i have a textfile with this content (id;date;user):  8559;2014-06-13;Carlos 8584;2014-06-23;1A Auto 8398;2014-06-02;LRDream 7738;2014-05-19;Felicitia Motors 8475;2014-06-06;Motori 8331;2014-06-30;Otto Burner 8521;2014-06-24;Mirage 3699;2014-06-30;LR DMJ 8050;2014-05-19;1A Auto 7428;2014-05-20;Carlos   Goal is to output this data sorted by 1) month and 2) username.  <?  $data = file("data.csv");  foreach ($data as $value) { $bla=explode(";",$value); $new[$bla[0]]['date']=substr($bla[1],0,-3); $new[$bla[0]]['user']=$bla[2]; }  function comp($a, $b) { if ($a['date'] == $b['date']) { return $a['user'] - $b['user']; } return strcmp($a['date'], $b['date']); }  usort($new, 'comp');  foreach ($new as $value) { echo $value['date']." - ".$value['user']."<br>"; }  ?>   This sorts the months correctly but the users are not really sorted:  2014-05 - Carlos 2014-05 - Felicitia Motors 2014-05 - 1A Auto <--- 2014-06 - LR DMJ 2014-06 - Mirage 2014-06 - Motori 2014-06 - LRDream <--- 2014-06 - Carlos <--- 2014-06 - Otto Burner 2014-06 - 1A Auto <---   What wrong with the code?  Thanks! NBG

I have CSV data loaded into a multidimensional array. In this way each "row" is a record and each "column" contains the same type of data.  I am using the function below to load my CSV file.  function f_parse_csv($file, $longest, $delimiter) {   $mdarray = array();   $file    = fopen($file, "r");   while ($line = fgetcsv($file, $longest, $delimiter))   {     array_push($mdarray, $line);   }   fclose($file);   return $mdarray; }   I need to be able to specify a column to sort so that it rearranges the rows.  One of the columns contains date information in the format of Y-m-d H:i:s and I would like to be able to sort with the most recent date being the first row.


cyberlink youcam is not opening my webcam.it is showing that some other program is using my webcam and i have to close that program first and restart the youcam to get started.and the problem is that I dont know which program is using my webcam.

Yesterday I was working on my laptop. Suddenly I noticed that the indicator light of the webcam was on, despite the fact that I wasn't making a video call or using the webcam in any other way at the moment.  It freaked me out.  It freaked me out that some unknown application on my computer was using my webcam without my permission, and possibly sending that video stream to god knows where on the Internet.  In the end, it turned out to be Skype which was in the process of crashing. (Despite me making no calls at the time.) So that story ended well.  But next time I see the webcam indicator light, I want to be ready. I want to be able to know exactly which app is using the webcam so I could destroy it.  Does anyone know how I can find out which app is using the webcam?  (I'm on Windows XP.)


Is the w in cow a vowel or a consonant? Assuming it is considered a vowel, would it likewise be so in how?  I learned that the vowels are "a, e, i, o, u, and sometimes y."  If w can be a vowel, what other letters can be vowels? What is the definition of a vowel?  By the way, I know w can be a vowel, for example in the word cwm, described in the OED as:     A valley; in Physical Geogr., a bowl-shaped hollow partly enclosed by steep walls   lying at the head of a valley or on a mountain slope and formed originally by a   glacier; a cirque.

In school we are taught the vowels: A, E, I, O, U, and sometimes Y.    got me thinking about when the letter Y is considered to be a vowel.  I understand (perhaps incorrectly) that in words like bicycle and why it is a vowel. What about the word voyeur (as mentioned in the XKCD alt-text)?   If I've got this backwards, and Y is almost always a vowel, how can I tell when it is a consonant? Thinking back, I don't think my education ever covered the difference between them, we just memorized which letters were which.


Encountered this today where there were no issues before, console logs follow:  Hit:3 https://download.virtualbox.org/virtualbox/debian bionic InRelease      N: Skipping acquire of configured file 'contrib/binary-i386/Packages' as repository 'https://download.virtualbox.org/virtualbox/debian bionic InRelease' doesn't support architecture 'i386'   Is this a problem with the repository, or with my own config? The same operation had no issue as recently as 3 days ago.

I installed Ubuntu 18.04 and then while installing Virtualbox i get the 'i386' error message after I did:  $ sudo apt-get update Get:1 http://nl.archive.ubuntu.com/ubuntu bionic InRelease [242 kB] Hit:2 http://security.ubuntu.com/ubuntu bionic-security InRelease                                                                 Hit:3 http://ppa.launchpad.net/danielrichter2007/grub-customizer/ubuntu bionic InRelease                                          Hit:4 http://nl.archive.ubuntu.com/ubuntu bionic-updates InRelease Hit:5 http://nl.archive.ubuntu.com/ubuntu bionic-backports InRelease Get:6 http://download.virtualbox.org/virtualbox/debian bionic InRelease [4429 B] Get:7 http://download.virtualbox.org/virtualbox/debian bionic/contrib amd64 Packages [1426 B] Fetched 248 kB in 1s (209 kB/s)      Reading package lists... Done N: Skipping acquire of configured file 'contrib/binary-i386/Packages' as repository 'http://download.virtualbox.org/virtualbox/debian bionic InRelease' doesn't support architecture 'i386'   I found several answers on Askubuntu for the 'i386' message but I don't know how to apply this to my situation


I have been facing this issue even when I boot through Gparted LiveCD. My goal is to install Windows dual booting with Ubuntu (My wife is not comfortable with linux)  Don't ask me about the ext2 and fat32 partitions here, I don't have any clue myself as to when and how they got created. Also let me know if it would be safe to remove these.  Suggestions? Advice?

I want to shrink my second (LVM) partition, in order to create a new partition in the newly freed space. I am using the Live CD to do so, because I know I can't resize/move this partition while it is in use. When I opened GParted in the Live CD, I realized that I could not resize the partition, because when I right-click it, the option "resize/move" is disabled.  I tried to unmount it, to "lazy" unmount it (umount -l /dev/sda2) but it didn't work.  A screenshot from GParted:


I generated a grid with 300m spacing but the ids generated from top to bottom in sequential oder. How could I get in horizontal from left to right sequence.

I am using QGIS 3.2.0 on a Mac (and also have QGIS 2), and I have a fishnet grid (probably created in Arc) that comprises of nearly 2 million grid cells. As a result, every change I make to the attribute table takes hours, so I can't experiment as I would usually.  I need to label each grid cell such that the north-westernmost cell is "1", and the numbers proceed by rows, until the last number goes into the south-easternmost cell. Using the row-number doesn't work, as that's not how the table is sorted. I've done this before, but cannot remember how.


i'm writing a program based on the Quadratic Equation everything looks good to me and there are not syntax or logical errors from what i see and also Eclipse isn't detecting any errors before running.  this is the output from the code: Exception in thread "main" java.lang.StackOverflowError     at QuadraticEquation.getDiscriminant(QuadraticEquation.java:33)     note it continues like this for about 50 lines or so  public class QuadraticEquation {     private double a;     private double b;     private double c;     public QuadraticEquation() {       double a = 0;     double b = 0;     double c = 0;     }      public QuadraticEquation(double newA, double newB, double newC) {         a = newA;         b = newB;         c = newC;     }      public double discriminant1 = Math.pow(b, 2) - 4 * a * c;     public double discriminant2 = Math.pow(b, 2) - 4 * a * c;      public double getA() {     return getA();     }     public double getB() {     return getB();     }        public double getC() {     return getC();     }      public double getDiscriminant() {     double discriminant = (b * 2) - (4 * a * c);         return getDiscriminant();     }      public double getRoot1() {         double r1 = (-1*b) + Math.sqrt(discriminant1) / (2*a);         return getRoot1();      }     public double getRoot2() {         double r2 = (-1*b) - Math.sqrt(discriminant2) / (2*a);         return getRoot2();     }         public void setA(double newA1) {         a = newA1;     }     public void setB(double newB1) {         b = newB1;     }     public void setC(double newC1) {         c = newC1;     } }   import java.util.Scanner;  public class TestEquation {      public static void main(String[] args) {     Scanner input = new Scanner(System.in);     QuadraticEquation Quadratic = new QuadraticEquation();            System.out.println("Please enter the values of the following variables: ");          System.out.println("a: ");         Quadratic.setA(input.nextDouble());          System.out.println("b: ");         Quadratic.setB(input.nextDouble());          System.out.println("c: ");         Quadratic.setC(input.nextDouble());          if (Quadratic.getDiscriminant() < 0) {              System.out.println("The equation has the following roots:");              System.out.println("The first one is " + Quadratic.getRoot1());              System.out.println("The second one is " + Quadratic.getRoot2());           }         else if (Quadratic.getDiscriminant() == 0) {              System.out.println("The equation has one root:");              System.out.println(Quadratic.getRoot1());          }          else {          System.out.println("The equation has the no real roots");          return;          }     }  }

What is a StackOverflowError, what causes it, and how should I deal with them?


From my local machine I can copy files from a remote machine  scp remote:/some/file/path ~   But what if I'm already SSHed into the remote machine? Can I do something like this  ssh remote cd /some/file scp path local:~   where local somehow resolves to the machine I SSHed from. This would of course be possible if the local machine is running an SSH server and the remote is configured to connect to it, but that isn't always an option.  Is something like this possible?

If I'm logged in to a system via SSH, is there a way to copy a file back to my local system without firing up another terminal or screen session and doing scp or something similar or without doing SSH from the remote system back to the local system?


I have written the following Java code to get a the first day of a week of year.      Calendar cal = Calendar.getInstance(Locale.GERMAN);     cal.clear();     cal.set(Calendar.DAY_OF_WEEK_IN_MONTH, Calendar.MONDAY);     cal.set(Calendar.YEAR, 2016);     cal.set(Calendar.WEEK_OF_YEAR, weekNumber);      DateFormat sdf = new SimpleDateFormat("dd.MM.yyyy");      System.out.println( sdf.format(cal.getTime()) );   By using the input week of year 53 it should result into an error acutally because this week of year does not exist in 2016. Instead it shows me the next possible first date from next year.  Is there a neat way to correct my code or do I have to check the input week of year by myself?  Thanks for your help.

I find it curious that the most obvious way to create Date objects in Java has been deprecated and appears to have been "substituted" with a not so obvious to use lenient calendar.  How do you check that a date, given as a combination of day, month, and year, is a valid date?  For instance, 2008-02-31 (as in yyyy-mm-dd) would be an invalid date.


