If a,b,c are positive prove that $(1+a)^7.(1+b)^7.(1+c)^7>7^7.a^4 b^4 c^4$  My approach I tried (1+a)(1+b)(1+c) =1+[a+b+c+ab+bc+ac+abc] Find the AM of Square Bracket, them AM $\ge$ GM But if I add 1 then AM>GM. Please help me with my approach


A square matrix has the same minimal polynomial over its base field as it has over an extension field

I think I have heard that the following is true before, but I don't know how to prove it:     Let $A$ be a matrix with real entries. Then the minimal polynomial of $A$ over $\mathbb{C}$ is the same as the minimal polynomial of $A$ over $\mathbb{R}$.   Is this true? Would anyone be willing to provide a proof?    Attempt at a proof:  Let $M(t)$ be the minimal polynomial over the reals, and $P(t)$ over the complex numbers. We can look at $M$ as a polynomial over $\Bbb C$, in which case it will fulfil $M(A)=0$, and therefore $P(t)$ divides it. In addition, we can look at $P(t)$ as the sum of two polynomials: $R(t)+iK(t)$. Plugging $A$ we get that $R(A)+iK(A)=P(A)=0$, but this forces both $R(A)=0$ and $K(A)=0$. Looking at both $K$ and $R$ as real polynomials, we get that $M(t)$ divides them both, and therefore divides $R+iK=P$.   Now $M$ and $P$ are monic polynomials, and they divide each other, therefore $M=P$.  Does this look to be correct?    More generally, one might prove the following     Let $A$ be any square matrix with entries in a field$~K$, and let $F$ be an extension field of$~K$. Then the minimal polynomial of$~A$ over$~F$ is the same as the minimal polynomial of $A$ over$~K$.


Sorry  I am new in bicycling , but I think  the head is least like to be in contact with any other things during crash normally down from head rather the head might come in contact in other vectors . So I am curious how effective bicycle helmates are .


If $E$ is Lebesgue measurable, show that there exists a closed set $F$ with $F \subset E$ and $m(E\setminus F)<\epsilon$

Just having trouble with this problem. First, it says to prove that if $E$ is Lebesgue Measurable, and $\epsilon>0$ is arbitrary, then there is an open $O$ such that $E \subset O$ and $m(O\setminus E)<\epsilon$. Now for this part, since $E$ is Lebesgue measurable, I was able to take the definition of being Lebesgue outer measurable (the infimum of open coverings of $E$) and easily construct $O$ from that, and it works out.  But now I want to show that there is an $F$ closed with $F \subset E$ and $M(E\setminus F)<\epsilon$. The problem is, I can't figure out how to construct this $F$! The idea seems obvious intuitively, but I feel like I am given no tools for constructing a closed subset of an arbitrary set that satisfies these conditions. Am I missing something obvious here?  Thanks!!


OK "User was removed" but what was the answer for which I earned and then lost rep points?

From time to time I lose 10 rep points for a "User was removed" reason. I'm really curios to know in what way I helped that user, that is, what was his\her question, and what did I answer? Currently, there's no way to know that and trace back my answer.  Can SO add a link for the origin of the Rep points lost?


I need to retrieve some files from an unbootable Ubuntu VM. The VM is installed into a VDI file.  How can I go about doing this?


Narrower kerning of symbols generated by Tikz

I'm using LaTeX to render a set of custom glyphs. Each glyph is perfectly rectangular, at a 3.5 x 5 aspect ratio, and they're defined something like this (the following example just lines the borders of the glyph):  \newcommand\glyph[1][1]{%   \begin{tikzpicture}[scale=0.1]     \draw[lightgray] (0,0) to (0,4);     \draw[lightgray] (0,0) to (3,0);     \draw[lightgray] (3,0) to (3,4);     \draw[lightgray] (0,4) to (3,4);   \end{tikzpicture}% }   Each glyph is rendering correctly. When I invoke them in text:  \begin{document} \glyph\glyph\glyph\glyph \end{document}   I get some decently-kerned glyphs:    However, this isn't enough. I'd like to get the gap between characters down to a couple of pixels, if possible. How would I go about this?


Is there a way to make ext-filesystems use less space for themselves in Linux?

I have a bunch of external and internal HDDs that I use on a Linux system. I only have Linux systems, so using a Linux file-system would only make sense, right? However I'm currently using NTFS everywhere, because it gives me the most usable space out of HDDs.  I would like to switch to Linux file-systems now though, mostly because of permissions and compability (e.g. I can't get my LUKS encrypted NTFS partition to resize under Linux, keeps telling me to chkdsk under Windows).  However when I formatted those HDDs I tried out a bunch of different filesystems and every Linux filesystem, even ext2 which as far as I know has no journaling, used a lot of space for itself. I don't recall exact values, but it was over 100GB that NTFS got me more on a 2TB HDD, which is a lot.  So my question is: Is there a way to make ext-filesystems use less space for themselves? Or is there another filesystem (I've tried ext2, ext3, ext4, NTFS and vfat - None of them came even close to the usable space NTFS offered me) with perfect Linux support and great usable space?  I'd love to hear about how and why filesystems (especially ext2 which has no journaling) use that much more space than NTFS and I don't know where else to ask. I'd mostly prefer a way to use ext4 without journaling and anything else that uses up this much space, if that's possible.


Is an object initialiser guarantees to run in order?

I have the following object being created:  var i = 0; var foo = new Foo(); foo.A = ++i; foo.B = ++i; foo.C = ++i;  Assert(foo.A == 1); Assert(foo.B == 2); Assert(foo.C == 3);   The same object can we written using an object initializer:  var i = 0; var foo = new Foo {     A = ++i,     B = ++i,     C = ++i }  Assert(foo.A == 1); Assert(foo.B == 2); Assert(foo.C == 3);   Is the order that the properties are set guaranteed in the case of the object initializer?


This question is asked often in Ask Ubuntu, sometimes with few hints about the situation.   Please provide a list of possible reasons to help troubleshoot the problem.


Minecraft Scoreboard Item give Tag Problem

I'm trying to give an item a tag in Minecraft 1.11, but it shows me this error:   The dataTag does not match for 4be19781-14d9-467c-ba54-d574273e095c   The commands I'm using are:  /scoreboard players tag @e[type=Item] add T1 {Item:{id:"minecraft:tnt",Count:1}} /scoreboard players tag @e[type=Item] add T2 {Item:{id:"minecraft:arrow",Count:1}}


Replacing string that have a pattern what uses :

i am trying to replace some string pattern in a string, but I cant archive my goal.. input: :randomword: NO REMOVE :random_word_word: :random: NO REMOVE :random: NO REMOVE :random: :random: NO REMOVE  expected: NO REMOVE NO REMOVE NO REMOVE NO REMOVE  actual '' '' 'NO REMOVE' 'NO REMOVE'  current regex Regex.Replace(input, ":.+:", "");


Make project into exe that works without java installed

Right now im in a course in Agile development and at our demo it is an demand that the project is an EXE and it should work without Java installed.  I tried to talk to my teacher but he wont budge on the demand so is there anyway that i can make my project into and exe that can be executed without java installed.  sidenote: my last resort is to make an installer that force him to install java and then run the exe!


How to put multiple \multicol environments in same row

I'd like to make a boolean table with some inputs x, y, z and some outputs a, b, and label the first three columns In and the last two Out. The  shows me how to merge all columns across a table, is there a way I can merge the first n in a row, and then the remainder in the same row?


Which sentence uses the correct capitalization for the name of the season?     I will travel in the summer of 2013.   or     I will travel in the Summer of 2013.


I'm having a bit of trouble understanding how the gauge condition is found.  Consider the potentials $V$ and $\vec A$ and $V'$ and $\vec A'$ so that $$\vec E = -\vec\nabla V -\frac{\partial\vec A}{\partial t} = -\vec\nabla V' -\frac{\partial\vec A'}{\partial t}$$ $$\vec B = \vec\nabla \times \vec A=\vec\nabla \times \vec A'$$  The 2 sets of potentials are then related like this:  $$\vec A' = \vec A+\vec\nabla\theta$$ $$V' = V-\frac{\partial\theta}{\partial t}$$ For a function $\theta$.  The equations for the potentials are the following:  $$\vec\nabla^2\vec A-\varepsilon\mu\frac{\partial^2 \vec A}{\partial t^2}=-\mu\vec J+\vec \nabla(\vec \nabla.\vec A+\varepsilon\mu\frac{\partial V}{\partial t})$$  $$\vec\nabla^2V -\varepsilon\mu\frac{\partial^2 V}{\partial t^2}=-\frac{\rho}{\varepsilon} -  \frac{\partial}{\partial t}(\vec\nabla . \vec A+\varepsilon\mu\frac{\partial V}{\partial t})$$  They can be decoupled by choosing the right potentials so that $(\vec\nabla . \vec A+\varepsilon\mu\frac{\partial V}{\partial t})=0$  The above part is the theory in general.  Now to find the correct potentials where this is the case, let's say that this last part is true for potentials $\vec A'$ and $V'$, i.e.   $$\vec\nabla . \vec A' + \varepsilon\mu\frac{\partial V'}{\partial t}=0$$  Filling in the relations between the 2 sets of potentials from earlier gives:  $$\vec\nabla . \vec A + \nabla^2\theta + \varepsilon\mu\frac{\partial V}{\partial t} -\varepsilon\mu\frac{\partial^2\theta}{\partial t^2}=0$$  Yet my book tells me that this means that  $$\nabla^2\theta - \varepsilon\mu\frac{\partial^2\theta}{\partial t^2}=0$$  I don't see why this is the case.


How to find all empty files and folders in a specific directory including files which just look empty but are not?

Let's say that in my folder ~/list I have a large amount of folders each with their own sub-folders and sub-sub-folders etc, and there are lots of files almost on each level. However some of these files and folders are empty, so how can I recursively search through them all to find the empty files and folders? And then have them displayed in a list of file locations so that I know where each one is (it should also be clear which is a file and which is a folder because not all files have file extensions). I am running Ubuntu GNOME 15.10 with GNOME 3.18.  Please note that it would also be very useful if it would also tell me if a file looked empty but wasn't (for instance if it had spaces or linebreaks in it or something). And would differentiate between a real empty file and one that just looks empty in the output.


