|f(x)-g(x)|=|f(b)-g(b)|$ Note that for some partition $P$, $$d_∞(Tf,Tg)= \left | \int_{0}^{a}\left \{ f(t)-g(t) \right \}dt \right |\leq \int_{0}^{a}\left | f(t)-g(t) \right |dt=U(|f-g|)=U(|f-g|,P)$$ $$=\sum_{k=1}^{n}(t_{k-1}-t_{k}) \sup_{x\in [t_{k-1},t_{k}]}\left | f(x)-g(x) \right |\leq a\left | f(c)-g(c) \right | \; \text {for some c}\in [0,a]$$ $$\leq a\left | f(b)-g(b) \right |= a d_∞(f,g)$$ Thus, there exist $K$ since $a$ is arbitrary number in $[0,1]$ Why this is a wrong disproof? P.S. I haven't learned about the Banach space (which I've seen in other proof.)

I am solving the following problem and its parts. Let (C[0,1],$d_\infty$) be the metric space of continuous functions on [0,1] where the distance function is defined by $d_\infty(f,g)=\sup_{x∈[0,1]}|f(x)−g(x)|. $ Let $T : (C[0, 1], d_\infty)\to (C[0, 1],d_\infty$) be defined by $(Tf)(x)=\int_0^xf(t)dt$ Prove that: T is not a contraction, i.e. there does not exist 0 < K <    1 such that $d_\infty(T f, T g)\leq K · d_\infty(f, g)$ holds for any $f,g ∈ C[0,1]$. Ive tried an example but I haven't really got anywhere. My work is as follows: $$f'(t)=\int_0^xtdt=\frac{x^2}{2}=F(x)-F(0)$$ so we pick $t$ & $t^2$ such that $d$($t$,$t^2$)=sup[$t$-$t^2$] with max value = $\frac{1}{4}$ and $d$(T$t$,T$t^2$)=sup[$\frac{t^2}{2}-\frac{t^3}{3}$] with max value =.167


I am convinced that the moderation of the christianity.se site fails the values of Stack Exchange, certainly in spirit, but also in the letter of those values. Specifically, I am convinced that moderators "David" and "Caleb" are simply censoring any questions, answers, and comments that they simply do not like.  A year ago they banned me from that site, and I put up with the ban. But these  moderators have not changed their m.o. at all.  These moderators need moderation. They are both shameless while their actions are shameful.  How can this be discussed and evaluated in a context outside of the christianity.se site that these moderators obviously control in a nepotistic manner? The discussion needs to be drawn outside of their sphere of control.

One or more of the following things happened to me on a Stack Exchange site:   My post(s) were wrongly deleted or locked by a moderator A moderator posted a wrong comment on one of my posts I was suspended, but did not do anything wrong I asked a meta question, but the question was closed and/or deleted A moderator discredited me in public ...   I think a moderator has abused their power, but I feel powerless against them.  What recourse do I have now? What can I do when I feel that a moderator has abused their power, and has been repeatedly unfair in their dealings with me?


Use the Gram Schmidt Orthogonalization Procedure to transform the basis $\{(1,2,1), (1,0,1), (3,1,0)\}$ into an orthogonal basis for $R^4$.  I haven't been able to understand how to use the Gram Schmidt Orthogonalization Procedure properly, I just couldn't grasp it during my lecture. If anyone could explain how to do this, that would be awesome!

