Is a "Perfect" Vacuum theoretically possible

I came across this answer to another stack exchange question and wondered about how true the claim was.   It starts with a disclaimer that claims that      A perfect vacuum is impossible   Now I know that perfect absolute zero is a theoretical impossibility because of many theories regarding quantum physics make it so, namely it's impossible to know the position and momentum of atoms at the same time: If they weren't moving you'd know where they were and that they had no momentum. So making something totally absolute zero is impossible. However is there a similar (or even dissimilar) theoretical impossibility regarding a perfect vacuum. If there were no atoms in the space then you'd have nothing to know the position and momentum of.  Because of this question:  (and the fact the answers are a little ambiguous anyway) I'm more loosely defining a vacuum as a space that has absolutely no complete atoms or perhaps, if it makes it actually practical to answer, molecules in it at all, ignoring zero point energy, radiation etc.  Lets also assume that the space is defined by a solid container. One that hypothetically doesn't degrade.  I'm not saying that it would be easy, ensuring no residual atoms were present would be practically impossible I'm sure but I see no reason why it would be theoretically impossible. Granted I'm not in any kind of physics related field so my knowledge is rudimentary at best.


When underfilling a vbox, leave all the space at the bottom

I have a XeLaTeX document in which it is easy to underfill some vboxes. This is ok for me, as long as the extra space is left at the bottom of the page (by default it is distributed between the boxes in the page). How can I instruct XeLaTeX to do that?


I have a simple function called return_funcs here: >>> def return_funcs(): ...     functions = [] ...     for i in range(4): ...             functions.append(lambda: i) ...     return functions  And when I use return_funcs this is what I get: >>> for func in return_funcs(): ...     func() ... 3 3 3  I was expecting something like: 1 2 3  Why do I get this unexpected output, and how can I fix it?


JS - Passing function to addEventListener

I am creating a simple to-do list.  I am stuck on the feature of completing a to-do item.  The event listener that I set up to handle this seems to be responding to the initial "add" button instead of the "done" button.  I've attempted to step through my code, but it seems as if I am not understanding the event listeners properly and/or the dynamic ways of Javascript.  Code below (have taken out everything that seems irrelevant)  HTML:
To Do List
 <input id="item" type="text"> <button id="add">Add</button>

   Javascript:  var item = document.getElementById("item"); var add = document.getElementById("add"); var list = document.getElementById("list"); var counter = 0;  add.addEventListener("click",addItem); clear.addEventListener("click",clearItems);  function addItem(){     var li = document.createElement("li");     li.id="li"+counter;     var itemVal = document.createTextNode(item.value);     var doneButton = document.createElement("button");     doneButton.innerHTML = "Done";     li.appendChild(itemVal);     li.appendChild(doneButton);     list.appendChild(li);     doneButton.addEventListener("click",itemCompleted(li.id,itemVal));     item.value="";     counter++; }  function itemCompleted(elementID,value){             window.alert("Should only show after clicking 'Done' for an item") }


How to read XML with namespace using PHP

I'm going crazy trying to figure out how to correctly iterate a large (>100 MB) XML file using PHP. I know how to process other XML files; as long as there are no <ns2:*> items it works great, but this file seems impossible. Please help me out. Example of the XML file: <result version="3.0" xmlns="xml:output" xmlns:ns2="xml:common">     <products>         <product groupingId="347849" language="en">             <ns2:name>Example Name</ns2:name>             <ns2:description>Example description.</ns2:description>         </product>     </products> </result>  I process other XML files this way (this does not work when I load the file structured like the example above).             $xml = new XMLReader();             $xml->open($file);                                          while ($xml->read() && $xml->name != 'product') { ; }             $i = 0;             while ($xml->name == 'product') {                 $xmlProduct = new SimpleXMLElement($xml->readOuterXML());                 echo $xmlProduct->name;             }  Everyone's happy. But that's not the case now. (I need the XMLReader + SimpleXMLElement combo in order to stream large XML files.) If you know how to fix this, please let me know. Thanks. Solution: $values = $xmlProduct->children('ns2', TRUE);


Formatting datetime2 in LaTex to 4th September, 2016 without the current day?

I'm currently using  \usepackage[UKenglish]{babel} \usepackage{datetime}   and I'm getting  Sunday 4th September, 2016  with the commands \today or with \newdate{example}{01}{09}{2016} (outside of \begin{document}) and \displaydate{example} inside the document.  How can I reformat this date to not have the name of the day in it (Best would be with using datetime2)? So like 4th September, 2016. With the "th" as a high letter like this:   Full document example:  \documentclass[a4paper, 12pt, DIV=calc, headings=small]{scrreprt} %Used packages \usepackage[UKenglish]{babel} \usepackage[utf8]{luainputenc} \usepackage{datetime}  %Other definitions \pagenumbering{arabic}  \newdate{sample}{31}{01}{2017}   \begin{document} \displaydate{sample}\\ \today \end{document}


Installing a process as a service on Windows 8 without "Administrator" account?

I am trying to start httpd.exe on windows 8 as a service. This is the instruction that is giving me problems:  Start apache in a DOS box: >httpd.exe Install as a service: >httpd.exe -k install   The first command works fine, but the second fails as follows:  C:\Apache24\bin>httpd.exe -k install Installing the Apache2.4 service (OS 5)Access is denied.  : AH00369: Failed to open the WinNT service manager, perhaps you forgot to log in as Adminstrator?   The account I am using is a local account with administrator privileges. When using this account I am able to install software, administer other users accounts, etc. I do not see an "Adminstrator" or "Administrator" account on the "Control Panel\All Control Panel Items\User Accounts\Manage Accounts" screen. I have tried the following, as suggested in another post:  runas /noprofile /user:Administrator cmd   That results in a prompt for a password, which I do not seem to know. The PC came with Windows 8 preinstalled and if I was ever asked for an Administrator password I can not recall my response.  So my question is, how can I install a running application as a service on Windows 8 without knowing the password to the "Administrator" account? Or, how can I discover or reset the password to the "Administrator" account?


How does assignment of variable overrides previous one in Java script

I was playing around Java script. I was expecting an output of 10 twice. Since I have declared  var a = b = 10;  here I struck, got error saying "a" is undefined and hiding that console.log(a); next console.log(b) gives me output as 10. I am not getting how "a" become undefined, even the console is after the function execution it must be undefined to b as well. or Is this wrong way to assign a value. Any clarification is on scenario is much appreciated.    (function(){ var a = b = 10; })(); console.log(a); console.log(b);       (function(){ var a = b = 10; })(); //console.log(a); console.log(b);


Unable to login at times on meta.unix.stackexchange.com

This is on meta. On certain questions like  I see the question but unable to put my preference or opinion on it as it says I'm logged into unix.stackexchange.com and stackexchange and elsewhere. I'm not even able to get a correct login page for the meta.unix.stackexchange.com site. Going to  is also unhelpful. I also tried registering in the hopes that something might be broken or dis-connected and maybe I had to re-register again but nothing. It dumps me right back to the homepage. I don't even get any questions for signing up.   Can somebody help.  Update - It is a HTTPS-Everywhere issue. After I take out the two HTTPS-Everywhere rules about stackexchange it works.


I have downloaded the latest version of ubuntu Desktop 14.04.1 LTS. The gcc version is gcc (Ubuntu 4.8.2-19ubuntu1) 4.8.2. I would like to change it to the 4.7.2 20130108 [gcc-4_7-branch revision 195012].  I will be very thankful if you could please help me through it.


Can "backup" be used as a verb in the context of data management?

I have heard backup being used as a verb in the sense of     I have to backup my hard disk   by non-native English speakers (the English noun backup is also used in other languages, for example in German, so it may be a false friend). The correct expression seems to be     I have to make/create a backup of my hard disk.   I know that "to back up" is correct English, but has a different meaning.   Microsoft uses "back up" in the above sense, see , but the Oxford and Miriam-Webster dictionaries do not seem to support this use.  Has to backup (or to back up) become part of the English language?


Placing figures inside a two-column document

I'm trying to get images in my document in two different ways:   On top of the entire page, centered On top of a single column   I tried it with both twocols and multicols. I ruled out twocols because it forces a new page every time you turn it on, because I need the abstract to be wide and the rest of the cover page to be two columns.  Here are some examples of both points (screenshot from a downloaded PDF):   I want to achieve both, but somehow I can only solve the first point with:  \end{multicols}  \begin{figure}   \centering     \includegraphics[width=0.5\textwidth]{figure}   \caption{Dataflow pipeline of the edge detector}   \label{fig:workflowedge} \end{figure}  \begin{multicols}{2}   Is it awkward to turn off multicols, then turn it back on again?  For my second point, I've tried everything, but almost always, the image doesn't show up at all! The only way I can get it to show at all is by specifying the H placement specifier, but that places the image inside the text where I defined it, not on top of the column.  This is my best try, but it hides the image and breaks all references to ??:  \begin{figure}[t!]   \centering     \includegraphics[width=0.25\textwidth]{figure}   \caption{Dataflow pipeline of the edge detector}   \label{fig:workflowedge} \end{figure}   and I'm getting the warning:  Package multicol Warning: Floats and marginpars not allowed inside `multicols' environment!.   How can I make a figure a non-float?  I also tried the figure* environment, but that just creates an image centered on top of the page, like my first point.


Why does my sourdough starter have in the top the liquid separated from the flour? 2 days after beginning a new one, a liquid (water) appeared on top of it, it appeared after I fed it the first time. To feed it I discarded half of the starter and then I added 5 tbsp of flour and 5 tbsp of tap water to feed it. Then, on the next day the liquid appeared like that. I don't think it's OK, so I discarded that liquid, and then waited a full 24 hours to feed it again like that.


With SEDE, is there a way to run a query across all sites in the network?

My apologies if this question is off-topic here, but it is a discussion about how to use a network-wide tool specific to SE.  The question in its entirety is in the title, really.  How can I use the StackExchange Data Explorer to run a query across all sites in the network?  I cannot seem to find a way to search more than one (set with the drop-down next to Compose Query) – is this  or is there a workaround?


Migrating a question after it has been closed

On  we get a number of questions that end up closed that belong on other sites. I read on here that they will be migrated under certain circumstances. If those are not met, however, and the question receives 5 close votes from users, how do I then migrate the question to another site? In the past I have been reopening the question and then closing and migrating it. It seems like there should be a better way.  FWIW,  is an example.


Once you apply spin to a bezier curve with a set amount of set amount of steps, is it possible to go back after switching over to object mode and increase/decrease the amount of steps?


Do not allow edits on different posts within 5 minutes

We have discussed the problems with the "suggested edits" review queue for a while here.  Some people make extremely minor edits in quick succession. Often it is people who make the same style of edit to a lot of posts - add or remove one specific tag to a question, only removing "Thank you" from posts, or only removing a specific keyword from the title. Unfortunately, these extremely minor edits are often approved. The people who make these edit suggestions are then rewarded with +2 rep, and the serial approvers are closer to a badge. And since the edits were approved, the "edit ban" does not kick in.   I suggest that we do not allow people to suggest edits to different posts within 5 minutes. This should discourage "serial minor edits", while encouraging people to take some time making proper edits.