Mathematical Induction. Horses made me question my understanding

I recently read about the false inductive proof that all horses are the same colour. There are some mathSE threads about this already (, ).  After reading this, I now realise I have never really understood mathematical induction. It seems obvious for sums, but when presented with this example I was stumped.  I have some questions:  Question 1. The inductive step   for all horses are the same colour goes roughly as follows:      Assume that there are n horses, numbered 1 to n. By induction horses 1   through (n-1) are the same colour, and similarly horses 2 through n   are the same colour. The overlapping sets H_0 = {1,2,...,(n-1)} and   H_1 = {2,3,...,n} imply that horse 1 and horse n are the same colour.   Thus all horses are the same colour.   I have an issue with one of the statements:      By induction horses 1 through (n-1) are the same colour, and similarly horses 2 through n are the same colour.   I understand why horses 1 through (n-1) are the same colour (by hypothesis), but why can we just say horse n is the same colour? It seems to imply the numbering is arbitrary to me, but then induction is completely invalid unless we can define an order?  Question 2. The base case:   If we grant the inductive step reasoning (of which I am unsure whether that is valid), the induction relies on the fact that for some k, two distinct k-1 subsets have shared elements, from which we can conclude they are all the same colour. So the base case should be n=2 (or should it be n=3?).   However the trick used in the inductive step seems to imply the numbering of the horses is arbritary (as I briefly mentioned above), so a subset of size n=2 would seem to require we prove all subsets of size 2 have horses which are the same colour, which makes the induction step redundant?  General Question 3.   How do we choose what inductive steps are valid, and what base cases are required? I realise this is poorly phrased, but is there a way in general, or a set of heuristics to enable a valid basis to be chosen?  A slightly modified version of Mathematical Induction that seems to me more intuitive  Perhaps my understanding of induction is incorrect. It seems to me mathematical induction is more intuitive when presented as follows:     For each positive integer n > n_0, Let p(n) be a statement.      Step 1. We first show that If p(k) then p(k+1) is true for every   positive integer k. To do this we choose an arbitrary k and show, by   direct proof usually, this implies (k+1)      Step 2. Choose a base case n_0 on which we induct on to all n > n_0.   Here we use the fact that we have shown that for an arbritrary k, k+1   is implied. Choosing a valid basis allows the "induction domino   effect" to work its magic.      Then we have shown p(n) is true for every positive integer n > n_0   That seems to me easier to understand. Although do we need to explicitly show our base case implies n_0 + 1?   I suppose this is a different way of asking the same question I asked above, namely how do we choose valid base cases?  Hopefully this question isn't too rambling. Please let me know if anything requires clarification.


I motion to reopen  as there's a lot of evidence It says  If Kotlin becomes more popular in the future, we will reconsider.  Evidence of maturity There's a  from 2 years back, but since then a lot of things have happened, especially to Kotlin:  Kotlin is coming up on its 5th major update widespread adoption in Android (and some backend) Gradle kts build scripts official support from Google.  See also the comments on the rejecting answer.  I think this is a quite compelling evidence that Kotlin is now trending:  Kotlin is in quite notable positions in  especially when compared to , when it wasn't even on the list. 24.8M views according to   Trigger I just asked a  and noticed that even basic highlighting is missing (fun/val are the most common keywords and they're not highlighted).


I have two hashMaps :  private HashMap<String, HashMap<String, Integer>> attributesCountPerCategory;   and  private HashMap<String, Integer> attributesCount;   I also have the method:  public void increaseAttributes(String attr, String category){     HashMap<String, Integer> attributes = this.attributesCountPerCategory.get(category);     if (attributes == null) {         this.attributesCountPerCategory.put(category, new HashMap<String, Integer>());         attributes = this.attributesCountPerCategory.get(category);     }      Integer c = attributes.get(attr);     if(c == null){         attributes.put(attr, 0);         c = attributes.get(attr);     }     attributes.put(attr,c++);      Integer c2 = this.attributesCount.get(attr);     if(c2 == null){         this.attributesCount.put(attr,0);         c2 = this.attributesCount.get(attr);                 }     this.attributesCount.put(attr,c2++);         }   So when I am calling this method a NullPointerException is thrown even though I am checking for null values in object references. The exception is thrown in the below line:   HashMap<String, Integer> attributes = this.attributesCountPerCategory.get(category);   What could be the problem?


Determine whether the set $W$ is a subspace in $\mathbb{R}^{3}$

Determine whether the set $W=\{(2a-2,3b,2a-3b)\}$ is a subspace in $\mathbb{R}^{3}$. Describe the set.  I have tried putting the set into matrix form but don't know which is correct. I also know that it needs to be closed under addition and multiplication but can't figure out how to show that.


How is gradient boosting like gradient descent?

I am reading the useful Wikipedia entry on gradient boosting (), and try to understand how / why we can approximate the residuals by the steepest descent step (also called the pseudo-gradient). Can anyone give me the intuition on how the steepest descent is linked / similar to the residuals? Help much appreciated!


Not sure what I did but I no longer see the keyboard shortcuts for something when I hover over the TMenu. For example when in edit mode if I would hover over Loop Cut it used to say "Shortcut: Spacebar, Ctrl R" and now it just says "Cut mesh loop and slide it". Still to new to have everything memorized and really rely on these hints to keep me moving forward. Anyone know what I need to enable to show these again?


How can I filter questions with ZERO answers for a tag?

I tried to answer SEO-related questions which are not having even a single answer in Pro Webmasters. But I was not able to filter a single question with no answer in the SEO tag. Why does it show questions with answers even if I filter “unanswered” in the SEO tag? If no question is available in this case, it should say ”No question is available for this filter criteria”.  I’m sure that there are lot of unanswered questions in SEO tag. How can I filter those questions?   Screenshot:


Refresh Apex not working on Lightning Record Form Save

I'm not able to understand how refreshApex works in LWC.  Here is what i'm trying to achieve:  On a web component show -    Show most recent 10 records of Account a form (I used a lightning record form for creating new records , this comes with a save button which creates a new Account record and also refreshes the most recent view   This is the HTML code:  <template>  <lightning-card title="Recent Accounts" icon-name="standard:account">     <lightning-datatable data={accounts} columns={columns} hide-checkbox-column="true" key-field="Id"></lightning-datatable> </lightning-card> <lightning-card title="Create New Account">     <lightning-record-form          object-api-name="Account"         fields={fields}         onsuccess={handleSuccess}>     </lightning-record-form> </lightning-card>  </template>   JS:  import { LightningElement , wire , track} from 'lwc'; import { ShowToastEvent } from 'lightning/platformShowToastEvent' import { refreshApex } from '@salesforce/apex' import getAccRecs from '@salesforce/apex/GetRecentAccounts.getRecentAccs' import NAME_FIELD from '@salesforce/schema/Account.Name' import INDUSTRY_FIELD from '@salesforce/schema/Account.Industry'  /* eslint-disable no-console */  export default class refreshApexComp extends LightningElement {      wiredRslt;     @track fields = [NAME_FIELD,INDUSTRY_FIELD];     @track accounts;     @track columns = [         {             label : 'Name',             fieldName : 'Name',             type : 'text',             sortable : false         },         {             label : 'Industry',             fieldName : 'Industry',             type : 'text',             sortable : false         }     ];      @wire(getAccRecs) wiredCallbackResult(result){         this.wiredRslt = result.data;         if(result.data){             this.accounts = result.data         }     }      handleSuccess(event){         const evt = new ShowToastEvent({             title : "Account created successfully",             message : "Record Id " + event.detail.id,             variant : "Success"         });         this.dispatchEvent(evt);          refreshApex(this.wiredRslt);       }   }   Can someone tell me what am i missing here / doing in a wrong manner?  EDIT: I tried wiring the apex method to a property instead of a function and then use refreshApex on the same and it worked fine. This is the HTML and JS code.  <template> <lightning-card title="Recent Accounts" icon-name="standard:account">     <lightning-datatable data={accounts.data} columns={columns} hide-checkbox-column="true" key-field="Id"></lightning-datatable> </lightning-card> <lightning-card title="Create New Account">     <lightning-record-form          object-api-name="Account"         fields={fields}         onsuccess={handleSuccess}>     </lightning-record-form> </lightning-card>  </template>  export default class refreshApexComp extends LightningElement {      wiredRslt;     @track fields = [NAME_FIELD,INDUSTRY_FIELD];     @track accounts;     @track columns = [         {             label : 'Name',             fieldName : 'Name',             type : 'text',             sortable : false         },         {             label : 'Industry',             fieldName : 'Industry',             type : 'text',             sortable : false         }     ];      @wire(getAccRecs) accounts;      handleSuccess(event){         const evt = new ShowToastEvent({             title : "Account created successfully",             message : "Record Id " + event.detail.id,             variant : "Success"         });         this.dispatchEvent(evt);          refreshApex(this.accounts);       }   }


Every time I try to open Eclipse in Ubuntu 18.04.2 I get an Unsatisfied Link Error and it will not open. I tried uninstalling but that did not help.  The error message:  An error has occurred.  See the log file /home/NAME/.eclipse/org.eclipse.platform_3.8_155965261/configuration/1549828758313.log   log file:  !SESSION Sun Feb 10 20:52:07 CET 2019 ------------------------------------------ !ENTRY org.eclipse.equinox.launcher 4 0 2019-02-10 20:52:07.624 !MESSAGE Exception launching the Eclipse Platform: !STACK java.lang.ClassNotFoundException: org.eclipse.core.runtime.adaptor.EclipseStarter     at java.base/java.net.URLClassLoader.findClass(URLClassLoader.java:466)     at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:566)     at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:499)     at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:626)     at org.eclipse.equinox.launcher.Main.basicRun(Main.java:584)     at org.eclipse.equinox.launcher.Main.run(Main.java:1438)     at org.eclipse.equinox.launcher.Main.main(Main.java:1414)   In terminal error message:  OpenJDK 64-Bit Server VM warning: Ignoring option MaxPermSize; support was removed in 8.0 Gtk-Message: 21:05:17.924: Failed to load module "canberra-gtk-module"


Is $K = \bigcup\limits_{i:\text{even}} \mathbb{F_{2^i}}$ a field? If so what is char(K)? Is $K \cup \mathbb{F_{2^8}}$ a field?


Accessing the Locale Date format with in program automatically

Is there a function which will help us to write the date using the Locale settings in Javascript.For example in my machine as per the Locale settings the format is M/D/YYYY so in my program the date should be printed in this format. If i change my the Locale settings in computer format to YYYY-MM-DD then my program should automatically print in this format without hardcoding the format. This is the expected behavior of my program. As some of the suggestions given on using toLocaleDateString method, On using toLocaleDateString it always returns in M/D/YYYY format only even then the computer Date format is changed to YYYY-MM-DD. I searched in internet i don't find any proper answer please guide me to do this. Any help is appreciated.


Why the inconsistency between 2001 and 2010, the two odysseys of Clarke?

I started to read 2010 and I don't understand why some of the facts of 2001 are different from what the characters say in 2010. For example:   The most obvious one, Discovery One travels to Saturn in 2001, whereas in the second odyssey they say that it went to Jupiter. The monolith, AMH-2, is on Saturn in 2001, while on Jupiter in the second odyssey. HAL is called CARL (in French) in the first book.


Is there any way to prevent the current CMD input being erased by a blank history suggestion?