I am trying to deploy a Salesforce Lightning Community from a Sandbox to Production.  I've included the Network and SiteDotCom in the change set, but I am getting this error:     Sorry, your target org is running on an earlier version of Salesforce and can't accept the current file. Please wait for your target org to be updated and try again.   Is there anything I can do to get around this? (apart from setting up the community manually)  Or do I need to wait until the Production Org has been updated to the same version as the Sandbox?

I am getting Error: Cannot import data from a newer release! while deploying siteDotCom from one sandbox to another sandbox. Version of source sandbox is 44 and target sandbox is 43.Could this be the reason for the error.  Below is the site-meta.xml file:  <?xml version="1.0" encoding="UTF-8"?> <SiteDotCom xmlns="http://soap.sforce.com/2006/04/metadata"> <label>testSite</label> <siteType>ChatterNetworkPicasso</siteType>


I need to convert values like 100000 to the Brazilian currency format (Real) 1.000,00 and I am using javascript. That would be in this pattern. 0,00 1,00 10,00 100,00 1.000,00  I managed to create the decimals using this expression. if (v.indexOf('.') === -1) {     v = v.replace(/([\d]+)/, '$1,00');   }  Now I'm having trouble separating when I have values above 1000,00 which would be 1.000,00. I'm using the keyup that calls the function and writes the value in another field (Total) and this function that does all the work of converting the number to "Reais" I did this function String.prototype.formatMoney = function () {   let v = this;       if (v.indexOf('.') === -1) {     v = v.replace(/([\d]+)/, '$1,00');   }    v = v.replace(/([\d]+)\.([\d]{1})$/, '$1,$20');   v = v.replace(/([\d]+)\.([\d]{2})$/, '$1,$2');   console.log(v);    return v; };  My regex knowledge is weak, can somebody help me please?

I would like to format a price in JavaScript. I'd like a function which takes a float as an argument and returns a string formatted like this: "$ 2,500.00"  What's the best way to do this?


Let $\Gamma$ be some set of well formed formulas and let $\alpha \in \mathrm{WFF}$. Prove the following statement:   $\Gamma \models \alpha$ if and only if $\Gamma \cup \{(\lnot\alpha)\}$ is not satisfiable.   So far I have done this:      edit: whatever I did was wrong, so can you tell me what could be done?

Let $\Gamma$ be a set of formulas and $\phi$ be a formula. Show that $\Gamma \cup \{\neg \phi\}$ is satisfiable if and only if $\Gamma\not \models \phi$.   This seemed pretty obvious but I wanted to see if my proof made sense:  Proof: $(\Rightarrow)$  To derive for a contradiction, suppose that: $\Gamma \models \phi$. That means for all truth assignments $v$, for $\gamma \in \Gamma$, if $v(\gamma) = T$, then $v(\phi) = T$.  But this contradicts our assumption that $\Gamma \cup \{\neg \phi \}$ is satisfiable by the fact that $v(\phi) = T$ cannot happen so: $\Gamma \not \models \phi$ .  $(\Leftarrow)$   So by the definition of $\Gamma \not \models \phi$, we have that there is some truth assignment $v$ which satisfies $\Gamma$ but does not satisfy $\phi$. So  that means $v(\phi) = F$ since $v(\phi) \not = T$ which implies that $v(\neg \phi) = T$ which means $v$ satisfies $\Gamma \cup \{\neg \phi\}$.    I feel like I'm missing something in the forward direction, but at the same time... It looks pretty trivial as well. Am I missing anything crucial?  Thank you!


I want to parsing some program's log and I want to check the existence of a core file in the log directory.   Assume the path is the log directory, and core file names always begins with string core (e.g., name is core.20161027.183805.28273.0001.dmp). Then is there any directed API I can use to check a core file in the path directory?  Thanks

How do I check whether a file exists or not, without using the  statement?


I have earned "HO HO HO" hat today (24th-Dec), Check below ScreenShot.   But actually its displaying "Post or vote on Christmas", Check below ScreenShot for that.    May i know whats the reason behind that Or i have had any mistake to understand that?

I just got the  hat which states "post or vote on December 21".  Does SE have a time machine now?


I am using Ubuntu 9.04 and I want to install newest version (Ubuntu 12.04). Using start-up disk creator I prepared Ubuntu ISO and saved it into USB but when I boot it it shows an error:  'SYSLINUX 3.63 Debian-2008-07-15 EBIOS Copyright (C) 1994-2008 H. Peter Unknown keyword in configuration file boot:   NOTE: I've already tried to open USB drive and open 'SYSLINUX' and delete 'ui' in it.

I am trying to install linux on my laptop, a Toshiba Satellite C6550-S5200. I did it once but something happened so I removed it then I had to destroy all data on hard drive so now I have nothing on it. Well I got a iso file burned to a CD and to a flash drive. With the flash drive I get.   SYSLINUX 4.06 EDD 4.06-pre7 Copyright (C) 1994-2012 H. Peter Anvin et al  With the CD it will start booting it but somewhere loading it up, the dots turn all orange and stay that way and my CD drive turns quiet.  Oh and some more info the images work because I tried loading them up on another pc and it worked just fine.  I manage to get the CD to boot I just had to let me pc boot up first then insert the CD and have it boot the CD then. Once I get done installing ubuntu it works fine but I have to leave the PC on 24/7 for if I turn it off the PC will freeze 5-10 seconds after booting back up no matter how I install it.


Is it possible to switch from Ubuntu 17.10 to something newer that is supported so I can download software without loosing all of my files and setup?    My computer has a root password and I'm not sure how it was set up but I am afraid to mess anything up and loose everything, and or not have a working computer because nobody around here will touch my computer with Ubuntu.  If I do the regular updated that pop up will this fix my problem?  I have a bunch of stuff set up to my liking on this computer, and I have no idea how to start from scratch and update.    I can't download software after trying to download zoom it halted a perfectly working OS from being able to launch newly downloaded programs.   I was told on another Ubuntu forum that I never need to update from 17.10 if I am happy with it, which I am.   Thanks

Recently I have installed an older version of Ubuntu on my old machine. Whenever I try to install any software, I get an error saying it couldn't be found:  $ sudo apt-get install vlc Reading package lists... Done                Building dependency tree        Reading state information... Done     E: Couldn't find package vlc


Is the following statement  true？     Let $U,V \subset R^n$ and let $f:U \to V$ be a continuous bijection. If $U$ is an open set in the topology induced by the Euclidean norm, then $V$ is also an open set.   I think, it has something to do with the fact that preimage of any open set under $f$ is open too (one of the equivalent definitions of continuity). However, it also has to do with some specific topological properties of $\mathbb{R}^n$, as the generalization of this statement to the arbitrary topological space is clearly false (take the Sierpinski space $(\{0, 1\}, \{\emptyset , \{1\}, \{0, 1\}\}$ and function $f(x)$ that maps $1$ to $0$, and thus is a continuous bijection of two one-element sets)

The  states that, given an open subset $U\subseteq \mathbb{R}^n$ and an injective and continuous function $f:U\rightarrow\mathbb{R}^n$ then $f$ is a homeomorphism between $U$ and $f$'s image.   I tried proving it by using another theorem:  if $g:K\rightarrow X$ is injective and continuous, $K$ is compact and $X$ is  then $g$ is a homeomorphism between $K$ and $f(K)$.  But I'm not sure on how to prove this (sub)-theorem? or perhaps there exists an easier proof of the invariance of domain theorem?


I was making a minecraft rig Timys rig v7 and when I went to render it only this rendered. it renders in blender mode to. but the sword and lighting is ugly as heck

So I'm at that step where I am finally ready to Render my first big project. Aaaaaand it's been stuck on the first 4 tiles for the last 2 hours?   I am using a MacBook Pro Processor: 2.5 GHz Intel Core i5 Memory: 4 GB 1600 MHz DDR3 Graphics: intel HD Graphics 4000 1024 MB  (I include these because I have no idea what affects a computers ability to render but I assume it's one of them, most liekly the graphics card).  So anyways here are the pictures, as you can see I played with changing the resolution, the sample size and the max steps to see if I got different results but it just keeps getting stuck at those 1st four tiles. I've rendered a few other small projects successfully but this was my first time changing some values. I assume i've managed to accidentally change the wrong values and thats causing some conflict thats either stopping the render itself or is making it just too much for my computer.  My goal was the render this particular picture at a good enough resolution and clarity that it could then be made into a poster. So i wanted the resolution to be good and the sampling to be high.       Since writing this there has been no change to any of the numbers at the top of the render result (the time left, etc)


How do I prove that a group ring RG is not a division ring, assuming that R is commutative and G=(g_1,g_2,...g_n) finite? I understand that I need to show there exists some element of RG that is not a unit. But how do I find such element? Would the element g_1+g_2+g_3+....+g_n work?

Let $G$ be a group. Let $K$ be any field and consider its group algebra $K[G]$. It is known that if $G$ is a finite group then $K[G]$ is never a field. Or even if $G$ is not finite: if $G$ has at least one non-trivial torsion element, then $K[G]$ is not a field.  Question: Do there exist infinite groups $G$ such that $K[G]$ is a field or a division ring?


I would like to closely mimic the  (\citestyle{acmauthoryear} and \bibliographystyle{ACM-Reference-Format}). As far as I know, there is no style in biblatex that adapts it (any other suggestions to make this style work without \documentclass{acmart} appreciated).  I am quite happy with biblatex-apa, but I would like to change the parenthesis of \parencite and \textcite from ( to [.  \parencite now: (Doe & Nakamoto, 2017); wanted: [Doe & Nakamoto, 2017]  \textcite now: Doe and Nakamoto (2017); wanted: Doe and Nakamoto [2017]  MWE:  \documentclass{book}  \usepackage[american]{babel} \usepackage{csquotes} \usepackage[style=apa]{biblatex} \DeclareLanguageMapping{american}{american-apa}   \begin{filecontents}{mybib.bib}  @inproceedings{John,  author = {Doe, John and Nakamoto, Satoshi},  title = {Some title},  year = {2017}, }  \end{filecontents}   \addbibresource{mybib.bib} \begin{document}  \parencite{John} \textcite{John}  \printbibliography \end{document}

I need to customize the author-year citation in biblatex for a template at work. Right now biblatex cites like this:     Ruschmeyer u. a. 1995, S. 123   They way I was told it needs to cite is:     [Ruschmeyer u. a. 1995, S. 123]   This seems pretty simple and I thought it would be done in a second, but after reading through the biblatex documentation for the second time, I still don't really have a clue.


I am looking for suggestions to evaluate this F.T which involves bessel function of the second kind (of zero order) I = $$\int_{-\infty}^{\infty} K_0(\sqrt{z^2+a^2}) e^{i kz} dz $$ Can this Integral I be solved analytically? Are there any analytical approximations I can use? Thanks

Does anyone have any suggestions for performing the following Fourier transform:   I = $\int_{-\infty}^{\infty} K_0(a \sqrt{x^2+1}) e^{i kx} dx $   where $K_0$ is the modified Bessel function of the second kind.