We were going over inverse functions in class and the method for mathematically finding an inverse function (i.e. replace y with x in the function and solve implicitly for y). I noticed, however, this method seemed impossible for a function such as $\mathbf {f(x)=x^3+x}$ After trying for a while, I used the solve() function on my calculator to find y implicitly. The result was $$y=\frac{6^\frac 13\left(2^\frac 13\sqrt {3(27x^2+4)}+9x\right)^\frac 23}{6\left(\sqrt{3\left(27x^2+4\right)}+9x\right)^\frac 13}$$  I have graph this and it is indeed the inverse function. My question is: How was this conclusion reached? (no this question was not for homework, yes I am aware of and okay with the fact that this may be well beyond my level; I'd like to know anyways)  EDIT: Someone else asked the exact same question on this forum. I had actually read the responses to that particular post, they did not answer my specific question and, to the best of my knowledge, gave methods to solve for the graph the inverse function. Also while the question titles are the same, the nature of the question really is not at the heart of it.


For an Internet-only business, should I use the schema.org type Organization or LocalBusiness?

I have an Internet-only business and am trying to determine which schema.org type to use:  or .  I did some research on Google and found that LocalBusiness appears to be a subtype of Organization. For an Internet-only business, would Organization be too broad? Or should I use LocalBusiness because it's more specific?  Schema.org defines Organization as:     An organization such as a school, NGO, corporation, club, etc.   It defines LocalBusiness as:     A particular physical business or branch of an organization. Examples   of LocalBusiness include a restaurant, a particular branch of a   restaurant chain, a branch of a bank, a medical practice, a club, a   bowling alley, etc.


How do you use commas when referring to a person and yourself in a sentence while naming the person?

The sentence is:     My wife, Anne, and I are going to the dentist this afternoon.   I am unsure with this because it sounds like the sentence is talking about 3 different persons: (1) Wife (2) Anne (3) I. But what I really intend for it is that  it is talking about only 2 different persons. (1) Wife whose name is Anne (2) I.  Is the use of the commas in the sentence correct?


Generate random numbers following the exponential distribution in a given interval $[a, b]$

I  know that to genarete ramdom variables following exponential distribution just do:  $$X=-\frac{1}{\lambda}ln(U)$$  where $U\sim U(0,1)$  Now, to find a distribution restricted to the interval $(a, b)$, I used the truncated distribution () coming in the following cumulative distribution  $$H(t)=\frac{e^{-\lambda a}-e^{-\lambda t}}{e^{-\lambda b}-e^{-\lambda a}}$$  However I don't Know to find the inverse function $H^{-1}$. Also I don't know if this expression is correct. I thank


fire simulation don't show fire but smoke

Im trying to do a fire simulation.  Although I have it as fire on setting Physics property panel, my simulation still showing only smoke. Can anybody please tell how to fix this? Thanks in advance.


If $f$ and $g$ satisfy the sine/cosine addition formulae, then what is $g'(0)$?

The question is:    Question.  Let $f,g:\mathbb R\to\mathbb R$ be two functions that satisfy$$f(x-y)=f(x)\cdot g(y)-f(y)\cdot g(x)$$ and $$g(x-y)=g(x)\cdot g(y)+f(x)\cdot f(y)$$ for all $x,y \in \mathbb{R} $.  If the right hand derivative at $x=0$ exists for $f(x)$, then what is $g'(0)$ ?  My try:  By some simple substitutions I figured out that $f(0)=0$ and $g(0)=1$. If in the second equation, we put $x=y$, it will give $g(0)=(g(x))^2+(f(x))^2$. If $g(0)=0$, sum of the two squares becomes $0$ which implies the squares themselves are zero, I neglected $g(x)=f(x)=0$ as a trivial solution and hence took $g(0)=1$. But how do I proceed after this?


I am trying to understand subgroups.I know a given a group G under a binary operation ∗, a subset H of G is called a subgroup of G if H also forms a group under the operation ∗.   So if I where to list 5 subgroups of $\mathbb{Z}$ could I simply say, $\mathbb{Z}_2$, $\mathbb{Z}_4$, $\mathbb{Z}_6$, $\mathbb{Z}_7$, $\mathbb{Z}_9$, are all subgroups of $\mathbb{Z}$?


Preprint on CV - should I include journal I submitted to?

I'm in a discipline where it is common to make preprints publicly available on arXiv as soon as they're ready to be submitted to a journal, so naturally I list them on my CV. Before the review comes in I would just list the paper as "Preprint" and after it's been officially accepted I would list it as "To appear in XYZ". I wonder what is the best course of action between those two states, that is, after the paper has received positive reviews but there are still corrections to be applied and it has not been officially accepted (but I'm willing to bet that it will be). Is it reasonable mention that the paper is "Submitted to XYZ" in such a case? That has the benefit of providing more complete information, and is definitely a statement that I can justify if pressed. Or is it always preferable to stick with "Preprint" until officially accepted?


I am using a scrtipt with instruction 'SH -c command', where command is an alias from bash, this alias can not be interpreted into Bourne shell. ¿Do you have any idea for set this alias into Bourne shell and getting that it works in the new shell? Thanks everyone !


"My sister and I" versus "I and my sister"

I've been told to put "I" at the last part of the subject, as in "My sister and I walk to school." Is saying "I and my sister walk to school." wrong?


upgrading Ubuntu 11.10 to 16.04LTS - can I skip in between upgrades?

I'm upgrading an old laptop running Ubuntu 11.10. Do I need to upgrade sequentially through all the versions until i get to the current to 16.04. Is there a quicker way - can I skip in between upgrades?


Aura Component + HttpCallout + Large File Response

Trying to figure out how best to build interfaces that retrieve external files between 1-10 MB and display them in the UI.  Right now I have a Lightning Aura Component that calls a web service via HttpRequest and retrieves file metadata, so that users can browse externally stored files.  A second HttpRequest allows the user to either preview or download these files, depending on file type.  Both methods are synchronous currently.  This works, but the current version has to cap file sizes for preview/download at around 5.7 MB, based on the  of 6 MB.    We have also been concerned about the , which we could easily hit if there are multiple users requesting files larger than 1 MB at the same time that other long-running synchronous processes are executing in our org.  Needless to say, I was enthused when I heard that asynchronous processing was coming to Aura Components in Summer '19 in the form of support for Continuations ().  But as I began to test this, I realized my callouts were failing at much lower file size thresholds than 6 MB.  Apparently continuations have specific limits listed in the  whereby callouts and responses can't exceed 1 MB.  Bummer.  Is there a special architecture whereby I can retrieve files of up to 10 MB and display them in the UI, which can be deployed to users at scale?  EDIT OCTOBER 2019  No longer concerned about these types of synchronous concurrent transactions due to a Winter '20 change from Salesforce, .  While the file size cap of 6 MB is still a minor frustration, we no longer have to worry about hitting governor limits due to the volume of requests for external files.


Does a bias resistor determine the forward voltage drop across an LED?

I hadn't really given this much though before but when I look at the forward voltage drop of a LED, it gives a graph such       Can I simply set the resistor to a value produce a current and get the corresponding forward voltage drop or is there an associated resistor within the LED for which I need to account?


The task is on translating. I want to know is it acceptable to use Perfect Gerund (action of the Gerund has happened before the main action) instead of Gerund.     "I've been a bad wife to him", - she thought. "Just yesterday I scolded him for not wiping/not having wiped his feet before he entered the kitchen. I'll never see him again."


Adding jQuery to act on the Select/Option that is dynamically created

I am adding Select/Option based on the user input.   How do I write a jQuery that reacts to Select/Option that is dynamically created based on user input.  Here is my jsfiddle,   I tried adding the simple jQuery to react to new Select/Option whose id is selecta. But this does not work.         // Select option for topic         $("#selecta").change(function() {         // varible to hold string         console.log("changed");         var str = "";         var val = "";         $("select option:selected").each(function() {             str += $(this).text() + " ";             val = $(this).val();         });         var divbox = document.getElementById('textbox');         divbox.innerHTML ="Selected"+ str+"";         console.log(str,val);         }).change();   Problem here :   I have a initial Select/Option and user gets to select two options. And based on this selection, new Select/Option is added to the page. I cannot figure out how can i added jQuery change trigger to this new Select/Option. Based on user's selection to this, page needs show other elements.


This will depend on whether he's suitable for the job.    This will depend on whether he's suitable for the job or not.   This will depend on whether or not he's suitable for the job.         It is still not defined whether we're following that approach.   It is still not defined whether we're following that approach or not.   It is still not defined whether or not we're following that approach.         "Or not" doesn't really seem to be needed to complement "whether". Why do people use it then? Is it redundancy and nothing more? Or is it for emphasis? Or are there cases when "or not" is required for the sentence to be grammatical?


When is 'Challenging Smite' a viable option for top laners

I saw some top laners who use smite and teleport as spells and (if I'm correct), it's becoming pretty regular and although I don't play as a top laner, maybe when I have to adjust, I know I may find this useful.  My questions are when and who :  When to use it / what are some of the conditions needed since it was told that this strategy isn't always going to be useful in every top laner,  Who are the champions that will really take advantage of this?


Resampling method used in QGIS Raster save as?

I have what seems like a simple question, but I haven't been able to find the answer in the QGIS documentation.   I have a raster that is 250 m resolution, and I want to resample it to 1000 m resolution. This means that for every 16 pixels in my original raster, I will have 1 pixel in my new raster. I would like to retain the mode (most frequent value) of the 16 pixels.   Based on the suggestion from Radim , I am using this approach:   Load raster into QGIS Right click on layer name, select 'Save as' Change the resolution in the dialog box from 250 to 1000:    However, I haven't been able to figure out what technique is used to go from 16 cells (at my original resolution) to 1 cell (at my new resolution). Based on inspecting some specific pixels, it doesn't appear to be either the mean or the mode.   (Note: I would like to use the mode, so if anyone has a better technique, I am all ears)


Prove that $\vert \tan^{-1}x-\tan^{-1}y \vert \le \vert x-y\vert\enspace \forall x,y \in ℝ$

Prove that $$\vert \tan^{-1}x-\tan^{-1}y \vert ≤ \vert x-y\vert \quad \forall x,y \in \mathbb{R}. $$   What I did was to put $x \to x+h$ and $y \to x$ and then take $\lim_{h \to 0}$. This gives $$\lim_{h \to 0} \frac{\vert \tan^{-1}(x+h)-\tan^{-1}x\vert}{\vert h \vert} \le 1$$ which gives $$\frac{d \tan^{-1}x}{dx} = \frac{1}{1+x^2} \le 1.$$ But this proves it only for $x$ and another value $x+h$ very close to it and not $\forall x,y$. Please help.


I'm trying to print, in a pdf file, just one page from another large pdf file. Does anyone have a clue? I'm using foxit reader, and when I try ctrl+P appears just the installed printers as an option to print. There is no print to file button like in other programs such as libreoffice. Thanks in advance.


