This is a simplified version of java.util.Map  public interface Map {     interface Entry{         int getKey();     }      void clear(); }   My question is why it is done that way?   How the inner interface should be implemented? Can I just implement the inner one?

I have just found a static nested interface in our code-base.  class Foo {     public static interface Bar {         /* snip */     }     /* snip */ }   I have never seen this before. The original developer is out of reach. Therefore I have to ask SO:  What are the semantics behind a static interface? What would change, if I remove the static? Why would anyone do this?


I organize all of my photos into folders. I have years of photos organized properly by year_date_event_name. I would like to import the folders directly into the Photos app as Albums named as the folder name.   I can't seem to even find a way to import the folders as albums, let alone having the folder name used as the album name.   I'm guessing a script would be the best way to do this? Any suggestions would be greatly appreciated.

In iPhoto I relied heavily on the events feature. I had about 100 events. In Photos for OS X I'm totally ok with the new albums that replaces events somehow. But I am looking to automatically create an album of the pictures I import.  In iPhoto you could drag a folder into the program and it automatically created an event with the name of the dragged folder. Is there some similar mechanism to automatically create an album? The only way I found to create the similar behaviour is to drag a folder to Photos for OS X, import all of the photos, go over to the last imported section and create an album out of these images. Is there a better workflow?  Thanks in advance for any ideas.  Edit: I read the question here () but it doesn't help me very much unfortunately.


Find the number of real root in the equation  $2\cos \left ( \frac{x^{2}+x}{6} \right )=2^{x}+2^{-x}$  I got one  root ,i.e.   $\cos \left ( \frac{x^{2}+x}{6} \right )$  Is it correct??

How many real solutions are there of the equation $2 \cos (\frac{x^2 + x}{6}) = 2^x + 2^{-x} $? Please illustrate.


Trying to figure out if you have integral domains A and B that are isomorphic then their respective field of fractions,F and K, are also isomorphic by $\theta(ab^{-1})=\theta(a)\theta(b)^{-1}$. How can you $\theta$ is an isomorphism?  For one-to-one I figure show ker$\theta$=0 and use pigeonhole to show onto but not sure.  And for addition  would showing $\theta(ab^{-1} + cd^{-1}) = \theta(ad+bc)(bd)^{-1})$ be on the right track.  Any help appreciated.

If two integral domains $D$ and $D'$ are isomorphic show that their corresponding field of quotients (fractions) $Q(D)$ and $Q(D')$ are isomorphic.


He is one of those writers who have/has won the Booker prize.   which is correct: 'has' or 'have'?  And why?

Let us say, I have been given two sentences in an MCQ test and I need to pick up the correct one.   He is one of the men who do the work. He is one of the men who does the work.   Somehow, I lean towards the second one ("It is I who am to blame", the one sentence memorized to take care of cases like this), but I have found some grammar books supporting the first one.


Let's say am running a Spring Boot app via CLI using java command java -Dserver.port=5743 -jar somejar.jar and I want the logs to be printed within the cli and also copy into files. So far I could do only one at a time either on CLI or file

In bash, calling foo would display any output from that command on the stdout.  Calling foo > output would redirect any output from that command to the file specified (in this case 'output').  Is there a way to redirect output to a file and have it display on stdout?


I am simulating an airport which has only one runway. When it is busy, planes wishing to take off or land have to wait. Implement a simulation, using two queues, one each for the planes waiting to take off and land. Landing has the higher priority. The user enters commands takeoffflightSymbol, landflightSymbol, next, and quit. The first two commands place the flight in the appropriate queue. The next command finishes the current takeoff or landing and enables the next one, printing the action (takeoff or land) and the flightsymbol. But I can't seem to find the problem for the following code. Help!  public class Runway {    public Scanner in;    public Queue<String> takingOff;    public Queue<String> landing;     public Runway()    {        in = new Scanner(System.in);        boolean done = false;        while (!done)        {           System.out.println("Type TAKEOFF/LAND followed by Fight Number to Queue a plane");           System.out.println("Type NEXT to perform the next action, or QUIT to close the simulation");           String action = in.next();           if (action.equals("TAKEOFF"))           {               String flight = in.next();               takingOff.add(flight);           }           else if (action.equals("LAND"))           {               String flight = in.next();               landing.add(flight);           }           else if (action.equals("NEXT"))           {               handleNextAction();           }           else if (action.equals("QUIT"))           {               System.exit(0);           }           else {               System.out.println("ERROR - not a valid command");           }        }    }     public void handleNextAction()    {        if (landing.size() > 0)        {           String flight = landing.remove();           System.out.println("Flight " + flight + " is landing. ");        }        else if (takingOff.size() > 0)        {           String flight = takingOff.remove();           System.out.println("Flight " + flight + " is taking off.");        }        else        {           System.out.println("There are no flights waiting to take off or land");        }    }     public static void main (String[] args)    {        Runway simulator = new Runway();    } }   When the simulation is running, other than the quit function, all the other functions produce java.lang.NullPointerException errors.

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


What is the difference between the following two commands to source a file and then print the env variables?  sh -c . envvars.sh; env   And:  ./envvars.sh; env   More specifically, what do the following do:  ". envvars.sh" vs. "./envvars.sh"   And:  "sh -c envvars.sh" and "./envvars.sh"

I'm trying to write a shell script that, when run, will set some environment variables that will stay set in the caller's shell.  setenv FOO foo   in csh/tcsh, or  export FOO=foo   in sh/bash only set it during the script's execution.  I already know that   source myscript   will run the commands of the script rather than launching a new shell, and that can result in setting the "caller's" environment.  But here's the rub:  I want this script to be callable from either bash or csh.  In other words, I want users of either shell to be able to run my script and have their shell's environment changed.  So 'source' won't work for me, since a user running csh can't source a bash script, and a user running bash can't source a csh script.  Is there any reasonable solution that doesn't involve having to write and maintain TWO versions on the script?


I am confused about the definition of "differential".  Sometimes I see it is a pushforward mapping $df:TM\rightarrow TN$, which gives another tangent vector when acting on a tangent vector.    Sometimes it acts as a cobasis in contangent space, which contracts with tangent vectors and gives a real number, $df:TM\rightarrow \mathcal{R}$    How are the two definition compatible with each other?  Thank you very much.

I have seen that if $f$ is a smooth function on a smooth manifold $M$ then differential of $f$ at the point $p$ is defined by $(df)_p(X_p) = X_p(f)$ but i am not able to see that how it can be derived by the usual definition of differential map of a smooth map between manifolds which is as follows: If $\phi: M \to N$ is a smooth map between smooth manifolds then the differential of $\phi$ is $d\phi_p: T_pM \to T_{\phi(p)}N$ via $v \mapsto v_{\phi}$ such that $v_{\phi}(g) = v(g \circ \phi)$.  Can someone tell me the relation between the two?  Thanks!


I think I might have changed some cursor settings unintentionally. When I go to edit mode and try to select 2 objects using the shift key, it does not allow me to do so.. and also the mouse cursor changed to crosshair from a pointer. How can I get this back please?   The reason as to why I need to select both objects in edit mode is so that I can make use of the Knife Project tool Below is a screenshot of my settings

Whenever I enter edit mode, with 2 separate meshes (cubes), I can only select vertices/edges/faces of 1 mesh.  Example (the screen shot did not include the mouse cursor):    Also, when I enter edit mode with both meshes selected, one of the meshes has a red border and cannot be selected (it also has this border in Object mode):


I have a site that is generating this warning:     When we tested a sample of URLs from your Sitemap, we found that some URLs redirect to other locations. We recommend that your Sitemap contain URLs that point to the final destination (the redirect target) instead of redirecting to another URL".   Why is this a problem, and how do I correct it?

I noticed that I have three warnings when I submitted my Sitemap. They all say this:      When we tested a sample of URLs from your Sitemap, we found that some   URLs redirect to other locations. We recommend that your Sitemap   contain URLs that point to the final destination (the redirect target)   instead of redirecting to another URL.   I'd like to try and resolve this issues but I'm not sure what to do.  Sitemap url for reference:


I have main class. It is located in package "view"  public class Main extends Application {  @Override public void start(Stage primaryStage) throws Exception{     try {        AnchorPane root = (AnchorPane) FXMLLoader.load(getClass().getResource("start.fxml"));         Scene scene = new Scene(root, 757, 562);         primaryStage.setScene(scene);         primaryStage.setTitle("Course Work");         primaryStage.show();     } catch(Exception e) {         e.printStackTrace();     } }  public static void main(String[] args) {     launch(args); } }   It successfuly load file start.fxml. Which is also located in package "view".  <?xml version="1.0" encoding="UTF-8"?>  <?import javafx.scene.text.*?> <?import javafx.scene.control.*?> <?import javafx.scene.layout.*?>  <AnchorPane maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" prefHeight="562.0" prefWidth="757.0" styleClass="anchor-pane" xmlns="http://javafx.com/javafx/8" xmlns:fx="http://javafx.com/fxml/1" fx:controller="controller.Start">    <children>       <Button layoutX="48.0" layoutY="466.0" mnemonicParsing="false" onAction="#start" text="Ок">          <font>             <Font size="14.0" />          </font>       </Button>    </children> </AnchorPane>   Controller for this start.fxml is located in package "controller".  public class Start { private Stage stage;      @FXML     public void start(ActionEvent event) throws Exception {         try {             AnchorPane root = (AnchorPane) FXMLLoader.load(getClass().getResource("sample.fxml"));             Scene scene = new Scene(root, 757, 562);             stage.setScene(scene);             stage.setTitle("Course Work");             stage.show();         } catch (Exception e) {             e.printStackTrace();         }     } }   In method "start" I want to create new stage using sample.fxml. However I had some problems with it. For example - java.lang.NullPointerException. How can I fit it?


On some sites, the only flags I used are spam flags. And in this case, the flagging history sidebar is empty. Example on Drupal Answers:    But on sites where I also have some other flags, the spam flags show up fine in the history.

Today I've helped flag a lot of spam for this: .  When I've visited my profile on WebApps to see my flag history of flag, the information about my flagging history was missing.  Note that these spam flags were my only flags on this site.    Normally, I should have more information like when I'm looking at my Stack Overflow account.    Is this a bug?


This is an exercise from Conway I am stuck at. Here $n($$\gamma$ $,$ $w$) is the winding number and $(6.2)$ is like below.    I need to prove that $h$ is continuous using only the definition of winding number, not Cauchy Theorem. In fact I have to use the result of the exercise 9 to prove the Cauchy Theorem. So, I have to use some $\delta$ $-$ $\epsilon$ argument. But, I can't find a way to do so. Could anyone help me how to solve the exercise 9?  The definition of winding number is like below.