In the CMD interpreter on Windows, the ↑ arrow key replaces the current input (not sure what the accurate term is) with commands in the command history; commands that have previously been executed.   An odd idiosyncrasy of CMD is that on a fresh instance, when there are no previous commands in the history, the accidental pressing of the Up arrow key replaces the current input with the last "command" in the history; nothing, essentially clearing the input:      What's more, pressing the ↓ key doesn't return the previous command as you would expect; it's permanently lost. Essentially then, in the command prompt, the Up arrow doubles as a "clear input" key.  Can this be fixed at all?


second derivative of the inverse function

I know that the derivative of the inverse function of $f(x)$ is $g'(y) = \frac{1}{f'(x)}$ But how to derive the formula for the second derivative of g(y) knowing that $\left[\frac{1}{f(x)}\right]' = -\frac{f'(x)}{(f(x))^2}$ ?  I just started studying this chapter, so please try to be as simple as possible ;-) Thank you.


Why can't I create a partition table on my USB flash drive using GParted?

I have a blank USB flash drive I want to put a new filesystem on. If I try adding a new partition it complains "No partition table found on device /dev/sdc". Creating a msdos partition table seems to work correctly, except that when I go to add a new partition it complains with the same error. What am I missing?


I'm struggling on getting a good explanation for the unexpected signs of Principal Component for months. I tried to replicate a result and I got exactly the opposite signs for all components. While I searched through forums for an answer, I found this website   From what I have read from this website, I understand that we can reverse the sign  of components based on other criteria - e.g. EURO trend - as what have been mentioned by @amoeba. I'm wondering if there is a book or academic literature that says that we can flip the sign in this way (i.e. based on external factor)? I need a strong support for my research paper if I flip the signs of all components in this way. Hence, I would greatly appreciate if someone can recommend me some books that talk about this issue?  And also @amoeba mentioned that the signs are consistent in sliding PCA. Does it mean that we should have the same combination for each window (for example +a, +b, -c in first window & -a, -b, +c in second window)? So, if I think the signs in second window are correct, then I will flip the 1st window's vector and both vectors will have the same sign by then. What if they have different combination (e.g. +a, -b, -c in second window)? I think their correlation could have changed from time to time and hence we will have different combinations in different windows?


I am trying to run a python script in a number of files, and read the output for. Currently it only checks if the file exists by:  if file == "output":   But this output dosn't confirm if the run is finished properly. When the run is finished properly, the last-but-one line of the file is: " This run finished at "  How can I read this last-but-one line file? With my current knowledge in python (novice), I have managed to do:  #!/usr/bin/python3 import os input = "FeMnPSi_EOS_10." for subdirs, dirs, files in os.walk(input):     for file in files:         if file == "out-Dy-eos2":             print("file found")             ifile=input+"/"+file             with open(ifile, "r") as if1:                 for line in if1:                     if "This run finished at" in line:                         print("Ends Properly")   The problem with this code is:   It does not know, if the "This run finished at" line is the penultimate line of the file.   I am not sure, but guess, here python has to read the file sequentially....for this 10000+ lines for each file.   So, can I make it better in checking if the line do exist, and among last two line, without reading the whole file?


“situation where” vs. “situation in which”

In my mother tongue I can use the word where not only to describe something connected to a location, but also to substitute in which.   My question is: Is it correct to use where in a sentence like this?       Describe a situation where you had to show leadership.   Or it would be better to use in which instead?


Error related to tikz-cd and user-defined commands

My LaTeX document looks like this:  \documentclass{article}     \usepackage{tikz-cd}  \newcommand{\commSq}[8] {     \begin{tikzcd}         #1 \ar[r, "#2"] \ar[d, "#6"] & #3 \ar[d,"#4"] \\         #7 \ar[r, "#8"] & #5     \end{tikzcd} }  \begin{document} %1 \begin{tikzcd}     A \ar[r, "f"] \ar[d, "g"] & B \ar[d,"h"] \\     C \ar[r, "i"] & D \end{tikzcd} %2 \commSq{A}{f}{B}{h}{D}{g}{C}{i} \end{document}   I figured that the part the code below %1 and the code below %2 do the same thing. However, using the command \commSq instead yields the error "Package pgf Error: Single ampersand used with wrong catcode. [...]" and I get this output:    What am I doing wrong here?


I saw the following sentence:     Sally, who I saw in town yesterday, is a friend of my sister.   But I think it should use whom instead of who, since Sally is the guy I saw, so why not use whom?


Text is over image and not wrapped around it

My problem is image is displayed correctly, however text is not wrapped over the image, but is on top of it, as the image is not there.  Sample code:  \begin{figure}   \includegraphics[width=\textwidth]{architecture.png}   \caption{Mesos architecture}\label{fig:architecture} \end{figure}


According to some reliable sources, the residue theorem can be stated as: the sum of residues of a function on the whole complex plane(including infinity) is zero.  Now consider $$f(x) = \frac{\csc(\pi/x)}{x^2}$$ which has singularities at $+1, -1, 0, \infty$.  By Laurent expansion, I found that the residue is $\frac{1}{\pi}$ for $1, -1$ and $0$, and the residue at infinity is $\frac{-1}{\pi}$.  Obviously, this contradicts the residue theorem.  What mistakes did I make?


You can easily find a lot of  of the SARS-CoV-2 virus. But although it should be trivial for an electron microscope to measure the size, I am not able to find accurate size information.  What is the size (diameter) of the SARS-CoV-2 virus? (Why does some virus particles seem to have a different size?)


Proper capitalization of commonly used acronyms and initialisms

I was always under impression, that acronyms ought to be written all caps. However reading  site very often I see some of the common acronyms written as proper names (first cap). For example "Nato" instead of "NATO".   I know that BBC is quite strict in proper English usage, so what would be the reason behind this?


Traveling without EU Visa (from Netherlands to Spain) with US Refugee travel document

I was planning to visit my family in Tenerife. All appointments in Spain consulate SF are booked until the end of February.  As a green card holder (ex-asylee) I have only a Refugee travel document. I can travel with this document to some EU countries without a visa (Netherlands one of them). I know that for domestic flights inside EU customs don't check the visa.  Do you think how likely I might get into the problem if I'll fly from Holland to Tenerife without Schengen Visa? What will be the circumstances?  According to this document I don't need a visa:


How can I run a YouTube video in Picture in Picture mode on iOS?

On iOS, while watching a video in YouTube app, when I go to the Home Screen, the video stops playing. I found no setting to enable it.  I know it is available for Android, but is there a way to do so in iOS? Is there any setting, or a 3rd party app that I can use?


Possible sizes of finite fields and the relation to the characteristic of the field

In my abstract algebra class we discussed the idea that for a finite field $F$, that the characteristic of $F$ is a prime number. The proof would go more or less like : Suppose that $char(F) = nm$ for $n,m \in \Bbb Z$ and $n,m \geq 2$. Then $nm(1_F)=n(1_F)m(1_F)=0$ implying that either $n(1_f)=0$ or $m(1_f)=0$ since $F$ is an integral domain, but this contradicts the minimality of $char(F)$. This lead me to two questions:  $1$)What effect does $char(F)$ have on the size of $F$  $2$)Are there finite fields of cardinality $k$ for any $k\in \Bbb Z, k \geq 2$


How can I uninstall Oracle VirtualBox? "error processing package"

I installed VirtualBox from Ubuntu Software app. It showed some errors about UIF-something while installing. I have also created a password for rebooting (I have a dual booted laptop with secure boot on). Later when I tried to add an iso file to the PC created in VirtualBox it showed some errors. To uninstall Virtual box I looked in installed software in Ubuntu software app, but it was missing even though I can open it from desktop. I run the following command: sudo apt-get remove virtualbox-\* But it shows the following errors: After this operation, 216 MB disk space will be freed. Do you want to continue? [Y/n] y debconf: DbDriver "config": /var/cache/debconf/config.dat is locked by another process: Resource temporarily unavailable  (Reading database ... 278213 files and directories currently installed.) Removing virtualbox-6.1 (6.1.22-144080~Ubuntu~eoan) ... debconf: DbDriver "config": /var/cache/debconf/config.dat is locked by another process: Resource temporarily unavailable dpkg: error processing package virtualbox-6.1 (--remove):  installed virtualbox-6.1 package pre-removal script subprocess returned error exit status 1 dpkg: too many errors, stopping debconf: DbDriver "config": /var/cache/debconf/config.dat is locked by another process: Resource temporarily unavailable vboxdrv.sh: failed: modprobe vboxdrv failed. Please use 'dmesg' to find out why.  There were problems setting up VirtualBox.   To re-start the set-up process, run   /sbin/vboxconfig as root.   If your system is using EFI Secure Boot you may need to sign the kernel modules (vboxdrv, vboxnetflt, vboxnetadp, vboxpci) before you can load them. Please see your Linux system's documentation for more information. Errors were encountered while processing:  virtualbox-6.1 Processing was halted because there were too many errors. E: Sub-process /usr/bin/dpkg returned an error code (1)


What tradeoffs should I consider when deciding to use an SPI or I2C interface?  This accelerometer/gyro breakout board is available in two models, one for each interface.  Would either one be easier to integrate into an Arduino project?


Deleting all photos from iCloud immediately 2018

I would like to delete all of my photos from icloud immediately. The only way I have found to do this is select each individual picture and delete it. There does not seem to be a select all option anymore.   I already know about this. I just don't want to have to wait 30 days.   On your iDevice/s (iPhone, iPad, etc), go to Settings > Photos & Camera > and turn off the "iCloud Photo Library" option.


How does NAT know where to transfer the first incoming packet?

Say me and another identical computer are together in a local network (I am 192.168.1.5 or A, and he is 192.168.1.6 or B, for example) behind NAT (say our public IP is 5.5.5.5), and we have a torrent client running. We both have a certain file, let's call it "file.txt". An outside computer (let's call him C) wants to get a piece of the file. So he tries to make a connection (or rather requests the file or something, I'm not so sure how the protocol works) to 5.5.5.5 right? Now how does NAT know to which one of us (A or B) the packet is supposed to go? I must stress (if it wasn't clear enough already) that the outside packet (coming from C) is the first ever packet from that address, which means that neither me nor B know of the existence of C.


Test of whole distribution for two samples

I have a fundamental question: is it reasonable to use a statistical test to find out if 2 datasets are similar or not? Some comments have called out the T-test as being unable to answer that question. Why is the T-test insufficient? Furthermore, what other tests are there to determine differences in distributions for the two sample problem.


Bluetooth does not detect any devices [Ubuntu 16.04]

My bluetooth does not detect any devices - phones, other laptops, bluetooth speaker, keyboards, etc.  It just keeps searching and searching.     I am very new to Linux, so I would really appreciate some help on this. Please tell me what additional information you guys need so that you can help me.  Output of: lspci -knn | grep Net -A2; lsusb  02:00.0 Network controller [0280]: Broadcom Corporation BCM43142 802.11b/g/n [14e4:4365] (rev 01)     Subsystem: Lite-On Communications Inc BCM43142 802.11b/g/n [11ad:66a5]     Kernel driver in use: wl Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub Bus 001 Device 004: ID 04ca:2012 Lite-On Technology Corp.  Bus 001 Device 003: ID 0bda:57b3 Realtek Semiconductor Corp.  Bus 001 Device 002: ID 045e:07fd Microsoft Corp. Nano Transceiver 1.1 Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub   Thanks in advance!  Regards, Kristiyan


Is there a way to follow people's activity?