Cycles: Shadeless "Shadow-catcher" Material for Rendering onto Footage

I am superimposing CGI over video footage, and have run into a problem in making materials for objects that act as 'shadow catchers'.  Essentially I want a shader that is shadeless—like an emitter—but catches shadows and light from other objects. This is so I can reconstruct objects in footage so other objects in the scene interact convincingly with them.  Here's an overcomplicated diagram to illustrate my point:   (In this particular scenario, the problem could be glossed over by using RGB curves, but that is definitely not the case with more complicated scenes)  Isn't this a common situation? How to the real guys do it? Thank you.  (I am welcome suggestions of other ways of doing this.)


not able to install Unity tweak in Ubuntu 12.04: 404 Not Found error

While installing Unity tweak, I am getting following error:   sudo add-apt-repository ppa:freyja-dev/unity-tweak-tool-daily sudo apt-get update sudo apt-get install unity-tweak-tool  W: Failed to fetch http://ppa.launchpad.net/freyja-dev/unity-tweak-tool-daily/ubuntu/dists/precise/main/source/Sources  404  Not Found W: Failed to fetch http://ppa.launchpad.net/freyja-dev/unity-tweak-tool-daily/ubuntu/dists/precise/main/binary-i386/Packages  404  Not Found E: Some index files failed to download. They have been ignored, or old ones used instead.


Placing Intermediate and Output Files in Another Folder

I am trying to figure out a way to cleanly separate the TEX files from all of the intermediate and output files. Various approaches I've tried, including the one described by  don't seem to work. I'm using TexMaker + MikTex (portable). Ideally, I would like my file/directory structure to look something like this:   texproject   texfiles   1.tex 2.tex  intfiles   1.out 1.log 1.aux 2.out 2.log 2.aux  pdffiles   1.pdf 2.pdf     Instead, what I have, is the jumbled-up mess where all of these files live in the same directory. I've tried setting the ouput-directory, for example, on pdflatex but this doesn't work. The pdf file still gets created in the same place but now it doesn't show up in the previewer. This should be pretty easy to solve but I've so far been unsuccessful. How can I set up my environment to use the above structure when compiling?  Update: I believe I have narrowed this down to something specific to TexMaker. If the desired aux and out directories are passed via the command line to pdflatex, everything builds as it should. Yet, I get numerous message boxes popping up saying that files can't be found and the PDF doesn't display in the internal viewer. I can't see any obvious options within TexMaker to change to address this. So, has anyone been able to make the scenario I'm describing work with TexMaker?


What is the difference between correlation, causation and prediction?

Suppose we have a set of events $\Omega$, containing events $A$ and $B$. My econometrics professor tried to distinguish the following three terms today.    Causation --- $A$ causes $B$ if the occurrence of $A$ always leads to another specific outcome $B$. For example, clapping my hands causes a sound to be emitted.  Prediction --- $A$ predicts $B$ if on average, $B$ is the expected outcome from $A$ occurring. In other words, whereas causality is deterministic, prediction is probabilistic. For example, studying for a test would predict doing well on the exam. But there's no guarantee.   Correlation --- $A$ and $B$ are correlated if when one occurs the other does too. But there may be some hidden variable causing both.    Are these distinctions meaningful? Or did he make these terms up?   My Questions   What is the difference between causation and correlation?  Are "causes" always deterministic?


What is the association bonus, and how does it work?

I was just awarded +100 reputation on all of my Stack Exchange accounts.  What is this bonus for? It simply says "Association Bonus" on my reputation overview.  Also:   What privileges does the association bonus grant users? Can I lose the association bonus? Does it make my reputation 101 everywhere? Can I earn the association bonus on sites I haven't joined yet? Does it matter which site I earn the 200 reputation on? Will I get an association bonus every time my reputation on a site crosses 200 points? Does the association bonus allow me to answer protected questions? Does the association bonus count towards the reputation cap? Can I get the association bonus if I only have a profile on one site? What else is there to know about the association bonus?


Terminal move cursor with mouse in any way?

Is there any way at all to use the mouse cursor to move the cursor in terminal, like click where you want it and press a key to move it there?  This is one of the most annoying things I've ever found using the terminal  I know Ctrl+A will move to the beginning of the line but sometimes these commands are so long


Prove the given identity using the shortest method possible

Prove the given identity.   $$\left(\sin\frac{9\pi}{70}+\sin\frac{29\pi}{70}-\sin\frac{31\pi}{70}\right)\left(\sin\frac{\pi}{70}-\sin\frac{11\pi}{70}-\sin\frac{19\pi}{70}\right)=\frac{\sqrt{5}-4}{4}$$   Please provide the shortest method possible. I didn't get any idea to start the solution


Python Text Content Not Updating in Animation

I'm trying to create a timeline that graphically shifts across the screen and a text box which displays the currently selected year as the timeline shifts.  To accomplish this, I've created a Python script - my first in Blender.  It uses the timeline's X-location to calculate what year should be displayed and then updates the text content. Everything works great in the design space.  When I scrub the timeline and play the animation, the year updates as expected.  However, when I go to render the animation, the text content is set to whatever value is currently displayed in the timeline of the design space.  It doesn't update; it's like it doesn't take the script into account in the final rendered image - but only in the animation.  If I render the current frame to an image, it displays accordingly since the timeline accurately reflects the Python update. Is there a Render setting or a change required in the Python to get this to update in the output FFMPEG animation?  Thanks. import bpy  text = bpy.data.objects['YearAD'] lbl = bpy.data.objects['ADBC'] timeline = bpy.data.objects['timeline']  def update(self):     loc = timeline.location.x          yr = round((-970 - 2020) / (122.71 + 169.293) * (loc + 169.293) + 2020)     text.data.body = str(abs(yr))     if yr <= 0:         lbl.data.body = 'BC'     else:         lbl.data.body = 'AD'  def register():     bpy.app.handlers.frame_change_pre.append(update)      def unregister():     bpy.app.handlers.frame_change_pre.remove(update)      register()


I have upgrade ubuntu from 19.10 to 20.04 and after upgrade my gnome-terminal display weird characters as shown in attached image.


What happens to energy when waves cancel out?

So this is basically     again, but I'm not understanding the answers given (or they don't address what I am confused about) Basically given that waves can be reflected one could conceivably  reflect two waves so that perfectly cancel each other out (I do not mean standing wave, I mean reflected so they end up  going in the same direction and are "off" by exactly half a wavelength)  Suppose that we have 2 sources of same frequency light aimed directly at each other call this line l horizontal, and let P be a plane containing l and consider a perfectly reflective square (or cube ) S contained in P oriented 45 degrees to l and intersecting l on 2 adjacent sides of S so that the 2 light sources are perpendicularly reflected (in same direction) now slide the square S perpenticularly to l so that l intersects l at a single point p \in l. Now we have a way to "combine" 2 waves that are not in the same direction and we can choose p so that the two waves are "precisely" out of sync and cancel perfectly.  Of course I mean ignoring quantum / wave particle duality   loss of heat/friction etc Perhaps  one should visualize this instead as sound waves bounced perfectly so they cancel out or..    @ACuriousMind  while this could just be a comment  on a different thread my comment did not recieve any attention, thus I decided to make it another topic


Motivation for the term "separable" in topology

A topological space is called separable if contains a countable dense subset. This is a standard terminology, but I find it hard to associate the term to its definition. What is the motivation for using this term? More vaguely, is it meant to capture any suggestive image or analogy that I am missing?


Switch axes and handedness of a quaternion?

I have a quaternion, coming from a system with the following:(intertial sensor)  Right handed. Forward direction: Y axis Right direction: X axis Up direction: Z axis   I need to convert this into a coordinate system that is: (Unreal engine)  left-handed. Forward direction: X axis Right direction: Y axis Up direction: Z axis   I have tried negating the axis, and angle, I have tried switching values, i cannot get this to work. All help greatly appreciated! I am working in C#, with Microsoft.Xna.Quaternion.


Problem:  If $n>4$ and is composite, then $n$ divides $(n-1)!$.   My Attempt: I have tried to solve this problem using the approach described by @Michael Hardy but have not succeeded as of now. I wish to know how one can solve this problem using his  approach. For reference, Michael's answer is given below:      Suppose $p$ is prime and $p\mid n$.  Let $k$ be the multiplicity of $p$ as a factor of $n$, so that $p^k\mid n$.   $$ \underbrace{(n-1)! = 1\cdot2\cdot3\cdot4\cdot5\cdots\cdots p\cdots\cdots p \cdots\cdots p\cdots\cdots(n-1)}_{\text{Does $p$ show up at least $k$ times here?}} $$If $p$ appears at least $k$ times in the usual factorization of $(n-1)!$ displayed above, then $p^k\mid(n-1)!$.  If this works for every prime factor of $n$, then they're all there, so $n\mid(n-1)!\,{}$.   I guess, the question really boils down to proving the fact that the prime number $p$ shows up at least $k$ times in $(n-1)!$.


Installing node with apt-get or downloading the Linux Binaries (.tar.gz)

What is the difference between installing node.js with 'sudo apt-get install nodejs' or downloading the Linux Binaries (.tar.gz) and following  instructions?  Is the outcome the same?


Prove that $A \cup B = A \cap B$ if and only if $A=B$.  My method was:  We must prove two implications, so we will proceed by proving the first implication. We will do this by proving the contrapositive: If $A \neq B$, then $A \cup B \neq A\cap B$. So, we assume that $A \neq B$. Let $k \in A$ and $k \notin B$. Then $k$ is in $A \cup B$ and not $A \cap B$, and $A \cup B \neq A \cap B$. Therefore this is true by definition.   Since $A = B$, for every $k \in A$, $k$ is also in $B$. Hence $A \cup B = A=B$ and $A \cap B = A=B$. Therefore, $A \cup B = A \cap B$.  I know I'm close in the first part of the proof, but I am not sure about the second part when I try to prove the other direction.


Error when signing up to my web application java

I have a java web application that allows users to search contents, when i try to sign-up a new user i get the following message! HTTP Status 500 – Internal Server Error  Type Exception Report  Description The server encountered an unexpected condition that prevented it from fulfilling the request.  Exception  java.lang.NullPointerException     DBConnector.queries.selectUserNamePass(queries.java:30)     Users.signupS.processRequest(signupS.java:42)     Users.signupS.doPost(signupS.java:109)     javax.servlet.http.HttpServlet.service(HttpServlet.java:647)     javax.servlet.http.HttpServlet.service(HttpServlet.java:728)     org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)  any one has an idea how to solve it?


What does that ae stand for next to the YouTube symbol?

Please answer quickly, i'm getting suspicious about my Internet company.


I have a 6th gen iPad (v13.1.3) and an iMac 27 2019 (latest 10.15) on the same wifi network. I can choose my iPad from the dropdown of the sidecar menu, but I always get "Unable to Connect to “iPad name” error message while connecting. I tried it with both wifi and cable without any success. Previously about a week (and few versions) ago I was able to connect. I can see any options to set or debug the connection.  Any idea how can I fix this?