There's a question in my complex analysis book:     Let $G$ be a region and let $\gamma_0$ and $\gamma_1$ be two closed smooth curves in $G$. Suppose $\gamma_0\sim\gamma_1$ and $\Gamma$ is a homotopy between them. Also suppose that $\gamma_t(s)=\Gamma(s,t)$ is smooth for each $t$. If $w\in \mathbb{C}-G$, define $h(t)=n(\gamma_t;w)$ and show that $h:[0,1]\rightarrow\mathbb{Z}$ is continuous.    This is an exercise right after the section that proves the following version of Cauchy's theorem:     If $\gamma_0$ and $\gamma_1$ are two closed rectifiable curves in $G$ and $\gamma_0 \sim \gamma_1$ then $$\int_{\gamma_{0}}f=\int_{\gamma_1} f$$ for every function $f$ analytic on $G.$   I must be missing something. It seems like you can just say the following:      'Proof:' Since $\frac{1}{z-w}$ is analytic in $G$ ($w$ isn't in $G$), and $\gamma_0\sim\gamma_t\ \forall t\in[0,1]$ (consider a rescaled version of $\Gamma$), then by Cauchy's theorem, $n(\gamma_t;w)=n(\gamma_0;w)=n(\gamma_1;w)$. Thus, the winding number is constant along $t$ and thus certainly continuous.   My problem with that is that this doesn't require the assumption that $\Gamma$ is a smooth homotopy. I think the author had meant for the reader to work harder for this result. What is the proof 'supposed' to look like?


Please tell me some good skills to improve my ball control, whether it be in air or on ground, and my dribbling skills, as I'm a huge fan of this game.

I play football (soccer) for my community traveling team. Our usual ball handling exercise is getting the ball around a course of cones.  What other ways can I improve my ball handling abilities?


I know that in blender you can use blueprints to model any vehicle but I couldn't found any blueprints for this bus VDL Jonkheere Mistral 30 from the Jutc company and I would love to start a project for it. I also tried writing a letter to the manufacturers asking permission for blueprints and didn't get a response. However I do have alot of images of the bus as I am from Jamaica but I'm not sure if the images needs to be flat like how a typical blueprint would look like (Front view, side view etc). I need professional advice thanks.

I am trying to change the floor covering using a picture. How can I define the floor?


I'm working on a program and it compiles fine, but it gives me a "MSVCR110D.dll is missing.."-error. I run Visual Studio 2013 on Windows 7 64bit, I also use boost 1.55.0 and SFML 2.1. Google and a fellow superuser post didn't help me out. I got told to install c++ redistributable  but that didn't help me either. I'm not that good with C++ yet so excuse me if I missed something.

I'm not really sure if this belongs on SuperUser or StackOverflow, but it doesn't seem to be a coding problem so I'm gonna run with this.  I've started working on a C++ game using Visual Studio 2013 utilizing FreeGLUT and FreeImage. I can compile and run it on my desktop without issue, but when I try compiling the same code on my laptop I get the error "msvcr110d.dll is missing from your computer." After which there is about a 50% chance that Visual Studio freezes, and I'm forced to restart the computer as Task Manager cannot stop the process (another problem I'm still working on).  Google searches have told me to install Visual C++ Redistributable 2012, however this was already installed on this laptop (both x86 and x64), and reinstalling (from ) has not helped at all. I also tried installing Visual C++ Redistributable 2013 (x86 & x64, from ), but to no avail. Both of those links do feature an ARM download. I'm not sure what that is, and attempting to install it results in a pop-up saying I can't install it on this version of Windows (Windows 8 that is), so I'm assuming I don't need that.  Looking in the C:\Windows\SysWow64 folder, I can see msvcr110.dll but not msvcr110d.dll. It looks like the release version was installed, but not the debug. I do see msvcr120d.dll, which should be the 2013 version right? So shouldn't Visual Studio 2013 be using that, instead of msvcr110d.dll?  Running a standard C++ HelloWorld project doesn't have this issue, so I imagine it must have something to do with FreeGLUT or FreeImage. However it compiles and runs on my desktop without issue, so I believe everything is coded & linked correctly. I've added the include directories, library directories (both of which were debug), and added opengl32.lib & FreeImaged.lib as additional dependencies.  Installing Visual C++ Redistributable hasn't helped, so is there another way of solving this issue? Should Visual Studio 2013 be using msvcr110d.dll at all, or it should be using msvcr120d.dll? Do I need that ARM install from the MSVCR download page? I'm using Windows 8 64 bit (brand new laptop as well so I don't think there's any corruption issues). Thanks in advance for your help.  Doug


I've downloaded the STL files of a puppet that should be ready to be printed with a 3d printer and I've used two 3d tools to display the relative components of the puppet's body. First of all I used Blender, but unfortunately I can't see anything, as you can see from the picture that I have attached. I've also used the program that Windows uses by default and this time I was able to see the content inside. So now I have two problems to fix within Blender :  I want to understand how to see the content of the STL file as soon as I open the file in blender  I want to see the the measures in cm of the single parts of the objects   thank you.

I try to import .obj files from this project:  - the files contain Polygon Mesh Data.  When I import the obj file into blender, the outliner shows a new mesh added, but nothing is visible in the 3D viewport:      Any help will be appreciated.


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?


I checked the top 50 users of a particular city using a query in the Stack Exchange Data Explorer. You can see the result , and I am not able to find my name in the list, while my city name is the same. Is there a problem with data updates?

I was querying data from  using a LINQ query in LINQPAD and found that the data I got back is quite obsolete. I searched for Shekhar-Pro (me) by using a where clause on ID 399722 and the data returned was for 8 Jan 2011. Why was the data so old? Isn't the data updated in real time, or at least frequently? If not, where can I get realtime data?


I can create bibliography at the end of my beamer presentation manually in IEEE style using  \begin{the bibliography} \bibitem{} \end{thebibliography}   When I do this, I do not get   [1] Author, Paper, etc...   but I get as shown in the attached image. I want square brackets with numbers. How to do it?

Instead of the default icons or the text option, I would like to have numbered entries in my bibliography.  I added the line:  \setbeamertemplate{bibliography item}{}  to get rid of the icons, but can't figure out how to get numbers to display in their place. The references in the content slides are numbered, but without the corresponding number in the bibliography it's not very helpful.  MWE:  \documentclass[t]{beamer}  \setbeamertemplate{navigation symbols}{} \setbeamertemplate{bibliography item}{} \setbeamertemplate{frametitle continuation}[from second]  \setbeamertemplate{footline}{     \hspace*{0.1cm}     \text{short title}     \hspace{1cm}     \insertshortauthor     \hspace{3.5cm}     \insertsectionhead     \hfill     \insertframenumber     /     \inserttotalframenumber     \hspace{0.1cm} }  \title{a title} \author[me]{my full name} \institute{where I work} \date{today}  \begin{document}  \begin{frame}     \titlepage \end{frame}  \begin{frame}     \frametitle{1st slide}     Some text. \cite{ref_1} More interesting text. \cite{ref_2} Some even more interesting stuff. \cite{ref_3}  \end{frame}  \begin{frame}[allowframebreaks] \frametitle{References}     \tiny{\bibliographystyle{abbrv} }     \bibliography{refs} \end{frame}  \end{document}   Bib file:  @inproceedings{ref_1,   title={title 1},   author={A. Author},   booktitle={book title},   year={2010} } @article{ref_2,   title={title 2},   author={B. Author},   journal={Journal},   volume={35},   number={10},   pages={1217--1256},   year={2010},   publisher={Publisher} } @incollection{ref_3,   title={title 3},   author={C. Author},   booktitle={book title},   pages={595--606},   year={2012},   publisher={publisher} }   Resulting bibliography:


Searched this question a lot in different places but could not find any answer that could satisfy me. So I am here to clear my concepts regarding virtual displacement. Now I am clarifying my doubt. As my textbook "A Student’s Guide to Lagrangians and Hamiltonians" by Hamill says on p.11:  A virtual displacement, $δx_i$, is defined as an infinitesimal, instantaneous displacement of the coordinate $x_i$, consistent with any constraints acting on the system.  And it gives the relationship, $$\delta x_i=\sum_{\alpha=1}^n\frac {\delta x_i}{\delta q_\alpha}$$ The time co-ordinate is frozen in virtual displacement. Now my question is if time is frozen then no displacement should occur. So how the "Virtual displacement" come? What does it mean? Again $\frac {\delta x_i}{\delta q_\alpha}$ how is it getting the dimension of a displacement? I think the $x$'s and $q$'s dimension is same [L]. So it should be dimensionless. Please illustrate it so that I do not face any difficulties with virtula-displacement term. I will be too much helpful if you also give an example to show how to calculate virtual displacement.

Why is the  formulated in terms of virtual displacements rather than real displacements in time?  EDIT In other words, which step of the derivation of D'Alembert's principle (or Largrange's equation) will not work if one uses real displacements and why?


This question is different from , as it is about the usage in a physics research paper.  Basically, I am not sure when to use Arabic numerals and when to use their corresponding English words when writhing a physics research paper.  E.g.    The 3 parameters are fixed. The three parameters are fixed. The value of the parameter is five. The value of the parameter is 5.   Are 1 and 2 both acceptable? Or is one of them better perceived? And again, is 4 better than 3?   If 4 is better than 3, and 2 is better than 1. I can then have both numerals and words to represent small numbers in a paper. Is this acceptable?  Can I always use Arabic numerals?

The junction has a stop sign on each of the four entrances.   The junction has a stop sign on each of the 4 entrances.   The first is preferred, for some reason, by many English texts. Why? I haven't seen this phenomenon in other languages.


Our company has been asked to recently switch off our computers over the weekends to conserve power.  Is it possible to remotely switch on a Computer if   I'm able to establish a VPN to the Office Network and I know the IP Address of my Machine.   I would think as long as I can be a part of the office network (because of the VPN I've established) there must be someway to power it on or at least schedule it to power on at certain times of the day. By the way this is not some VM. Its a Physical Machine.

Possible Duplicate:          May I know how can one remote start up a machine that is in a shut down state?


In Harry Potter, if charms will work and wands will shoot out things only on uttering spells, then it is almost impossible for mute people to survive as a part of the magical community.  Is there a way in which even the mutes can perform magical charms, with the help of anything else?

You need to say the words to cast a spell. How would a deaf or mute wizard/witch do that?


I'm studying linearized gravity, for which the weakness of the gravitational field is expressed as ability to decompose the metric into the (flat) Minkowski metric plus a small perturbation, i.e. $$g_{\mu\nu}=\eta_{\mu\nu}+h_{\mu\nu},\;\;\;\;\; \left|h_{\mu\nu}\ll 1\right|.$$ Let's restrict to coordinates in which $\eta_{\mu\nu}$ takes its canonical form, $\eta_{\mu\nu}=\mathrm{diag}\left(-1,+1,+1,+1\right)$. The assumption that $h_{\mu\nu}$ is "small" allows us to ignore anything that is higher than first order in this quantity. My teacher said that we thus obtain $$g^{\mu\nu}=\eta^{\mu\nu}-h^{\mu\nu},$$ where $h^{\mu\nu}=\eta^{\mu\rho}\eta^{\nu\sigma}h_{\rho\sigma}$.  I understand why we can raise and lower indices with $\eta$ (due to perturbative order of corrections), but - and I know it's silly - I can't see why there should be a relative minus sign in the expression for $g^{\mu\nu}$.