Is there a way to follow a particular person (or List<Person>) easily? Some people answer the questions in a very educative way, and I don't want to miss them.


We know that derivative of $x^n$ is $nx^{(n-1)}$ if $n$ is an integer. My question is how do we define derivative of $x^r$ is $r$ is an irrational number. For example what is the derivative of $x^\sqrt2$ or $x^\pi$?


Confused, whether java uses call by value or call by reference when an object reference is passed?

public class program1{      public static void main(String args[]){          java.util.Vector vc=new java.util.Vector();          vc.add("111");         vc.add("222");          functioncall(vc);          vc.add("333");          System.out.println(vc);      }      public static void functioncall(java.util.Vector vc){               vc=null;          } }   The output of above program is [111,222,333]. but, when I run the following program the output is [333]. Confused when we pass an reference , how it works whether it is call by value or call by reference? and why  public class program1{      public static void main(String args[]){          java.util.Vector vc=new java.util.Vector();          vc.add("111");         vc.add("222");          functioncall(vc);          vc.add("333");          System.out.println(vc);      }      public static void functioncall(java.util.Vector vc){          vc.removeAllElements();        } }


Help on dealing with items divided with slash

I am using a number of items in text that are divided with a slash. For example dates in different calendars or names of locations, such as 585/1190~CE (the first number is the year in Islamic lunar calendar, the second is according to the Common Era calendar), or Mosul/al-Mawsil (the first is a common English spelling, the second is the transliteration of the original name).  The problem I am running into is that Latex cannot split such items when they are at the end of a line---and such item ends up sticking through the margins. Adding spaces around the slash helps, but it looks ugly and this is not how it is supposed to be in academic writing. I wonder if there is a workaround to solve this issue. Namely, I do not want to use spaces around "/", but I would like Latex to break an item after a slash when necessary.


Now I am using subfile to compile document independent, I want to insert a picture in the sub document like this: \documentclass[../../../dolphin-book-2020.tex]{subfiles}  \begin{document}  \subsection{GitHub Slow}  balabalabala.......   \begin{figure}[htbp]     \centering     \includegraphics[scale=0.2]{githubspeedup}     \caption{GitHub Speed Up}     \label{fig:githubspeedup} \end{figure}   \end{document}  when I compile using this command in macOS Catalina 10.15 :  /Library/TeX/texbin/latexmk -pdfxe -pvc -xelatex -interaction=nonstopmode ./github-slow.tex  show this error: (/usr/local/texlive/2020/texmf-dist/tex/latex/listings/lstlang1.sty) (/usr/local/texlive/2020/texmf-dist/tex/latex/listings/lstlang1.sty)  Package fontspec Warning: Font "FandolFang-Regular" does not contain requested (fontspec)                Script "CJK".   ! LaTeX Error: File `githubspeedup' not found.  See the LaTeX manual or LaTeX Companion for explanation. Type  H <return>  for immediate help.  ...  l.31 ^^I\includegraphics[scale=0.2]{githubspeedup}  [1] (./github-slow.aux)  LaTeX Font Warning: Some font shapes were not available, defaults substituted.   LaTeX Warning: Label(s) may have changed. Rerun to get cross-references right.   ) (see the transcript file for additional information) Output written on github-slow.xdv (1 page, 28900 bytes). Transcript written on github-slow.log. === TeX engine is 'XeTeX' Latexmk: Index file 'github-slow.idx' was written Latexmk: Missing input file: 'githubspeedup' from line   '! LaTeX Error: File `githubspeedup' not found.' Latexmk: References changed. Latexmk: Log file says output to 'github-slow.xdv' Latexmk: Errors, so I did not complete making targets Latexmk: Failure to make the files correctly     ==> You will need to change a source file before I do another run <== Collected error summary (may duplicate other messages):   xelatex: Command for 'xelatex' gave return code 1       Refer to 'github-slow.log' for details  === Watching for updated files. Use ctrl/C to stop ... ^CLatexmk: User typed ctrl/C or ctrl/break.  I'll finish. Collected error summary (may duplicate other messages):   xelatex: Command for 'xelatex' gave return code 1       Refer to 'github-slow.log' for details Latexmk: Use the -f option to force complete processing,  unless error was exceeding maximum runs, or warnings treated as errors.  what should I do to make it work? I have already added picture path in the main file dolphin-book-2020.tex like this(all the picture store in the folder and no picture store in sub folder): \graphicspath{{./Pictures/}}  and this is the file structure:  I have tried define picture path in dolphin-book-2020.tex like this: \graphicspath{{../../../Pictures/}{../../Pictures/}{../Pictures/}{./Pictures/}}   this is the folder nested structure:  I also tried to write all possible path of picture: \graphicspath{     {Pictures/}     {../../../Pictures/}     {../../Pictures/}     {image/}     {/Users/dolphin/Documents/GitHub/dolphin-book-2020/Pictures} }  still could not found file.


Do we ever see a human in Star Wars wearing glasses or other visible, non-mask vision-correcting devices?  I know that Vader and the StormTroopers see augmented vision displays inside their helmets, but that's not what I mean.


Are Stack Exchange users aiming to wide with close-as-duplicate?

I notice that many times when I ask a question, users are very keen to try and close it as a duplicate. This happens when my question is not a duplicate, it is questions similar to another but from a different angle, or a more specific or more general question, or a new idea or insight into a topic previously covered but not in a way that would directly answer that topic. Often my question will be linked to the nearest matching topic as a 'duplicate', without any real thought or sensitivity being applied.  Duplicate questions are obviously undesirable for the overall quality of the knowledge base created, I understand that.  Compared with a newsgroup, I find this anti-engagement behaviour is not very generous and at times very aggressive and you have to fight back just to try and get people to engage with the question rather than putting down the meta-question.  Why are they so keen to close you down? Do they get a bounty or something?


How do I decrypt files on SD card that I encrypted on a different device?

I encrypted my phone and SD card on my Note 2. I broke that phone, but recovered the SD card. How do I decrypt the SD card to get all files out (I do have password for it) with the new phone?


Ubuntu 13.10 recognizes wifi networks but won't connect (BCM4313)

So, I partitioned my hard driver and installed Windows 7 and Ubuntu 13.10 in partition C:.  First I installed Windows and got the wifi device working by installing the proper drivers for Broadcom BCM4313.  Then, after installing and while loged in Ubuntu 13.10, it recognizes my network and asks for the password, but won't connect.   Also I tried this  and despite the fact that I don't know what it means, Terminal didn't recognize the second command line as well.   Please, send help. And sorry for my bad english.


Same Ed25519 key for signing and encryption?

I know this has been asked before, but it's still unclear whether this is an OK practice. The advice seems to never do this unless you have to, but I can think of some examples where this could be useful. For example, a program that supports encryption and signing like GPG could support generating Ed25519 keys and then use them for encryption (by converting them to Curve25519 keys) and signing (leaving them as Ed25519 keys). This would mean that only Ed25519 keys would have to be generated, preferable from the user input perspective since handling multiple key types could get confusing.


Autocomplete polygon or autocomplete freehand in QGIS

Is there any similar function or plugins for QGIS as in ARCMAP for polygons called autocomplete polygon or autocomplete freehand. I am digitising polygons on a DEM as geomorphological research.  I need to digitise polygons next to each other with 0 overlap.   I'm a searching for this function in QGIS 3.4.9-Madeira on a Mac.


It's currently impossible to read long lines of code in the Android app, as swiping will move from question to answer


Why don't electromagnetic waves require a medium?

As I understand it, electromagnetic waves have two components which are the result of each other, i.e., when a moving electric charge creates a changing magnetic field at point X then a changing electric field is created at point Y and this repeating process is what creates EM waves, so therefore, it requires no medium. Is my understanding correct?  One thing that I'm surprised to know is that light is also called an electromagnetic wave.  Does this include light of any kind, for example: light from a bulb, a tube, and also from the Sun? How do they contain electric and magnetic fields?


Let $f:\mathbb R \rightarrow \mathbb R$ be a non-constant, thrice  differentiable function such that $f(1+1/n)=1$ for all $n \in \mathbb Z$.  then what is the value of $f^{\prime \prime}(1)$?   Answer is 0


I have a rather basic, maybe even dumb, question. I was wondering why speed is defined as it is:  $s = d/t$  Of course, what the equation means is not too difficult to understand. However, there are many ways that d and t could be related, for instance:  $s = d + t$  I am not sure who the first person to define speed was, but I was wondering how they made the decision to define speed as distance divided by time.


How to select a font color to go on a very busy background?

I'm a developer and don't have much design experience. I'm creating a landing page for a project I'm working on. I want to use the below image as the background for my landing page.   As you can see the text on it is not visible. I have tried using a few colors and none of them look good on that image because some part of the text gets joined with the image.   Can you please advise me on what color I should use?    Thank you


Problem with spacing in syntactic trees using tikz

I am trying to get a tree like this using the tikz package  and the syntax for this, according to a manual, is \begin{tikzpicture}[mytree] \node (top) {DP} child {node {D\\the}} child {node {NP} child {node {Adj\\brown}} child {node {NP\\dog}}}; \end{tikzpicture}  However, just copying and pasting this code gives me  It seems that \\ is not recognized. Am I missing something here?


why neutral does not shock. how can a neutral be neutral in ac current?

When I probe my city mains with one probe in the live and one in earth (which should be 0 volt) it shows a voltage of around 250v. But when I probe the neutral and the earth it shows no voltage. I know that current runs in one direction for 50 times in a second. So the neutral should act like live for 50 times in a second. Then neutral should show some voltage with the earth, which it doesn't. If you touch the neutral wire you won't get shocked but if you touch the live the wire you get shocked why and how?


How does order-preserving encryption work?

Order-preserving encryption (OPE) is, apparently, a method of encrypting data so that it's possible to make efficient inequality comparisons on the encrypted items without decrypting them.  I've been coming across this term in various places (including ) lately, but I have no idea how such encryption schemes are supposed to work.  Any obvious methods I can think of to allow such comparisons on encrypted data would result in catastrophic security failure.  Certainly, I assume that OPE must involve some kind of security tradeoff compared to traditional encryption, but given that it seems to be actively  and , it seems that it must be possible to implement in a way that retains at least some level of useful security.  I just don't see how.  Given that  didn't turn up any convenient Wikipedia articles or other popular summaries of OPE, I figured I'd try asking for one here before diving into the academic literature.  (At worst, I may try to answer my own question later, if nobody else beats me to it.)  So, to summarize, my question is: How does order-preserving encryption work, and what security properties does it provide?


Can I drive in the USA with a French drivers license?

Question is pretty much in the title. I have a French drivers' license, and will be driving in the USA in a couple weeks. Is it accepted as-is, or must I get a translation? What preparation do I need to do?