I would like to better understand the gram-schmidt process. The statement of the theorem in my textbook is the following:     The Gram-Schmidt sequence $[u_1, u_2,\ldots]$ has the property that $\{u_1, u_2,\ldots, u_n\}$ is an orthonormal base for the linear span of $\{x_1, x_2, \ldots, x_k\}$ for $k\geq 1$. The formula for $\{u_1, u_2,\ldots, u_n\}$ is:   \begin{equation} x_k   = \left|\left| x_k - \sum\limits_{i<k}\langle x_k, u_i\rangle u_i \right|\right|_2^{-1} \left(x_k - \sum\limits_{i<k}\langle x_k, u_i\rangle u_i\right) \end{equation}   Note that I am primarily interested in how all of the vectors are orthogonal. The norm term in the above equation tells me that all the vectors will be unit vectors and hence we get an orthonormal set. Anyway, I see how this works algebraically; Let $v = x_k - \sum\limits_{i<k}\langle x_k, u_i\rangle u_i$. Now, take the dot product of $\langle v, u_j\rangle$ for some $j<k$: \begin{equation}   \langle v, u_j\rangle = \langle x_k, u_j\rangle - \sum\limits_{i<k}\langle x_k, u_i\rangle\langle u_i, u_j\rangle \end{equation} When we assume in the induction hypothesis that we have an orthonormal basis for $i<k$ then the sum is zero except when $i=j$. This leaves us with: \begin{equation}   \langle v, u_j\rangle = \langle x_k, u_j\rangle - \langle x_k, u_j\rangle = 0 \end{equation}  OK, I can logically follow algebra, but how can I see this geometrically? Can someone provide both 2D and 3D examples/plots? Since I am specifically interested in seeing how all the vectors meet at 90 degrees.


Its pretty uncomfortable to use Ctrl+TAB to switch between vertex/edge/face selections in edit mode. Is there a way to make custom shortcuts for each of them?  Allso Is there shortcut for sculpt mode? And if not can I create one and how.  Thanks!

I want a keyboard shortcut for switching between selecting things; vertices, faces and points. One key for each, not a pop up menu where i have to select with the mouse. Does this exist? Modelling should be like playing a piano or something, a key for everything, minimal aiming the mouse pointer att small icons, this aiming the mouse att small icons all the time is so.. breaks the flow.. Im sure it exists but i cant find it anywhere?


When a ballerina pulls her arms in, her rotational kinetic energy increases because angular momentum is conserved. That means that work must have been done on her. I saw somewhere that there is work done because she has to pull her arms in against a centrifugal force.   Actually, the particular example is from the Feynman lectures volume I, chapter 19 section 19-4. Here is the problematic part: "When we move a weight horizontally we do not do any work. If we hold a thing out and pull it in, we do not do any work. But that is when we are not rotating! When we are rotating there is centrifugal force on the weights. They are trying to fly out, so when we are going around we have to pull the weights in against the centrifugal force. So the work we do against the centrifugal force ought to agree with the difference in rotational energy."  I have two questions: what is this centrifugal force in the quote above, and how is it that by pulling her arms in against this force, she has done work? A centrifugal force is a fictitious force from what I know of, so the kinetic energy increase cannot be accounted for with this.   The second question is explained here: Suppose you have some bar that you are holding at arm's length, perfectly horizontally (meaning ignore gravity). Because the bar is still, there is no net force. You now pull the bar towards you. The bar must have accelerated, so you did some positive work on the bar. However, because at the end of the process, when the bar is next to your body, it is at rest, you must have done negative work, decelerating the bar to make it come to rest. Therefore,the total work done on the bar must be zero. Note that this property does not depend on whether or not other forces are acting upon the bar, as it is only the net force that does work. So how is it, that by saying that there some force pulling the bar away from you (the centrifugal force for the ballerina), you have done work? It must be the same thing, because if the bar is at rest initially, and at rest when near your body, there must be no net force, so it is the same situation as if there was only one force applied to the bar.  We could say that you accelerated the bar and let the other force decelerate it, meaning that in all, you did work on the bar. However, the net work on the bar would be zero, because the other force did negative work on it by decelerating it. And we are interested in the net work done on the arms of the ballerina, not the work she does herself. So what part am I missing? Thanks for any answers and sorry for the long question.   To clarify, the bar in question is not rotating. So the net force on the bar is zero.

This may be a very basic question but I am not seeing how it works. Consider the standard example of an ice skate rotating about his/her center of mass and pulling in his/her arms. The torque is zero so we have conservation of angular momentum. This implies that $\omega$ increases to keep $I\omega$ constant, but then $K_{rot}=\frac{1}{2}I\omega^2$ doesn't stay constant, it increases. This implies that there is work done, but what force is doing this work?


I am trying to copy a folder to remote Ubuntu server using command line ssh connection, i understand it's doable to transfer a file using scp but i have many files in a folder iam trying to copy to that remote server, how is that done? anyone?  Thank you.