From what I've read, in the framework of linearised gravity, one perturbs the metric around a Minkowski background, $\eta_{\mu\nu}$, such that  $$g_{\mu\nu}(x)=\eta_{\mu\nu}+h_{\mu\nu}(x)\tag{1}$$  where $h_{\mu\nu}(x)$ is a small perturbation, i.e. $$\big\lvert h_{\mu\nu}\big\rvert<<1.\tag{2}$$  The inverse metric is then found by assuming the following ansatz:  $$g^{\mu\nu}(x)=\eta^{\mu\nu}+\tilde{h}^{\mu\nu}\tag{3}$$  where $\tilde{h}^{\mu\nu}$ is also small (i.e. $\big\lvert \tilde{h}_{\mu\nu}\big\rvert<<1$).   Using this, it is easy to find that  $$g^{\mu\nu}(x)=\eta^{\mu\nu}-h^{\mu\nu} \tag{4}$$  to first order.   My question is, what is the justification for this ansatz? Is it simply that one expects the inverse metric to have a similar form to the metric in order to satisfy $$g^{\mu\alpha}g_{\alpha\nu}=\delta^{\mu}_{\;\nu}~?\tag{5}$$


I'm a little bit confused. This is a very easy question but I'm solving lots of exercises and I want to be crystal clear about that.  I want to verify how this sum works.  $$\sum_{k=0}^n (-1)^k\binom{n}{k}$$  Let's take $n=2$. So we will have  $$(-1)^0\binom{2}{0}+(-1)^1\binom{2}{1}+(-1)^2\binom{2}{2}=2-2=0$$ Is that true ?  Thank you

Given a positive integer $n$. How to prove that $\sum\limits_{k=0}^{n}(-1)^k \dbinom{n}{k} = 0 $ ?   I've tried using mathematical induction, then:  $$p(1)=\sum_{k=0}^{1}(-1)^k \binom {1}{k}=0 $$  And my induction hypothesis is: $$p(n)=\sum_{k=0}^{n}(-1)^k \binom {n}{k}=0 $$ So, i need prove: $$p(n+1)=\sum_{k=0}^{n+1}(-1)^{k} \binom {n+1}{k}=0 $$ Let $\sum_{k=0}^{n+1}(-1)^{k} \binom {n+1}{k}$, $$\begin{align} \sum_{k=0}^{n+1}(-1)^{k} \binom {n+1}{k} &= \sum_{k=0}^{n}(-1)^{k} \binom {n}{k}+(-1)^{k} \binom {n+1}{n+1} \\ &=0 + (-1)^{k} \end{align}$$ What am i doing wrong?


I'm completely stumped on this one. Any help is much appreciated.

The following is the problem at hand:  $A^4 = 2A^2.$ Prove that $(I-A^2) = (I-A^2)^{-1}$  My attempts at a solution:  $I = A^{-1} * A,$ therefore we can start with $(A^{-1}A - A^2) = (A^{-1}A - (1/2)A^4) = (A^{-1}A - A^2) = (A^{-1}A - (1/2)(A^{-4})^{-1}) = ???$  I'm having problems with the fundamentals of this question. Sure, I can play around with the individual matrices on the left side, but that doesn't help to handle the inverse of a sum of matrices, like how the transpose of a sum is equal to the sum of the transpose of its individual matrix terms. How do you approach this without delving into more complex matrix operations?


I have response as <int xmlns="http://tempuri.org/">3</int>. When I try to fetch using StringRequest in volley i get exception as Attempt to invoke virtual method 'int java.lang.String.length()' on a null object reference. Is there any way that I can get the integer value from xml using volley. This is my code   StringRequest volleyReq = new               StringRequest(Request.Method.POST, url,                 new Response.Listener<String>() {                     @Override                     public void onResponse(String response) {                         try {                              Toast.makeText(getActivity(), finalMsg,Toast.LENGTH_SHORT).show();                           } catch (Exception e) {                             e.printStackTrace();                             Crashlytics.logException(e);                              showErrorlayoutwithBtn(Global.SERVER_OUT_OF_REACH);                          }                     }                 },                  new Response.ErrorListener() {                     @Override                     public void onErrorResponse(VolleyError err) {                         Log.e("Error in time json", err.getMessage());                         err.printStackTrace();                         //pbInOut.setVisibility(View.GONE);                         ShowCustomToast(errorToast, Global.FAILURE_RETROFIT);                     }                 }) {             @Override             protected Map<String, String> getParams() {                 Map<String, String> map = new HashMap<>();                 map.put("UserID", usrId);                 map.put("latitude", latitude);                 map.put("longitude", longitude);                 return map;             }         };         volleyReq.setRetryPolicy(new DefaultRetryPolicy(                 2000,                 5,                 DefaultRetryPolicy.DEFAULT_BACKOFF_MULT));          MyApplication.getInstance().addToRequestQueue(volleyReq);   and here is my stack trace     2019-04-02 11:01:13.650 6595-6649/com.hrdelight.android.hrdelight   E/Volley: [288] NetworkDispatcher.processRequest: Unhandled exception   java.lang.NullPointerException: Attempt to invoke virtual method 'int   java.lang.String.length()' on a null object reference       java.lang.NullPointerException: Attempt to invoke virtual method 'int java.lang.String.length()' on a null object reference           at java.net.URLEncoder.encode(URLEncoder.java:204)           at com.android.volley.Request.encodeParameters(Request.java:491)           at com.android.volley.Request.getBody(Request.java:477)           at com.android.volley.toolbox.HurlStack.addBodyIfExists(HurlStack.java:245)           at com.android.volley.toolbox.HurlStack.setConnectionParametersForRequest(HurlStack.java:219)           at com.android.volley.toolbox.HurlStack.executeRequest(HurlStack.java:97)           at com.android.volley.toolbox.BasicNetwork.performRequest(BasicNetwork.java:131)           at com.android.volley.NetworkDispatcher.processRequest(NetworkDispatcher.java:120)           at com.android.volley.NetworkDispatcher.run(NetworkDispatcher.java:87)   Is there any way that I can get the integer value from xml using volley

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


My textbook is asking me to: Prove the first absorption law by showing that if A and B are sets, then A ∪ (A ∩ B) = A.  I am a little unclear by how to prove this?

What I've done so far is stated that    $(A \cup A) \cap (A \cup B)$  by distribution $A\cap (A\cup B)$        by 1, definition of $\cup$ $A\cap A$              by 2, definition of $\cup$ $A$                   by 3, definition of $\cap$   I'm not sure if I need to state that $A\cup B = \{x\mid x\in A\lor x\in B\}$ somewhere in there.  I'd really appreciate some help on this one. Thank you!


I've created a macro that inserts a reference to a table When I did the macro, I configured the access to this macro through a button. But, now I want to change it to use the keyboard instead of icons. Does anyone know how to change from icon to a keyboard access?

Is there a way to configure Outlook 2007 so by pressing a [CTRL]+[letter] combination, a macro is activated?


Most so called experts would say online that registry cleaning speeds up your computer. I just found a handful opinions that say otherwise i.e.   Also there are some indirect answers here, but they are from like 4 years ago.   Would I be better off with not cleaning registry at all? Because benefits are dubious and the risk of messing it up is higher

I have heard that you should keep the registry clean on Windows. Is this actually important or is it just myth?


I used to keep all of my photos (literally 40K or so) on my iPhone. I did eventually fall into the iCloud trap, and have still not figured out a way to assure that a healthy number of my full resolution photos will be available to me when I am on a plane: the one time I know I'll have 5 hours with nothing to do but edit photos from the last decade. I know that "recent" full resolution photos are stored  on the phone, but going back to what date? And how does that help if I choose a  picture from 2014 to edit? Thoughts about how to edit while in "airplane mode?"

Following the update to iOS 10.3.1, my phone warned me (unnecessarily as it turned out) that I had too little space to store all my photos at full resolution, and suggested that I switch to "optimized" storage (which for those unfamiliar with the feature stores a uselessly blurry simulacrum of the original only), which I foolishly did.    I immediately realized my mistake, and restored the "Download and Keep Originals" setting. But this appears to have had no effect. I still see only the placeholders, until I click on an individual photo and wait for it to download.  So the question is: what does "Download" mean? Does it mean   download all photos automatically (e.g., in the background over time) or  download a photo only when it is viewed?   If the answer is 2, is there a way to force all my photos to sync at full resolution to my iPhone without clicking on each individual photo (which would take about a month of continuous clicking, with no breaks for sleeping)?


I have 4 Geforce GTX 1080.  Nvidia 378.66 driver Windows 10 64bit.  Blender v2.78b  Blender User Preferences -> System -> Cycles Compute Device -> None  Cycles render does not recognize my 4 Geforce GPU boards. I worked in previous Nvidia and Blender versions.  Therefore the GPU Compute under render settings is also grayed out.    I see that my original post has been marked as a duplicate but the solution to post  is not applicable to mine.  I have no CUDA option in User Preferences -> System -> Cycles Compute Device It says "None" there    Solutions?

In Blender The GPU-Compute button is greyed out. I have a fully updated system with a Nvidia GTX video card and the current version of blender.


I am a new user of Beamer presentation template and noticed that when I click on an entry from the ToC it goes to the next slide instead of the target one. However, when I open the pdf file in a pdf viewer such as Foxit and click on the bookmark it goes to the right slide. Why is this discrepeancy cause and is there a solution for it?

When I include a table of contents in a Beamer slide show, each section entry in the TOC ends up linking to the second slide in that section. I would have expected it to link to the first slide. What am I doing wrong?:  \documentclass{beamer}  \begin{document} \begin{frame}{Test TOC}   \tableofcontents \end{frame}  \section{Section 1}  \begin{frame}   \frametitle{Test 1} \end{frame}  \begin{frame}   \frametitle{Test 2} \end{frame}  \end{document}   Just to clarify: when I click Section 1 in the TOC, it takes me to the slide Test 2.  UPDATE: I am actually not sure if it takes me to slide Test 2. When I click the link, the viewer (Evince and Okular) displays most of Test 2, but with a tiny strip of the slide Test 1 visible at the top of the window. I suspect that the viewer may treat the link as pointing to the very bottom of slide Test 1 and then aligns that with the top of the window. Could this be the explanation?


I am using  to estimate a pdf for some data. The problem is that the resulting pdf takes values larger than 1. As far as I understand, this should not happen. Am I mistaken? If so why?

On the , there is this line:      $p(\mathrm{height}|\mathrm{male}) = 1.5789$ (A probability distribution over 1 is OK. It is the area under the bell curve that is equal to 1.)    How can a value $>1$ be OK? I thought all probability values were expressed in the range $0 \leq p \leq 1$. Furthermore, given that it is possible to have such a value, how is that value obtained in the example shown on the page?


The DHCP server on our SBS 2003 server shuts itself down automatically after a couple of hours of having a Hamachi gateway running on the same LAN.      The server incorrectly assumes that Hamachi might start assigning DHCPs to other clients on the LAN.  While the Hamachi gateway client does indeed have a DHCP server, it only assigns IPs to computers making inbound VPN connections- not to PCs on the LAN.  Does anyone know of a way to override this behaviour on SBS 2003? Perhaps a registry hack?  I know the server has good intentions when it disables its DHCP server in this situation... however, in avoiding a non-existent problem, it is actually creating a real problem.