Should I use "make" or "makes" in this sentence?

In this sentence should I use make or makes?  Massive scale, along with rapid growth make/makes it different.


$ sort -t $'\t' -k 1rn,1 -k 2,2rn -k 3f,4 listaprezzi  2050        900           bananas     5 1905        700           grapes      17 250         4000          oranges     10 230         9200          figs        4 220         5000          lemons      10 200         8000          pears       8   I want to sort 1st column of listaprezzi numerically in reverse (option rn), 2nd also rn, and third alphabetically (f). What is the correct command?  I've tried many ways but having no success.


$\cos(\arcsin(x)) = \sqrt{1 - x^2}$. How?

How does that bit work?  How is  $$\cos(\arcsin(x)) = \sin(\arccos(x)) = \sqrt{1 - x^2}$$


I have a doubt about this sentence:  "If your product arrives broken our Returns Department will organise a replacement as long as you contact them within 24 hours of having received the parcel."  Can the "Returns Department" be referred to as "them" even though it is singular? Using "it" just doesn't sound right to me.


Combining Tikz concepts/librarys to draw a complex picture with relative alignment/distances

I think all of the problems has been asked by me or others in the past. But my over all problem is that I am not able to combine all this solutions to the real picture I want to draw. Normally it is nice to seperate a complex problem into more simple ones and ask. But here I try to ask the complex question because I experienced that the solutions influence (in my case negativ) each other.    Description of the needs/prolems:   The left nodes (Phase) should be rotaed. I would prefere a solution with \rotatebox (node contents={\rotatebox{90}{#1}}}). The nodes (better would be rows) on the right are centered horizontal. Logical the picture have four rows and the nodes on the left and right need to display that. This means that one node (e.g. right of B) is centered vertical against its left node. Please see that PhaseC belongs to C1, C2 and long C3, so that the vertical alignment should represent that. () Connecting the nodes with arrow shouldn't be so hard I think. All have to be done relative. That means no cm, mm, pt or something like that. The number of nodes is not fixed. It could be that in row one are less nodes then in row four.   Some solutions:  \documentclass[tikz]{standalone} \usepackage{xltxtra} \usepackage{polyglossia} \setdefaultlanguage[spelling=new]{german} \usepackage{tikz} \usetikzlibrary{scopes,matrix,positioning,chains}  \begin{document} \begin{tikzpicture}     [         items/.style = {             draw,             align=center},         phase/.style = {             items,             fill=red!20,             node contents={\rotatebox{90}{#1}}}     ]     {[         start chain=P going below     ]         \node [on chain,phase=PhaseA];         {[             start branch=A going right,             every on chain/.append style=items,             every node/.style=on chain         ]             \node {One};             \node {Two};             \node {Three};             \node {Four};         }         \node [on chain,phase=PhaseB];         \node [on chain,phase=PhaseC];         \node [on chain,phase=PhaseD];         {[             start branch=D going right,             every on chain/.append style=items,             every node/.style=on chain         ]             \node {D1};             \node {D2};         }     }      % B     \node [right=of P-2,items] {right of B};      % C     \matrix (C) [         matrix of nodes,         row sep=5pt, %2\textheight doesn't work here, maybe a \nodeheight exists?         every node/.append style=items,         right=of P-3]     {         C1 \\         C2 \\         long C3\\     }; \end{tikzpicture} \end{document}   Produce this    Number 2 and 5 are not fullfilled. And I think number 6 would make problems in the future.


I'm trying to build an entropy function from the scratch as asked by my leader. I have a dataset Ttrain, with many variables, sex being one. I'm having to extract the categories(male and female), and then calculate the probabilities and entropy subsequently, in a loop using the following code:  def entropy3(c):     import math     u=c.unique()     a=[]     b=[]     z=[]     for i in range(len(u)):         a=Ttrain[(c==u[i]) & (Ttrain.survived==1)].survived.count()         b=Ttrain[(c==u[i]) & (Ttrain.survived==0)].survived.count()         p=a/(a+b)         q=b/(a+b)         z=-(p)*math.log(p,2)-(q)*math.log(q,2)         return z   Now, when I run print(entropy3(Ttrain.sex)), I get 0.85, which is the entropy for the category female. Which means the loop does not iterate to the other category. Will be grateful if somebody could point out where am I going wrong. I'm very new to programming so please excuse any conceptual errors.


Do undefined elements in an array have an impact in JS?

I couldn't find a question that specifically targets the issue I'm having hence this question is being asked.  I have an array that holds 5 numbers:  var numbers = [0,1,2,3,4];   Once a number is clicked on the frontend (website), the number is removed from the array using the below code:  delete numbers[1];   This removes the correct number but leaves a space where the number was (the space is undefined). I believe this is causing an issue. After a number is removed from the array, I use another function to randomly pick any of the remaining numbers in the array however it sometimes fails. After much thought, I've realized it may be because there are empty spaces in the array after a number is removed and as a result, the code fails to work due to the undefined element.  Is my analogy correct or am I mistaken?  (I have also attempted to use the splice method to remove the number however that then causes an issue with the length of my array because if I later want to remove another number, it removes the wrong one due to the numbers moving around etc).


Seeking detailed description of qgs file structure?

Is there a detailed description on the .qgs file structure somewhere?   I checked at  and got     The requested URL /qgis.dtd was not found on this server.   and at  which wasn't very detailed.


Creating account didn't log me in / didn't create an account

I've created account on Server Fault with the "Join this community" button. It seems to be created as I see my picture and a starting 101 reputation on top. But when I tried to upvote I got a message I need to login and where I clicked on a different question it showed me I'm not logged in.    I think it didn't even create my account since later I clicked the signup button again, it asked me with which Google account I want to create it (I've two associated with my Chrome browser).


How do you log out of Stack Overflow? There isn't any logout button.


Is there a "Places" menu for Ubuntu Unity?

I'd like to know if it's possible to put a "Places" tab in the upper menu of Ubuntu, such as CentOS, Debian, etc.  Thanks


Irrationality of $r\sqrt{5}$ for rational number $r$?

As $5$ is a prime number, thus $\sqrt{5}$ is an irrational number.  Now I am thinking about how to prove -  If $r$ is a rational number, then how do we prove $r\sqrt{5}$ is an irrational number?  I was thinking that since $r$ is a rational number, then $r$ can be expressed as the fraction in simplified form that is $r = \frac{a}{b}$ such that $a,b \in \Bbb{Z}$ and $gcd(a,b)=1$. So $r\sqrt{5} = \frac{a\sqrt{5}}{b}$, but How can this guarantee us the irrationality of $r\sqrt{5}$?   ALso let $c =r\sqrt{5}$, then $c^2 = 5r^2$, if we could prove it is a prime number, then its square-root $c$ must be irrational and ths proved but unfortunately we donot have $c^2$ prime as it has more than one factors like $r$ , $5$


Best way of showing data with many columns?

We have a website where we showcase statistics of various reports of students. There is one report for which there are many columns i.e. 13 in total and every column is important to show. However it is not fitting different screens with different height and width. An example of the same report I am attaching below, please open the image in another tab for better viewing purpose:    Tabular way definitely doesn't look good and it is hard to see the report unless one zooms in. Is there a better UX way to showcase all these data at one place which will also look good in different screen sizes?


How To have different login screen wallpaper on ubuntu 16.04

I would like to know if there is any way to change the login screen wallpaper, without changing the desktop wallpaper. In other words, how to independently change the login screen wallpaper. Thanks.


How do I pass a string into subprocess.Popen (using the stdin argument)?

If I do the following:  import subprocess from cStringIO import StringIO subprocess.Popen(['grep','f'],stdout=subprocess.PIPE,stdin=StringIO('one\ntwo\nthree\nfour\nfive\nsix\n')).communicate()[0]   I get:  Traceback (most recent call last):   File "<stdin>", line 1, in ?   File "/build/toolchain/mac32/python-2.4.3/lib/python2.4/subprocess.py", line 533, in __init__     (p2cread, p2cwrite,   File "/build/toolchain/mac32/python-2.4.3/lib/python2.4/subprocess.py", line 830, in _get_handles     p2cread = stdin.fileno() AttributeError: 'cStringIO.StringI' object has no attribute 'fileno'   Apparently a cStringIO.StringIO object doesn't quack close enough to a file duck to suit subprocess.Popen.  How do I work around this?


What happened to this user's rep, badges, and name?

This user is only displaying 56 rep.   But surely (s)he has much more than that.        The user has also never given out any bounties.  Also, badges are missing:


After Initializing values in an int array, updates to the array will not be present in the Serial

I've been looking into Serializing Objects so that I can send Objects through networking easily and quickly. There's one big Issue in this though. After I initialize a value in my array, the serialized Object for that array will always stay as the initialized number. I'm not even sure if this is the case as I'm pretty sure ints have a default value of 0. So wouldn't it stay as 0 instead of what I change it to?  public static void main(String[] args) throws FileNotFoundException, IOException, ClassNotFoundException {     FileOutputStream ostr = new FileOutputStream(new File("ObjectFile.yeh"));     FileInputStream istr = new FileInputStream(new File("ObjectFile.yeh"));     ObjectOutputStream out= new ObjectOutputStream(ostr);     int[] hi = new int[5];     hi[0]=3;     out.writeUTF("This is an Array");     out.writeObject(hi);     hi[0]=5;     out.writeObject(hi);     out.writeUTF("Array Over");     out.close();     ObjectInputStream in = new ObjectInputStream(istr);     System.out.println(in.readUTF());     int[] h = (int[]) in.readObject();     System.out.println(h[0]);     int[] j = (int[]) in.readObject();     System.out.println(j[0]);     System.out.println(in.readUTF());     in.close(); }   When I run the following code it prints  This is an Array 3 3 Array Over   How should I solve this problem?  Update:  After further experimentation I found that after an Object is Serialized once, it's serial doesn't seem to change. As shown here I edit the String array and it's contents don't change after being sent through the Object Stream      public static void main(String[] args) throws FileNotFoundException, IOException, ClassNotFoundException {     FileOutputStream ostr = new FileOutputStream(new File("ObjectFile.yeh"));     FileInputStream istr = new FileInputStream(new File("ObjectFile.yeh"));     ObjectOutputStream out= new ObjectOutputStream(ostr);     String[] hi = new String[5];     hi[0]="Hi";     out.writeUTF("This is an Array");     out.writeObject(hi);     hi[0]="Hello";     hi[1]="Hoopla";     out.writeObject(hi);     out.writeUTF("Array Over");     out.close();     ObjectInputStream in = new ObjectInputStream(istr);     System.out.println(in.readUTF());     String[] h = (String[]) in.readObject();     System.out.println(h[0]+" "+h[1]);     String[] j = (String[]) in.readObject();     System.out.println(j[0]+" "+j[1]);     System.out.println(in.readUTF());     in.close(); }   And this prints  This is an Array Hi null Hi null Array Over


How can I recover from deleting the /usr/share/themes directory?