The Message module was working fine but I noticed one of the messages wasn't getting created by Rules. I suspect it's due to locale being enabled recently and creating with the UI gives this error.  For message types where I haven't created a different language, it seems to work fine.  2 errors in log:  Warning: array_flip(): Can only flip STRING and INTEGER values! in EntityAPIController->load() (line 219 of /usr/share/nginx/html/sites/all/modules/entity/includes/entity.controller.inc).   .  EntityMalformedException: Missing bundle property on entity of type message. in entity_extract_ids() (line 7930 of /usr/share/nginx/html/includes/common.inc).   The relevant lines in common.inc are:  // Explicitly fail for malformed entities missing the bundle property.     if (!isset($entity->{$info['entity keys']['bundle']}) || $entity->{$info['entity keys']['bundle']} === '') {         dpm($info);// My dpm       throw new EntityMalformedException(t('Missing bundle property on entity of type @entity_type.', array('@entity_type' => $entity_type)));     }   You can see where I added dpm(). $entity is empty but $info gives the below screenshot.   Any pointers for someone who just isn't used to debugging things like this? I've deleted every message in on the site with VBO but the error persists.   After two and half years of dev, this site was supposed to go into a proper beta next week in a friend's business but the entire UI relies on the Message module. :/    And here is a dpm of the ids for the flipping error.    Any help appreciated. I didn't expect it to all fall apart this weekend.  Edit: Closed as it is indeed a duplicate. I don't have the skills to deal with it so will just rewrite to use node functionality instead.  Edit 2: Calmed my head today and looked at things that weren't my own code. Turns out it was the Reply module which I use on Message. Reinstalling it gets rid of the errors. I don't know why it happened. It's been a part of Message for like a year during development.

I've got fatal error EntityMalformedException: Missing bundle property on entity of type node. in entity_extract_ids() (line 7700 of .\includes\common.inc) when trying to access user/xyz.  I tried to retrieve info about the malformed node at line 7700, where the error message is built, thinks like :  if (!isset($entity->{$info['entity keys']['bundle']}) || $entity->{$info['entity keys']['bundle']} === '') {  dpm($info);// or dpm($entity);  throw new EntityMalformedException(t('Missing bundle property on entity of type @entity_type.', array('@entity_type' => $entity_type))); }   dpm($entity) returns an unexpected user object, and $info a huge qty of things.   Could somebody put me on the right way ?  I already read whatever I could find about Missing bundle property errors, but none helped solving.  dpm($entity) returns  uid (String, 2 characters ) 70 name (String, 9 characters ) John pass (String, 55 characters ) $S$DUwPuOuDPiDL4nRTYXqc7a5uOfMKey7pyhOFUEKka1XM... mail (String, 30 characters ) john@example.com theme (String, 0 characters ) signature (String, 0 characters ) signature_format (String, 13 characters ) filtered_html created (String, 10 characters ) 1396286331 access (String, 10 characters ) 1397146661 login (String, 10 characters ) 1396513460 status (String, 1 characters ) 1 timezone (NULL) language (String, 2 characters ) fr picture (NULL) init (String, 30 characters ) john@example.com data (Array, 5 elements) roles (Array, 1 element) og_user_node (Array, 0 elements) message_subscribe_email (Array, 1 element) field_bio (Array, 0 elements) field_name_first (Array, 1 element) field_name_last (Array, 1 element) field_facebook_url (Array, 0 elements) field_linkedin_url (Array, 0 elements) field_twitter_url (Array, 0 elements) user_trusted_contacts (Array, 1 element) group_group (Array, 1 element) group_access (Array, 1 element) metatags (Array, 0 elements) rdf_mapping (Array, 3 elements) realname (String, 13 characters ) John Doe content (Array, 13 elements) entity_view_prepared (Boolean) TRUE privatemsg_disabled (Boolean) FALSE


Is there a dense set in $\Bbb{R^2}$ that every vertical line or horizontal line intersect in finite points. I think that we can consider $\Bbb{Q} ×\Bbb{Q}$ but every vertical line or horizontal line don't intersect in finite points.

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


I have 2 workbooks with 60 plus worksheets. I need to copy data from one workbook to the other but would like to capture and use the worksheet name within the cell. This is because when I create the workbook I make a master worksheet and then copy it 60 plus times. The above would make the cell ref for each worksheet the corresponding worksheet cell in the other file.

How can I get the sheet name in a cell? (I have more than one sheet, I want to get the current on each sheet)


Can anyone simply explain why the following expressions do not take the definite article “the”? I know (as a native speaker) that no article is needed; just looking for the precise grammar functioning here.      Room 7   (Bob is in Room 7)     Page 44   (Please open to page 44.)

Last week in college, a student [with a thick South Asian accent] asked me:     "Excuse me, where can I find the room 401?".   I realized that to my native English ears, the word "the" sounded non-native. This had me realize that we sometimes use no article.  I am learning French; in French, we seem to always use some kind of article before nouns. It surprised me, at that moment, to realize that English doesn't always do the same! (That, and using the definite article in "the room 401" seems to make sense if I think about when definite articles are used).  Is there a grammatical name or concept for this "no article" aspect of our language? Are there any websites that can explain this to me?


How would you remove everything between all instances of brackets like in  var item = '
1. Get this   more text
'  I've tried using the solution from  with the global tag, formatted like : item = item.replace(/\/<.*>/, ''), but that just outputs nothing.  Really lost here

I have this gigantic ugly string: J0000000: Transaction A0001401 started on 8/22/2008 9:49:29 AM J0000010: Project name: E:\foo.pf J0000011: Job name: MBiek Direct Mail Test J0000020: Document 1 - Completed successfully  I'm trying to extract pieces from it using regex. In this case, I want to grab everything after Project Name up to the part where it says J0000011: (the 11 is going to be a different number every time). Here's the regex I've been playing with: Project name:\s+(.*)\s+J[0-9]{7}:  The problem is that it doesn't stop until it hits the J0000020: at the end. How do I make the regex stop at the first occurrence of J[0-9]{7}?


There is a photographer who shoots mostly indoors with natural light (no soft box) but sometimes he also shows outdoors photos in natural light conditions. His site is at .  I'm trying to learn from his photos by looking at their histograms. I don't know if is possible to know from the histograms if he over/under exposes. Most of his photos have no clipping on the darker or brighter regions.  He shoots with a Sony RX1 and uses his custom-made Aperture presets.  Notes: Most of his photos are of products, details outside windows preserved and have a great white balance. However, when his hands are shown the skin tone is distinct depending on the products and sometimes hands are looking pale or tanned.

I realize that an image histogram is a graphical display of an images tonal distribution (i.e. horizontal darks to lights, vertical pixel distribution), but how does one really use it and why? I mean, can't you determine everything you need just by looking at the image?


I am trying to validate phone number using regex, and I want to create a phone number format like this:     (+971 12 123 1234)   Can anyone help me do this?

I'm trying to put together a comprehensive regex to validate phone numbers. Ideally it would handle international formats, but it must handle US formats, including the following:   1-234-567-8901 1-234-567-8901 x1234 1-234-567-8901 ext1234 1 (234) 567-8901 1.234.567.8901 1/234/567/8901 12345678901   I'll answer with my current attempt, but I'm hoping somebody has something better and/or more elegant.


In the history tab, for every post which I have reviewed, there is a link to my account. Can it have a value other than a link to my account? If not then is it necessary to show it for every entry?

The current format of showing review history works fine without bug. But, we should intend to change the format of that page to add some more precise.  We are showing the reviewer name in the review history. I think there is no need of showing that, as the reviewer is seeing his/her own history.    We should remove that and get some more space for other reasonable details. We can also have titles for the details showing on like post, action, time, etc. Provided screenshot is for suggested edit review history. We can have unique format changes for each review type.


The following question is from my Field Theory assignments.  Prove that  $Aut_{\mathbb{Q} } { \mathbb{R}} $  is identity group.  I took $f:\mathbb{R} \to \mathbb{R}$ be an automorphism. Now  which result I should use to prove that all the automorphism which are $\mathbb{Q}$ -module homomorphisms are identity. Let $f'$ be such an automorphism and q belongs to $\mathbb{Q}$. So, $f'(q) = qf'(1) =q$.but how to prove that $f'(q) =1$ . Kindly guide.

Is an automorphism of the field of real numbers $\mathbb{R}$ the identity map? If yes, how can we prove it?  Remark An automorphism of $\mathbb{R}$ may not be continuous.


I've been wondering for a while, if there is a word for when something turns out to be the complete opposite of what you believed.  So, something that would fit in a sentence like below would be great:     It was so ____, he was at the complete opposite end of town.

I'm looking for a word that means the opposite of what one would expect. This word might be used to express the surprise that a teenager's grandmother uses text messaging much more than he does, or that a city seems brighter at night than it does during the day.   I'm not seeking the word ironic or irony which refer to the use of something to describe its opposite experience or emotion.


I'm calling an internal web page to my div every second with setInterval (that is to say reloading div). It's working fine but users should click a button inside of that reloading div and it fails.   This is my code:  HTML:

   JavaScript:        And this is the calling page's HTML:

30 Minutes
 1 BTC

                       <input type="text" class="form-control" id="hrs" value="0">                       Hrs

                       <input type="text" class="form-control" id="mnt" value="0">                       Mnt

                       <input type="text" class="form-control" id="sec" value="0">                       Sec

 Nobody
               <button class="btn btn-success pay" data-id="2">Get Ticket!</button>

   I'm trying to make this part clickable  <button class="btn btn-success pay" data-id="2">Get Ticket!</button>   with this JavaScript code below:     When I disable reloading thing, button working fine. I'm sure that the problem is setInterval part.  Thanks in advance.

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


I have this code:  $('a[href*=#]').click(function() {    $('html, body').animate({     scrollTop: $($.attr(this, 'href')).offset().top   }, 500);    return false; });   But I need a 600ms delay after click the link so my page have chance to perform other actions that I set to 500ms, thank you in advance

I want to fade out an element and all its child elements after a delay of a few seconds. but I haven't found a way to specify that an effect should start after a specified time delay.


could someone please explain why is needed to connect common grounds on rc switch. I am trying to understand inner working of this device and why connection with the ground has not been done internally.     Device is called Turnigy RC switch and documentation is provided here:

I was reading about Serial communication in computers and embedded systems and found the following statement -      Computers connected by wires must have a common ground reference,   typically provided by a ground wire in the cable. ()   What is the reason for this? I thought that the ground wire was only for protection against electrical leakage. What would be the need for a common ground wire in communication networks?