We are using LogMeIn Hamachi to link two remote sites together by VPN.  This is working perfectly, the only problem is that the DHCP service on our SBS 2003 server shuts itself down after an hour or so of Hamachi being enabled, as it identifies the virtual DHCP server on the Hamachi gateway PC and believes it is a rogue DHCP server.  Hamachi is not installed on the SBS server, but on a regular Windows XP machine on the same LAN.  As far as I can see, the Hamachi virtual DHCP server is not really a rogue DHCP server in this scenario. No client on the LAN will ever get an IP address from Hamachi (same subnet but different, non-overlapping DHCP scopes) however, it's obviously not doing something right because the server's DHCP service does not want to coexist with it.  Does anyone know of a way to prevent the DHCP service on the SBS 2003 server from shutting down if it believes it sees other DHCP servers on the network? I want to treat this as a false positive and see what happens if we ignore it- there is no way for IP conflicts to happen due to the non-overlapping IP scopes.    I don't quite understand how a DHCP server with IP 192.168.1.50 can conflict with one on 1.0.254.169..... that's not even the same subnet!


I'm trying to get a definitive and clear answer to the question of what a  actually is. Textbooks seem to give quite vague explanations, all starting with Einstein's idea that a quanta is a form of light which has a frequency associated with it, finite energy, and is localised in space. The frequency is said to be that of electromagnetic waves. Does it only have a single frequency, or can it have a group? Is the frequency that of the electric field, or the magnetic field, or both, or is it not possible to say? Is it always localised in space, or does it actually disperse, or is either option valid? Can we write down a wavefunction for a photon, or give a set of conditions that wavefunctions must satisfy in order to be considered a photon?  Photons seem to be one of the foundation ideas of quantum mechanics, so I am concerned that without a clear definition or set of concrete examples, the basis for understanding quantum experiments is a little fuzzy.  Remember I'm looking for a clear definition! On the other hand if you think there is no clear definition, I would also like to know.  EDIT: Although this question is assumed to be the same as asking "what is a quantum of light?", according to Lamb's :  "G.N.Lewis, in 1926, coined the word 'photon' to describe something completely different from the Einstein light quantum."

I am currently trying to learn some basic quantum mechanics and I am a bit confused. Wikipedia defines a  as a quantum of light, which it further explains as some kind of a .     What exactly is a quantum of light?   More precisely, is a quantum of light meant to be just a certain number of wavelengths of light (something like "1 quantum = a single period of a sine wave" perhaps?), or is the concept completely unrelated to wavelengths? In other words, how much is a single quantum?


What are the main ressources HAProxy needs handling millions of requests per hour? What hardware is recommended (CPU, Cored, Ram...)?

This is a  about  Related:      I have a question regarding capacity planning. Can the Server Fault community please help with the following:   What kind of server do I need to handle some number of users? How many users can a server with some specifications handle? Will some server configuration be fast enough for my use case? I'm building a social networking site: what kind of hardware do I need? How much bandwidth do I need for some project? How much bandwidth will some number of users use in some application?


I would like to create a table or array with the layout in the figure below, ideally with the nicematrix package wich allows the marginal annotations. I've read the package documentation and there is maybe a couple of solutions to my question one involves tikz and \CodeAfter, the other \newcolumntype{x}{!{\OnlyMainNiceMatrix{\vrule somelength}}}, I don't know enough of tikz, or how to you get the right somelength, Asking because of exhaustion, no more limit breaks :)  Some ugly latex with NiceArray $\begin{NiceTabular}{| c c| c c| c c | }[columns-width = 0.5cm,     cell-space-top-limit = 0.15cm, cell-space-bottom-limit= 0.15cm]  \hline   6 &  &  8 &  & 10 & \\ \cline{1-1} \cline{3-3} \cline {5-5}   & 0 & & 0 & & 150 \\    \hline   7 &  & 11 &  & 11 & \\  \cline{1-1} \cline{3-3} \cline {5-5}   & 175 & & 0 & & 0 \\    \hline   4 & & 5 & & 12 & \\  \cline{1-1} \cline{3-3} \cline {5-5}   & 25 & & 100 & & 150 \\   \hline \end{NiceTabular}$  With NiceTabular \begin{table} \label{lab} \centering \begin{NiceTabular}{@{}Wl{2.5cm}|Wl{0.5cm}Wr{0.5cm}|Wl{0.5cm}Wr{0.5cm}|Wl{0.5cm}Wr{0.5cm}|Wl{2.5cm}l@{}} \toprule & \Block{2-2}{A}  & & \Block{2-2}{B} & &\Block{2-2}{C} & &\Block{2- 2}{D}\\  & & & & & & & &\\ \midrule \Block{2- 1}{E} & 6 &  &  8 &  & 10 & &  \Block{2- 1}{5}\\ &  & -- & & -- & & 15 & &\\ \hline \Block{2- 1}{F} & 7 &  & 11 &  & 11 & & \Block{2- 1}{1}\\ & & 175 & & -- & & -- & &\\ \hline \Block{2- 1}{G} & 4 & & 5 & & 12 & & \Block{2- 1}{2}\\ & & 25 & & 100 & & 5 & &\\ \hline \Block{2-1}{Demanda} & \Block{2-2}{200}  & & \Block{2-2}{100} & &\Block{2-2}{300} & &\Block{2- 2}{600}\\  & & & & & & & &\\ \bottomrule \end{NiceTabular} \caption{Cap} \end{table}

How to create transportation table like this table?


Is there a way to install Gnome on trusty tahr?

I followed the instructions for compiling GNOME Shell and it did compile with a few errors here and there but it didn't run. I installed GNOME Shell using sudo apt-get install gnome-shell but I got version 2.31.x, while the latest is 2.91.5 or something. So is there a way for me to install the latest build?   Is there some repository available for the latest build?


So I just got the new Microsoft Sculpt Ergonomic Mouse:   The built in software allows you to edit all the buttons, except the big blue windows button. So its technically a 5 button mouse, but the software only allows you to edit 4 of the buttons.  I was wondering, if there was some way... maybe though registry edits or something, where I can change the function of the windows button on this mouse.  Same question applies to keyboards.

using the , by downloading the , i can rebind the mouse keys, but the WINDOWS key i can't change it, and that is the only key i may(and want) to rebind because i have it (twice) on the keyboard, and i can't find an option to change it, am i missing something? Or is there any way to bypass this limitation    i found that the keys are saved here: HKEY_CURRENT_USER\Software\Microsoft\IntelliPoint\ModelSpecific\5025\EventMapping\4  but i've been trying to change the [4](4 is middle mouse button) but i didn't found any for the windows key


While showing recommended questions :  Recently active sorting shows new questions :    Newest questions sorting shows recently active questions :

Select New questions, show Recommended and sort by Newest and the  in my list is from 2012:  EDIT The very old questions now appear to be gone (yay) but the ordering seems inconsistent (boo):


I am trying to setup WordPress on CentOs6 for the first time and facing issue with proper file permission. I am using Linode VPS hosting and have chosen centOS6 as my OS.I am able to install WordPress at following location  /var/www/html/wordpress   As per WordPress doc Wordpress folder should have 755 permission.I have cross checked using WinSCP, and folder permission has been set as 755  But still while I am trying to update / create something new inside my WordPress installation, I am getting an error indicating that it is not able to create directory.  I have noticed one more issue, there is an .htaccess file inside wordpress folder and its permission are also 755, but still Wordpress says     If your .htaccess file were writable, we could do this automatically, but it isn’t so these are the mod_rewrite rules you should have in your .htaccess file.   It seems that there is something wrong with file permission but being new to Linux and its file permissions, I am not sure what is wrong and how it can be fixed  can any one suggest me where I am doing wrong

This is a  about File Permissions on a Linux web server.   I have a Linux web server running Apache2 that hosts several websites. Each website has its own folder in /var/www/.  /var/www/contoso.com/ /var/www/contoso.net/ /var/www/fabrikam.com/   The base directory /var/www/ is owned by root:root. Apache is running as www-data:www-data. The Fabrikam website is maintained by two developers, Alice and Bob. Both Contoso websites are maintained by one developer, Eve. All websites allow users to upload images. If a website is compromised, the impact should be as limited as possible.  I want to know the best way to set up permissions so that Apache can serve the content, the website is secure from attacks, and the developers can still make changes. One of the websites is structured like this:  /var/www/fabrikam.com     /cache     /modules     /styles     /uploads     /index.php   How should the permissions be set on these directories and files? I read somewhere that you should never use 777 permissions on a website, but I don't understand what problems that could cause. During busy periods, the website automatically caches some pages and stores the results in the cache folder. All of the content submitted by website visitors is saved to the uploads folder.


I need help with this exercise.  I need to prove $$\int_{0}^{1}x^{-x}\ dx=\sum_{n=1}^{\infty}n^{-n}$$  I think I should use some convergence theorem, but I'm stuck.  Thanks a lot!


I read this book sometime in the early 2000s, and I believe it was published around then too; definitely no later than 2007.  I vaguely remember the cover being minimalist blue with a naked woman's body curled like an embryo. However this was in Australia, so the cover may have been different elsewhere. Or my memory is completely wrong.   I picked this up from the adult sci-fi section in the library, however it may have been YA as I don't remember it being too risque.   Plot points I remember:   I believe the book is set on a future Earth where the rich live in skyscrapers above the clouds of pollution and the poor live down on the ground below the pollution.  The MC is a young woman who is poor, living on the ground working in a factory and making just enough to scrape by.  At the factory where she works there is an explosion and her friend or family member is injured and burned and they don't earn enough to get healed.  In exchange for her friend being healed, the MC sells her young youthful body to a rich older woman who will inhabit her body and be young and strong again.  Part of this exchange was that the MC was to be given a basic cyborg? (I say cyborg, but it may be bio-created) body or the old woman's body in return, I can't quite remember.  The MC's consciousness wakes up in an experimental enhanced body that has an internal AI that communicates with her. I think she also had enhanced senses and strength, and maybe the ability to choose how she looks? As the MC now has an enhanced body that can handle space travel she now has the ability to go to space, and as such the book ends with her in space.

I read this book between 1999 and late 2004. I am pretty sure it had a blue cover and may have been published by Penguin. It was a paperback.  The story goes, as far as I can remember, that after an accident her body was too badly damaged and she was implanted into a cyborg or bionic shell, which had been cast aside by other wealthy people who upgrade their "cyborg bodies" when they get bored or for new upgrades. Undamaged real bodies were a premium and the poor could sell their healthy bodies for money to purchase older model cyborg bodies.  I think the protagonist has recurring memories or that they play a part in it somehow.


Suppose you just have some sample medians, and want to estimate the population median. Assume the samples are random, independent of each other, and of the same size.  Should you use the mean or the median of the sample medians? Does it give an unbiased estimator?  (Asking for a friend.)

I do a bunch of real estate reporting and the median price is often reported, particularly by the NAR (National Association Of Realtors). As best I can tell, they only get the medians of real estate prices from each area.  My question is, how should the national median be calculated, given the data restrictions? As a median of medians, as a simple average of medians, or weighted average of medians or something entirely different? Second, how valid would these estimates be? I know that the NAR is not getting the total transaction table, so can a reasonably accurate representation of the median still be estimated at the national level? I ask, in particular, because regional density and prices and market variances are so large.


I have just used this  to follow some of the steps to manually create the .deb file from the .zip file that is on the AMD site. Then I installed them one by one using the Debpackage installer. So I didn't used the command line, but the graphical interface of my OS.  The problem is that when I log in I get this message: "AMD Testing use only"  Here is my fglrxinfo:   :~$ fglrxinfo display: :0  screen: 0 OpenGL vendor string: Advanced Micro Devices, Inc. OpenGL renderer string: AMD Radeon HD 6500M/5600/5700 Series OpenGL version string: 4.2.12337 Compatibility Profile Context 9.01   Have I done something in the wrong way?