Value of $\lim_{n\rightarrow\infty}b_{n}$ is

If $b_{n+1}=\sqrt{2+b_{n}}$ for $n=1,2,3,\cdots\cdots$. Then $\lim_{n\rightarrow\infty}b_{n}$ is , given $b_{1}=3$   Try: let $b_{n}=2\cos(x_{n})$. Then put into $b_{n+1}=\sqrt{2+b_{n}}$  We have $$2\cos(x_{n+1})=2\cos\bigg(\frac{x_{n}}{2}\bigg)$$  Could some help me how to calculat $\lim_{n\rightarrow\infty}b_{n}$  Thanks in advanced


Prove that infinite intersection of subspaces is a subspace.

I was reading a section in a Linear Algebra textbook and I have a small doubt.  I could prove that intersection of any finite collection of subspaces is a subspace. I did this by first doing it for two subspaces, and then extend it easily. But, I am not sure how it would extend to intersection of infinite collection.  My argument for a finite case involves first proving that intersection of two subspaces $W1$ and $W2$ is a subspace. Then let $W12=W1 \cap W2$, and then the same argument will work for $W12$ and $W3$, and so on.  But is the above method enough to conclude that even an intersection of an infinite collection would be a subspace.  Thanks in advance for your help.


How do I get airside at Boston's Logan airport without a boarding pass?

My minor daughter is traveling by herself internationally, leaving from Boston's Logan airport.  It's the first time she's traveled via air on her own, and I'd like to go with her to her gate (past security) to make sure she doesn't have any hassles.  I've seen some indications that it's possible to do this, but I've not had any luck figuring out how to do it.  Is this possible?  If so, how? Do I need the airline to OK it? TSA? Someone at Massport?  --  Closed, and the dupe helped me.  The airline is United, and they explicitly say on their website (I was missing the key phrase "gate pass" in my searches):


I installed current MacTeX version (20150613) and then updated TeXShop to most recent version, Version 3.61.  In the BibTeX engine setting, I wrote biber, and in the document I additionally have:  %!TEX TS-program = xelatex %!TEX encoding = UTF-8 Unicode %!BIB TS-program = biber  \usepackage[backend=biber]{biblatex} \addbibresource{bibliography.bib}   I'm typesetting with XeLaTeX through Typeset ⌘T command multiple times and references are not resolved. It seems that biber is not invoked. If I go to terminal and manually invoke biber document.bcf, my references get resolved in the next typesetting pass.  What am I missing?


How does an outlet know what wattage to put out?

In the UK, if that makes any difference, I was wiring a motor and then I wondered (and kinda needed to know), how does a plug socket know how much power to put out? because all the input ampages on all the plugs sad different things but can all be plugged into the same socket.  How does this madness work?!? XD


So i have a insert query with multiple rows (1 000 row per query) and it work fine, so tried to make the same for update query but i didn't find any solution,  this is my code :   $sth = $db->prepare("UPDATE table SET salutation = ? , fnamn = ? , enamn = ? , mob = ? WHERE id = ?");  for ($i=0; $i < count($recipents); $i++) {  if(isset($recipents[$i]['id']))     $sth->execute(array($recipents[$i]['salutation'], $recipents[$i]['fnamn'], $recipents[$i]['enamn'], $recipents[$i]['mob'],$recipents[$i]['id'])); }   so please if someone has any idea how to update multiple rows in one query i will be very appreciative.


Using nuclear devices to terraform Mars: Elon Musk's nuclear proposal?

has recently suggested . In the past, comet related ideas were mooted, but Musk seems, to me anyway, to be a  man in a hurry and perhaps his idea has some merit, as waiting around for suitable comets may take a while and involve large energy expenditure.      The businessman has often stated that he thinks humans should colonize Mars, and now it seems he’ll stop at nothing to get his way.   “It is a fixer-upper of a planet,” Musk told Colbert. “But eventually you could transform Mars into an Earth-like planet.”   There’s a fast way and a slow way to do that. The slow way involves setting up lots of pumps and generators to warm up the red planet so that its frozen carbon dioxide melts and wraps the planet in a thicker atmosphere. The thicker blanket of CO2 helps the planet warm up further, thus melting more carbon dioxide, and the positive feedback loop continues. (This is essentially what we’re doing on Earth, and it’s called global warming.)   There's a simpler and cheaper way to warm up Mars. “The fast way is, drop thermonuclear weapons over the poles,” said Musk.   I can't immediately find an estimate of the volume of the carbon dioxide on (or under) the Martian surface but this source  gives an estimate of water ice volume:     Water on Mars exists today almost exclusively as ice, with a small amount present in the atmosphere as vapor. The only place where water ice is visible at the surface is at the north polar ice cap. Abundant water ice is also present beneath the permanent carbon dioxide ice cap at the Martian south pole and in the shallow subsurface at more temperate latitudes. More than five million cubic kilometers of ice have been identified at or near the surface of modern Mars, enough to cover the whole planet to a depth of 35 meters. Even more ice is likely to be locked away in the deep subsurface.   Physically, and I do want to stick to the physics, particularly the atmospheric physics, rather than engineering,  is this idea feasible?   Has Musk done his homework as regards:   The amount of nuclear material needed? (And the undoubted outcry over its transport from Earth using potentially highly explosive rockets in the first place)? Is the gravity of Mars strong enough to retain the water vapour involved?  I am guessing it is. Will  atmospheric pressure help retain the water vapour produced or is his idea enough to produce a relatively dense atmosphere? Finally, Musk is a businessman selling a possible project, and that implies, understandably I suppose, that  dramatic publicity is involved. Would a set of mirrors in orbit do the job just as efficiently, although over a longer timescale?


$X$ be a Hausdorff topological space , let $f:X \to X$ be a continuous map such that $f\circ f=f$ , then is $f(X)$ is closed in $X$ ?

Let $X$ be a Hausdorff topological space , let $f:X \to X$ be a continuous map such that $f\circ f=f$ , then is it true that $f(X)$ is closed in $X$ ?


Avoid running the script if a variable is not defined

I have a script looks like:  c=0 for f in */*; do cp -v "$f" "/myhome/CE$(printf '%0*d' 2 $BATCHNUM)-new-stuctures_extracted/test-$(printf '%0*d' 5 $c)" c=$((c=c+1)) done   However, the user must provide a variable call BATCHNUM and otherwise I need to force this script stop running. It will be better if I could force the script that calls this script to stop too (or even the #1 script that calls #2 script which calls this script).


Does unopened whole wheat flour have to be refrigerated?

The organic whole wheat flour that I bought is in a sealed thick plastic bag and has never been opened. Should it be refrigerated (or frozen)? And does opened white flour need to be refrigerated?   My question refers to unopened whole wheat flour. And the second part of my question refers to white flour which I now understand is better in the freezer. Thank you!


How do I find the angle between two vectors?

I have 3 points on my screen:  a = a point which is (c.x, 0) makes a line pointing straight up b = a user input touch, can be anywhere on the screen c = a moving object         a _______.________ |      |       | |      |       |  |   b  |       | |  .   |       | |   \  |       | |    \ |       |  |     \|       | |      | c     | |______._______|   I have drawn some lines so that you can see the vectors.  I want to be able to get the angle between a and b. I have tried this, but it doesn't work, does anyone know what I'm doing wrong?:  //v1 moving object float boxX = this.mScene.getLastChild().getX();  float boxY = this.mScene.getLastChild().getY();  //v2 user touch float touchX = pSceneTouchEvent.getX(); float touchY = pSceneTouchEvent.getY();       //v3 top of screen float topX = boxX; final float topY = 0;  float dotProd = (touchX * topX) + (touchY * topY);  float sqrtBox = (touchX * touchX) + (touchY * touchY); float sqrtTouch = (topX * topX) + (topY * topY);  double totalSqrt = sqrtBox * sqrtTouch; double theta = Math.acos(dotProd / Math.sqrt(totalSqrt));   The answer I usually get is between 0 and 1. How do I fix this so that I get the angle in degrees?


Using principal component analysis (PCA) for feature selection in regression

I have a dataset $D$ made of $m$ samples and $n$ features with $n \gg m$. For each sample I have a score $s$ which I would like to be able to predict.  As the number of features is very high (compared to the number of samples), I have performed PCA (Principal Component Analysis) and built a regression model for $s$ based on the first 3 principal components (out of 45). I cross-validated the results and am happy with the performances of my model.  Now I would like to understand what is happening in terms of my original features. In particular I would like to understand which features are relevant in predicting $s$, and select them to build a model which does not involve PCA.  How can I perform this last step (if you have R based solutions it is better, but not essential)?


What do the different Canon DSLR image size settings mean?

When setting image quality in my Canon EOS 1200d dSLR there are two options for the L, M and S1 size. What is the difference betwen these settings (I couldn't find it in camera documentation) ?


Who were the other two heroes with Superman in the newspaper article who left?

In Justice League, we see a newspaper article showing three heroes who died (left to their home planets) but it was too fast that I missed catching the faces.   Who were the other two heroes who are dead?


Is it possible to initialise a generic class in a generic function

I have a simple utility function like following:  public static <T, S> HashSet<S> convertSet(Set<T> list, IConverter<T, S> converter) {     HashSet<S> result = new HashSet<>();     if (list != null)     {         for (T item : list)             result.add(converter.convert(item));     }     return result; }   I want that the result of this funtion is of the same type as the input data, so I tried to change the function to following:  public static <T, S, ST extends Set<T>, SS extends Set<S>> SS convertSet(ST list, IConverter<T, S> converter) {     // following is not working of course!     // I can't create a new object of the generic type!     SS result = new SS();     if (list != null)     {         for (T item : list)             result.add(converter.convert(item));     }     return result; }   Is there any way to write this so that it works? In c++ we have templates and the compiler will generate all necessary functions itself, is there anything like this in java?  Or any annotation library so that I can annotate my function with all Set classes I want to support and which will generate the concrete functions for me?  I want to avoid to write a function for each Set class manually...


I have built a REST based API (using asp.net WebAPI) which returns RSS feeds to my mobile application. There are around 30,000 active users of my mobile application which access this RSS feed. As per Google analytics, there are around 500 users using the REST API any point of time. I expect this number to grow over the period of time.  To improve the performance of the API, i cache the RSS feed in memory so that subsequent requests are  served from memory only. The cache is refreshed every 3 hours.  Question: Given that most of the action is happening in memory, do i need to get a VPS hosting with SSD or a normal HDD (RAID 10) will suffice ?  EDIT: Using Windows Server 2012 R2 softsyshosting


Is there a way to target the arrow from an OP bow via command block?

I am trying to make an effect trail for a specific weapon in MC, a bow with power 120.  I want to use a command block to target any arrow with the damage it should be doing (63) and summon a trail of splash potions.  I also want to kill any arrow entities that have inGround=True  Is there any way to do this or do I have to come up with something else?  Attempt:  /execute @e[type=Arrow,damage=63,inGround=0] ~ ~ ~ summon ThrownPotion ~ ~ ~ {Potion:{id:potion,Damage:8197}} /kill @e[type=Arrow,inGround=True]   Each unfortunately just affects all arrows.  Is this even possible?