I deleted the  /usr/share/themes directory, how can I recover it? Is there any way to check if there is any missing file/directory in /Computer directory? This was a bad try to change GIMP and Inkscape themes ("gtkrc" file). I changed all "gtkrc" files that I found in the system (stupid me...) and now my windows and apps are distorted =(


Sage question:   Define the polynomial ring $\Bbb Q[c][x]$.Find the $c$ values where $x^2 + x + c + 1$ has a double root.   Sage code I have used to answer the first part "Define the polynomial ring $\Bbb Q[c][x]$".  K.<c>=QQ['c']     R.<x>=K[]  f=x^2+x+c+1     f   How do I find the code for the $c$ values where $x^2 + x + c + 1$ has a double root? Also, can you give some examples so that I can construct some programming code in sage?  P.S: This is a sage question. I know that for $c=-\frac 34$ this will be a square but I want the command that I can run in Sage to get this result in Sage. I asked it  but got the downvotes and I don't know why! If someone will downvote me here then please explain to me what do I have to include. I have given a code that I used to answer the first part "Define the polynomial ring $\Bbb Q[c][x]$", so this is my try.


Get starttime of a process in windows / linux?

I have the ID (pid) of this process. Now i want to find out when the process with this id has started.  Note1: The process is not a java thread. Note2: JNA Solutions would also be welcome  From my java context i want to get this information. How can it be done?  UPDATE: see Note2.


Link markdown in chat fails if the link contains a url

The chat markdown parser fails to properly create a link when the link itself contains multiple "http://". Example  Markdown:  View older versions of [StackOverflow](https://web.archive.org/web/*/https://stackoverflow.com/)   Expected result:     View older versions of         View older versions of " rel="nofollow">StackOverflow   This bug only appears in the timeline, and when looking at the   Outside the visual oddities of this bug, this bug also generates invalid html as a side effect of it.


Python how to check if a string represent a float?

I'm developing a small menu in python where at some point the user is being asked for a float number.  The user could pass:  1.23 1 //it's valid... 23.34e-10 //scientific notation   The user is asked for inserting a float value, if the value is not a float (for example the user could write a generic string...) the program doesn't have to crash but just to re-iterate until the user pass a valid float value. So actually the structure is  var = ""; while(var is not a float):    var = raw_input("");   Does exists a fast way to do that? or should use somehow a regular expression?


Finding center of point layer in ArcGIS Pro

I have a point layer that has Lat/long coordinates. How to find the center of a given point layer. For more understanding, I attached a drawing. How is it possible to do this?  I tried to use the tools "Mean center", "FeatureToPoint", but they give false results and find exactly not the center, can there be other tools or can you somehow find it using python, I have an attribute table that contains only the lat/long coordinates (-180 :180) (-90: 90). Maybe you can use some formulas?


Using permutation or otherwise, prove that $\frac{(n^2)!}{(n!)^n}$ is an integer,where $n$ is a positive integer.

Using permutation or otherwise, prove that $\displaystyle \frac{(n^2)!}{(n!)^n}$ is an integer,where $n$ is a positive integer.  I have no idea how to prove this..!!I am not able to even start this Can u give some hints or the solution.!cheers.!!


I'd like my web app to log into files with this path: webapp/logs/  I can set the absolute path in the log4j.properties file, but the production environment's directory structure will be different.  Is there any way I could do it?   Here is how I do:  log4j.appender.f=org.apache.log4j.RollingFileAppender log4j.appender.f.layout=org.apache.log4j.PatternLayout log4j.appender.f.layout.ConversionPattern=%d{ABSOLUTE} %5p %c{1}:%L - %m%n log4j.appender.f.File=log.out log4j.appender.f.MaxFileSize=100KB   This is printing logs into a file named log.log in my eclipse directory (c://eclipse). I'm using Tomcat 6.


I want to figure out how many Topologies are in the set X

I have the set $$X = \{1, 2, 3\}$$  and I want to figure out how many different topologies I can get from the set $X$  so what I have done is assumed that the empty set and the whole set are in $T$  and that any union of elements will satisfy, $X \in T$, as well as any intersection of elements.  therefore all possibilities will be considered topologies.  so after I assume this, my answer I acheived was a simple $3!*3! + \emptyset = 37$.  Leading me to the fact that I believe there are 37 different topologies possibel from this set $X$.  Any help, disccrestions, criticims, or corrections would be great, i only have 75% confidence in this result.   thanks in advance


Fantasy book where (some) magicians can transform into dragons, based on genetics

I thought the story was written by Trudi Canavan, but apparently I was wrong.    It was a book or maybe a series of book. I think I’ve read it 5-15 years ago in Germany. Not sure when it might have been published. Not sure whether I read it in English or in German. The story was about a girl (or boy?) whose parents came from different sides of the mountains, which was a forbidden union according to the powers that be (see below). The character travels the (forbidden) path to the castle in the mountains, where magicians allegedly live, seeking their father. I think that the castle was actually a training academy for magicians. It turns out that some of the magicians can transform into dragons or are actually dragons, depending on some combinations of recessive alleles in their genome. The exact genetic circumstances are only revealed towards the end of the story. This is what fascinated me about the story: that mystical “some magicians are dragon” theme actually had a (more or less) scientific basis the whole time, but the knowledge of that had been completely lost to the characters at the time the story took place. The “dragon-magicians” ruling the land divided the human population into two groups with different genes and forbid any interaction between these groups, such that new dragon-magicians could not be born. (I think this was revealed fairly late in the story). At some point the main character is also revealed to be a dragon-magician, I think (due to their special heritage of two different peoples, see above). Transforming into a dragon for the first time in your life was a risky process, as there was a danger of losing your human consciousness and essentially becoming a (highly dangerous and magical) animal driven by instincts. Thus the first transformation was usually performed in some kind of specialized magical prison cell for dragons. However, the “dragon-magician” population has declined for some reason and there are very few left. One of the remaining few dragons has gone mad, but regains their sanity due to something involving music. I believe it had to do with the main character playing an old/forgotten melody on the flute. There was also a time-travel episode into a time when the dragon society was prospering. During that time, the mad dragon wasn’t yet mad but already loved/played music.


adding linux client to windows active directory domain

We have Ubuntu 14.04 LTS as client in virtual manager. I have to join it in a network with a system running Windows server 2008.   How can I join a Windows Active Directory?


How to handle duplicate question, where it's on different Stack Exchange sites?

I came across  on Super User and noticed there's  (with what I believe is also the correct answer) on Stack Overflow.  Is there a way to mark or link nicely the question in Super User to the one on Stack Overflow?  I guess that actually they both should be on the same site, so maybe one of them should be migrated?


let $n \gt 1$ be an integer, and consider $n$ people; $P_1, P_2,..., P_n$ let $A_n$ be the number of ways these $n$ people can be divided into groups, such that each group have either one or two people  determine $A_1, A_2, A_3$  So I have  $A_1 = 1$ way $A_2 = 4$ way $A_3 = 12$ way  But I am not sure if this is right... Can anyone confirm?  edit:  My way of getting this is  $A_1 = 1 $ because {P1} only has 1 way to sort  $A_2 = 4$ because {P1,P2} = {P1,P2},{P2,P1},{P1P2},{P2P1}  etc.


How to move S3 bucket to different location

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


Circles importing as crossed boxes into Adobe Illustrator

I am reading into Illustrator a PDF output from R (grid graphics I believe) in which the circles show as boxes with crosses inside them.  These pictures illustrate:  In OSX Preview:    In Illustrator:    Any idea why this is happening, and how to work around it?  The following Illustrator message pops up when opening the file, which may be significant.


Shutdown dialog only appears after about 30 seconds in GNOME while using Caffeine extension

When I want to shutdown my PC I click the top right corner and then press the power button after which a dialog pops up with the options: power off, restart, cancel.   Normally this pop up shows up right away. But since a week or so it takes about 30 seconds. During that time I can move my mouse but I can't open applications or do anything else.  When I cancel and try it again, it does open right away.   I didn't change settings or install weird stuff, only some updates of my icon theme. (I apparently had installed the ).  What could be the cause? And how can I diagnose this issue and see what it taking so long?


NullPointer exception when using ImageView.SetImage()

I am slowly teaching myself how to code and have come across something that has stumped me  I am getting a nullpointer exception when using setImage to change an image around.  I am aware this is possibly down to the imageview not being initialized when I am making the change, but I am not sure if that is the case.  I currently have this piece of code which is dealing with my scene switches  public void initSceneSwitch(String scr) {         try {             Parent root = FXMLLoader.load(getClass().getResource("/main/resources/fxml/" + scr + ".fxml"));              sceneDisplayed = new Scene(root);             sceneDisplayed.getStylesheets().add(getClass().getResource("/main/resources/css/GameTheme.css").toExternalForm());                       primaryStage.setScene(sceneDisplayed);             primaryStage.show();             sceneChange(scr);          } catch (IOException e) {             e.printStackTrace();         }     }   This will deal with image switches, in the long term, with the possibility of more variables which determine which image to display  public void sceneChange(String newScene) {         switch (newScene) {             case "UILoadingScreen":                  break;             case "UIMainScreen":                 UIMainScreen uiMS = new UIMainScreen();                  Image img= new Image("/main/resources/icons/test.png");                 uiMS.getImageView().setImage(img);                 uiMS.getImageViewAnchorPane().getChildren().add(uiMS.getImageView());                 break;                           default:                  break;         }      }   The nullpointer exception occurs on uiMS.getImageView().setImage(img);.  This is where I am confused, from thinking about how my code is running "along a line", I would think that both my controller and fxml file would have been loaded and initialized before I am making the method call to change images around.  Can anyone point me in the general direction of what I need to be looking at, because my brain hurts


How to realize curvate bracket after which two formulas follow in vertical order

I would like to write a equation which defines quantity f(X) to be a if X>0 and b else. I would like to do so writing f(X)= followed by a curvate bracket and then a if x>0 and b else aligned vertically.   By curvate bracket I mean a \bigg version of {.


get the value from force:RecordData on Init handler

Is there a way we can get the value from force:RecordData on init ? I am getting the onclick event of a button.  <aura:handler name="init" value="{!this}" action="{!c.doInit}"/>     <aura:attribute name="recordId" type="String"/>      <aura:attribute name="showButton" type="Boolean" default="false"/>     <aura:attribute name="Opportunity" type="Object"/>        <aura:attribute name="parentOpp" type="Object"/>     <aura:attribute name="oppLoadError" type="String"/>     <force:recordData aura:id="oppRecordLoader"                       recordId="{!v.recordId}"                       fields="Id,                               Name,                               AccountId,                               Cohort_Sem__r.End_date__c,                               LeadSource,                               Staff_Referral_Detail__c,                               lead_source_detail__c"                       targetRecord="{!v.Opportunity}"                       targetFields="{!v.parentOpp}"                       targetError="{!v.oppLoadError}"                       />   JS:  doInit: function(component, event, helper) {                     var opp = component.get("v.parentOpp");                   console.log('Name Value: '+ opp.Name);     }   Error:     Action failed: c:createIWSRecord$controller$doInit [Cannot read   property 'Name' of null] quickActionHandlerHelper.js failed to create   component - forceChatter:lightningComponent


How to efficiently compute $\,25^{37}\pmod{55}$?