I've installed the  (beta) following the step in  for Ubuntu Quantal Quetzal. My system is 64 bit and my graphic card is an ATI RadeonHD 6670, this g.c. is Officially Supported (Catalyst & Open Source), you can confirm that from this .  I don't have any problem, except the AMD testing use only watermark. I see the following frame in any stage into the OS (logged, unlloged, etc.) except in the terminals.     I found different versions of how to remove this image, but this change according to the system, so I want an answer from this popular (trusted) site.   How to solve this issue in Ubuntu 12.10 32b? This procedure is different in a 64b system?


My windows installation was working perfectly fine until i clicked "Reset BCD" in EasyBCD in Windows 8. After clicking that EasyBCD told me to add Win 8 entry via Add Entry Menu so i did. After restart, win 8 would not start. Neither would recovery F11.  Attempts i made to Restore :    Ran boot-repair from ubuntu live cd several time. Used Win8 system recovery disc created via virtualbox with win 8 preview iso.  Automated repair from Win8 system recovery disc Ran following commands from cmd started from Win8 system recovery disc      bootrec /fixmbr        Result : Success message        bootrec /rebuildbcd        Result : after hitting (Y) "The requested system device cannot be found"   System refresh started from Win8 system recovery disc gives error that device is locked. System reset started from Win8 system recovery disc gives error that required partition or device is missing or not accessible. Used automated repair from  disc. It gave success message. Used Fix boot problem from . Copied Recovery partition to usb. Booting from usb gave this error      Your PC needs to be repaired.    Error Code : 0XC000000f    Press Enter to try again    Press F8 for Startup Settings    F8 & Enter does nothing   I cannot install WIn7 or Win 8, error it gives :  "windows cannot be installed on this disk. The selected disk is of the GPT partition style."

I installed Windows 7 and Windows 8 in EFI mode on a hard disk some days ago. Today, the bootloader got missing/corrupted.  I currently have the Windows 8 installer on a flash drive and tried using the Automatic Repair option to repair the bootloader but it didn't do anything. The Startup Repair option is also missing in the Windows 8 installer.  How I can repair/recreate the EFI bootloader from the Command Prompt?  BCDEDIT returns the following message:  The requested system device cannot be found.


I know most of the result regarding Continuity, Completeness. But I got stuck into a question which I found in a question paper. Let $f:X \longrightarrow Y$ Where $X,Y$ metric space.Then show that for any Cauchy sequence $\{x_n\}$ in $X$ if $\{f(x_n)\}$ is Cauchy in $Y$, then $f$ is continuous. Please help me. Thanks in advance.

Let $(X,d)$ and $(Y,\rho)$ be metric spaces and $f:X\to Y$ be a function and suppose for any Cauchy sequence $(a_n)$ in $X$, $(f(a_n))$ is a Cauchy sequence in $Y$.  Is $f$ continuous?  Let $f$ be continuous, is it uniformly continuous?


When I boot Ubuntu or Fedora, they show a black screen with a bunch of [OK] messages for startup processes.  It seems like an old style DOS system. Nowadays, iOS and Windows don't show those terminal-like results. Elementary OS doesn't show it (most of the time) either.  Can I hide them in Ubuntu?  The answer to  doesn't work in my case because my /etc/default/grub already has GRUB_CMDLINE_LINUX_DEFAULT="quiet splash" but it still shows the boot text.   Output of apt-cache policy plymouth | grep Installed:  Installed: 0.9.2-3ubuntu17   Here's my /etc/default/grub  GRUB_DEFAULT=0 #GRUB_HIDDEN_TIMEOUT=0 GRUB_HIDDEN_TIMEOUT_QUIET=true GRUB_TIMEOUT=10 GRUB_DISTRIBUTOR=`lsb_release -i -s 2> /dev/null || echo Debian` GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi=force" GRUB_CMDLINE_LINUX=""      Update 7 Mar 18:   After running:  sudo apt-get clean, apt-get autoremove, apt-get update, apt-get upgrade   The result is the same: First Ubuntu boots with the logo and 5 loading dots Then, the screen show these: (a lot of them)  ... [ OK ] Started CUPS Scheduler. <more yidi yada> [ OK ] Started Run anacron jobs. [ OK ] Started ACPI event daemon. [ OK ] Started Set the CPU Frequency Scaling governor.        Starting Hold until boot process finishes up... any system changes.pp link was shut down.   Then Ubuntu shows login screen with username.  Also:  $ sudo dpkg-reconfigure -a [sudo] password for user:  Unknown option: a Usage: dpkg-reconfigure [options] packages   -u,  --unseen-only        Show only not yet seen questions.        --default-priority   Use default priority instead of low.        --force          Force reconfiguration of broken packages.        --no-reload      Do not reload templates. (Use with caution.)   -f, --frontend        Specify debconf frontend to use.   -p, --priority        Specify minimum priority question to show.         --terse         Enable terse mode.  $ sudo dpkg-reconfigure plymouth [sudo] password for user:  update-initramfs: deferring update (trigger activated) update-rc.d: warning: start and stop actions are no longer supported; falling back to defaults update-rc.d: warning: start and stop actions are no longer supported; falling back to defaults Processing triggers for initramfs-tools (0.125ubuntu12) ... update-initramfs: Generating /boot/initrd.img-4.13.0-36-generic

Is there a way to easily turn on/off showing the boot messages (loading the services) when Ubuntu starts? Is it something in Grub2?  I am running 10.04.


Given  I was wondering whether it would be viable to detect patterns like Foo: Does the quick brown fox jump over the lazy dog?  in a question's title and show a sort of warning  It looks like you are including a tag in your title. The format [TAG]: Question and similar are strongly discouraged and you should include tags in the appropriate section below.  I believe this could educate new users, especially those coming from a forum background. Seriously my eyes hurt every time I see iOS - How to blablabla NSString: cannot blablabla ...  I'm aware of  but it's two years old and it has been dismissed with - in my opinion - questionable reasons. Specifically Jeff stated  [It's] not really a problem so long as they are not happening "too often". It is the ritual and systemic use of tags in this manner that I object to, not the mere presence of it at all.  This was two years ago. Right now I feel like this format is being abused and we are doing nothing for discouraging it. Also I strongly believe that moving the tags box before the question title (as proposed in ) would help a lot. Clearly people think about narrowing the topic down before making the question, and I think it's also why we get so many tags in the titles.

So we have lots of questions that are titled like this:  Specifically, questions that have one of their tags in front of their title. Thankfully, these silly users usually use a hyphen or a colon afterwards, which makes it really easy to . Can we clear up this clutter?  Perhaps with a filter that strips off the excess when posting? EDIT: As an added bonus, see  for another style of question title that bugs the heck out of me.


I know that for vectors to form a basis, they must span the subspace. Other than that, I'm not sure how to solve this problem.

So the question asks: Let A be a $2\times 2$ matrix, and suppose that there exist scalars $λ_1,λ_2$ in$\mathbb{R}$ and nonzero vectors $v_1,v_2$ in $\mathbb{R}$ such that $Av_1=λ_1v_1, Av_2=λ_2v_2$, and $λ_1$ does not equal to $λ_2$.Prove that the vectors $v_1,v_2$ form a basis of $R^2$.   So so far I got:   As the eigenvector $v_1,v_2$ are corresponding to two different eigen values$λ_1,λ_2$ respectfully.   Therefore the eigenvectors $v_1,v_2$ are linearly independent.   And since $v_1,v_2$ spans A in $\mathbb{R}$.   Hence,  $v_1,v_2$ forms a basis of $\mathbb{R}$.   Does this proof look right? Do I need to write a linear combination of $v_1,v_2$ to show they span A?


Is there a simple method of calculating this limit?  $\lim_{n\rightarrow\infty} \sum_{x = 1}^{n}{\frac{x}{n^2+x^2} }.$

How to find the value of $\lim_{n\to\infty}S(n)$, where $S(n)$ is given by $$S(n)=\displaystyle\sum_{k=1}^{n} \dfrac{k}{n^2+k^2}$$   is unable to calculate it.  This is a question from a questions booklet, and the options for the answer are--  $\begin{align} &A) \dfrac{\pi}{2} \\ &B) \log 2 \\ &C) \dfrac{\pi}{4} \\ &D) \dfrac{1}{2} \log 2 \end{align}$


While reading some lecture notes I have come across the following:  Consider the linear model $ Y=X\beta+\varepsilon $, $\mathrm{Var}(\varepsilon)=\sigma^2 I$ (all the usual Gauss-Markov assumptions apply). Let $\tilde{\beta}$ be an unbiased linear estimator of $\beta$ with $X\tilde{\beta}=AY$, and let $P=X(X^TX)^{-1}X^T$. First note that $AP=P$ ...  However, I can't see why $AP=P$; I've tried writing $A=P+K\implies AP=P^2+KP \implies AP=P+KP$, but I'm not sure why $KP=0$.

In classic OLS regression it is well-known that $(\mathbf{I}-\mathbf{H})\mathbf{y}=\mathbf{r}$, where $\mathbf{I}$ is the identity matrix, $\mathbf{H}$ is the , $\mathbf{y}$ is the vector of response (dependent) values, and $\mathbf{r}$ is the vector of residuals.  My question is whether the scalar $\mathbf{y}^T(\mathbf{I}-\mathbf{H})\mathbf{y}=\mathbf{y}^T\mathbf{r}=\mathbf{y}^T\mathbf{y}-\mathbf{y}^T\mathbf{\hat{y}}$ has some meaningful interpretation.


If I have a domain like http://example.com/ which would be the best to use for every new project I create. Would it be a subdomain http://exampleprojectname.example.com/ or a new domain http://exampleprojectname.com/ or a new folder http://example.com/exampleprojectname. Which one would be the best and good for seo.

For example, in the past, links to www.example.com wouldn't have meant Google would pass any value to say, forum.example.com. What is the current status of this? (Please provide a reference if possible).


I saw the following:  $$\begin{align}  \int \tan x \ \mathrm{d}x &= \int \sin x \sec x \ \mathrm{d}x \\  \int \tan x \ \mathrm{d}x &= -\cos x \sec x - \int - \cos x \sec x \tan x \ \mathrm{d}x \\ \int \tan x \ \mathrm{d}x  &= -1 +  \int \tan x \ \mathrm{d}x \\ 0 &= -1   \end{align}$$  I figure the mistake has to do with constants of integration, but I can't quite point it. Can someone explain to me what happens, please? I browsed a bit around here, looking for $0=1$ and the tag fake-proofs, but I didn't found it, so I apologize in advance in case this is a duplicate of something (just provide me the link and I'll delete this, no problems).  Thanks!

I had a calculus final yesterday, and in a question we had to find a primitive of $\tan(x)$ in order to solve a differential equation.  A friend of mine forgot that such a primitive could easily be found, tried to integrate $\tan(x)$ by parts... and then arrived to the result $0 = -1$.  The kind of thing you're pretty satisfied to "prove", except during an important exam. :-°  So afterwards I tried to do the same :  $$\begin{align*} \int \tan(x)dx &= \int \sin(x) \times \frac{1}{\cos(x)}dx \\[0.1in] &= -\frac{\cos(x)}{\cos(x)} - \int - \frac{\cos(x) \times \sin(x)}{\cos(x)^2}dx \\[0.1in] &= -1 + \int \tan(x)dx \end{align*}$$  And therefore we get :  $$ \int \tan(x)dx = -1 + \int \tan(x)dx \implies 0 = -1$$  What? The reasoning sounds about right to me. Could someone explain where something went wrong?  Thanks,  Christophe.