Companies like Alitalia and KLM show on their web sites hand luggage dimension limits as:     max 55 x 25 x 35 cm   (Equivalent in inches should be: 21.5 x 10 x 13.5 in.)  Would hand luggage measuring 55 x 20 x 40 cm still be accepted as valid?  The sum of all dimensions in both cases is 115 (cm), although the lengths are distributed slightly differently across dimensions.  Some hand luggages like  measure 55 x 20 x 40 cm (and are classified on the web site as hand luggage, good for cabin).


Search for two sequential patterns with any number of characters in between using grep

I want to look for lines with "word1 ... word2" where '...' could be any different characters. So far I have used two greps for the same like this:  grep "$word1" $filename | grep "$word2"  Is there a faster way to do this by suppose something like this:  grep "$word1*$word2" $filename  where maybe * could be some special character which can be any other character(s)?


Stop Windows asking me to eject ATA device

Recently reinstalled windows and have AHCI enabled (perhaps it has something to do with AHCI mode). Basically, I have the option now to eject my hard drives in the "Safely remove hardware and eject media" facility at the bottom right of the tray bar. Except that, I would not want to eject my operating system hard drive, and probably don't really want to eject my data hard drives at any time either. Is there any way to stop windows from giving me this option? I don't want it.


Rudin 3.4. Calculate $\lim\limits_{n \to \infty} \left(\sqrt{n^2 + n} - n\right)$.   The solution to this seems obvious: after enough arithmetic, let $n \to \infty$ and get $\frac{1}{2}$. I am not sure how to rigorously justify the final step, though. Here is what I have:     Leveraging multiplication by the conjugate, we get:    \begin{align*} \sqrt{n^2 +  n} - n & = \left(\sqrt{n^2 + n} - n\right) \cdot \frac{\sqrt{n^2 + n} + n}{\sqrt{n^2 + n} + n} \\ & = \frac{n^2 + n + n \sqrt{n^2 + n} - n \sqrt{n^2 + n} - n^2}{\sqrt{n^2 + n} + n} \\ & = \frac{n^2 + n - n^2}{\sqrt{n^2 + n} + n} \\ & = \frac{n}{\sqrt{n^2 + n} + n} \end{align*}   Multiplying through by $\frac{\frac{1}{n}}{\frac{1}{n}}$ gives:   \begin{align*} & = \frac{\frac{1}{n} \cdot n}{\frac{1}{n} \left(\sqrt{n^2 + n} + n\right)} \\ & = \frac{1}{\frac{1}{n} \sqrt{n^2 + n} + 1} \\ & = \frac{1}{\sqrt{\frac{1}{n^2} \left(n^2 + n\right)} + 1} \\ & = \frac{1}{\sqrt{1 + \frac{1}{n}} + 1} \end{align*}   Clearly, a limit of a quotient is the quotient of the limits. The limit of a constant is $1$, so that take scare of the numerator. The limit of a sum is the sum of the limits, so that gets us the limit of $\sqrt{1 + \frac{1}{n}}$ and the limit of $1$, which is a constant.    However, obvious though it is that this limit is $\frac{1}{2}$ because $\frac{1}{n} \to 0$, I cannot find a theorem in Rudin justifying this. Proving it from scratch would not be too much of a problem, but my question is: is there a general, all-purpose justification for a result like this that says, in effect, that we can "plug in" the limiting argument? If the function were continuous, this would be fine, but we don't have continuity for another chapter.  EDIT: This isn't a duplicate because the linked question does not address my specific questions on this exercise.


I saw a lot of samples of C# code with the => syntax.  Can anyone explain about what the usage of this syntax?  select x => x.ID


What are all the friendly and enemy ultimate sounds?

When ultimates are used in Overwatch, a unique voice line sound effect is played, and it sounds different depending on which team used the ability. Does anyone have a list of what the two voice lines are for each character? Also some enemy voice lines seem to be much harder to hear (Widowmaker, Symmetra), so an indication of the relative volume would be great as well.


I want to put a folder called, say, Fonts in the Finder sidebar. Normally, putting a folder there gives you a generic folder icon (see the Fonts folder below):     However, I want to change the sidebar icon of the Finder folder to something like a stylized f. How would I do this?  One possible way would be to change the generic folder icon into the stylized f, but this would only really be viable if I wanted to put one folder there. Is there a better way?


I have this question and I don't know exactly how to solve it; the question is:  Give the number of shortest paths from (-2,5) to (2,-1)? please, I need a help...


Unlike in the UK and most of the European countries (where one can buy a SIM over the counter in any of the shops), getting a SIM in India is a tedious process. One has to provide a copy of ID proof (both photo ID and an address proof) and then wait couple of hours, sometime one day to get the SIM activated. This doesn't seem to be a concern for an Indian resident as we can wait.  I am looking for information from tourists/visitors outside India who were on a short visit (tourist/business) and managed to get a cell connection. I would like to keep this information handy so that I can share it with my friends when they visit India.


Can someone explain to me why the greatest common factor of (a,b) is equal to gcf(a mod b, a)

So when I want the gcf of a,b I could use the euclidean algorithm for example.  But why is gcf (a mod b, a) = gcf (a,b)    (because 0<=a<=b and in a mod b, a is always smaller than the rest from a mod b?)   So essentially my question is: how does the gcf(a mod b, a) work.  A dumb question:   why is the result of a mod b even smaller than a and how is that linked to the greatest common factor of a,b?    Thank you.


I have just installed Kubuntu 16.04 using Asia (Rangoon) Timezone. The calendar and some numbers are showing in Myanmar Language.How can I change these language to English while retaining Rangoon Timezone?


Windows 8.1 and Ubuntu Desktop 13.10 dual boot problem

I installed Ubuntu after Windows 8.1 on different partitions.  Then I installed EasyBSD. I added an Ubuntu partitions entry. Then I selected "grub2" but Ubuntu can not open, the computer just waits.  I reset then tried to load Ubuntu but Windows8.1 boot manager not grub2 comes up.  My boot repair program report link:


Are there theorems in number theory which are true for a large interval, but are known to be false for an arbitrarily large number outside that range?

As an example, it is certainly trivial to verify that  is true for all numbers up to 10^10 using a reasonably powerful computer. We now have mathematical proof of that theorem for all numbers, but are there other examples showing the opposite? E.g. a certain theorem is known to be true for all numbers up to 10^20, but there is also a known counter example at a much larger value.   Obviously it's easy to make up such a theorem for the purpose of the question, so I would like to limit the scope to theorems that were actually researched by the mathematical community.


$o(g^{k})=\frac{o(g)}{\gcd(o(g),k)}$ order of a power of a group element.

Lets say $g \in G$ where G is a group. Also $\operatorname{ord}(g)=n$. Then we have to prove that:  a) $\operatorname{ord}(g^k)=l $, where $l$ is the least number bigger than (or equal to)  $1$, such that $n\mid k*l$.  b) $\operatorname{ord}(g^k)=n \Leftrightarrow \gcd(k,n)=1$  With a) I tried to go like:   $(g^k)^l=g^{k*l}=g^k=g^n*g^k=g^{n+k}$ and then from second and last equality: $k*l=n+k$ from what I have that $k(l-1)=n$, and I am stuck. It may be simple or maybe I've gone a wrong path.  With b) I have no idea how to start, but it seems like a conclusion from a).  I would appreciate any help or hint. Thanks in advance!


How electrically neutral do stars remain through their lifetime?  As an example, I could imagine processes such as coronal mass ejections leaving the Sun in a slightly charged state.  Are there such processes that will leave a star with overall charge?


How to make a footer that sticks to bottom when content is short but not fixed in CSS?

How to make a footer that sticks to the bottom when content is shorter than screen height and float to bottom of the content when content is longer than screen height ?Now I am doing like this.  html  <body> <div class='container'>  </div> <footer>  </footer> </body>   CSS  .container{   position:relative;   min-height:500px; }  footer{  height:200px;  background-color:black;  position:absolute;  bottom:0px; }   This code is fine when the content is shorter than the screen size or very short. But my issue is when the content is very much longer(eg.twice of the screen size), footer sticks to the bottom when it first loads the page. But when I scroll down, the footer is stacked to the top of the new scrolled content.


How to rank a million images with a crowdsourced sort

I'd like to rank a collection of landscape images by making a game whereby site visitors can rate them, in order to find out which images people find the  most appealing.  What would be a good method of doing that?   Hot-or-Not style? I.e. show a single image, ask the user to rank it from 1-10. As I see it, this allows me to average the scores, and I would just need to ensure that I get an even distribution of votes across all the images. Fairly simple to implement. Pick A-or-B? I.e. show two images, ask user to pick the better one. This is appealing as there is no numerical ranking, it's just a comparison. But how would I implement it? My first thought was to do it as a quicksort, with the comparison operations being provided by humans, and once completed, simply repeat the sort ad-infinitum.   How would you do it?  If you need numbers, I'm talking about one million images, on a site with 20,000 daily visits. I'd imagine a small proportion might play the game, for the sake of argument, lets say I can generate 2,000 human sort operations a day! It's a non-profit website, and the terminally curious will find it through my profile :)


Do all massless particles (e.g. photon, graviton, gluon) necessarily have the same speed $c$?

I suppose there was a discussion already on .  But I silly wonder whether all the massless mediators of four fundamental forces, i.e.  Graviton: $g_{\mu\nu}$ (gravity)  Photon $\gamma$: $A_\mu$ (electromagnetism)  Gluons: $A_\mu^a$ (strong interactions)  Necessarily travel at the same speed? Is there a no-go theorem or theoretical proof to say that it is impossible to have these three mediators have different speeds?   Or does QCD confinement makes the story of gluons any different from gravitons and photons?  [ps. excluded massive $Z^{0}$ and $W^{\pm}$ bosons (weak interactions)]  Another way to say this: Speed of photon, graviton, gluon all equal to $c$? or  Whether all massless particles necessarily have the same speed?  Note add: Notice however, in condensed matter systems, there can be emergent gauge fields and emergent massless particles (Dirac or Weyl cones), but their speeds need not be the same, unless there is some emergent symmetry...


If row spaces of two $m\times n$ matrices are equal, then matrices are row-equivalent

I'm trying to prove that if two $m\times n$ matrices $A$ and $B$ over a field $F$ have the same row space, then they are row-equivalent.   Intuitively, it makes sense. Indeed, if $\mathrm{row}(A) = \mathrm{row}(B)$, then each row $[a_{i1}, ..., a_{in}]$ of $A$ is generated by rows of $B$ and vice versa, that if, for any $i = 1,...,m$ we have $$[a_{i1},...,a_{in}] = c_{i1}[b_{i_11},...,b_{i_1n}] + ... + c_{it_i}[b_{i_{t_i}1},...,b_{i_{t_i}n}]$$ and $$[b_{i1},...,b_{in}] = d_{i1}[a_{i'_11},...,a_{i'_1n}] + ...  d_{ip_i}[b_{i'_{p_i}1},...,b_{i'_{p_i}n}].$$  This seems similar to the condition an elementary operation being applied to a row, but I can't seem to make this final step to make it rigorous. One idea was to prove by induction is that is $A_k$ is equivalent to $A$, then $A_{k+1}$ is equivalent to $B$, where $(A_k)_{ij}$ is equal to $b_{ij}$ if $i < k$ and to $a_{ij}$ otherwise, but I have a feeling that this is wrong.   Edit: This question has been marked as a duplicate of another question for some reason. However, that question asked how to prove that two row-equivalent matrices have the same row space, while my question asks how to prove the converse.