Most efficient way to do this question?  $25^{37}\cong (mod 55)$  Attempt:  $25^2 \cong 20 (mod55)$  Then I don't know the best way to continue... I know how to brute force it but I'm just curious what the best way is?


Gravity in 2d space and inverse linear law

In our three-dimensional universe, gravity obeys the inverse square law. In a four-dimensional universe, gravity would be expected to obey the inverse cube law et cetera.  In a two-dimensional universe, one would similarly expect gravity to obey an inverse linear law. I've seen it claimed that this is not actually true, when you work it out according to general relativity there would actually be no gravity at all in such a universe. Is this true? If so, is there a layman's explanation of why? Is it related to the fact that gravitational potential wells would be infinitely deep?  Would electrostatic forces follow the same law as gravity?  If there existed infinitely long strings in our universe, would they have the same gravitational effect as point particles in a 2d universe?


Every separable metric space has a countable base

A collection $\{V_{\alpha}\}$ of open subsets of $X$ is said to be a base for $X$ if the following is true: For every $x\in X$ and every open set $G\subset X$ such that $x\in G$, we have $x \in V_\alpha \subset G$ for some $\alpha$. In other words, every open set in $X$ is the union of а subcollection of $\{V_{\alpha}\}$.   Prove that every separable metric space has a countable base.   Proof: Let $(X,d)$ be a metric space and $D=\{d_j\}_{j\in \mathbb{N}}$ be the countable and dense subset of $X$. Let $U$ is an open set in $X$ then for $x\in U$ $\exists \varepsilon_x>0$ such that $N_{\varepsilon_x}(x)\subset U$. Then $\exists d_j\in D$ such that $d(x, d_j)<{\varepsilon_x}/{4}$ $\Rightarrow$ $d_j\in N_{{\varepsilon_x}/{4}}(x)\subset U$.   It's easy to check that $N_{{\varepsilon_x}/{4}}(d_j)\subset N_{{\varepsilon_x}}(x)$. Indeed, if $z\in N_{{\varepsilon_x}/{4}}(d_j)$ then $d(z,d_j)<\varepsilon_x/4$ and since $d(x, d_j)<{\varepsilon_x}/{4}$ then by triangle inequality: $$d(z,x)\leqslant d(z,d_j)+d(x, d_j)<{\varepsilon_x}/{4}+{\varepsilon_x}/{4}<{\varepsilon_x}.$$  Hence $z\in N_{{\varepsilon_x}}(x)$ and inclusion $N_{{\varepsilon_x}/{4}}(d_j)\subset N_{{\varepsilon_x}}(x)$ holds.  By the way $N_{r}(d_j)\subset N_{{\varepsilon_x}}(x)\subset U$ for $r\in \mathbb{Q}$ and $r<{\varepsilon_x}/{4}$. Thus for every $x\in U$ we associate an open ball with center at some point $d_j$ of $D$ and rational radius $r$ such that $x\in N_{r}(d_j)\subset N_{{\varepsilon_x}}(x)\subset U$.  Thus $$U=\bigcup\limits_{d_j\in U} N_{r_j}(d_j).$$ This set equality can be verified very easy. Inclusion $\subseteq$ I described in above paragraph. Converse inclusion is not difficult: if $z\in \bigcup\limits_{d_j\in U} N_{r_j}(d_j)$ then $z\in N_{r_j}(d_j)$ for some $d_j\in U$. But these balls  arranged so that $N_{r_j}(d_j)\subset U$ then $z\in U$.  Hence collection of balls $\{N_{r}(d): r\in \mathbb{Q}, d\in D\}$ is a countable base.  Is my proof correct? Can anyone check it please? Sorry if this topic is repeated but I would like to know is my proof correct.


Is there a way to edit a question without bumping it to the front page?

Given that the Stack Overflow trilogy is to be a resource for googlers, I usually try to go back over my questions/answers and improve them in whatever way that I can. However, I feel this may be inappropriate if there is already an accepted answer because edits bump the (already answered) question to the front page I am wondering if I should refrain from this habit.  Is there any way that I can edit my posts without bumping them? If there isn't, I really think there should be a way to do this (hence the 'feature-request' tag).


Change periods on x-axis in time series?

I want my graph to only show the following time periods 1986, 1992, 1998, 2004, 2010, 2016, instead of the ones shown in the graph. Someone knows a solution? Thanks!  The data in .dat-file is in the format:  date value 1986-03-01 0.11 1986-06-01 0.45 ... 2016-03-01 0.78   Latex code:  \usepackage{pgfplots} \usepackage{amsthm, amsfonts, amsmath, amssymb, mathrsfs, enumerate,graphicx} \usepackage{subcaption} \usepgfplotslibrary{dateplot} \usepackage{filecontents} \pgfplotsset{height=5cm,width=8cm,compat=newest} \usepgfplotslibrary{dateplot}  \begin{figure}[H] \begin{subfigure}{.5\linewidth}\centering \begin{tikzpicture} \begin{axis}[legend style={at={(0.5,-0.35)},anchor=north},   date coordinates in=x,   x tick label style={/pgf/number format/1000 sep=},   xticklabel={\year},   ylabel=,   xlabel=Time,   enlargelimits=0.10,   legend columns=1, ] \addplot[no markers, color=black]   table [x=date, y index=1] {msardhp.dat}; \legend{} \end{axis} \end{tikzpicture} \end{subfigure}% \caption{} \end{figure}


Fire and forget method in C#  I refered different issues for 'Fire and Forget in C#'  i.e.  . . and few several,  but i have an another issue with the same.i wrote following code  static void Main(string[] args)     {         for (int i = 0; i < 5; i++)         {             //fireAway(i);             Task.Factory.StartNew(() => fireAway(i));         }         Console.WriteLine("Main Finished");         Console.Read();     }  public static void fireAway(int i)     {         System.Threading.Thread.Sleep(5000);         Console.WriteLine("FireAway" + i);     }   where i am expecting output like  Main Finished  FireAway0  FireAway1  FireAway2  FireAway3  FireAway4  but output is  Main Finished  FireAway5  FireAway5  FireAway5  FireAway5  FireAway5  very honestly i am new to threading concept, i need help. How can i meet with expected output..?


Quaternions: Why is the angle $\frac{\theta}{2}$?

The equation for creating a quaternion from an axis-angle representation is $$x'= x \sin\left(\frac \theta 2\right)$$ $$y' = y \sin\left(\frac \theta 2\right)$$ $$z' = z \sin\left(\frac \theta 2\right)$$ $$w' = \cos\left(\frac \theta 2\right)$$ But why $\frac \theta 2$? Why not just $\theta$?


How to track traffic flows to each IP on home network?

first-timer here.  I will try to explain this as clearly as possible, as I'm not an engineer or anything.   My Router: ASUS RT-AC87U - DD-WRT firmware installed, SNMP enabled.  Topology:  I have two switches off the router. behind switch 1: 2 W8 Desktops  behind switch 2: TV, Roku, Xbox.   On wireless: 2 Rokus, 4 iPhones, W8 laptop, chromebook, 2 Kindles  What I'm looking to do: I would like to be able to see traffic data to each individual IP I choose, particularly the rate at which it's flowing. Mostly because there are some devices sucking large amounts of data and I want to understand what they are, where they are receiving the data from and at what rate. And partly because I'm a geek and granular data is just something I prefer.  I installed PRTG and put an SNMP trap on my router, but the data isn't very useful to me. It put probes on there like eth0, vlan1, vlan2, br0 etc.  I tested with my machine when no other device in the house was streaming. What I saw was about 30K kbps, on eth0 and about half of that on vlan1. I'm sure there's an explanation for this that I don't understand, but at the end of the day - I stil can't get what I need when two different traps are displaying 2 different speeds for only 1 device. Plus the wireless devices are mostly what I'm interested in.  Is there a way I can configure the traps so it's 1:1? Will it require scripting? Do I need another solution besides PRTG? Is any of this even possible on a home router?   I will thank you all in advance for any insight/solutions you can provide, and I'll apologize as well if this is a redundant question that I couldn't find the thread to.  Thanks.


"Add comment" appearing for my own deleted answers

A few moments ago I deleted one of my own answers here:   I am logged in to the site, and am a 10K+ user, yet within my deleted answer I see:     add comment (requires 50 reputation)   Clicking this does nothing.  I do not recall the ability to add a comment to a deleted answer.  Is this a bug?


I'm a level 173 Nord. I checked each city and town yet I haven't been able to fight the Ebony Warrior. I have all the DLC that exist for for this game yet no matter where I go, I can't find him.  I've even checked Raven Rock, Tel Mithryn, and Skaal village but there is no sign of him. I've fought quite a lot of legendary dragons and I know that they appear when the Ebony Warrior decides to challenge you.  If you could me that would be great cause I've been itching for a good fight in an long time. I'm on Xbox 360.  Plus when I go on random rampages as a vampire lord I never see the ebony warrior anywhere just a ton of guards and a few townsfolk. (I go on rampages cause I can't find him)


I am writing a research paper. There are a few known results for which I want to add citation in my paper. However, all those results have already been cited in a well-reputed book. Can I cite the book directly? For example: Result 1 [book citation], Result 2 [book citation],...,etc. or should I add the proper citation of each of the results? like this: Result 1 [this journal], Result 2 [that journal],...,etc. Note that the results in the book are not explicitly explained in any section. They are just briefly stated in the chapter notes. And, if I cite the book directly, I am feeling like I am not adding to the citation count of the original authors who deserve it.


grub-install: this GPT partition label contains no BIOS Boot Partition

I have an installation of Ubuntu 15.04 that has been working fine for some weeks. Today, my box locked up to the point I had to power it off in order to clear the error. When I did so, it stopped booting.  When booting, it comes up and displays a cursor and nothing else.  I tried following the advice here:  but when I do so, it gives me this error:  Installing for i386-pc  platform. grub-install: warning: this GPT partition label contains no BIOS Boot Partition; embedding won't be possible. grub-install: warning: Embedding is not possible. GRUB can only be installed in this setup by using blocklists. However, blocklists are UNRELIABLE and their use is discouraged.. grub-install: error: will not proceed with blocklists.   Any advice as to what to try next?


A roulette wheel has $21$ red numbers, $21$ black numbers, and $4$ zeros. A player places $20$ dollar bets on the red numbers. If the roulette spins a red number, the player get his $20$ dollars back, and wins another $20$ dollars. If the roulette does not spin a red number, the player loses his bet. The player sits down with $40$ dollars, and keeps on playing until he has no more money. How many spins can he expect to be able to play until he has no more money?


get first X characters from the cat command?