I am trying to get some files off of my school Linux account using ssh. I have got the connection to work using:  scp <school_server>: ~/folder I want ~/where I want to go.    But when it goes to transfer folder it gives me the message:  not a regular file    The file contains .java files, and I want the whole folder.


The line shapefile is obtained from the Dissolve toolbox of all routes, so there is only one polyline in this shapefile. The point shapefile is already there. The  should allow me to get another shapefile which will be split according to the points. I notice that some of the lines are split, but some of them are not. The common feature for those lines don't get split is there is no turning line at that point, as shown below. This means the line is split perfectly when the point is the intersection, but for those points are just in the middle of a line, the split function will not work. Also, the points used to split the line are obtained from this line shapefile, so they are perfectly located along the line. This is a new question, which is not the same as the similar questions asked before since the problematic points are all the middle points along the line without intersecting with other lines. Any comments on this issue?    The following picture shows the problematic points where the line can't be split.  I am using ArcGIS Desktop Advanced License 10.3.1.

Why does  not split at every point encountered, even if run in an iterative fashion?  Following the suggestions of a thread here and several others, I made a set of points in order to split polylines at specified intervals. In order to do this, I used linear referencing to turn my lines into routes. Then, I exported the attribute table, divided each length by 5, and set points at multiples of 1/5 the length of the line. I used this as the event table to create a layer of events. So, each line has 4 equally spaced points along it, and I thus ultimately need the 5 segments separated by those points.  Curiously, though, when I try to do the second part "Split Line at Point," it seems that only one point is used on a given line at a time, and I'm not sure how it chooses the point (maybe order in its attribute table?) I could run the tool multiple times, but this doesn't seem to solve the problem either. For example, I could see how it would continue splitting segments as more segments are generated, but on e.g. the 4th run I see that some lines are still only split 3 times, even though there is a point within a line segment that was never split and existed before I ran the tool. I'm not sure how the splits are generated, but in any case, it doesn't seem to do what I want it to do, which is produce a split at "each" point.  What should I do to split lines at ALL points along the line?


Can we define the energy density of gravity field? If so, what is the formula, and the newtonian approximation? In newtonian mechanics, we can easily obtain the gravitational potential energy. But if the mass gets bigger, and is necessary to use GR, things gets more complicated. What is the potential energy in this case? I am not well-aware about tensor or those sort of things, so please explain in easy words.

Starting  with the Einstein-Hilbert Lagrangian  $$ L_{EH} = -\frac{1}{2}(R + 2\Lambda)$$  one can formally calculate a gravitational energy-momentum tensor   $$ T_{EH}^{\mu\nu} = -2 \frac{\delta L_{EH}}{\delta g_{\mu\nu}}$$  leading to  $$ T_{EH}^{\mu\nu} = -G_{\mu\nu} + \Lambda g_{\mu\nu} = -(R_{\mu\nu} - \frac{1}{2}g_{\mu\nu}R) + \Lambda g_{\mu\nu}. $$  But then, in the paragraph below Eq. (228) on page 62 of  paper, it is said that this quantity is not a physical quantity and that it is well known that for the gravitational field no (physical) energy-momentum tensor exists.  To me personally, this fact is rather surprising than well known. So can somebody explain to me (mathematically and/or "intuitively") why there is no energy-momentum tensor for the gravitational field?


After following many other answers from similar situation I finally was able to boot USB live distros in my Samsung Ativ 500t, a pretty old PC with horrible hardware Intel Atom Cherry Z3760 with PowePC GPU. After many efforts when I select in Grub Try or Install Ubuntu/Mate/Lubuntu and others, it seems to start, gives some errors of GPIO not being able to be address in IrQ and some logo of start shows up to finally say that the media of installation cannot be found. I understand this particular hardware is not so easy to handle (32 bits for processor and EFI), but it seems I’m close to getting it to work, it seems that for some reason after getting into GRUB the partitions just get lost. What can I do to solve the error: (initramfs) unable to find a live medium containing a live file system  when trying to install or try any Ubuntu and derivatives in my Atom Z3760? I have already tried different pendrives, and I have already tried removing and plugging it back in. Can someone help me?