I'd like to create an evenly distributed two columns table on a page. In order to have the vertical division centered, I used tabularx:  \begin{table}[H] \begin{tabularx}{\textwidth}{X X} a & b \\ c & d \\ e & f \\ \end{tabularx} \end{table}   However, I have two problems:   for long words, I want it to look like this (made in MS Word - ignore the borders, they are there just to help visualize):    but in LaTeX I have:    I've tried a solution with multirow, unsuccessfully. I keep getting the message Overfull \hbox (86.11789pt too wide), but I don't understand why... maybe because the word is too long for its cell?

LaTeX tends to break words at the end of the line when that causes better typography. Great. I'd like to have some sort of influence on where the words are broken, though.  For example, LaTeX currently breaks cryptography into cryptog-raphy when it does not fit, while I would much rather break it into crypto-graphy.  I've tried putting an mbox around it (or around both parts of the word) but that just ends up overflowing the hspace.  Is there a way I can put a box around the word but still allow a break at designated points, i.e. after crypto and before graphy? I'm fine with doing this on a per-word basis manually.


I saw a  in which it was shown that $$(7+50^{1/2})^{1/3}+(7-50^{1/2})^{1/3}=2$$ Since there are multiple values we can choose for the $3$rd root of a number, it would also make more sense to declare the value of this expression to be one of $2, 1 + \sqrt{-6},$ or $1 - \sqrt{-6}$  We may examine this more generally. If we declare $x$ such that  $$x=(a+b^{1/2})^{1/3}+(a-b^{1/2})^{1/3}$$ $$\text{(supposing } a \text{ and } b \text{ to be integers here)}$$ one can show that $$x^3+3(b-a^2)^{1/3}x-2a=0$$ Which indeed has $3$ roots.  We now ask      For what integer values of $a$ and $b$ is this polynomial solved by an integer?   I attempted this by assuming that $n$ is a root of the polynomial. We then have $$x^3+3(b-a^2)^{1/3}x-2a$$ $$||$$ $$(x-n)(x^2+cx+d)$$ $$||$$ $$x^3+(c-n)x^2+(d-nc)x-nd$$ Since $(c-n)x^2=0$ we conclude that $c=n$ and we have  $$x^3+3(b-a^2)^{1/3}x-2a=x^3+(d-c^2)x-cd$$ And - to continue our chain of conclusions - we conclude that $$3(b-a^2)^{1/3}=d-c^2 \quad\text{and}\quad 2a=cd$$ At this point I tried creating a single equation and got $$108b=4d^3+15c^2d^2+12c^4d-c^6$$ This is as far as I went.

In  to  by Eesu, Vladimir Reshetnikov proved that $$ \begin{equation} \left( 26+15\sqrt{3}\right) ^{1/3}+\left( 26-15\sqrt{3}\right) ^{1/3}=4.\tag{1} \end{equation} $$  I would like to know if this result can be generalized to other triples of natural numbers.      Question. What are the solutions of the following equation? $$ \begin{equation} \left( p+q\sqrt{3}\right) ^{1/3}+\left( p-q\sqrt{3}\right) ^{1/3}=n,\qquad  \text{where }\left( p,q,n\right) \in  \mathbb{N} ^{3}.\tag{2} \end{equation} $$   For $(1)$ we could write $26+15\sqrt{3}$ in the form $(a+b\sqrt{3})^{3}$   $$ 26+15\sqrt{3}=(a+b\sqrt{3})^{3}=a^{3}+9ab^{2}+3( a^{2}b+b^{3})  \sqrt{3} $$  and solve the system $$ \left\{  \begin{array}{c} a^{3}+9ab^{2}=26 \\  a^{2}b+b^{3}=5. \end{array} \right.  $$  A solution is $(a,b)=(2,1)$. Hence $26+15\sqrt{3}=(2+\sqrt{3})^3 $. Using the same method to $26-15\sqrt{3}$, we find $26-15\sqrt{3}=(2-\sqrt{3})^3 $, thus proving $(1)$.  For $(2)$ the very same idea yields  $$ p+q\sqrt{3}=(a+b\sqrt{3})^{3}=a^{3}+9ab^{2}+3( a^{2}b+b^{3}) \tag{3} \sqrt{3} $$  and  $$ \left\{  \begin{array}{c} a^{3}+9ab^{2}=p \\  3( a^{2}b+b^{3}) =q. \end{array} \right. \tag{4} $$  I tried to solve this system for $a,b$ but since the solution is of the form  $$ (a,b)=\Big(x^{3},\frac{3qx^{3}}{8x^{9}+p}\Big),\tag{5} $$  where $x$ satisfies the cubic equation $$ 64x^{3}-48x^{2}p+( -15p^{2}+81q^{2}) x-p^{3}=0,\tag{6} $$ would be very difficult to succeed, using this naive approach.      Is this problem solvable, at least partially?   Is $\sqrt[3]{p+q\sqrt{3}}+\sqrt[3]{p-q\sqrt{3}}=n$, $(p,q,n)\in\mathbb{N} ^3$ solvable?


Is there a word or a phrase that has to do with renaming an act (that is deemed morally questionable) so that it may seem more neutral and therefore acceptable to the general public? It has nothing to do with understating the horrors of what is done, rather it is more on giving it a different label so that the there is more distance between the public and whatever reprehensible act was done, making it an easier pill to swallow.   The only example I could find online is renaming 'acts of torture' with 'abuse' in the Abu Ghraib scandal to make it seem more neutral.

What is a word that means to say in a positive sense? For instance, when writers say that a person was sexually assaulted instead of saying raped.  Or people use let go instead of fired.  What is that called?


I would like to gain insight about this question. I have read it is related with the conservation of momentum, but cannot really differentiate it from the oscillating charge. The monopole radiation and how it would be produced seems quite intuitive for me, on the other side: a mass (or charge) appearing and disappearing.

I have read that "thanks to conservation of momentum" there is no dipole gravitational radiation. I am confused about this, since I cannot see the difference with e.m. radiation. Is this due to the non-existence of positive and negative gravi-charges? Is this due to the non-linearity of Einstein equations? How the conservation of momentum enters here?  An example of my confusion below  Q: Why I cannot shake a single mass producing dipole gravi-radiation? A: You need another mass to shake it. Q: Isn't it the same with electromagnetism?


Does any example of this particular type of function, stated below exist?          f:$R\to R$ is continuous at every rational numbers and discontinuous at every irrational points. I can't find any example. If there does not exist any such function then why?

Possible Duplicate:          I think I saw somewhere(but I'm not sure) that there is no function $g$ on $[0,1]$ that is continuous at all rational points and discontinuous at all irrational points. Please, is this true? If yes how can I show it?  Thanks.


What's this situation called when you work at a place where you are never appreciated for what you do until one particular day you forget to do something which attracts all the negative sentiments from people around you who would constantly nag and make sniping remarks. It makes you feel like one negative thing nullifies all the positives in you. How would you describe this situation in phrases/expressions/idioms? Idioms needed for both the family situation as well as professional setting.

I was amused by the expression "Paid a penny and only farted" (related by @FumbleFingers), which suggested a similar Japanese saying: 大山鳴動鼠一匹 - "Find only a small mouse coming out after hearing rumblings and experiencing shaking of the big mountain."  It’s humorous. I chuckled when I read it, and I wrote to the author that I love it.  With that said, the word "fart" reminds me of another Japanese proverb, 百日の説法屁一つ- "A fart ruins 100 days of sermons by the priest", which means that a small mistake (the sound of a fart in front of the congregation) brings all his efforts to naught.  It can’t happen in big Western churches. But it could well happen in a small wooden temple where a priest would preach to 30 – 50 provincial followers. Can you imagine how the proud priest being called 'the venerable' would be embarrased when his loud fart is heard by all his followers during his serious sermon and they start to giggle here and there in the hall?  We also have a similar saying" 九仞の功を一簣に欠く, which literally means "Collapse a 9- meter sand tower with the last pile of sand."  What is the English equivalent of the saying "A fart ruins 100 days of sermons by the priest (bishop): a small mistake depreciates the value of (vitiates) all labor and effort to naught," preferably in such a humorous way?


I tried to install ZTE's software for mobile broadband but it got error while installing itself.  Now I was ok with the network-manager which itself detects my USB modem. But, everytime while installing or removing or updating, I'm seeing this.  Actually here, I'm trying to remove crossplatformui which is part of ZTE: software:  sudo apt-get --purge remove crossplatformui Reading package lists... Done Building dependency tree Reading state information... Done The following packages will be REMOVED:  crossplatformui  0 upgraded, 0 newly installed, 1 to remove and 2 not upgraded.  1 not fully installed or removed.  After this operation, 0 B of additional disk space will be used.  Do you want to continue [Y/n]? y  (Reading database ... 480896 files and directories currently installed.)  Removing crossplatformui ...  ztemtvcdromd: no process found  dpkg: error processing crossplatformui (--remove):    subprocess installed post-removal script returned error exit status 1 No apport report written because MaxReports is reached already Errors were encountered while processing: crossplatformui E: Sub-process /usr/bin/dpkg returned an error code (1)   Can anyone help me how to remove that crossplatform?  And can anyone give me a simple idea to auto reconnect my USB modem to Internet?

A few weeks ago I installed a 32 bit .deb file through the 'force architecture' command (on my 64bit notebook), however the procedure was unsuccessful and I used the apt-get purgecommand to uninstall the app. It seems there are some leftovers of the app I uninstalled which has now broken system update. Synaptic recommended a sudo apt-get install -fwhich I did in the terminal with this initial response:  Reading package lists... Done Building dependency tree        Reading state information... Done The following package was automatically installed and is no longer required:   libntfs10 Use 'apt-get autoremove' to remove them. The following packages will be REMOVED:   crossplatformui 0 upgraded, 0 newly installed, 1 to remove and 0 not upgraded. 1 not fully installed or removed. After this operation, 0 B of additional disk space will be used. Do you want to continue [Y/n]?   I chose 'Y' then got this response:  (Reading database ... 187616 files and directories currently installed.) Removing crossplatformui ... ztemtvcdromd: no process found dpkg: error processing crossplatformui (--remove):  subprocess installed post-removal script returned error exit status 1 Errors were encountered while processing:  crossplatformui E: Sub-process /usr/bin/dpkg returned an error code (1)   It seems the app I installed crossplatformuiis still on my system and has caused update manager to stop running with a partial upgrade warning. What do I do now?


Why is the hydrogen bond different from other bonds that allows ice to float in water rather tan sink.   I don't want the math. I want the reason that bond is different than the rest.  Why, not how.

Can someone explain me why is ice less dense than water?  As I know, all solids are usually denser than the liquids (correct me if I am wrong).


SELECT * FROM workers ORDER BY salary DESC LIMIT 2;  I have this SQL statement to get the salary of the two best paid workers but I'm getting a SQL command was not ended correctly. EDITED: SELECT  worker_id, last_name, job_id, salary     FROM (SELECT w.*,                 rank() over (ORDER BY w.salary desc) rnk           FROM worker w          )    WHERE rnk <= 5;

Is there a way to make an Oracle query behave like it contains a MySQL limit clause? In MySQL, I can do this: select *  from sometable order by name limit 20,10  to get the 21st to the 30th rows (skip the first 20, give the next 10). The rows are selected after the order by, so it really starts on the 20th name alphabetically. In Oracle, the only thing people mention is the rownum pseudo-column, but it is evaluated before order by, which means this: select *  from sometable where rownum <= 10 order by name  will return a random set of ten rows ordered by name, which is not usually what I want. It also doesn't allow for specifying an offset.


I've posted a post on Stack Exchange just a few minutes ago from Chrome on Android 10, since I'm developing in TermUX and the Stack Exchange app on Android is no longer available. Why is the code in my post, which can be viewed when I edit it, not showing up? It's my latest post on PHP, with the php tag.

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 .


The main argument: which is advisable of the following two?        A, B and C   A, B, and C      Oxford (or serial) comma is useful to avoid ambiguities in phrases that involve lists such as the example given in . I tend to use it in long lists or that which could enclose conjunctions like 'and' or 'or' within them like so     The methods used include regression analysis, trial and error, and statistical inference.   However, how necessary is it when it concerns single-worded lists, especially when it concerns notational identifiers like A, B, C?

Should I put a comma before the last item in a list?     I would like crackers, cheese and some soda.   I would like crackers, cheese, and some soda.


While writing a post, if the hyperlink tool is used on a code block containing [ or ], the tool will add extraneous backslash \ characters in front of the brackets.  Example:  user:351462 [support] -> .

Adding a hyperlink for inline code with square brackets via the tool button (or Ctrl+L) gives the wrong enclosing:  E.g.:     text [] text   produces:     text  text   instead of     text  text


Sorry if this has been talked about before and please point me to those references. I am now running my own Ubuntu web server however I have been hitting problems with authorities and FTPing up files. Right now I have all of my web stuff under /var/www. But every time I do something there, I then have to do a chown www-data:www-data to make sure everything keeps working properly. In reality, I want to be able to FTP into my server upload what I want and just have it work without having to worry about authorities every time.  Should I have put everything under /home/user/public_html/mydomain1.com and home/user/public_html/mydomain2.com? What authorities should that then have? user:www-data? user:user?  Do I need to make any changes to the Apache config?  Update: How do I setup proFTP to make sure that I can access /var/www if that is the route I continue one?

Has anyone got a nice solution for handling files in /var/www? We're running Name Based Virtual Hosts and the Apache 2 user is www-data.  We've got two regular users & root. So when messing with files in /var/www, rather than having to...  chown -R www-data:www-data   ...all the time, what's a good way of handling this?  Supplementary question: How hardcore do you then go on permissions?  This one has always been a problem in collaborative development environments.


After upgrade to Ubuntu 20.04 cannot install lapack, blas, openmpi with apt. In earlier Ubuntu versions, procedure was simple: apt -y install gfortran apt -y install build-essential liblapack* libblas* apt -y install openmpi* libopenmpi*  Doing this in 20.04 only gfortran ended successfully. Let me remind you Sheldon Cooper's "Oh Ubuntu! you are my favorite Linux-based operating system". So don't lose your reputation among nerds.

I was trying to install all python packages using sudo apt install python3*, but it gave me this error: newtron@newtron:~$ sudo apt install python3* Reading package lists... Done Building dependency tree        Reading state information... Done E: Unable to locate package python3*


For some strange reason, all the icons on my desktop accessing websites became 'Microsoft Edge' when I switched from Chrome to Edge for one browsing session! I tried everything to get rid of it, but no luck! Also, when I want to make Mozilla Firefox my default browser, as soon as I click OK, an 'Edge' page comes up thus nullifying my preference! Apparently, Microsoft has a wired software app overriding one's choice? How can I disable it or get rid of it so I can get back my browser of choice?

Is there any possibility to completely disable the new Edge browser? The old IE could be disabled in Settings → Default Programs, but in Windows 10, the checkbox is missing for Edge.  Is there any way to get rid of Edge, or at least to disable all entry-points?


I have installed the texlive 2017, and found out that it contains biber. So I clicked the biber icon, but all I can get is a black screen that disappears in like one second. What is wrong with it? How can I execute the program? Could anyone please help me?

Running the minimal example  \documentclass{article} \usepackage{filecontents} \begin{filecontents*}{\jobname.bib} @ARTICLE{example,   author  = {Other, Anthony Norman},   title   = {Some things I did},   year    = {2014},   journal = {J.~Irrep. Res.},   volume  = {1},   number  = {1},   pages   = {1-10} } \end{filecontents*} \usepackage[backend=biber]{biblatex} \addbibresource{\jobname.bib} \begin{document} Hello\cite{example}. \printbibliography \end{document}   I get the warning There were undefined references.  I have read  and know that I need to run:   LaTeX Biber LaTeX   However, my editor is only set up to run BibTeX. How do I go about setting up my editor/IDE to be able to run Biber, and how do I run the LaTeX/Biber/LaTeX cycle?  Answers (sorted alphabetically by editor name)                    Answer guidelines   Each answer should be for one editor. If the editor is cross-platform, if possible give a single answer with notes covering the minor platform variations. Please edit the question to include new answers in the 'link list' Each answer should be 'stand alone', i.e. don't say 'It's almost the same as editor Y but ...' for the editor part Instructions for 'build tools' such as arara or latexmk are welcome but should explain how to set up the editor in question as not all editors allow simple addition of arbitrary tools


I see this was asked a couple of times about three years ago and at the time the feature request was apparently denied:        Is this still the case? If so, why? I have precisely zero interest in having certain questions polluting a list that I might actually find useful if I could at least tailor it a bit to my needs.

I was going to make a filter for the "" by excluding some sites from it.  I noticed  which talks about "negative filtering" but does not explain how one can do it or if it is possible.  There does not seem to be a way to do this, though.  On the filter page, my only options are:  So how can I do "All sites except [list]"? It would also be nice if this could include similar functionality with the meta checkbox.  Something like "All main & meta sites except..."


Is there a general formula for the boundaries of a correlation coefficient given a set of other correlation coefficients? I have seen the formula for three random variables where two correlations are known. For example, given correlations R_ac and R_bc the boundaries of R_ab are given by:  R_ab <= R_ac*R_bc +/- sqrt[(1-R^2_ac)(1-R^2_bc)].   Is there a more general formula? Suppose I have a 4x4 correlation matrix:  ---                --- |  1                 | |  R_ab 1            | |  R_ac R_bc 1       | |  R_ad R_bd R_cd 1  | ---                ---   Is there a boundary formula for R_ab if I know R_ac, R_ad, R_bc, R_bd, and R_cd?  For example, and this is a complete and total guess on my part, something like...  R_ab <= R_ac*R_cd*R*R_bd +/- [(1-R^2_ac)(1-R^2_cd)(1-R_bd)]^(1/3).   Cristian

There are three random variables, $x,y,z$. The three correlations between the three variables are the same. That is,  $$\rho=\textrm{cor}(x,y)=\textrm{cor}(x,z)=\textrm{cor}(y,z)$$  What is the tightest bound you can give for $\rho$?


see the sentence. "It matters a lot."  here it uses matters, but when I question like "Does it matter?" why we don't use s with matter?

Why do we use have instead of has with doesn't like in the following sentence:  He doesn't have(not has) to go there.  Please explain the grammatical reason behind it.  Thanks


I installed Ubuntu on the same hard drive as my Windows 7 (different partition of course)  Edit: Windows wouldn't boot and after trying to fix mbr with Windows recovery console Windows isn't recognized in boot anymore.  I really don't want to re-install Windows. How can I make Windows boot up again?    As for how I installed Ubuntu:      I had Windows 7 already installed.    Used Windows tools from within windows to shrink partition to free up space for Ubuntu    Rebooted into Ubuntu from CD.    Used Ubuntu installation disk tools Something else option. to create new partition for Ubuntu from unallocated space.    Installation was done and then Windows stopped booting.     I managed to get to Windows recovery console by pressing Shift+f10 but now I'm not sure how to fix the Windows boot record.  I tried using fixmbr, bootrec, bootsect /nt60 all /mbr.  Doesn't seem to work...

I installed Windows on my computer, followed by an installation of Ubuntu. However, now I'm unable to boot into my Windows install.  What can I do to fix this?


Messing around with fun physics, and it got me thinking. I probably am not the only or the first one to think of it. I am wondering what more experienced physicists on this site can contribute to this thought experiment.  We are constantly moving because earth is constantly rotating on its axis. Using quick numbers and assuming.. a lot of things. Is there a way, and do we have the technology to harness the energy the earth constantly exerts on us?  I am a 95kg adult, and assuming I am at the equator I have a linear velocity of about 463m/s.  Using the $$v_{linear}=\frac{\Delta x} {\Delta t}= \frac{2 \pi R}{86400s} = \space \sim463\space m/s $$  This gives me a Kinetic energy of $\sim 1.03 \times 10^{7}J$  Spanning over the time period of a day on the earth, I assume, gives me about 118 watts of power per second.   What are some the pros and cons to this thought?

Is there any way to harvest large amounts of energy from the Earth's rotation?


I have a ring of vertices, and I would like to connect them with another edge together quickly.  I tried bridging 4 vertices together, but that took too long and made faces. Extruding with 'E' would also take too long. I couldn't find any way to do it before, but here is an example of what I would like to do:  How do I do this? I tried the bridge loop method, but it does all of the vertices at once, and it creates triangles, which I do not want either.

There's a way to fill with faces only the area between the larger circle and the the smaller one? I mean.. It's a wheel and I'm trying to fill the rubber part of it.  Using the fill function F it fills everything inside the bigger circle.


On Fedora 14 I use to use an app called 'Connect To' (I think it was default app) to make SSH connections. It was GUI based SSH connection tool.   Now I have migrated to Ubuntu (11.10 to be precise). I use terminal based OpenSSH. OpenSSH is pretty good but sometimes I wish it was GUI app. I have tried a few but none do the job like 'Connect To' on fedora.  Is there any Connect To equvalent on Ubuntu ?

Cannot find "connect to server" in 11.04, looks like unity doesn't have it. Is there other very similar way to connect to another Ubuntu computer via SSH? (not in terminal)


Proving the existence of gravitational waves might revolutionise cosmology, but the method used by LIGO is quite similar to the famous  built more than a hundred years ago.  Might the Michelson-Morley experiment have failed due to some technological errors? Could putative gravitational waves found by LIGO be nothing but aether wind ripples?  May be this g-waves which were predicted by Einstein are actually ripples caused by aether wind and this thing was first predicted about 500 years before.

I am bit confused about this one. I am not very acknowledgeable about gravitational waves and LIGO. But if it is basically a Michelson interferometer and can detect shifts in vacuum, doesn't this means that we detected the luminiferous aether and if not, why? Is there an analogy or direct correlation between gravitational waves and aether?


I am trying to import around 130k images via url. I thought it would be convenient to write a cli artisan command.  I am using laravel and "Spatie/MediaLibrary".  This is my script:  public function handle()     {        Article::where('index_block_position',0)->each(function($article){             if($article->featured_image != ''){                 try{                     $featuredImage = $this->mediaLibrary->addMediaFromUrl($article, 'http://myoldwebsite.com' . $article->featured_image, 'featured_image');                     $libraryImage = $this->mediaLibrary->addMediaFromUrl(MediaLibrary::first(), 'http://myoldwebsite.com' . $article->featured_image);                     $article->index_block_position = 1;                     $article->save();                     $this->info("Article {$article->id} image: {$featuredImage->id} - Library image: {$libraryImage->id} - added");                     Log::useDailyFiles(storage_path().'/logs/featured-image-migration.log');                     Log::info("Article {$article->id} image: {$featuredImage->id} - Library image: {$libraryImage->id} - added");                 }catch (\Exception $e){                     $this->info("image: {$article->featured_image} - exception: {$e->getMessage()}");                     Log::useDailyFiles(storage_path().'/logs/featured-image-migration.log');                     Log::info($e->getMessage());                 }             }         });         $this->info('All done!');     }   Unfortunately, after 10 or so images added I get the following error:  Symfony\Component\Debug\Exception\FatalErrorException: Allowed memory size of 134217728 bytes exhausted (tried to allocate 24576 bytes)   I am not sure how i can make this work because i have 130k images to import and the memory limit of 128M is already exhausted after 10 images...  I would appreciate suggestions.

I have a bunch of client point of sale (POS) systems that periodically send new sales data to one centralized database, which stores the data into one big database for report generation.  The client POS is based on PHPPOS, and I have implemented a module that uses the standard XML-RPC library to send sales data to the service. The server system is built on CodeIgniter, and uses the XML-RPC and XML-RPCS libraries for the webservice component. Whenever I send a lot of sales data (as little as 50 rows from the sales table, and individual rows from sales_items pertaining to each item within the sale) I get the following error:  Fatal error: Allowed memory size of 134217728 bytes exhausted (tried to allocate 54 bytes)   128M is the default value in php.ini, but I assume that is a huge number to break. In fact, I have even tried setting this value to 1024M, and all it does is take a longer time to error out.  As for steps I've taken, I've tried disabling all processing on the server-side, and have rigged it to return a canned response regardless of the input. However, I believe the problem lies in the actual sending of the data. I've even tried disabling the maximum script execution time for PHP, and it still errors out.


I have a simple home automation program written in Python that reads events from USB and sends commands to a server. It runs on a headless Ubuntu server. Basically, the program does a while true loop. Now if this program should be interrupted for whatever reason, I want it to automatically restart. A few moments or even minutes of down time would not be a problem. What is the easiest way to do this? I could write a cron job to check whether the program is still there, but is there another way to do this that I might not know about?

I want to have a process which will be restarted if it crashes. I googled a bit and found that an easy solution is to use .  I didn't understand how to configure it.   What is the easiest way to acomplish such a functionality? How to configure it?


I am out of my depths to understand what could be going wrong here. I am using luatex (TL 2018) to compile a simple pgfplot example.  This is the error message I get     example_surf.tikz:8: Package tikz Error: Sorry, the system call 'lualatex -shell-escape -halt-on-error -interaction=batchmode -jobname "main-figure0" "\def\tikzexternalrealjob{main}\input{main}"' did NOT result in a usable output file 'main-figure0' (expected one of .pdf:.jpg:.jpeg:.png:). Please verify that you have enabled system calls. For pdflatex, this is 'pdflatex -shell-escape'. Sometimes it is also named 'write 18' or something like that. Or maybe the command simply failed?   This is strange, because in my latexmkrc I have  $pdflatex = 'lualatex %O %S --shell-escape'; $pdf_mode = 1; $postscript_mode = $dvi_mode = 0;   Clearly, we can see that shell-escape is enabled.  Here is a MNWE.  \RequirePackage{luatex85,shellesc}  % not sure if this is required \documentclass[tikz]{standalone} \usepackage{pgfplots} \usepackage{grffile} \pgfplotsset{compat=newest} \usetikzlibrary{plotmarks} \usetikzlibrary{arrows.meta} \usepgfplotslibrary{patchplots} \usepackage{amsmath} \usepgfplotslibrary{external} \tikzset{external/force remake} \tikzexternalize  \begin{document}      \input{example_surf.tikz}  \end{document}   The file example_surf.tikz is a simple 3D surface plot from the pgfplots manual.  \begin{tikzpicture}     \begin{axis}         \addplot3 [         surf,         shader=interp,         ] {x+y};     \end{axis} \end{tikzpicture}   What am I doing wrong?

I'm trying to generate a gif from a tikz picture, using tikz's external library. Ultimately, my plan is to   Convert a picture to gif write a node style that converts the nodes' coordinates to pixel offsets in a map file use them together on a web page.   If somebody has done this before, I'm glad to get a pointer.  However, I have adapted the example from the tikz documentation which uses convert in a system call. The only difference to the original example is that I don't add code to include external and that I changed the desired output format to gif:  \documentclass{standalone}  \usepackage{tikz} \usetikzlibrary{external}  \tikzset{   gif export/.style={     external/system call/.add=     {}     {; convert -density 300 -transparent white "\image.pdf" "\image.gif" },     %     /pgf/images/external info,   } } \tikzexternalize \tikzset{gif export}  \begin{document}   \begin{tikzpicture}     \draw (0,0) node[draw,minimum width=1in] {TestNode};   \end{tikzpicture} \end{document}    The resulting main.pdf is empty, the externalization library creates an empty main-figure0.pdf and main-figure0.dpth an additional file called } is created, but I don't know what I can do with it.   I have the impression that the closing } after "\image.gif" is causing problems. When I change that line to end with  "\image.gif"},   (no space between gif and }), the resulting converted file is called main-figure0.gif} and also empty.  but I have no idea how I can fix this.


When doing partial fraction decomposition, there are three cases:  Case 1: Denominator has distinct linear factors.  $f(x) = \dfrac{P(x)}{(x - a_1)...(x - a_k)} = \dfrac{A}{x - a_2} + \dfrac{B}{x - a_k}$ where $a_1, ..., a_k$ are pairwise distinct.   Case 2: Denominator has repeated linear factors.  $f(x) = \dfrac{P(x)}{(x - a)^c} = \dfrac{B_1}{x - a} + ... + \dfrac{B_c}{(c - a)^c}$  Case 3: Denominator has an irreducible factor of degree 2:  $f(x) = \dfrac{P(x)}{(x - a)(x^2 + bx + c)} = \dfrac{A_1}{x - a} + \dfrac{C_1x + C_2}{x^2 + bx + c}$  In cases 1 and 2, the numerators are all given constant placeholders ($A, B$), but in case 3, the numerator is given a polynomial of degree one as the placeholder ($C_1x + C_2$). I'm curious as to why this is the case. What is the difference between case 1 and 2 and 3 that necessitates this difference in the numerator? What is the reasoning behind this?  I would greatly appreciate it if people could please take the time to elaborate on this.

For repeated, linear factors, (the term $(x-r)^m$ appears in the denominators for some integer $r$ and $m$, where $m > 1$) there is a partial fraction for each power upto and including $m$. Why?  Why can't you just have one partial fraction for the term with the $m^{th}$ power? Could someone give me an explanation about why you need a partial fraction for each power?


I'm a little lost on this one. So I need to show that (r-1)! raised to the kth power is less than or equal to c(n,k) (the number of permutations with k-cycles) divided by S(n,k) (the number of partitions of n into k blocks), and I need to show that that is less than or equal to (n-k)!. This inequality makes no sense to me. One hint we have is: If we have positive integers a1, . . . , ak such that the sum i=1 to k of ai equals t, what choices of ai maximize or minimize the product i=1 to k of ai? Any ideas on how to approach this proof? We  were just taught this definition so it's a little confusing to me.

For all positive integers $n,r,k$ that $n=rk$, how to prove the inequality $$(r-1)!^k\le \frac{c(n,k)}{S(n,k)}\le (n-k)!$$ $c(n,k)$ is unsigned Stirling numbers of the first kind and $S(n,k)$ is Stirling numbers of the second kind.  Any help would be appreciated!


I'm trying to prove the following inequality $\forall x,y \in \mathbb R$ :    $$\lfloor x \rfloor + \lfloor x + y \rfloor + \lfloor y \rfloor \le \lfloor 2x \rfloor + \lfloor 2y \rfloor$$ If one thing is clear for me it is that the basic definition isn't enough to prove this, I would always get an additional $1$ on the left hand side.    Thanks for your trouble.

The identity is this: $\lfloor 2x \rfloor + \lfloor 2y \rfloor \geq \lfloor x \rfloor + \lfloor y \rfloor + \lfloor x+y \rfloor$  I am truly stumped. Help is appreciated. Thank you!


I would like to know if my solution to the following exercise is correct.  Let $A$ be an integral domain (with a unit) which has a field $\mathbb K$ as a subring and such that $A$ is a finite-dimensional vector space over $\mathbb K$.  Show that $A$ is a field.  Here is what I do : let $n=dim_{\mathbb K}A$. Let $x$ be in $A$. Then $\{1,x,x^2,...,x^n\}$ is a linearly dependent family in A as a vector space. Therefore there exist $\beta_0,\beta_1,...,\beta_n \in \mathbb K$ such that $$\sum_{i=0}^{n}\beta_ix_i=0$$ Therefore $$\beta_1x+\beta_2x^2+...+\beta_{n-1}x^{n-1}+\beta_nx^n=-\beta_0$$  So $$x(\beta_1+\beta_2x+...+\beta_nx^{n-1})=-\beta_0$$  Since $\beta_0 \in \mathbb K$ it has an inverse so $$x \times (\beta_1+\beta_2x+...+\beta_nx^{n-1})(-\beta_0^{-1})=1$$  Therefore $x$ has an inverse, therefore $A$ is a field. Is there anything to add or to justify ? Where does the integrity of the ring come in ? Thanks in advance for your time.

I'm reading Galois Theory by Steven H. Weintraub (second edition), and finding that I'm at least somewhat short on the prerequisites. However the following proof looks wrong to me - am I misunderstanding something, or is it actually an incorrect proof?  Lemma 2.2.3. Let $F$ be a field and $R$ an integral domain that is a finite-dimensional $F$-vector space. Then $R$ is a field. Proof. We need to show that any nonzero $r \in R$ has an inverse. Consider $\{1, r, r^2, \cdots\}$. This is an infinite set of elements of $R$, and by hypothesis $R$ is finite dimensional as an $F$-vector space, so this set is linearly dependent. Hence $\sum_{i=0}^n{c_i r^i} = 0$ for some $n$ and some $c_i \in F$ not all zero.  It then goes on to show, given the above, that we can derive an inverse for $r$. However, if I consider examples like $r = 2 \in Q[\sqrt{2}]$, $r = \sqrt{2} \in Q[\sqrt{2}]$ or $r = 2 \in Q[X]/{<X^2>}$, the set $\{1, r, r^2, ...\}$ doesn't look linearly dependent to me. I do believe the lemma is true (and might even be able to prove it), but this does not look like a correct proof to me. Am I missing something? [Edit] Well yes, I am. Somehow I had managed to discount the possibility of any $c_i$ being negative, despite repeatedly looking at each fragment of the quoted text in an attempt to find what I might be misunderstanding.