Consider a  unit square  $OABC$ where,$O\equiv (0,0),A \equiv (1,0),B \equiv (1,1), C \equiv ()$.If  two point $P_1$  and  $ P_2$is chosen randomly and uniformly  in or on the square.how do we find the expected value of  angle $\angle P_1OP_2$? My Attempt:- If $(X_1,Y_1)$  and   $(X_2,Y_2)$ are the coordinates of the point chosen , Then ezch of the  x and y coordiantes follows  a uniform distribution in $(0,1)$  .If $\theta $ be the angle $\angle P_1OP_2$ ,then $$ cos( \theta) =\frac{x_1x_2+y_1y_2}{\sqrt{{(x_1^2+y_1^2)}{(x_2^2+y_2^2)}}}$$. The goal ,then , is to find the pdf of  $\theta$.Thanks for any responses/hints in advance


Creating a flowing effect with Cycles noise

I've got a Cycles noise node and would like to give it a flowing effect.  This is kind of what I mean:    I achieved this by sliding the noise distortion back and forth. The problem is that the result looks like it's moving forward, then rewinding; I'd like something that appears to continuously flow.  I can imagine that some clever texture coordinate mapping could do this. Or maybe something else?


Working with elementary type proofs of divisor functions

Proof conclusion to: Let m,n $\in$ $\mathbb{N}$ $\backslash$ $\{0\}$ . Prove that $s |\tau (m^{s}) - \tau(n^{s})$, where $\tau$ is a divisor function.   Hello, so I have a tiny question about the summarization of my proof.  I got to the point where I defined my $\tau$ divisor function and got them both $\tau(m^s)$= $\prod$ something +1 and $\tau(n^{s})$ = $\prod$ something +1.    I've noticed that the last terms of the polynomial are both one. Why is it with the +1 part, I can conclude with that:  s| $\tau(m^s)$ - $\tau(n^s)$.   The line for why that is, isn't quite clear.


Tikz plot from multiple-column data file

I would like to know how can I choose a column from a multiple data file, and how can I operate with them.  I mean in gnuplot I used this code to plot the second column depending on the first and also take the minus one time the second.  plot "file.dat" u 1:($2*(-1))  So could someone help me which is the equivalent of using in tikz?  Thank you!


I was thinking about buying a , and running Ubuntu on it. I have looked around the web, and a lot of stuff says that it's difficult for it to work on ARM processors. Has anyone figured out how to get a Raspberry pi to run Ubuntu?


How to autostart terminal and run commands?

I want to have the gnome-terminal autostart and run a single line like echo "Hello World", after the user is logged in. Ubuntu automatically logs in the user. What is the best way to achieve this? Tried to add gnome-terminal to the list of startprograms, but can't seem to add any additional commands. gnome-terminal -- 'echo "Hello World"' opens an empty terminal, but doesn't run the code.


I'm relatively new to Java and I am trying to make a login page for my desktop application. I have a thread called "listen" that should be called when the application first opens, its job is to check weather the username and password fields are not blank.   public class Login extends JFrame implements Runnable {     private JPanel contentPane;     private JTextField txtUsername;     private JPasswordField pwdPassword;     private JLabel lblUsername;     private JButton btnLogin;     private JLabel lblPassword;     private JCheckBox cboxRemember;     private Thread run, listen;     private boolean running = true;  public Login() {     createWindow();     run = new Thread(this, "Running");     running = true;     run.start();     }  private void createWindow() {      //application layout and actionListener for login button }  public void run() {     listen();  }  public void listen() {     listen = new Thread("Listen") {         public void run() {             while (running) {                 if (txtUsername.getText().equals("") || pwdPassword.getText().equals("")) btnLogin.setEnabled(false);                 else btnLogin.setEnabled(true);             }         }     };     listen.start(); }  public static void main(String[] args) {     EventQueue.invokeLater(new Runnable() {         public void run() {             try {                 Login frame = new Login();                 frame.setVisible(true);             } catch (Exception e) {                 e.printStackTrace();             }         }     });   } }   Whenever i try to execute my code the 'listen' thread throws a NullPointerException on this line if (txtUsername.getText().equals("") || pwdPassword.getText().equals("")) btnLogin.setEnabled(false); I'm not sure what am I doing wrong, any help will be appreciated, thanks.


What is the correct form? Does context play a role?  Are there noticeable trends towards the awkward "noone" or is it just a by-product of careless orthography on the Internet?


Show that $\mathbb{Z}[i]/(2+3i)$ is a finite field.    By applying some isomorphisms and realizing $\mathbb{Z}[i]$ as the quotient ring of $\mathbb{Z}[x]/(x^{2}+1)$, I found that:  $\mathbb{Z}[i]/(2+3i) \cong \mathbb{Z}[x]/(x^2+1,2+3x)$  However, I run into trouble as I can't divide $x^{2}+1$ by $2+3x$ in $\mathbb{Z}[x]$. What would be another way to approach the problem?  Thanks for the help.


Evaluate $\lim_{x\to \infty}\ (x!)^{1/x}$

Here's the problem... $$\lim\limits_{x\to \infty}\ (x!)^{1/x}$$  I've deduced the answer to this is $\infty$, but haven't exactly shown that.  I'm getting $\infty^0$, so did both tricks where you change it to  $$\exp\left({\lim_{x\to\infty}} \frac{1/x}{1/\ln(x!)}\right) = \exp\left(\frac{0}{0}\right)$$ And $$\exp\left({\lim_{x\to\infty}} \frac{\ln(x!)}{1/(1/x)}\right) = \exp\left(\frac{\infty}{\infty}\right)$$  And for both of which, I need to do L'Hospital on this $\ln(x!)$ which I haven't the slightest idea how to do... Any suggestions that don't include Stirling's Approximation? My prof eluded to this being out of the question unless we were going to prove Stirling's first


Error installing Canon LBP 2900 on Ubuntu 18.04

I've been trying to install Canon LBP 2900 driver on my Ubuntu 18.04 for the past few days. I tried following many tutorials such as , and also tried installing via GUI by downloading . I'm having problems installing.  Preparing to unpack cndrvcups-capt_2.71-1_amd64.deb ... Unpacking cndrvcups-capt (2.71-1) ... dpkg: dependency problems prevent configuration of cndrvcups-capt: cndrvcups-capt depends on cndrvcups-common (>= 3.21); however: Version of cndrvcups-common on system is 2.60-1.  dpkg: error processing package cndrvcups-capt (--install): dependency problems - leaving unconfigured Processing triggers for systemd (237-3ubuntu10.2) ... Processing triggers for ureadahead (0.100.0-20) ... Errors were encountered while processing: cndrvcups-capt   How can I get this printer working?


When I crafted a golden pickaxe to mine some Crimtane ore down in a dungeon right under my house. I went on a mining trip to get gold. (Also, I haven't found the merchant yet.. I've searched a lot..) Anyway, I crafted my pickaxe and I get Broken Gold Pickaxe.. And I dont know why its broken or not.. I'm confused.  How Do I fix the broken part of my golden pickaxe?


pronunciation rules for words with spelling -th- /θ/ /ð/

Is there a rule to identify which is the correct pronunciation for words with -th- spelling  (mother- think), this /θ/ or this /ð/?


IEEEtran Export to PDF version 5 or above

I'm writing a paper for an IEEE conference and am checking the PDF with PDFExpress. One of the errors that I'm getting is that the PDF version  of my paper is under 5:  (actually "version 5" in an Adobe Acrobat Reader version - editor)    I opened the file in Adobe Acrobat Reader and the file properties tell me that the PDF is version 4.  (that's the Adobe Acrobat version - editor)  In LyX, I opened Document > Settings… and unchecked Use Hyperref Support under PDF Properties. I think these will take care of errors (1), (2) and (4) from the error report. However, I don't see a way to specify a PDF version.    I found , which made LyX complain about a missing \begin{document}.  So now I'm completely lost. How may I specify what PDF version to export the document in?  ( Editors Note: The current version of the pdf open file format is 1.7 [2/7/2015]. Adobe Acrobat Reader is frequently, but not the only program, used to freely open pdf files.  Createspace supports submittal pdf file in version 1.4 and below.  They do not say they support pdf file format version 1.5 or above, which is this editors problem )    Technical specs:   LyX version 2.0.5.1 Mac OS X 10.7.5 (Lion) MacTeX version:


Thanks to the help of a few of the other guys I have my AC to DC rectifier working, and the rest of the power supply working.  Now while testing the power supply, my 18V AC transformer gets rectified and put into my circuit below   And I end up with 1.3-26V DC output selectable via the pot R2.  Now while running this @12V with a LED strip light, running about 600mA my heat sink got quite hot. Not hot enough to cause the thermal protection in the LM317 to cut in but hot enough to get me thinking.  Power dissipated = (Vin - Vout)*Il = (26 - 12)*0.6 = 8.4W  My heat sink is rated at 11 C/W and I pasted the LM317(TO-220) on.  Max C/W is = (MaxRunningTemp - ambientTemp) / power = (60-25)/8.4 = 4.2 C/W  Does that sound right, never done any heat sink calculations before. So I would need a heat sink rated at <4.2 C/W  I would not see my self running this over 500mA again but running this circuit at 5V would change a lot? The power dissipated would be 42W if 5V @ 500mA. What can I do to prevent needing a HUGE heatsink? and are my calculations above correct?


A prepaid sim card for vacations to use in France & UK? (2015)

I found some posts about this matter but they don't have an updated review for 2015.  I wish to purchase a SIM card - something like prepaid card for just one month or two for vacations - for use in France & UK.  I'd like something like internet oriented. Do you know any company selling such services that you can recommend?


what groups have only elements of prime order?

If there exist any group which has only elements of prime order? (except of $p$-elementary abelian, $Q_{8}$ and $D_{2p}$)


I so stuck with a problem of set theory. But first a recursive definition:   Define $R_0=\emptyset$ If $R_\alpha$ is defined, then $R_{\alpha+1}=\mathcal{P}(R_\alpha)$ (the power set). For a limit ordinal $\gamma$, if $R_\alpha$ is defined for all $\alpha<\gamma$, then define $R_\gamma=\displaystyle\bigcup_{\alpha<\gamma} R_\alpha$   We define $\text{BF}=\displaystyle\bigcup_{\alpha\in\text{OR}} R_\alpha$ (the class of well founded sets).  Next, my problem     Take $A\subseteq \text{BF}$ a proper transitive class such that $(A,\in)\models\text{ZF}$. Prove that $A$ is almost universal.    I think that the exercise is false because if it was true, then we could conclude that the strongly inaccessible cardinals doesn't exists. This because if $\kappa$ is strongly inaccessible then $R_\kappa$ satisfies the hypothesis but $R_\kappa$ isn't almost universal. I really appreciate any hint or/and suggestion.   Edit: my counterexample is wrong. But, then, how can I solve the exercise?


I have installed Chrome in Ubuntu 16.04 and selected it as my default browser then restarted the computer. But I am still seeing Firefox in the Launcher and not chrome.   How can I change this, please?


Just how offensive are the terms "retarded" and "gay"?

My college-age son and his friends use the terms "retarded" and "gay" pretty much interchangeably to mean substandard, bad, lame (in the sense of ineffectual or weak) or just plain wrong. I've suggested that he might want to be careful about where he uses such language, but he clearly isn't worried about being offensive with those terms. Now add this to the equation: Last night we watched a recorded version of Comedy Central's "A Tribute to Sam Kinison." Comedy Central censors a lot of words, including names of body parts (although, curiously, they let "dick" remain unbleeped), terms for sex acts, and so on. And we could clearly see that the word "retarded" had been bleeped (it's a very easy word to lip-read). Note that Comedy Central does not censor the word "nigger" on the Dave Chapelle show, although this is a word Jon Stewart goes to great lengths to avoid saying on his own show (also, of course, on Comedy Central). So I wonder: is the word "retarded" really that offensive? How about "gay" in the context described above? UPDATE From an Associated Press story ( reported in the Boston Globe today (Sept. 21, 2011):  WASHINGTON - Young people immersed in the online world see racist and sexist slurs and other name-calling that probably would appall their parents and teachers. And most consider it no big deal, a poll says. ... When the question is asked broadly, half of young people surveyed say using discriminatory words is wrong. But 54 percent think it’s OK to use them within their own circle of friends, because “I know we don’t mean it.’’ And they don’t worry much about whether the things they tap into their cellphones and laptops could reach a wider audience and get them into trouble. ... Demeaning something with “that’s so gay’’ is so common that two-thirds of young people see it used, and the majority aren’t offended at all, despite a public-service ad campaign that tried to stamp out the anti-gay slang. A similar effort by the Special Olympics and others to persuade kids not to use “retard’’ hasn’t hit home with half of those surveyed, who don’t find the word even moderately bothersome. Twenty-seven percent are seriously offended, however. Some teens just text the way they talk. Calling each other “gay’’ and “retarded’’ is routine in high school, says Robert Leader, 17, a senior in Voorhees, N.J. So teens text it, too.


How can friction do no work in case of pure rolling?

I have read various answers , on PSE and elsewhere , and most of them explain that the point of contact of the rolling object undergoes 0 instantaneous displacement in the direction of friction, I agree , but then there is a feeling that the friction does provide a torque , so how can it do 0 work . ( The pure rolling here is under a constant external force on the object so friction does act ).


Java - Compare Strings that may contain numbers, without the number of digits interfering

I have an issue with comparing Strings that sometimes contain numbers.   Let's say I have two Strings; s1 = "Chapter 9" and s2 = "Chapter 10"  Any human would say that, if these are to be sorted, s1 would end up earlier than s2 and that also happens in Windows folders. However, in Java it just checks one char at a time until one is greater/lesser than the other, which leads to it putting s2 earlier than s1 due to it having a '1' where s1 has a '9'  Is there a way of managing this that does not involve a lot of code and/or processing?


Defining projection of raster file which lacks prj file

I have two raster data. They must cover each other. My problem is, one of them doesen't have prj file, therefore I don't know what is the projection of this one. I can not cover this raster with the other one. Of course, I tried define projection function several times, but I don't know which projection should I use.   I use ArcMap 10.6.1


Unable to install Cisco Packet Tracer 7.3 on Ubuntu 20.04

I am trying to install Packet Tracer 7.3 (latest version) on Ubuntu 20.04 but do not succeed to so so because of two dependencies which are not installable ("libdouble-conversion1" and "qt-at-spi").  However I successfully installed the previous version (7.2.2) which was available in an Ubuntu installer format (.run file) but I nothing happens when I run it from my gnome desktop.  I am quite a newbie in Linux so I appologies if answers are obvious...  Thanks in advance ;-)  Denis


I just upgraded to ubuntu 14.04 from ubuntu 12.04 (Which I loved) and now, I cant install apt-fast. My net connection is very slow and I want to download using apt-fast but whenever I add the apt-fast ppa and update and try to install it, It says   package apt-fast not found  How do I fix this? thank you.  I really appreciate The effort made by askubuntu (Which includes you awesome people ;)) To help me. My problem has already been answered. Here is a screenshot of my software sources. The person who answered my question has apparently removed the comment that answered my question but here is the repository that helped me add apt-fast  sudo add-apt-repository ppa:saiarcot895/myppa  So if this helps I would like to upvote each and every person who helped me and I will accept one answer too, Just give me some time to test both of them ;)  anyway thank you guys to help me. You are awesome :-) XD


What causes iPhone low battery crashes? Is there a software fix?

Some iPhone users (especially those with devices that've been in use for a while) encounter a problem where the device crashes once the battery gets low. For example:        "After updating to iOS 7 my iPhone 5 has been doing something strange.   When the battery gets low (usually around 20-30%), iOS will shut down   completely, and when you try to power the phone back on it flashes on   the screen telling you to plug the phone in to charge it (saying that   the battery is almost completely dead).   The phone refuses to power   on until you plug it in, but once I plug the phone in and power it   back on, the battery life shows the last percentage it was at before   it crashed (20-30%). This has happened to me more than once, so I know   it's not just some crazy fluke."      "I have a 3GS that is almost 2 years old now and had a hard life. It   has now developed a tendency to crash when the battery gets below 25%.   it will restart using the top button ok but as soon as you put any   strain on the battery it crashes when at this low level. When the   phone is charged it seems to work fine."      "I have a weird problem with my iPhone 5. My phone switches off when   the battery is low. I was at 23% charge and just browsing facebook   when my battery died. The other day I was at 13% charge and it   switched off. Last week 17%.. It refuses to switch back on until it   was plugged into the wall. I have tried restoring the phone and set up   as new but I still have the same problem. It just seems to switch off   when the battery is low at different percentages."         It seems to happen on various model iPhones and versions of the OS; it's currently happening to me on a heavily used two year old 4S running iOS 6.1.1.   that:     "The common element in these crashes is low battery life, usually under 20 percent, although one crash occurred at almost 30 percent. When I give the iPhone power, it restarts immediately and shows the expected amount of battery life remaining. So it’s not that the battery is actually running out; instead, [iOS's] power management code is freaking out once the battery level falls to around 20 percent. I do see a number of LowBatteryLog files in Settings > General > About > Diagnostics & Usage > Diagnostic & Usage Data, though their contents don’t reveal a smoking gun. Letting the battery run down completely and then recharging entirely to recalibrate it made no difference."   (NB. TidBITS writes about this as it pertains to iOS 7 only.)  So, my question:   Do we know, technically, what is causing these crashes beyond simply "the power management code is freaking out"? Are there any software hacks, fixes or usage habits (beyond usual battery saving/care techniques and "just get a new battery/don't let the battery get low!") that might help avoid these crashes?   (I'm interested in general answers, but in case it's of use  are the low battery logs from my two most recent crashes.)


Can't install apt-file and ubuntu tweak in terminal

I tried to install the packages apt-file, ubuntu-tweak and checkinstall using sudo apt-get install <package name> in 10.10, but the terminal reported package not found even after sudo apt-get update. What am I doing wrong?


Rolle's Theorem and the Mean Value Theorem

Let $f\colon \mathbb{R} \to \mathbb{R}$ have derivatives of all orders. Suppose that $a < b$ and that $f(a)=f(b)=f'(a)=f'(b) =0$. Prove that $f'''(c) = 0$ for some $c$ in $(a,b)$.


How To Run A Shell Script Again And Again Having X Interval Of Time In Root?

I have a shell script in my Ubuntu Server 14.04 LTS at ./ShellScript.sh. I setup /etc/rc.local to run the shell script after boot but before login using below code.  To run run it boot write this command in terminal: sudo nano /etc/rc.local then add following and save.  #!/bin/sh -e # # rc.local # # This script is executed at the end of each multiuser runlevel. # Make sure that the script will "exit 0" on success or any other # value on error. # # In order to enable or disable this script just change the execution # bits. # # By default this script does nothing.  #!/bin/bash  ./ShellScript.sh  exit 0   Note: Keep in mind that I am working in root mode. Now when I run crontab -e then I got the following. Now What to do?                                                                                no crontab for root - using an empty one Select an editor.  To change later, run 'select-editor'. 1. /bin/ed 2. /bin/nano        <---- easiest 3. /usr/bin/vim.basic 4. /usr/bin/vim.tiny Choose 1-4 [2]:   After selecting 2, I got crontab: "/usr/bin/sensible-editor" exited with status 2  Now I want to run/execute this shell script again and again having 15min of time interval between every run after boot but before login. So Can I do it?  Answer:  First of all, you can't access crontab -e via root. You have to login via USER account. After login in USER account, Go to terminal and type crontab -e Here you will get some text like below.  # Edit this file to introduce tasks to be run by cron. # # Each task to run has to be defined through a single line # indicating with different fields when the task will be run # and what command to run for the task # # To define the time you can provide concrete values for # minute (m), hour (h), day of month (dom), month (mon), # and day of week (dow) or use '*' in these fields (for 'any').# # Notice that tasks will be started based on the cron's system # daemon's notion of time and timezones. # # Output of the crontab jobs (including errors) is sent through # email to the user the crontab file belongs to (unless redirected). # # For example, you can run a backup of all your user accounts # at 5 a.m every week with: # 0 5 * * 1 tar -zcf /var/backups/home.tgz /home/ # # For more information see the manual pages of crontab(5) and cron(8) # # m h  dom mon dow   command   Now I=in the end of file, you have to add */15 * * * * /ShellScript.sh line to run your script each after 15 min. Now save the file and its done.  Note: If you want different timing of interval to run script again and again then don't get confused. Here are some online tools that will generate Cron lines for you.


Reorder the data out put of a stored procedure

I have a stored procedure that produces data for call center solution. However, is there a way to modify the sp so that each time the data is executed it is delivered in a different order? For Example Today: 1,2,3 Tomorrow: 2,1,3 the next day 3,1,2 . Is there a manipulation I can execute that will scramble the order whenever it is executed?


How can I change the text size of bookmarks in Files / Nautilus?

I have a bunch of bookmarks in Files/Nautilus and would like to reduce the text size of/space taken up by the entries in the left hand bookmarks column, so that I don't have to scroll to access those at the bottom of the list (I use a trackball mouse that has no scroll wheel).    Is this possible? If so, how?


If a stick of ram dies in a 4 piece kit, do I have to replace the whole kit?

The Ram kit that I have is:  CORSAIR Dominator Platinum 32GB (4 x 8GB) 240-Pin DDR3 SDRAM DDR3 1866 (PC3 14900) Desktop Memory Model CMD32GX3M4A1866C9  And one of the sticks died. Is is possible for me to just replace the one stick? Where can I find something like that? (I don't see it on newegg/amazon).   Also, I think that the sticks work in pairs and I'm not sure some random stick will be a exact one I need of the right pair. Any ideas?