For a given hardware configuration, how do I find out if Ubuntu will run on it? What considerations should I take into account when choosing an Ubuntu version and  such as:    with a lighter desktop than the usual Gnome and Unity  with the even lighter LXDE desktop   Obviously Ubuntu does not run on some processor architectures. So how do I go about choosing the right version and derivate. How can I find out the minmal system requirements?


While it sounds crazy, some of us do not actually have twitter accounts and really do not use twitter at all, so we don't see tweets from .  This is especially true for users behind corporate firewalls where Twitter access is blocked.   So when there are access issues, the first stop for many users is , but it seems that updates there much less frequent than tweets, especially during an outage, and usually only after the fact.  Additionally, only major planned events are ever announced in advance there.  Minor outages, such as the recent  were never even mentioned, so unless someone was following @StackStatus on twitter (which would require an account), or thinks to check twitter feed, they won't be up to date on any on-going issues.  I realize updating a blog while in the middle of an outage or to announce a minor (and temporary) outage due to maintenance is not a productive use of time, so can StackStatus.net display the twitter feed, or even better, can tweets from @StackStatus automatically be added to the blog?  It would save many users from having to check 2 places every time they have an access issue.    Note there is similar sounding but essentially different suggestion:  - about attaching the twitter feed to the maintenance page for Stack Exchange sites. This request is different in that it is about posting twitter feed posts to the Stack Status blog.

The StackOverflow maintenance page states:     Routine maintenance usually takes less than an hour. If this turns   into an extended outage, we will post details on the .     Would it be worthwhile to add a latest tweet(s) from  on this page as well?  As we saw today, the outage was short enough to not merit a blog post, but caused enough of an impact to post a tweet about.  It could be done either via the  or using the embed code (as provided by Twitter):  Tweets by @StackStatus


Will notification of @user in comment to an answer actually notify user which was commenting on another answer of the same question? The user autocompleter doesn't autocomplete the name.   I think information on this is missing in .

How do the comment replies (aka "pinging users") work?  Who can I send an @reply to? How do I respond to a specific user when entering my comment? Will they be notified? What do people mean when they talk about "pinging" another user?  Related:


shakil@shakil-Aspire-5733Z:~$ sudo apt-get -f install [sudo] password for shakil:  Reading package lists... Done Building dependency tree        Reading state information... Done Correcting dependencies... Done The following extra packages will be installed:   linux-tools-common The following NEW packages will be installed:   linux-tools-common 0 upgraded, 1 newly installed, 0 to remove and 6 not upgraded. 3 not fully installed or removed. Need to get 0 B/88.0 kB of archives. After this operation, 312 kB of additional disk space will be used. Do you want to continue? [Y/n] y (Reading database ... 303158 files and directories currently installed.) Preparing to unpack .../linux-tools-common_3.13.0-53.89_all.deb ... Unpacking linux-tools-common (3.13.0-53.89) ... dpkg: error processing archive /var/cache/apt/archives/linux-tools-common_3.13.0-53.89_all.deb (--unpack):  trying to overwrite '/usr/bin/perf', which is also in package linux-lts-vivid-tools-common 3.19.0-18.18~14.04.1 dpkg-deb: error: subprocess paste was killed by signal (Broken pipe) Errors were encountered while processing:  /var/cache/apt/archives/linux-tools-common_3.13.0-53.89_all.deb E: Sub-process /usr/bin/dpkg returned an error code (1)  shakil@shakil-Aspire-5733Z:~$    I have already tried:   sudo apt-get autoclean  sudo apt-get clean  sudo apt-get autoremove -f  sudo apt-get autoremove  sudo apt-get install -f    Please, can anyone help me?