I have this code to get a COUNT DISTINCT data:   $param = 'email';      $stmt = $conn->stmt_init();     $stmt = $conn->prepare("SELECT COUNT(DISTINCT(?)) FROM contatos");     $stmt->bind_param('s',$param);     $stmt->execute();     $stmt->store_result();     $stmt->bind_result($count);      while ($stmt->fetch()) {         echo $count;     }      But echo $count always returns 1, but i have dozens of records...  What is wrong?  Thanks

Why can't I pass the table name to a prepared PDO statement?  $stmt = $dbh->prepare('SELECT * FROM :table WHERE 1'); if ($stmt->execute(array(':table' => 'users'))) {     var_dump($stmt->fetchAll()); }   Is there another safe way to insert a table name into a SQL query? With safe, I mean that I don't want to do  $sql = "SELECT * FROM $table WHERE 1"


If I have a function $y=x^x$, that can be denoted in hyperpower notation as $^2x$, but I will be denoting it as $ y= $ hyp$_2(x) $. In general, for hyperpowers, $y=x^{x^{x^{...}x}}$ or in my notation $ y= $ hyp$_\alpha(x) $. The problem with the hyperpowers I don't know how to calculate them for non-integer $\alpha$. Is it even possible to have non-integer $\alpha$?   Thanks.

This question has been in my mind since high school.  We can get multiplication of natural numbers by repeated addition; equivalently, if we define $f$ recursively by $f(1)=m$ and $f(n+1)=f(n)+m$, then $f(n) = m \times n$.  Likewise, we get exponentiation by repeated multiplication. If $g(1)=m$ and $g(n+1)=mg(n)$, then $g(n) = m^n$.  In my high school mind it was natural to imagine a new function defined by repeated exponentiation: $h(1)=m$ and $h(n+1)=m^{h(n)}$.  These definitions only make sense for $n$ a natural number, but of course there are standard very mathematically satisfying ways to define multiplication and exponentiation by any real number. My question is this:  Can the function $h$ defined above also be extended in a natural way to $\mathbb{R}^{>0}$?  The question is in the spirit of seeking an extension of $f(n)=n!$ to $\mathbb{R}$ and arriving at $\Gamma(x)$.  Let me focus the question, and attempt to make precise what I mean by "in a natural way." Take $h(1)=2$ and $h(n+1)=2^{h(n)}$. $h$ is now defined on $\mathbb{N}$, and $h(2)=4$, $h(3)=16$, $h(4)=2^{16}=65,536$ etc. Is it possible to extend the domain of definition of $h$ to all positive reals in such a way that  a) The functional equation $h(x+1)=2^{h(x)}$ continues to be satisfied for all $x$ in the domain.  b) $h$ is $C^\infty$. (Analytic would be even better but this seems maybe too much to hope for?)  c) All $h$'s derivatives are monotone.  These requirements are my attempt to codify what would count as "natural." I am open to suggestions about what would be a better list of requirements.  If such a function exists, I would like to know how to construct it; if it doesn't, I would like to know why (i.e. outline of proof), and if relaxing some of the requirements (e.g. just the first derivative monotone) would make it possible.  (If the function exists, I am also interested in the questions, "is it unique?" "Could we add some natural requirements to make it unique?" But my main query is about existence.)


I'm trying to understand how  $$\limsup_{n\to \infty}(n^n/n!)^{1/n} = e$$  i.e., the fact that the power series $$\sum_{n=1}^\infty (n^n/n!)z^n$$ has a radius of convergence of $\frac1e$  I haven't the slightest clue how to prove this, and am looking for any sort of nudge in the right direction, thanks.

I'm trying to find  $$\lim_{n\to\infty}\frac{n}{\sqrt[n]{n!}} .$$   I tried couple of methods: Stolz, Squeeze, D'Alambert  Thanks!  Edit: I can't use Stirling.


I am on Debian testing and using ext4 and ntfs . while ext4 has been brilliant in recovering lost data sometimes it also discards some pieces when electricity goes for a long time or any such similar event.   The same is the case for ntfs filesystem as well.   For this and other purposes I have been curious to know if there is a utility or way to know where any file resides on the hdd.   It would also help in asserting or discrediting the claim that ext4 or similar filesystems tend to bunch parts of a file in adjoining 'sectors' and hence don't need a defragmenter as its needed in MS-Windows systems.   I would be also interested in knowing if ntfs filesystems also have something similar. I know they use fuse as a glue to be able to access the filesystem.

Is there any Linux program which offers the same (or some of the) functionality of Sysinternals DiskView, especially being able to view to physical location of a file on a hard disk?  DiskView URL:


I have a directory where daily subdirectories are created, literally named according to $date. How can I delete folders and their contents that are older than 7 days according to the YYYYMMDD in the file name and not the metadata date? Say I have (skipped some for brevity):  20170817 20170823 20170828 20170901   I would end up with the following folders (which those should keep):  20170828 20170901   I created a variable that holds the date 7 days ago: dt_prev=$(date -d "`date`-7days" +%Y%m%d)  My thought was to ls -l a list of these folder names and compare row by row, but this involves cleaning that list, etc., and I figure there has to be an easier way.

I want to delete log files which are older than 5 days from a directory. But deletion should not be based on the timestamp of file. It should be based on the name of file. For Example todays date is 07/05/2012 and the directory contains 10 files of names like ABC_20120430.log, ABC_20120429.log, ABC_20120502.log, ABC_20120320.log etc. I want to be able to remove the files by extracting the date from the name of the file.


I have a portable air conditioner, it's currently reducing my room from 23-24C to 17-18C. 24C is not exactly hot and the main purpose of the unit is for when it does get hotter. I could expect my room to reach 30C. Will the AC be able to reach it's target of say 18C under 30C conditions? Will it take a longer time to reach it?

I've picked a portable HVAC unit. It's a 2.6 KW 10,000 BTU model. The only way I will be able to vent it is by cutting a hole in one of the glass windows and and using the special fitting. I wanted to test the unit out in the mean time by just throwing the vent hose out of the door but of course the door is still open quite far like this. Is this not going to allow me to get an idea of how well the unit works with the door open so much or will it be drawing to much warm air in?


new member here with a question.  My Wine Enthusiast Wine Cooler (Model 254 60), bit the dust.  The new boards cost $297 each and there are three in the unit.  I want to remove all of the boards and use a 12 volt power supply on a timer.  The connections would be (3) Peltier's, (3) fans cooling side and (3) fans heating (exhaust side).  All connections wired in series.  What kind of 12 volt power supply would I need to complete the task?  Thanks in advance....

Power supplies are available in a wide range of voltage and current ratings.  If I have a device that has specific voltage and current ratings, how do those relate to the power ratings I need to specify?  What if I don't know the device's specs, but am replacing a previous power supply with particular ratings?  Is it OK to go lower voltage, or should it always be higher?  What about current?  I don't want a 10 A supply to damage my 1 A device.


So I noticed my accepted answer rate went to 79% on SO. I went to mark answers on a couple of ancient questions that never got answered properly.   However, for one of these I cannot mark an answer.   The question in question is   What does one do when this happens?

I recently had a  where the bounty offer failed to solicit anything useful.  Further research, though, dug up a similar question which had an answer which provided some leads - those leads resulted in an answer.  I asked the answerer on the other question to post a similar answer to mine so I could accept it, but returning today to do so I find there is no accept tick on any of the answers.  The bounty system seems quite broken to me, and really needs some hard thinking about how it should work.  I squandered a bunch of rep (as much as I could afford on SU, which isn't that much) for no results.  Now when I find someone who deserves the bounty, I can't award it - I can't even accept his answer.  That combination of end-results is really annoying.  In my case I found someone who has done me a huge service and I would like to reward that with the bounty rep I offered for an answer to my problem... but I can't!  The only worse end-result would have been to have another answer auto-accepted for me because some well-meaning, but mistaken, individual voted it up during the bounty period without reading my comment that it did not resolve my problem.  And it was only some vague pointers anyway.  Could the system be modified to allow us to accept answers on questions where a bounty was offered and not awarded.  Even better, could we have the ability to award the bounty with the accept if a resolving answer comes in after the bounty period?  Could the bounty system be modified to never auto-accept.  I am OK with removing the question from the feature questions list after the bounty period, but why can't the bounty remain available until I accept an answer?  Perhaps it might only auto-accept after a month or 3 of the question owner not returning to the site?    Robert C Cartino suggested, and I concur:   Half the bounty amount is awarded to the highest voted answer (within the current restrictions). The answer is not auto-accepted. Instead, the banner at the bottom of the question ("This question has an open bounty worth 100 reputation ending in 1 hour") should be replaced with:      A bounty of 100 reputation points was awarded to Robert C. Cartaino [answer link] on xx/xx/xxxx at xx:xx xM.    but I would like to further suggest:   The remaining 1/2 of the bounty remain pending until the OP accepts an answer, if they ever do.   This seems no worse than the current behavior of forever discarding the remaining bounty.


I have the infinite series: $$\sum_{k=0}^\infty p^kk$$ where $0<p<1$.  I can see from a computer calculation that the series converges to $\frac{p}{(1-p)^2}$, but I can't see why.  Thanks in advance for any help.

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


I'm new to Ubuntu so go easy on me. I've heard great feedback and support from these forums so I'm crossing my fingers.  I booted ubuntu 16.04 on my new custom build pc, I went through all the installation steps and rebooted my system.   However, when i get to the log in screen, i enter my password and the desktop then flashes quickly, briefly seeing the Ubuntu logo and its version and then parts of the desktop template fade away and I am just left with the desktop wallpaper and the mouse, nothing else, no other options.  I can open terminal with ctrl + alt + 1 and I have tried various commands to fix the issue after reading the threads here, especially this one   I get the line 'compizconfig-settings-manager' has no installation candidate so that's no good  I feel like the video drivers may be an issue and i need to update them but the command line says everything is updated.   Can anyone help me with this I am very stuck and need a working computer ASAP. Much thanks to anyone. Here is my pc build: MSI GTX 970 Intel I5 6600k Asus z170 Deluxe MB Samsung 950 PRO SSD

After upgrading from 12.04 to 14.04 I could log in to my X session (albeit with really low graphics). While trying to fix the graphics, I managed to break the X session.  Now, after typing my password in the unity-greeter, the items disappear and I can only see the desktop background and the pointer. This happens for every user. I can still log in in tty's. How can I solve this?  Also, I cannot seem to be able to install nvidia-current as it tries to install nvidia-304 and it depends on old video-abi libraries. Is there a way to tell the package manager that nvidia-current should use a newer version?


I want to install Ubuntu on my laptop (i7 ivy bridge 32GB mem) and run a one or two Ubuntu guests.  Is there a step by step guide to help me do this?

I would like to know if anyone can help me with installing Ubuntu on VirtualBox


I am relatively new in the world of Blender, which I have started using as a scientist to make schematics for publications.   I am currently struggling in making a particle emitting from a particle system and use that as a particle.   Essentially what I want to do is make a sphere with spheres emitted from the vertices  and I want these spheres to have hairs on top as in image below:      In the latter case, I had to manually position the smaller spheres on the big sphere surface and manually delete half on the emitting hairs. I really don't want to do it manually all the time lol. Do you guys know how to do it easily?

In a scene with two particle system configured as boids and boids brain set to fight, one swarm attacks the other. I would like to emit child particles as lines (laser or something) to visualize some fighting action. I couldn't find a way to setup the line emitting particle system, either they are created from the plane or further cones will be added. Is there a way to do this as I saw on a  but I didn't get the trick? Blend file   At blendersushi  the author says:  PARTICLE INSTANCE MODIFIER > PARTICLES With this stacking thing, we can now pretty much emit Particles from emitted Particles, > if you know how to set it up. Not very obvious, but basically you Instance some meshes > (using Instance Modifier) and then add Particle System to the object with Instance > Modifier. Make sure you have "Use Modifier Stack" turned on.  But I can't get this to work.


Is there an open source library that, given ...  /a/b/c /a/b/c/d/e   would return ../..  or for that matter given  /a/b/c/d /a/b/c/e   would return ../d  ?

Given two absolute paths, e.g.  /var/data/stuff/xyz.dat /var/data   How can one create a relative path that uses the second path as its base? In the example above, the result should be: ./stuff/xyz.dat


This question is related to  (asked by user @GeraltofRivia). In fact it is what I understood the question to be before it was edited.     Let $n\in\mathbb{N}$. For what $1\le r\le n-1$ is $\binom{n}{r}$ divisible by $n$?   When $n$ is prime, this is obviously true for all such $r$. I believe that the case where $n$ is the product of two primes or a power of a single prime shouldn't be too hard to treat, however the general case looks like a combinatorial mess to me. Does anyone have some insight on how the problem can be solved for arbitrary $n$?

Is there any way of determining if $\binom{n}{k} \equiv 0\pmod{n}$.  Note that I am aware of the case when $n =p$ a prime.  Other than that there does not seem to be any sort of pattern (I checked up to $n=50$).  Are there any known special cases where the problem becomes easier?  As a place to start I was thinking of using $e_p(n!)$ defined as:  $$e_p(n!) = \sum_{k=1}^{\infty}\left \lfloor\frac{n}{p^k}\right \rfloor$$  Which counts the exponent of $p$ in $n!$ (Legendre's theorem I believe?)  Then knowing the prime factorization of $n$ perhaps we can determine if these primes appear more times in the numerator of $\binom{n}{k}$ than the denominator.  Essentially I am looking to see if this method has any traction to it and what other types of research have been done on this problem (along with any proofs of results) before.  Thanks!


We have just started learning about continuity and this is basically the first assignment on this subject so I'm very unsure about how everything works. My attempt of a solution is as follows; Let $g:\left[0,\frac{1}{2}\right]\ ->\left[0,\frac{1}{2}\right]\ $such that  $ g\left(x\right)\ =\ f\left(x\right)\ -\ f\left(x+\frac{1}{2}\right)$ Note that $g$ is continuous, hence by the fixed point theorem there exists a point $C$ in $\left[0,\frac{1}{2}\right]$ such that $g\left(C\right)\ =\ C$. Therefore there exists a $C$ in $\left[0,\frac{1}{2}\right]$ such that $ g\left(C\right)\ =\ f\left(C\right)\ -\ f\left(C+\frac{1}{2}\right)$. Now am I missing something? Because it seems just too simple to me.. also I didn't even use the fact the $f(0) = f(1)$ which is suspicious. Edit: I'm seeing now that i didn't use the theorem correctly, since it just says that $g\left(C\right)\ =\ f\left(C\right)\ -\ f\left(C+\frac{1}{2}\right)= C $. and C is not necessarily $0$..

Let $f:[0,1] \rightarrow \mathbb{R}$ be a continuous function. If $f(0)=f(1)$ then exists $x\in [0,1]$ s.t. $f(x) = f(x+\frac{1}{2})$   We have that $f\left(\frac{1}{2}\right)=f(0)$ or $f\left(\frac{1}{2}\right)>f(0)$ or $f\left(\frac{1}{2}\right)<f(0)$.  If $f\left(\frac{1}{2}\right)=f(0)$ then $x = 0$ Solves the problem.  if $f\left(\frac{1}{2}\right)<f(0)$ then by the intermediate value theorem  $$\exists k \in \left[0,\frac{1}{2}\right], f(0)>f(k)>f\left(\frac{1}{2}\right) \implies$$  $$\implies f(1)>f(k)>f\left(\frac{1}{2}\right)\implies \exists t \in \left[\frac{1}{2},1\right] s.t. f(t)=f(k).$$   Now how can I show that exists at least one value of k such that $t = k+\frac{1}{2}$? (The solution is similar if $f(\frac{1}{2})>f(0)$)


The guidance on this site concerning when to use the Welch t-test is somewhat general in nature ( ).  Are there specific, widely accepted rules of thumb such as related to: (1) Size of the difference in variances as opposed to statistical significance of the difference, (2) Sample size after which the robustness of the traditional t-test makes the Welch test unnecessary, (3) Other considerations that might best inform a decision on whether to use the Welch t-test, (4) What extent of benefit the Welch t-test might provide in various situations, and (5) Do the Welch and student t-test converge with large N? Any informed guidance would be greatly appreciated.

It seems like when the assumption of homogeneity of variance is met that the results from a Welch adjusted t-test and a standard t-test are approximately the same.  Why not simply always use the Welch adjusted t?


Although I have always regarded the terms as interchangeable, I have read somewhere that they’re not the same. I suppose this means that a record is not exactly the same as a row either.  I teach that the main difference is how you visualise the data — it is a column if you think of a table, but a field if you think of a form.  What is the real difference between them, and to what extent does it matter?  Thanks

I feel kind of embarrassed here, I've always used the terms "column" and "field" completely interchangeably, which recently caused some confusion in a technical discussion.   I was told, though, that this wasn't correct, that it should be (translating each term into spreadsheet terminology, ignoring data types and all the other stuff that make databases useful):   Database Column: like a spreadsheet column  Database Record: like a spreadsheet row Database Field: like a spreadsheet "cell" (a specific column of a specific row)   Is this right? I could have sworn that column and field are used more interchangeably than that. I certainly have been.  So we don't add fields to a table, we add columns to a table, and fields are only relevant when talking about data within a record?  Other thoughts on column vs field?  Edit: to clarify, the current context is MS SQL Server. My background before SQL server was MS Access, which might influence my use of these terms.


In almost all sagas we find Gods: e.g. in LOTR, Gods were mentioned, like Valar etc. But in Harry Potter, Voldemort was referred to as the Dark Lord (but he was just a normal wizard who chose the Dark and became extremely powerful); the tale was set in the 20th century and the oldest people mentioned were the four wizards after whom the houses in Hogwarts were named (Hogwarts was established in 990 AD).  Why were there no Wizard Gods or anyone whom Voldemort worshipped? At least in the movies no such things are mentioned.

The question of  made me wonder as to whether wizards, any of them, do practice religion. Whether there be magic-person only religions or shared muggle faiths, I do not recall any wizards (born in the wizard world anyway) saying that they did practice a religion.  Many of them do celebrate Christmas, but as was commented on the above linked question, there are many non-christian muggles that also observe Christmas. So I am not sure that can be an accurate identifier. Answering this question may link into identifying .


I am trying to reproduce this paper :   But, somehow I am stuck at equation (7). The equation that I am trying to solve for particle outside the well is : (1/g)*(g'') + (1/(r*g))*g' - (k_o)^2 = 0  where g = Radial wave function. r = Distance from origin.   The solution I arrived at is : A*J_0(i*k_o*r) + B*Y_0(i*k_o*r) where J ,Y are Bessel functions of first kind of order zero & second kind of order zero respectively.   My queries are : 1.) How can I reduce the solution in the form of equation (7) , i.e. , Psi = A*e^(-k_o*r) / (r^0.5) ?  2.) Am I solving the correct differential equation?

In the given paper, I am stuck at equation (7). The equation that I am trying to solve for particle outside the well is : (1/g)(g'') + (1/(rg))*g' - (k_o)^2 = 0 where g = Radial wave function. r = Distance from origin.  The solution I arrived at is : AJ_0(ik_or) + BY_0(ik_or) where J ,Y are Bessel functions of first kind of order zero & second kind of order zero respectively.  My queries are : 1.) How can I reduce the solution in the form of equation (7) , i.e. , Psi = Ae^(-k_or) / (r^0.5) ?  2.) Am I solving the correct differential equation?  Link to research paper:    Relevant equations from this paper:


Has there been any word on what level of canon the new Star Wars comics being produced by Marvel are?    Specifically, are they in continuity with the new movies and the Rebels TV show or are they considered part of the Legends canon?

For all types of derivative works, namely:   Movies Novels Comic books Other written works (including RPG materials) Cartoons Video games Derivative movies (such as the infamous Ewok movies and even more infamous )   According to what rules does something become "canon" and who is responsible for the evaluation of a published work?


If I upvote a comment, then delete one of my comments immediately after, I get a message stating something like "You can only comment every 5 seconds".  Is this expected behaviour? It seems like my upvote and delete were both classed as comment submissions.

I had an old question that I revisited in order to link it in a new answer. I noticed that in the comments Steven A Lowe had a funny comment that I -- at the time -- had responded to with "why can't I upvote comments?"  Well, of course, now I can.  So, I voted Steven's comment up then went to delete mine. I got the warning box that I can only submit comment votes once every 5 seconds. This seems like a bug to me. Deleting is not the same as voting.


I have noticed that in C++, a pointer can be declared using two different types of indentation (if that's the right word I'm looking for):  //Space followed by asterisk with variable name char *pointer;  //Asterisk followed by space and then variable name char* pointer;   Does the position of the asterisk affect anything about the pointer? If so, in what situations would I need to use one type of indentation over the other?

Why do most C programmers name variables like this:  int *myVariable;   rather than like this:  int* myVariable;   Both are valid. It seems to me that the asterisk is a part of the type, not a part of the variable name. Can anyone explain this logic?


Why is this table not spanning two pages ?  \documentclass[a4paper,12pt,oneside]{book} \usepackage{amsmath,amsthm} \usepackage{setspace} \usepackage{longtable} \textheight 21.0 cm \topmargin 0 cm \textwidth 16 cm \oddsidemargin 0.0 cm \linespread{1.8} \usepackage{graphicx} \newcommand{\bra}[1]{\langle#1|} \newcommand{\ket}[1]{|#1\rangle} \usepackage{amsfonts} \newtheorem{theorem}{Theorem}[section] \newtheorem{lemma}[theorem]{Lemma} \newtheorem{proposition}[theorem]{Proposition} \newtheorem{cor}[theorem]{Corollary}  \theoremstyle{remark} \newtheorem{remark}[theorem]{Remark}  \theoremstyle{definition} \newtheorem{definition}[theorem]{Definition}  \theoremstyle{example} \newtheorem{example}[theorem]{Example}  \theoremstyle{notation} \newtheorem{notation}[theorem]{Notation} \begin{document} \begin{tabular}{|p{0.33\columnwidth}|p{0.33\columnwidth}|p{0.33\columnwidth}|} \hline Notation &Meaning \\ \hline $\mathbb{Z}(d)$ & Integers modulo d. \\ $H(d)$ & Hilbert space d \\ $\Pi(d)$ & Finite geometry  \\ $\Gamma$ & Cell \\  $X$&  Position .\\ $P$&  Momentum . \\ $D(z)$ & Dis \\ ${\cal P}$ & Pa \\ ${\cal W}$ &  Function \\ ${\cal {\tilde W}}$  & W function \\ $ |X;a\rangle$ & position state \\ $ |P;a\rangle$ & momentum state \\ $S(\beta)$ &  transformation \\ $ |X \rangle$ & set \\ $B$ & origin \\ ${\mathfrak L}(1,2)$ & `F \\ $|{\mathfrak X}(x,y)$ & Weak mutually unbiased bases \\ $\Theta(u, \tau)$ & Theta function \\ $\varphi(N)$ & Line of  \\ ${\mathfrak K}(a,b)$ & set\\ ${\mathfrak Z}(a,b)$ & parallel lines  \\ $ \varphi (d)$& Euler totient function of $d$. \\ $\sigma_1 (d)$& Divisor function to power $1$ of $d$.\\ $ a \prec b$ & $a$ is  partially ordered in $b$.\\ $ a\cong b$& $a$ is isomorphic to $b$.\\ $\mathcal{Z}_d$ &integer modulo $d$. \\ $\{ \mathcal{D}(d) \} $& set of non-trivial divisors of $d$. \\ $ A\subseteq B$ & A is a subset of B. \\ $a \leq b$ & a is less than or equal to b. \\ $x$ & y \\ $x$ & y \\ $x$ & y \\ $x$ & y \\ $x$ & y \\ \hline \end{tabular} \end{document}


I have a dictionary of values read from two fields in a database: a string field and a numeric field. The string field is unique, so that is the key of the dictionary.  I can sort on the keys, but how can I sort based on the values?  Note: I have read Stack Overflow question here  and probably could change my code to have a list of dictionaries, but since I do not really need a list of dictionaries I wanted to know if there is a simpler solution to sort either in ascending or descending order.


When reading about the Calculus of Variation and Hamilton's principle I come across quotes      Hamilton's principle states that the differential equations of motion for any physical system can be re-formulated as an equivalent integral equation. Thus, there are two distinct approaches for formulating dynamical models.    This has me curious.  What systems submit to this transformation from differential equations to functionals?  Can the calculus of variations be applied to any differential equation, or are there restrictions?  What is special about "physical systems" which permit this sort of manipulation?

We see variational principles coming into play in different places such as Classical Mechanics (Hamilton's principle which gives rise to the Euler-Lagrange equations), Optics (in the form of Fermat's principle) and even General Relativity (we get Einstein's equation from the Einstein-Hilbert action). However, how do we explain this very principle, i.e., more mathematically, I want to ask the following:      If I am given a set of generalized positions and velocities, say, $\{q_{i}, \dot{q}_{i}\}$, which describes a classical system with known dynamics (equations of motion), then, how do I rigorously show that there always exists an action functional $A$, where    $$A ~=~ \int L(q_{i}, \dot{q}_{i})dt,$$    such that $\delta A = 0$ gives the correct equations of motion and trajectory of the system?    I presume historically, the motivation came from Optics: i.e., light rays travel along a path where $S = \int_{A}^{B} n ds$ is minimized (or at least stationary). (Here, $ds$ is the differential element along the path). I don't mind some symplectic geometry talk if that is needed at all.


Maybe I need to duplicate this  here I am not sure. I need to connect my macbook pro to HDMI port on 3d projector to be able watch full hd or 3d video. What cable should I buy/use?

This has always been a big want for me. I love using multi-monitor setups but only want a single laptop. Does the 2011 MBP Thunderbolt support chaining multiple monitors together? I know that you can add a monitor and say, a few hard drives, but can you connect it to 2 27" monitors and your flat screen TV (for example)? Thanks!


I am writing an article related to Computer Vision but to complete the maths under the technique I should proof the following equality.   $$\frac{\mathrm d}{\mathrm dx}(h*f) = \left(\frac{\mathrm d}{\mathrm d x}h \right)*f$$  I'm not mathematician and I'm not used to convolution analysis. So, How can I proof it?

Assume that $f(x),g(x)$ are positive and are in $L^1$. Moreover, they are differentiable and their derivative is integrable. Let $h(x)=f(x)*g(x)$, the convolution of $f$ and $g$. Does the derivative of $h(x)$ exist? If yes, how can we prove that $$ \frac{d}{dx}(f(x)*g(x)) = \left(\frac{d}{dx}f(x)\right)*g(x)$$  Thanks


[EDIT: Revisiting this question and seeing it is still wrongly marked as a duplicate] The following question on SE is not a duplicate as it asks about executing bash with the suid bit, which is a special case and does not work at all:  The first difference is that in my example I execute whoami, not bash. The second difference is that it actually works as expected on Ubuntu, but not on SuSE.  Suid bit works fine on my PC running Ubuntu, but not on a SLES test instance. The nosuid flag is not set on the mounted xfs file system on the SLES machine. ls shows that ony my machine and the SLE Server, the same permissions are set for the executable. So why does the executable still run as the current user instead of as the owner?  execsudo.c:  #include <stdio.h> #include <stdlib.h>  int main(int argc,char *argv[]) {     system(argv[1]);     return 0; }   bash:  gcc -o setuid-test execsudo.c ; sudo chown nobody ./setuid-test; sudo chmod +s ./setuid-test; ./setuid-test "whoami"  # Outputs current user instead of nobody   [EDIT 2]  I still have not worked out the problem, but I suppose it might be because the SuSE machine is a VM. A workaround might be to configure this behaviour via /etc/sudoers instead.

I was experimenting a bit and noticed something strange: setting the setuid bit on a copy of bash located at /usr/bin/bash-test seemed to have no effect. When I ran an instance of bash-test, my home directory was not set to /root and when I ran the whoami command from bash-test, my username was not reported as being root, suggesting that bash-test was not running as root. However, if I set the setuid bit on whoami, I was reported as being root in any shell, as expected.  I tried setting the setuid bit on /usr/bin/bash as well and observed the same behavior.  Why is bash not running as root when I set the setuid bit on it? Could selinux have something to do with this?


I am using classicthesis for my master's thesis. My supervisor told me to remove the "In: journalname" in the bibliography for references appearing in journals, and that "In:" should only be used for book entries. However, I do not understand how I can make this change while at the same time keeping the nice numeric-comp-like citations ([1-3] instead of [1,2,3]) and a bibliography that is numbered (not author-year style, but [1], [2], ....). I suspect this is where the magic should happen, but I just cannot make it work: \usepackage{csquotes} \PassOptionsToPackage{% %backend=biber, % Instead of bibtex backend=bibtex8, bibencoding=ascii,% language=auto,% style=numeric-comp,% %style=authoryear-comp, % Author 1999, 2010 %bibstyle=numeric,dashed=false, % dashed: substitute rep. author with --- sorting=none, % name, year, title maxbibnames=10, % default: 3, et al. %backref=true,% natbib=true % natbib compatibility mode (\citep and \citet still work) }{biblatex} \usepackage{biblatex}

How do I suppress the "In: " before the journaltitle? Like so:     In: Journal of Applied Physics


Each of $n$ balls is independently placed into one of $n$ boxes, with all boxes equally likely. What is the probability that exactly one box is empty? (Introduction to Probability, Blitzstein and Nwang, p.36).    The number of possible permutations with replacement is $n^n$ In order to have one empty box, we need a different box having $2$ balls in it. We have $\dbinom{n}{1}$ choices for the empty box, $\dbinom{n-1}{1}$ choices left for the box with $2$ balls, and $(n-2)!$ permutations to assign the remaining balls to the remaining boxes. Result: $$\frac{\dbinom{n}{1} \dbinom{n-1}{1} (n-2)!}{n^n}$$   Is this correct?

The question is: n balls are distributed into n holes at random. What is the probability that exactly one hole remains empty. I came up with $$P\left(A\right)=\frac{\:\dbinom{n\:}{1}\:\dbinom{n\:-1}{1}\:\left(n-2\right)!}{n^n}$$ but was told I’m way way off. Yes, I do realize I’m awful at probability. Thanks for the help.


When I visit sites like physics.stackexchange and math.stackexchange, instead of seeing the latex that I am used to, I see the dollar signs as though it hasn't compiled. This has just started recently and I am not sure why. Has this happened to anyone else? How can I fix this?

TeX rendering is broken on sites like Math and Physics when viewed over SSL.  For example:  :    And


I'm stuck in figuring out a problem, and I can't quite figure out a way out right now. any suggestion is highly appreciated.  we have a 10bit number(made up of 1s and 0s), and we do not know the number. what is the probability of having even number of 1s? So, what i did:  -0 ones  -2 ones  -4 ones  -6 ones  -8 ones  -10 ones  I started to look at each case. The first and the last can only be one number, I also found that the second has $90$ numbers possibilities of construction. When we have $4$ ones, i calculated we get 10*9*8*7 numbers etc. I'm getting really weird numbers though at the final step of adding it all in.   Is there an easy way to go about this counting problem? I feel my solution is very error-prone and tedious. :/

Let $A$ be a non-empty set and $n$ be the number of elements in $A$, i.e. $n:=|A|$.  I know that the number of elements of the power set of $A$ is $2^n$, i.e.  $|\mathcal{P}(A)|=2^n$.  I came across the fact that exactly half of the elements of $\mathcal{P}(A)$ contain an odd number of elements, and half of them an even number of elements.  Can someone prove this? Or hint at a proof?


I've got some customers who should use a specific IP in their network adapter, but manually setting it is a pain sometimes. So I would like to know if there's a shell command / batch that allows me to set it without having to open "Network" -> "Adapter Setting" -> "Ipv4" -> "Ip Address".

I need fixed IP in three wireless networks I log in frequently.  It is a pain to set those IP and gateway everytime I change networks.  I am willing to write a script to change my IP and gateway between those 3 fixed IPs and a choice to make it get IP automatically (when I´m in another network).  A plus feature to my script would be if it could discover the wireless network I am logged in and decide the IP automatically.  Is it even possible?  Thanks.


Let $G$  be a finite group, $p$ be  the smallest prime divisor of $|G|$, and $x \in  G $ an element of order p. Suppose $h \in  G $ is such that $hxh ^{−1} = x ^{10} $. Show that $p=3$  My try:  Since $o(x)=p$ and $hxh^{-1}$ and $x$ being conjugates have the same order we have $o(hxh^{-1})=o(x^{10})=p$  Also $o(x^{10})=\dfrac{p}{\gcd(10,p)}=p$  Then $\gcd(10,p)=1$ then $10^{p-1}\equiv 1(\mod p)$  I can see that $p=3$ satisfies the equation .Also $p\neq 2,5$.How to eliminate other possibilities of $p$?

Question. Let $G$ be a finite group and $p$ be the smallest prime dividing $|G|$.  Let $x$ be n element of order $p$ in $G$. Assume that there exists an element $h\in G$ such that $hxh^{-1}=x^{10}$.  Show that $p=3$.    What I have done so far is use the fact that $o(hxh^{-1})=o(x)=p$ and $o(x^{10})=p/\gcd(p,10)$.  By hypothesis we have $p=p/\gcd(p,10)$, giving $\gcd(p,10)=1$.  Here I am stuck.  I have not been able to make use of the fact that $p$ is the smallest prime divisor of $|G|$.  Can somebody help?


I'm confused about the source of Input Bias Current, is it generated by op amp, where the current "leak" from the op amp. or it's a must to operate the op amp? for example if I have in a data sheet a 1pA input bias current, should I provide a 1pA to the inputs of op amp? I know that the bipolar op amp needs a current to operate, but what about FET and CMOS op amp?   In short question: Should I build circuit to "provide" this current, or it's just given by the op amp itself?  Also, what is the difference between input bias current and the leakage current?  Note: if the type of op amp make a difference, I'm interested in LTC6078/LTC6079

Is it the current you have to drive in the input to get a specific, defined voltage at the output? And don't the currents cancel each other when applied to both inputs?


As student, I recently asked myself - and other mates did - why Stack Overflow had no special diet adapted to students, more indulgent than with developers. Indeed, we noticed that our questions were frequently downvoted or did not receive enough attention. I don't find it normal that a beginner does not really have the same chance than an experimented developer, as its reputation tends to stay low  Thus, although I perfectly understand that Stack should remain something for "professional developers" and not a MOOC-provider, I think that it should be fine to give a special status to students to avoid them being discouraged to ask questions that could seem obvious.  So I would suggest a scholarship proof from the university or school to avoid derives. It would witness of open-mindness

There is a distinct decline in the level of civility on all the sites here.  Some of this is due to new users coming in and posting spam and other nonsense, but the off-topic and downvote buttons are doing a pretty good job of keeping this under control. Unfortunately, a lot of this is coming from more experienced users, and the site's built-in moderation system does not (and probably cannot) handle this very well.  Folks are rushing to pound new users down with "this belongs on meta!", "this is off topic", "this is a duplicate!" and "read the Help!". (Which is correct, but should be done nicer) All this, of course, is accompanied by a flurry of downvotes.  This is not very welcoming to new users who don't know about meta, the Help, or what counts as off-topic. Now I am not proposing that we just allow off-topic, meta, or duplicate questions.  However, I think we could be gentler in the way we express these sorts of things.  Explain what meta and the FAQ are and provide useful links.  Just using please and thank-you when asking folks to read the FAQ or post something on meta would be an improvement.  I also think we could rein in the downvoting a bit.  Not that we shouldn't vote stuff down, but unless a new user's post is clearly spam, voting it down to -1 or -2 should be sufficient to send a message without piling on. I like Stack Exchange and I want it to become a resource for everyone, not just an elitist site for high-rep users on the sites.


The question is to show that $GL_2(\mathbb{F}_2)$ and $S_3$ are isomorphic where $S_3$ is the symmetric group of $\{1, 2, 3\}$ and the group operation is composition.  I have listed all the elements in both groups (there are $6$) and also classified them (self inverse, identity etc.). I have an idea as to which elements correspond to each other but if I specifically define the group homomorphism for each element it will take too long to prove it actually is a homomorphism.   Is there any other way to define a homomorphism between these two groups? I have seen similar questions but they were on permutation matrices which is not the case in this question so I am not exactly sure what to do.

I'm asked to show that $G=GL_2(\Bbb Z/2\Bbb Z)$ is isomorphic to $S_3$. I have few ideas but I don't manage to put them all together in order to obtain a satisying answer. I first tried using Cayley's theorem ($G$ is isomorphic to a subgroup of $S_6$), and I also noticed that $\operatorname{Card}(G)=\operatorname{Card}(S3)=6$ & that they're both non-abelian group.  Is this enough to say that considering $S_3$ is a subgroup of $S_6$ with the same cardinality than $G$, it has to be isomorphic to it ?  Could anyone give me some elements to get a more rigorous proof or lead me to an other path to show this statement ?  Thanks in advance


I came across this website trying to learn how to solve a three-way duel puzzle.. While I did find a similar version of this question had been asked, trying to rework it was not at all successful so I am hoping somebody can talk me through this version (very explicitly!)   It is as follows:  Archer, Brian and Chris have an argument and decide to fight a three-way duel to settle the matter. The rules of the competition are as follows: They will take turns to fire. As Archer hits his target only 50% of the time, he will have the first shot. Being more reliable with a 75% strike rate Brian will go second, and as the best shot, scoring 90% of the time Chris will go third. The survivors will continue to take their shots in this order until only one of them is left. Assume that any hit results in death. Assuming that each of them applies the strategy that will give them the best chance of winning, the probability (correct to three decimal places) that Archer is the ultimate winner =0.AAA, and the probability that Caesar wins = 0.CCC  I need to find the value of AAA, and CCC and apply them to the 2nd part of the puzzle.  Any and all help is greatly appreciated!

This puzzle is taken from Mathematical Puzzles: A Connoisseur's Collection [Peter Winkler]. I don't understand the solution. Alice, Bob, and Carol arrange a three-way duel. Alice is a poor shot, hitting her target only 1/3 of the time on average. Bob is better, hitting his target 2/3 of the time. Carol is a sure shot. They take turns shooting, first Alice, then Bob, the Carol, then back to Alice, and so on until one is left. What is Alice's best course of action?  The solution is that Alice is better of missing than hitting Carol or Bob, so she should shoot into the air. Indeed, then Bob will shot Carol, and it can be shown that it gives the greatest probability of survival for Alice. But I wonder if Bob should not voluntary shoot into the air too, so that Carol will do the same, and no one be shot. If this is the case, Alice survival probability is 1. What do you think of it? What is Alice survival probability?


I'm trying to understand what causes a black hole in terms of it's composition. We know a start can die and collapse into a neutron star, but if the neutro star is not dense enough to create a black hole, then what it is inside? I mean, what is more dense than a neutrons glued together?  Is a "quarks" star? are the neutrons destroyed and all the quarks inside put together?

Imagine a black hole originally formed from, for example, Rubidium atoms. On the other hand, one made from, for example, Helium atoms. Will it be there any difference between the two? Or perhaps once formed it all turns into the same type of matter?  Can the "composition" of the matter-energy in the black hole be inferred somehow?  Could one say that "black hole substance" is a distinct form or state of matter different from other forms or states of matter?


I have pressed Shift-Cmd-4 and selected an area. Now it is in screen capture app. But I need it inside clipboard to paste here. How to do that?

The revised Screenshot utility in Mojave brings the handy option of choosing if the resulting Screenshot should be copied to the clipboard or saved as a file, or saved to email, etc.  However this requires that I first press Cmd+Shift+5 to bring up the options, then select my desired option using the pointer. I find myself often needing to switch between saving to a file and saving to the clipboard and wondering if there is a way to do this by a keyboard command or modifier.   For example it would be great if I could use Cmd+Shift+4 to capture a selection, but modify the command to save-to-clipboard or save-to-file.  Grateful for any suggestions.


I am going to change the name on my Indian passport from Given Name:ABC XYZ, Surname: "Blank" ----> Given Name:ABC, Surname: XYZ. My US F1 student visa will remain on my old passport with the old name. As far as I've read, this should not cause issues while re-entering the USA as I will have proof of the name change.   The question I have is regarding an application for Schengen Visa (at the Slovenian embassy in the US): will they accept my US F1 visa with the old name as a proof of stay in the United States? Will having these two passports cause problems for getting the Schengen visa?

I am considering a name change, which seems to be a relatively straightforward action, when one remains in the same country: certain documents are replaced with new ones bearing the new name, and others are presented together with the name change document.  However, I travel internationally multiple times per year, and I often change temporary residence from one country to another. So I often deal with immigration and similar things. Furthermore, I have a lot of things going on like work and studies.  Quite obviously, if I change my name, I would often have to produce a proper translation of the name change document, which may include notarized translation thereof with apostille or, for example, traduction assermentée in France.  However, it would be great to hear about experiences of people, who have dealt with this issue first-hand, so I can weight the disadvantages against advantages of this correctly. In particular, I would like to know if anyone has encountered unforeseen difficulties with this, and how people rate the overall difficulty of such experiences.


Is there a way to calculate a p-value for the hypothesis that population coefficient regression coefficient $B_1$ is larger than that of $B_2$ when doing multiple regression on a sample group?  In the test I'm trying to perform $x_1$ and $x_2$ are both binary, but I'm interested in the general case as well.

If this is a duplicate question, please point to the right way, but the similar questions I've found here haven't been sufficiently similar. Suppose I estimate the model $$Y=\alpha + \beta X + u$$  and find that $\beta>0$. However, it turns out that $X=X_1+X_2$, and I suspect $\partial Y/\partial X_1 \ne \partial Y / \partial X_2$, and in particular, that $\partial Y/\partial X_1 > \partial Y / \partial X_2$. So I estimate the model $$Y=\alpha + \beta_1 X_1 + \beta_2 X_2 +u$$and find significant evidence for $\beta_1,\beta_2>0$. How can I then test whether $\beta_1> \beta_2$? I considered running another regression $$Y=\alpha +\gamma(X_1 - X_2) + u$$ And testing whether $\gamma>0$. Is this the best way?  Also, I need to generalize the answer to many variables, i.e. suppose we have $$Y=\alpha + \beta^1 X^1 + \beta ^2 X^2 + \dots + \beta^nX^n + u$$ where for each $j=1,\dots,n$, $X^j=X_1^j+X_2^j$, and I would like to test for each $j$ whether $\partial Y/\partial X_1^j \ne \partial Y / \partial X_2^j$.  By the way, I am primarily working in R.


I just want push notifications when my boss sends me email.

I have a lot of mail traffic on my phone. But I want to be notified only for mail from certain contacts like my family, colleagues/boss, critical automated systems or at least any contact in my phone contact list (with email typed in).  Are there such applications which can access email on my personal/corporate server? Standard IMAP (or at least POP3) + SMTP, not some proprietary protocols like Exchange/Gmail.


I am trying to prove that $$\sum_{k=0}^n {x+k \choose k} = {x+n+1 \choose n}$$ I have tried developing right side then induction but I haven’t reached anything. Any help is greatly appreciated.

After reading , the most popular answer use the identity $$\sum_{t=0}^n \binom{t}{k} = \binom{n+1}{k+1}.$$  What's the name of this identity? Is it the identity of the  modified.  How can we prove it? I tried by induction, but without success. Can we also prove it algebraically?  Thanks for your help.    EDIT 01 : This identity is known as the  because, on Pascal's triangle, when the addends represented in the summation and the sum itself are highlighted, a hockey-stick shape is revealed.


In the equation: $$\sin(x) =  x\prod_{n=1}^\infty \left(1-\frac{x^2}{n^2\pi^2}\right),$$  I know that if I set  $$0 = x\prod_{n=1}^\infty \left(1-\frac{x^2}{n^2\pi^2}\right),$$ all of the roots are really going to be the roots of $\sin(x)$. But why is this generally equal to $\sin(x)$? How can I know that $\sin(2.285672364)$ will be $\prod_{n=1}^\infty \left(1-\frac{(2.285672364)^2}{n^2\pi^2}\right)$, for example? (I mean, how do I know that the graphs of both functions will be the same?). How can I assume that the coefficients of $\frac{\sin(x)}{x}$ in the product expansion are going to be the same of the sum expansion, i.e. in the Taylor series? $\left(\frac{\sin x}{x} = 1 - \frac{x^2}{3!} + \frac{x^4}{5!} - \frac{x^6}{7!} + \cdots\right)$ like Euler showed in the 'Basel problem', by saying: $$\frac{x^2}{3!} = \frac{x^2}{\pi^2}\left(\frac{1}{1^2} + \frac{1}{2^2} + \frac{1}{3^2} + \cdots\right)$$ So: $$\zeta(2) = \frac{1}{1^2} + \frac{1}{2^2} + \frac{1}{3^2} + ... = \frac{\pi^2}{6}$$

How to prove the following product? $$\frac{\sin(x)}{x}= \left(1+\frac{x}{\pi}\right) \left(1-\frac{x}{\pi}\right) \left(1+\frac{x}{2\pi}\right) \left(1-\frac{x}{2\pi}\right) \left(1+\frac{x}{3\pi}\right) \left(1-\frac{x}{3\pi}\right)\cdots$$


I'm not sure, but it seems like the requirements for valid housing have changed in Terraria 1.2.   I usually build a big central chamber like in the image below, but since the 1.2 patch this setup doesn't work. The query tool give the "This is not valid housing" message.  The room is enclosed by bricks and platforms. It has a door, chair, table, background walls and light sources. This was usually enough for valid housing.    Have the requirements for valid housing changed in Terraria 1.2? If so, what are the new requirements? Or am I just doing it wrong?  Edit/Answer:  For those that don't find any answer in the "duplicate" question: Rooms have a max size. The exact maximum is elusive since there are a lot of variables. This  has a nice guide about house size.

I read on the wiki that people will move in under the following conditions:   You do something to please them An empty house is available with a light source, table, and chair (also with walls).   I have a house which is about 7x8, then a roof space above that; about half the area. I could put furniture up there too, but will anyone move in?


Hello i want to convert int Array into Required Format.  i have int array and how to convert it ? i want this String format  int a = [1,2,3,4] list a = [1,2,3,4] String = ["1","2","3"];

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


Is mass quantized? If yes, then why do we see all amounts of mass? Well , can it be said quantized just for smaller masses?

I learned today in class that photons and light are quantized.  I also remember that electric charge is quantized as well.  I was thinking about these implications, and I was wondering if (rest) mass was similarly quantized.  That is, if we describe certain finite irreducible masses $x$, $y$, $z$, etc., then all masses are integer multiples of these irreducible masses.  Or do masses exist along a continuum, as charge and light were thought to exist on before the discovery of photons and electrons?  (I'm only referring to invariant/rest mass.)


A proof is some explanation to convincing others that a statement is true (or false in case of a counterexample). As Yuri Manin once wrote: "A proof becomes a proof only after the social act of accepting it as a proof".   Since Mathematics is not comprehensively 'connected' to the nature, I am trying to compare it with another situation: there were many beliefs in history that every body was convinced their truth, it could even be as far as a superstition. But as time passed their validity changed.   My question is: Do we need other type(s) of intelligent creation (like intelligent aliens) for final check whether our proofs are true or not? Or, human mind is enough for checking their truth?  Note - My question is especially focus on non-empirical Mathematics.   EDIT - Also, there have been many mathematical proofs that had very subtle inconsistency detected by smart people; checking Fermat Last Theorem's proof by a colleague of Wiles came up with a subtle mistake is an example; Is it possible that a 'proof' has that type of mistake but not easy enough to 'see' even by nowadays' people for a long long time? any historical story?    PS - migrated from math.SE

I don't understand philosophy very well, and so I am wondering whether you can "prove" anything in philosophy. It always seems you can go a layer down, and find another question, almost endlessly until you get to the question of "why/how/are we here?"  Can you prove, absolutely, and 100% that something is true, in the field of philosophy?


So I have read  post and I have another question about it. The first answer says that if we lift an object up that is the energy we "give" to gravity and then gravity uses that energy to pull the object back down. But if we launch a rocket and that rocket goes in a stable orbit gravity will keep applying energy to it to pull it back down.   So let's say that the energy that was required to launch the rocket was 1000 Newtons, and that gravity uses a force of .1 Newtons per second to pull it back down. It will then take 10000 seconds to reach the energy that we used to launch it. So after that 10000 seconds where does gravity then get its energy from?

F = gravitational force between the earth and the moon,  G = Universal gravitational constant = 6.67 x 10^(-11) Nm^2/(kg)^2,  m = mass of the moon = 7.36 × 10^(22) kg  M = mass of the earth = 5.9742 × 10^(24) and  r = distance between the earth and the moon = 384,402 km   F = 6.67 x 10^(-11) * (7.36 × 10^(22) * 5.9742 × 10^(24) / (384,402 )^2  F = 1.985 x 10^(26) N   The above all i took from    Age of Moon 4.53 billion years (From google)  So Earth has been producing a force of 1.985 x 10^(26) N for 4.53 billion years I do not know how to calculate the total energy spent so far(Please some one do the favor) from force and time but it must be very huge. if E = mc^2 then atleast some of the mass of earth must have disappeared in producing this energy or where did the energy come from ?   Somewhere some one has answered if we place a ball above earth then during that time we did the work and when it fell down to the earth that work changed into kinetic energy ok accepted but the moon is being pulled towards earth for unlimited time where does the earth get the energy from to do so ?  @Emilio Pisanty Thanks for your reply.  "it needs to move the object in the direction that the force acts in"  Even though the force applied by earth is perpendicular to the direction of motion the moon's direction is definitely changed because of the force applied by the earth and the moon is moving a little towards earth from the straight line otherwise the motion would be a straight line. If earth did no work on moon why would the moon not go in straight line escaping earth's gravity. Even if we accept that earth does no work and spends no energy in making the moon orbit around it,By newton's law any body which accelerates needs force and since the moon keeps accelerating all the time(changing its direction of movement)where does moon gets this force continuously for such a long time.


I am looking for QGIS tutorials that cover the topics of making a user interface to update the attribute table or any related tutorial that might help.  Does anyone know of one?

I wish to familiarize myself with the capabilities of QGIS up to and beyond QGIS version 3.0.   Can you recommend some good web resources and tutorials that would show me QGIS' capabilities?   I am interested in both using QGIS through its GUI and in developing applications using QGIS.


Not sure how to start this. I know that $504 =2 \times 2 \times2 \times 3 \times 3 \times 7$.

Not sure what to do / how to start this... I have equcation of 504 is: $2 \cdot2 \cdot 2 \cdot 3 \cdot 3 \cdot 7$


I'm a bit frustrated by the fact that [testing] and [unit-testing] are now branded with Telerik's logo. Not because I have something against Telerik (it is a company from my country and I know people there), but because these tags are generic - they are used by Java, Ruby, Python, etc., etc. questions, so it is irrelevant to show Telerik in a [java] + [unit-testing] question.  It won't be just a rant:   I'd like to see opinions whether or not this is a good idea Can a "conditional branded tag" be implemented? For example, brand it only in combination with certain other tags. This would make the tag page (with the promoted links) require two entry modes - one from a branded tag, and one from a regular one. But this can be done by a simple GET parameter.

I don't see any problem with companies sponsoring tags that are products/proper names, like  or  being sponsored by Adobe or  being sponsored by Android. However, I just noticed that the  tag is sponsored by Red Gate.  Does it really make sense to let someone sponsor a tag that represents a general concept? I mean, if they're willing to pay for it, so be it. But it just seems silly to think that someone might be able to sponsor tags like  or .


I found somewhere on the internet that routers also have a MAC address. Is it true? If so, how can I make it undetectable?

When you hit up a site, such as cnn.com, does the TCP/IP packet contain the MAC address of your network card?  Could cnn.com theoretically record my MAC address?


I am trying to do a regular expression match with a variable that contains an asterisk.  The following set of commands in Bash does filename expansion with the asterisk in the variable on the left-hand side of the operator.  test='part1 * part2' [[ "$test" =~ ^(.+)\ .\ (.+)$ ]] && echo $BASH_REMATCH   Results in: part1 FILE1 FILE2 part2  But it should result in: part1 * part2  I have searched and searched but cannot figure out why this is happening.

For example:  me$ FOO="BAR * BAR" me$ echo $FOO BAR file1 file2 file3 file4 BAR   and using the \ escape character:  me$ FOO="BAR \* BAR" me$ echo $FOO BAR \* BAR   I'm obviously doing something stupid.  How do I get the output BAR * BAR?