Existence of a normal p-Sylow subgroup when $\lvert\mkern1mu G\mkern1mu \rvert=q^{2}\mkern1mu p$

If $\lvert\,G\,\rvert=p^{2}\cdot\,q$ where $q,p$ are primes, How can i show $G$ has a normal p-sylow subgroup ? I tried working with the sylow theorem but i cant reach any contradiction when $Np = q$ and $Nq = p,p^2$ Also tried searching the same question but couldn't find in Stack Exchange


Faced with a small unpleasant situation. The PREFETCH files give me the path to the source file as:  C:\USERS\MYUSER\APPDATA\LOCAL\MEDIAGET2\MEDIAGET.EXE  This greatly spoils the look of my software. Is there an option to return it to its normal form, as indicated in the source file?  C:\Users\Myuser\AppData\Local\MediaGet2\mediaget.exe  I tried to output via FileInfo, through Path.GetDirectoryName + Name. Did not work. Anyway, prefetch gives the path in UpperCase mode (despite the fact that it is not used anywhere in the code).  P.S. Do not advise please use ToLowerCase - it also does not look nice and is different from the paths from the other code.


Why is uniq ignoring Unicode and lines with a single letter?

I'm trying to combine both the American and British dictionaries into one large dictionaries, and I'm trying to remove all the duplicates from the superset, but it seems that uniq is not outputting words like, "épée" or single letters.  This is what I've tried using:  LC_COLLATE=en_US.UTF-8 cat american-english british-english |sort|uniq -u > unique_sorted_combined_dict   If I just do this:  LC_COLLATE=en_US.UTF-8 cat american-english british-english |sort > sorted_combined_dict   "épée" and other such words do show up, along with single letters.  Is there something I'm missing here with uniq?  I should note that I'm using uniq from the GNU coreutils on Ubuntu 12.10, if that makes any difference.


A bit of a tedious one, hopefully it's okay to ask this here...  I was hoping someone could help me figure out if this PC build will work with Ubuntu? I've had trouble installing Ubuntu on my laptop in the past and now am finally biting the bullet and buying a new desktop. I'd like to set up a duel boot Windows 7 / Ubuntu and hardware really isn't my area (software man). I will be using this PC mostly for various development projects including openGL 3D graphics stuff so I'd like to be sure that my graphics card is compatible with Ubuntu as well!  If anyone could tell me if my plans will work out and offer any advice you have in general I'd be very appreciative! I've tried looking through the compatibility databases but I don't have much confidence in myself when it comes to hardware! None of this spec is set in stone, feel free to suggest changes and if I'm in the wrong place please point me in the right direction :)  Processor Intel® Core™i5 Quad Core Processor i5-6600K (3.5GHz) 6MB Cache  Motherboard ASUS® Z170-E: ATX, LG1151, USB 3.1, SATA 6GBs  Memory (RAM) 16GB HyperX FURY DDR4 2133MHz (2 x 8GB)  Graphics Card 2GB NVIDIA GEFORCE GTX 960 - DVI, HDMI, 3 x DP (Special!!)  1st Hard Disk 2TB SATA-III 3.5" HDD, 6GB/s, 7200RPM, 64MB CACHE  1st DVD/BLU-RAY Drive 24x DUAL LAYER DVD WRITER ±R/±RW/RAM  Power Supply CORSAIR 450W VS SERIES™ VS-450 POWER SUPPLY  Sound Card ONBOARD 6 CHANNEL (5.1) HIGH DEF AUDIO (AS STANDARD)  Wireless/Wired Networking 10/100/1000 GIGABIT LAN PORT (Wi-Fi NOT INCLUDED)  USB Options MIN. 2 x USB 3.0 & 2 x USB 2.0 PORTS @ BACK PANEL + MIN. 2 FRONT PORTS


Trying to install Xbuntu on an old laptop with Celeron Processor

I have created two or three bootable CD's from downloads, one with Ubuntu 15.1 and one from mini.iso.  I either get a message that there is some problem with PAE which I have no idea how to deal with, or I get a BOOT: prompt after an ISOLINUX message statement mentioning Peter Alvin.  I have absolutely NO IDEA what I am supposed to do with this.  The bootable CD doesn't just start installing Ubuntu like I hoped it would.  What do I do with the BOOT: prompt?  or the PAE message?


Dense simple smooth immersed curves in manifolds.

The  is a smooth, simple, immersion of $\mathbb{R}$ into $T^2$. This line is even dense in $T^2$ (thus not all injective immersions are embeddings).  When I tried to concoct a curve with similar properties in $\mathbb{R}^2$ I found it much more difficult and eventually threw up my hands in defeat.  So I'm curious:   Is there a smooth, simple, immersed, dense curve in $\mathbb{R}^2$ (or $\mathbb{R}^n$)?  If not, is there a smooth, simple, immersed, dense curve in an open subset of $\mathbb{R}^2$ (or $\mathbb{R}^n$)?  In general, which smooth manifolds $M$ admit a smooth injective immersion $\gamma:\mathbb{R}\to M$ such that $\gamma(\mathbb{R})$ is dense in $M$.   An answer to any of these would be extremely enlightening. Thanks in advance.


Binomial coefficient: Search for multiples of 13

Question: The coefficients of how many terms in the expansion of (1+x)2018 are multiples of 13?  So, we've to investigate the powers of 13 in ${2018 \choose r}$, where 0 ≤ r ≤ 2018  I tried using the following: $$s_p(N!) = \left \lfloor \frac{N}{p} \right \rfloor + \left \lfloor \frac{N}{p^2} \right \rfloor + \left \lfloor \frac{N}{p^3} \right \rfloor + \cdots$$  where, $s_p(N!)$ denotes the highest exponent of prime p in n!, where n is a natural number.   ${2018 \choose r}$, may be written as $\frac{2018!}{r!(2018-r)!}$. Now, I tried to figure out the exponent of 13 in numerator for several values of r, but couldn't find a pattern that would lead me to the desired answer.   Could someone please give a detailed solution to this problem, and also explain how to approach such problems? Is there any generalisation for the multiples of a prime number p in ${n \choose r}$?  P.S. The answer, to the best of my recollection, is 1395.


Using a known limit to find an another limit

I'm following a well known Calculus text book to restudy Calculus. One of the example problems in the book asks the following: Using $$\lim_{\theta\to 0}\frac{\sin\theta }{\theta}=1,$$ show that $$\lim_{h\to 0}\frac{\cos h-1}{h}=0$$ The answer states that: Using the formula $\cos h=1-2\sin^2(h/2)$ and $\lim_{h\to 0}\frac{\cos h-1 }{h}=\lim_{h\to 0}-\frac{2\sin^2(h/2)}{h}$ Let $\theta=h/2$, $$\lim_{h\to 0}-\frac{2sin^2(h/2) }{h}=-\lim_{\theta\to 0}\frac{\sin(\theta) }{\theta}\sin\theta=-(1)\cdot(0)=0$$ I understand the logic behind this explanation. However, what I don't understand is: how is it possible that the solution claims that: $$-\lim_{2\theta\to 0}\frac{\sin(\theta) }{\theta}\sin\theta=-\lim_{\theta\to 0}\frac{\sin(\theta) }{\theta}\sin\theta \ ?$$ I'd be glad if you could help me with this question. Thank you very much in advance!!!


Where's the "belongs on serverfault.com" question close reason?

I've seen a couple of questions recently that IMHO would be better suited to .  Here's one .  I couldn't see such site listed in the close dialog though:    What am I missing and what's the proper protocol to migrate such questions to their respective SE site?


I am running a linear regression on SPSS. Basically I have 2 independent and 1 dependent variables; and I would like to understand which of my independent variable is more effective on the dependent variable.  When I put the constant value into the equation, it does not give significant results. However, when I don't put the constant value into the equation, it gives significant results and of course it gives a value for each variable. So, I can understand, which one is more effective.  Actually, my aim is not creating a model. I just would like to compare the effects of 2 independent variables? So can i ignore the constant value then?


To construct the half-normal probability plot, plot the absolute values in a certain statistical diagnostic (residual, leverage, Cook distance and others) versus $z_i$ where:  $\displaystyle z_{i}  = \Phi^{-1} \left(\frac{k + n - \frac{1}{8}}{2n +\frac{1}{2}}\right)$   $\therefore$ Applied Linear Statistical Models, (Kutner,Nachtsheim,Neter & Li, 2005) Fifth Edition, Pag 596  or  $\displaystyle z_{i} = \Phi^{-1} \left(\frac{k + n + \frac{1}{2}}{2n +\frac{9}{8}}\right)$  $\therefore$ Generalized Linear Models, (P. McCullagh & J.A. Nelder, 1989) Second Edition,  Pag 407  where  $\Phi$ is the cumulative distribution function of the standard normal distribution.  $k$ is the  $k$-th ordered absolute residual   $n$ is the sample size  I could not locate the mathematical justification for the difference of the $z_i$, and more importantly I don't have any intuition about where it comes from.      Any help? Could you please guide me?


What is the best community for website recommendations?

I was looking for a community to ask a question for a website recommendation but can't find one. What is the best or closest community for these questions?


Will be closed - "closed" adjective or verb?

If I say "The shop will be closed tomorrow", is the word 'closed' here an adjective or a verb?


giving a submit button a value CodeIgniter

I wanted to give my submit button a value. I have watched this video,    but I am using CodeIgniter so it gave me an error.  I have already done this:  <?php    echo form_open('Mycontroller/thisfunction/'.$this->uri->segment(3));   ?>         <button class="btn btn-info fa fa-save" type="submit" name ="1">&nbsp Save</button>         <button class="btn btn-primary fa fa-save" type="submit" name ="2">&nbsp Save1</button>      <?php        echo form_close();     ?>   and my controller:  public function thisfunction(){      if($_POST['1']){         echo "1";     }else if($_POST['2']){         echo "2";     } }   but I got the error Message: Undefined offset: 1 and Message: Undefined offset: 2..   I need this code because I will be using it like this:      if(THIS BUTTON IS USED){         redirect it to this page     }else if(THIS BUTTON IS USED){         redirect it to other page     }


Counterexample for the normalizer being a normal subgroup

Let $G$ be a group, and $H$ a subgroup.  $H$'s normalizer is defined: $N(H):=\{g\in G| gHg^{-1}=H \}$.   Prove $N(H)$ is a normal subgroup of G, or give counterexample.  Intuitively it seems to me that this claim is wrong, however, I'm having trouble with finding a counterexample.  Thans in advance for any assistance!


Where can I ask a question about general and specific hardware?

I have a number of questions about how computer hardware goes together in general, as well as specific questions about certain parts.  I can't find any good location to ask these, does anyone know a good place? Or can we make a place?


Travelling back to India with a phone purchased (and unboxed) in Netherlands

I am in Netherlands on tourist visa and wanted to buy a iPhone and go back to India. I would claiming the VAT return at Amsterdam Airport but do I need to declare in India and do I need to pay the duty??  I will be using this phone so this phone wont be sealed packed.