I have a text file I'm outputting to a variable in my shell script.  I only need the first 50 characters however.  I've tried using cat ${filename} cut -c1-50 but I'm getting far more than the first 50 characters?  That may be due to cut looking for lines (not 100% sure), while this text file could be one long string-- it really depends.    Is there a utility out there I can pipe into to get the first X characters from a cat command?


How to prepare a disk on an EFI based PC for Ubuntu?

My computer has UEFI based BIOS and I want to start over from scratch.  The PC came with Windows installed - I later installed Ubuntu alongside.  I want to completely re-build my whole disk and install only Ubuntu on it.    So it is not about how to install Ubuntu, it is about how to prepare a disk.  What is the most professional way and which tasks will I have to perform?


To run programs as sudo without password, I edited /etc/sudoers with wrong content.   Then I re-edited it with Mac's default text editor(course sudo cannot be used when /etc/sudoers is wrong).  I tried to run sudo agin, and get this error:   sudo: /etc/sudoers is owned by uid 501, should be 0 sudo: no valid sudoers sources found, quitting   What should I do? I cannot remember the root password (maybe I haven't ever set root password before).


Combinatorial Proof, Binomial Coefficients

I have the following question:      Give a combinatorial proof that if $0\le a,k\le n$ are integer than $$\sum_{b=0}^k\binom{a}{b}\binom{n-a}{k-b}=\binom{n}{k}.$$   I'm new to the notion of a combinatorial proof, I understand that it's a proof by counting, i.e. showing the two expressions are in fact counting the same objects, instead of an algebraic proof.  Now, I know $\binom{n}{k}$ represents the ways of choosing k objects from n objects. I know this may be obvious to some, but can someone lead me to the correct way of thinking for interpreting the left-hand side?  Am I right in saying it is something like the sum of all the different (k-b)-subsets from a collection of (n-a) objects, or am I completely wrong?   Thanks for your help!


Does git rebase and or git merge create filed with conflicts marked up?

After I got message about existing conflicts, I found that files with conflicts contain marks like  <<<<<<<<<<<<<<<   or   >>>>>>>>>>>>>>>   Is this correct? What is the name of this file format?


How to show Chart in Visualforce page which has renderas = pdf

I have VF page with renderAs = PDF.  I want to display a chart on that PDF?  I have tried  and   but these only works on HTML, not in renderAs = PDF.  Thanks in advance.


Is there an Ubuntu theme available to make it look like Windows 7?

I want to know is there any theme available make it Ubuntu look like Windows 7 ?


Gray cone obscuring/clipping the 3D Viewport

When looking at my objects in 3d view I'm seeing a gray cone that seems to be hiding other objects.   Can anyone help me turn this off and explain what it is please.  Screenshots attached.


Dollar signs breaks formatting of 'Hot Network Questions'

Related to  and .  This :    looks like this in the 'Hot Network Questions' section of e.g. :    I think Latex formatting of question titles should be disabled if the question comes from a site that don't use Latex formatting.


Find the limit. (If an answer does not exist, enter DNE.) $\lim _{x→∞} (\sqrt{9x^2 + x} − 3x)$

I was following this explanation until the 5th step. The most important misunderstanding is if $1x/1x$ is $1$, and one can multiply a quotient by $1$ and not change its value. However from what I can see the $9x^2$ is being divided by $x^2$. How is that going to work? And why is that allowed?


How to remotely run a Python script in an existing Blender instance?

I don't want to use /Application.../blender -P my_script.py but I want to tell a running Blender process to execute a script.   Is there an existing method to tell a running Blender process to execute a python script?  For example using http://localhost:123/run_script=myscript.py


Regex: Match a phrase if NOT preceded by word

In JavaScript, I am trying to match all occurrences of the following  initChart('something'); initMap('another');  initChart(); initMap();   UNLESS it is preceded by the word 'function', meaning, do not match  function initChart(param) { ... } function initMap(param) { ... }   Basically I need to strip out all occurrences that invoke the function, while leaving the function definition in tact.  I got this far  /init.*(.*)/i   This is what my script looks like to strip out matches:  var scriptRegex = /init.*(.*)/i; while (scriptRegex.test(responseHTML)) {    responseHTML = responseHTML.replace(scriptRegex, ""); }   But I'm stuck at how to tell it "only if it is NOT preceded by the word 'function'


A set of elements in a reduced unity ring

Let $(A,+,\cdot)$ be a unity ring with the property that if $x \in A$ and $x^2=0$ then $x=0$. Consider the set $M=\{a\in A | a^3=a\}$. Prove that:      a) $2a\in Z(A)$, $\forall a\in M$, where $Z(A)$ denotes the centre of the ring $A$;   b) $ab=ba$, $\forall a,b\in M$.   My attempts revolved around the fact that an idempotent element in a reduced ring is central. So, since for $a\in M$ we have that $(a^2)^2=a^2$, it follows that $a^2\in Z(A)$, $\forall a\in M$. The next thing I wanted to use in order to solve a) was that $Z(A)$ is a subring of $A$, so if I had proved that $(a+1)^2 \in Z(A)$, $\forall a\in M$, then we would have reached the desired conclusion. However, I couldn't prove this and I honestly doubt that it is true. Another idea that I had was to prove that $M$ is a subring of $A$. Of course, this didn't work out because I cannot even prove that $M$ is closed under addition. Again, I don't know if this is true and it most likely isn't. As for b), I think that a) should be of use, but I don't know how. It is a well-known problem that a ring with $x^3=x$ for any $x$ in that ring is commutative, but since $(M,+,\cdot)$ is almost definitely not a ring, this doesn't help. EDIT: Is there any chance that this question is simply wrong? I tended to believe this before asking it here too, but since nobody has made any progress on it until now I am even more inclined to think so.


Why can't Windows home editions connect to domains?

The company that I work for continuously hires new people, and I'm the one who has to go and purchase new computers.  The majority of them, if not all, come pre-installed with Windows Home editions.  I'm noticing that the Windows 7/8 Home editions are unable to connect to domains.  I'm having to buy the upgrades to the Pro editions.  I'm trying to understand as to why the Home edition of the OS is unable to connect to domains?


Ok so I have this question:   Two point charges of charge -2 µC and -3 µC respectively are separated by a distance of 15 cm. Point X is positioned at an equal distance away from each of the charges.      a. Determine the net electric field at X.     b. Find the point of equilibrium between the charges.   I've started writing out the formula for the electric field from charge -2 µC to point X, but I'm just confused about how you are supposed to do it when you don't know the distance between the charge and point X (the r or d value in the formula).


For the next U19 CWC happening in bangladesh 2016.  What is the age cut off for full icc member teams?  What is the age cut off for associate icc member teams?


I was reviewing my flagging history list and i saw a strange number after the question/answer I flagged. Have a look at in the image,        Now such type of number is there in few flag posts, while others don't have it. I just want to know is what this number indicates?


Traveling to US from Mexico w/o passport

I am a citizen of Mexico (where I was born) and of the United States. Is there any way that I could travel without my passport either by land or air? Only documents I have on me are my state ID and my social security card. Are there any other options I should consider?


Need adjective to describe certain kind of speech or communication

I've been looking everywhere for a word to characterize speech in a business setting e.g. ny management or HR, where it is filled with buzzwords, circular logic, and devoid of real substance. In writing, I've seen this sort of thing described as fluff. Is there an adjective meaning "filled with fluff"? The closest I've come is vacuous or glib (both meaning empty), but the former word seems to carry an added implication of stupidity and the latter suggests that the speaker is at least eloquent. Is there something between the two? Mundane and devoid of meaning?


Combine 2 commands into 1 Custom command?

I want a custom command named something like "ServerStart" or something which is a combination of two commands, one after the other.   The first command would be cd .Server The second being java -Xmx7168M -Xms7168M -jar server.jar   How do I do this so this becomes one Terminal command?


Tool/script that can expand all 'include' directives in a makefile

Let us say we have the following Makefile  include config.mk  # Generate summary table. results.txt : $(ZIPF_SRC) isles.dat abyss.dat last.dat     $(ZIPF_EXE) *.dat > $@  # Count words. .PHONY : dats dats : isles.dat abyss.dat last.dat  %.dat : books/%.txt $(COUNT_SRC)     $(COUNT_EXE) $< $*.dat  .PHONY : clean clean :     rm -f *.dat     rm -f results.txt   where all the variables are defined in config.mk  LANGUAGE=python COUNT_SRC=countwords.py COUNT_EXE=$(LANGUAGE) $(COUNT_SRC) ZIPF_SRC=testzipf.py ZIPF_EXE=$(LANGUAGE) $(ZIPF_SRC)   Is there any tool available that can expand all the include lines within the makefile so as to produce a bigMakefile? If such a tool does not currently exist, can a python/perl/awk/bash script be cooked up to achieve this goal?


Javascript parsing - recognizing undefined object name/value pairs

I'm using a callback to create an object, which I'd like to parse. I'm able to parse the object when the name/value pair I've specified exists, but unable to identify when the name/value pair in my object is undefined.   JSON Object with name/value pair populated:  parseMe([{"item1" : "", "item2" : "", "item3" : [], "item4" : "content goes here"}]);   JSON Object with name/value parsed undefined:  parseMe([{"error" : "Not available"}]);   Parsing logic EX:       var renderR="";     function parseMe(data){      renderR="";     if(data[0].item4!="collapse") renderR=data[0].item4;  //if name/value pair isn't equal to "collapse" render it.     else if(data[0].item4==='undefined'){      document.getElementById('div1').style.display='none';  //if name/value pair is undefined in object hide the div.      }     }


Why do some Americans pronounce K and B after vowels sounds like G and P

For example, ‘speaker’ sounds like ‘speager’ and ‘Stop it’ sounds like ‘stob it’.


Is the expanding of the universe also a cause which can induce gravitational waves from mass?

Gravitational waves arises when mass is rotating in another mass'orbital, in explosions and of course in case of colliding black holes. But are they also created when mass is moving and speeding because the space itself is expanding? And is there also a kind of 'red-shifting' of the waves because they are moving away?


What directory is '~' when I type 'cd ~'?

I'm only new to using SSH, but when I log in I end up in the directory ~, which in general is the same directory when FTPing in. I can still go to /, but I don't know what the ~ means. Home? Where is it in relation to /, or how could I find out?


Does a paladin's Divine Sense feature negate the Mirror Image spell?

My players went up against a homebrew creature I made, it was a fallen angel that could cast Mirror Image. Our paladin had the idea to use his Divine Sense ability to be able to tell which Image was the real one.  Before we settled how it would go about, we went into an argument that since the Mirror Image is in the same space, Divine Sense (and his Action) is wasted as the location would be the same. He countered that knowing the location of an enemy he could already see, he could point towards the real one.  I wanted to reward his clever use of the feature so I ruled that he would have to keep using his Action to use Divine Sense so that his allies could attack with impunity.  Did I call it right by Rules-as-Written?