For example:  $ sudo apt-get install curl Reading package lists... Done Building dependency tree Reading state information... Done You might want to run 'apt-get -f install' to correct these: The following packages have unmet dependencies: bsh : Depends: libjline-java but it is not going to be installed groovy : Depends: libjline-java but it is not going to be installed rhino : Depends: libjline-java but it is not going to be installed E: Unmet dependencies.   Try 'apt-get -f install' with no packages (or specify a solution).   I get the same or similar errors when I attempt to install clojure1.3, leiningen, and several other packages.   When I try the suggestion made in the error message, this is what happens:  $ sudo apt-get -f install  Reading package lists... Done Building dependency tree        Reading state information... Done Correcting dependencies... Done The following packages were automatically installed and are no longer required:   diffstat linux-headers-3.2.0-26-generic linux-headers-3.2.0-26 dh-apparmor dkms html2text libmail-sendmail-perl libsys-hostname-long-perl Use 'apt-get autoremove' to remove them. The following extra packages will be installed:   libjline-java Suggested packages:   libjline-java-doc The following NEW packages will be installed:   libjline-java 0 upgraded, 1 newly installed, 0 to remove and 0 not upgraded. 23 not fully installed or removed. Need to get 0 B/72.0 kB of archives. After this operation, 129 kB of additional disk space will be used. Do you want to continue [Y/n]? Y (Reading database ... 226243 files and directories currently installed.) Unpacking libjline-java (from .../libjline-java_1.0-1_all.deb) ... dpkg: error processing /var/cache/apt/archives/libjline-java_1.0-1_all.deb (--unpack):  trying to overwrite '/usr/share/java/jline.jar', which is also in package scala 2.9.2-400 Errors were encountered while processing:  /var/cache/apt/archives/libjline-java_1.0-1_all.deb E: Sub-process /usr/bin/dpkg returned an error code (1)  $ sudo apt-get upgrade Reading package lists... Done Building dependency tree        Reading state information... Done You might want to run 'apt-get -f install' to correct these. The following packages have unmet dependencies:  bsh : Depends: libjline-java but it is not installed  groovy : Depends: libjline-java but it is not installed  rhino : Depends: libjline-java but it is not installed E: Unmet dependencies. Try using -f.


My multimeter is rated for 600V but I need to measure a 10kV AC source. I was thinking of building a voltage divider but I wouldn't know how many resistors it would take to safely measure this high of voltage.

My multimeter is rated to 600V.  How can I readily (and safely) use it to measure higher voltages?


We have several questions tagged  talking about encryption, hashing, signing, etc. but no question asks about exchanging a secret via public key encryption in a secure way.  Does any solution exist, which would allow us to exchange a secret via a public channel (think: key exchange) using nothing but pen-and-paper and which can be handled by people who are not (what one might call) “math wizards” (read: people who can calculate whole algorithms using nothing but their brain) but who do know their way around maths and who do understand crypto?  As far as I’m aware there isn’t any such solution in classic (pre-computer) cryptography. But that doesn’t automatically mean it can’t be done.  Of course, potential solutions won’t offer the security we get and expect from computer-based solutions like RSA or elliptic curve cryptography. Yet, to keep it simple let’s assume we’re not trying to protect ourselves against nation-state adversaries here. Nevertheless, suggestions should provide a usable security margin.  What would be a not so neck-breaking way to exchange a secret over a public channel using nothing but pen-and-paper means? Is it even possible to do so in a somewhat secure way without using computers, mobile phones, or other, even more rudimentary tools — like mechanical machines — that aren't always available? (Hence the tag .)  To clarify: I am not looking for  made for the purpose of “demonstrating to a 12-year-old how encryption works” and/or to be used in a “fantasy story”. My question asks for an actually usable and secure solution (as mentioned above).

I have at least three, distinct motivations for having a simple way to use asymmetric key encryption by hand or without modern computers.  First, I was recently demonstrating to a 12-year-old how encryption works. I created some basic cyphers and had him figure them out. (I recommend this; it's quite fun.) Wanting to up the ante, I looked for ways to send messages back and forth using public-private key encryption, and I failed with flying colors.  Second reason for wanting this is that it would really help me understand how asymmetric encryption works. At the moment, I can't figure out a way to do solve this on my own, and I feel that betrays my lack of understanding in the subject.  Finally, (this one may be a stretch) I'm writing a fantasy story, and I'd like to do something unique with the form of exchange. One thought was to have a memorized key that the owner held, which she would use to sign her (paper) payment of 30 units for a loaf of bread, or whatever, combining her key with the shopkeeper's public key. (UPDATE: Note that this gets into digital signatures, rather than asymmetric key encryption. I'm hoping they are related, but if they're not, forget it.)  Any ideas how to accomplish this? If it's simply not feasible, I would appreciate an explanation as to why.  There are two similar questions on this site, but neither of them address asymmetric key encryption, unless I'm more misinformed than I thought: