I opened the site switcher and found that my Meta Stack Overflow reputation was not right:    On both Main and Meta Stack Overflow, the reputation counter on my profile page show that the real amount is the same:    Why does the site switcher have such a different amount? I have seen this problem for a few weeks now and it's starting to annoy me.

While using the top bar to navigate across communities, I noticed that the reputation displayed on meta sites on that list does not match the one of their corresponding main sites:    I have noticed on past situations that reputation gained takes a bit to "update" on the display on Meta sites (that is, if you gain rep on SO, for example, it will take some time for you to see your updated rep on MSO).  However, I have never noticed this behavior here, on the Sites List of the top bar. Furthermore, the "delay" here seems to be more severe, as the "outdated" rep showed is of several days ago (for example, I turned 3k on SO almost exactly a week ago, but the rep shown on MSO is still <3k).  Any idea what could be causing this behavior?    Update: 2 months later this persists: my main site rep updates correctly but their corresponding meta rep remains the same as in the image above.     Update: As per Catija's  I removed the site (MSO) and put it back in, but it didn't update the rep.   However, after removing one site (TWP Meta), waiting at least a day, and then adding it back I see that although the reputations still don't match, the number displayed did changed a bit (previously 29,924 but now 33,112):


"What can I help with?"   Part of our team is claiming it is not proper english and another part is claiming its the correct way for us to say it.    For context this is in reference to working on a chat bot that will be helping customers so we are trying to keep it concise and at a simple level to be approachable to all users.

Like many others, I commonly find myself ending a sentence with a preposition.  Yes, it makes me cringe.  I usually rewrite the sentence, but sometimes (in emails) I just live with it.  To, with... you know who you are.  Should I keep fighting myself on this one, or is it okay in some circumstances?


I would like to add an image in a zone, on the map, to show that an event ocurred. I don't mind if it is in an Annotation Text or any other functionality.  Is it possible somehow in QGIS?

Say for example, if there's a point data with old trees, then when you use the identify tool, you can see the photograph of the tree  Or even one level further, the labels displaying these images right away without any clicking needed  I believe the term is file streaming?


I have a couple of software to be installed on ubuntu I want to run a shell script while installing Ubuntu. Please help how I can proceed.

I would like to customize Ubuntu live CD by installing some additional packages. I have followed   but it doesn't seems to work. Can anyone provide clear instructions?   Note: I do not prefer Remastersys, manual way will be appreciated.  Customization  Packages that I want to install:   Thunderbird    Samba    SSH       Changes that I need:   Remove Games menu from the Application menu Firefox shortcut on Desktop Radiance as the default Theme Different default Ubuntu Wallpaper   Configuration file changes   I want the panel to be placed at the bottom I want to paste my Samba configuration file instead of default Samba configuration I have few Firefox shortcuts and folders I would like to show that in Desktop Also it will be nice if you say me how to change the icon sets   Recent Updates   I have customized Ubuntu 10.10 with Firefox shortcuts and few folders on desktops. Everything went smooth. But the installer gets crashes after choosing the timezone. How do i fix this issue? Also setting wallpaper affects the login screen. The wallpaper which i set is displayed on the login screen also. I just want the default one for the login screen.


In the following program, I am trying to get values in an array from user.  However, I am getting NullPointerException after entering only two values. Can someone explain why I am getting this exception?  import java.util.*; import java.io.BufferedReader; import java.io.IOException; import java.io.InputStreamReader;  public class MemoriseMe{      static int arr1[],count;      public static void main(String[] args) throws IOException      {         BufferedReader brObj = new BufferedReader(new InputStreamReader(System.in));          int firstQuery =Integer.parseInt(brObj.readLine());         System.out.println("Enter the elements : ");           String line = brObj.readLine(); // to read multiple integers line         String[] strs = line.trim().split("\\s+");          for(int i =0;i<firstQuery;i++)         {             arr1[i]=Integer.parseInt(brObj.readLine());         }     } }

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


So I implemented a queue in Java and I was Trying to implement a procedure that inserts an element at the end of the queue.But I get an error message "java.lang.NullPointerException".I am new at this and I don't know what this means or how to fix it.  class Node {  public int ielement; public String selement; public Node next;     public Node(int iel, String sel) {      ielement = iel;     selement = sel; } class Implement {   private Node head; private Node tail;   public Implement() {     head = null;     tail=null; } public void InsertAtTheEnd(int iel, String sel){     Node newNode=new Node(iel,sel);     if(!Empty())//if the queue is empty{     tail.next=newNode;     tail=newNode;}     else{     newNode.next=head;     head=newNode;         }  }     public static void main(String[] args) {     Implement k = new Implement();    k.InsertAtTheEnd(1, "b");    k.InsertAtTheEnd(3, "bes");    k.InsertAtTheEnd(4, "kes");}


my query:Is this possible of legitimate that schengen visit visa holder can travel from his/her origin home country to any schengen country ... for example: if i have schengen visit visa of Italy and i am traveling form my home country pakistan so can i go to sweden or spain rather italy directly from my home country??

In case, if I get a multiple-entry Schengen visa in one of the embassies in Ukraine, Kyiv - should my first trip be to the country which issued the visa?  Any there any requirements of this sort? Does this condition vary depending on embassy which issued the visa?  What are the possible consequences on not visiting that country first? Does it somehow depend on country where the embassy is (i.e. non-Schengen and not EU members)?


I know that every object has a gravitational pull regardless of how far or how small it is. It's just that generally this force is negligible.  Does the force produced by the sun and moon have any non-negligible effect on the gravity we experience on earth? I imagine the two most extreme cases would be when the sun and moon are both directly overhead or directly below.  I imagine that all the other planets have far less of an impact than the sun and moon right?

Using $g = \frac{Gm}{r^2}$, the force on a point mass located at 1 AU from the Sun ($m = 2 \cdot 10^{30} \text{ kg}$) is about ~0.006 N/kg.  Does that mean that, e.g., a 70 kg person is ~42g lighter during the day, and ~42g heavier at night? That seems like it could make a big difference for things like measuring gold bars or other weight-sensitive items. (Gold arbitrage: buy your gold during the day and sell it during the night! Risk-free profit!)  This makes me suspect that I'm overlooking something obvious, because a ~0.05% weight difference seems like something everyone would have noticed long ago. So what am I missing?    Edit: A few answers below indicate that there shouldn't be any weight difference, because the Earth orbits the Sun in free-fall. But if that's the reason, does that mean that a 1:1 tidally-locked Earth-Sun system wouldn't experience differential gravity from the Sun on opposite sides? That doesn't seem right.


I'm trying to add the "Shader" node to this drop-down menu but it's not available and I truly don't know how to figure it out or even find it otherwise lmao.  I promise I tried Googling first for about an hour, then just clicking around for an hour, but I'm stuck because I'm super-new to using Blender (I've managed to do very little in the two weeks since I started trying to learn) and tbf my ADHD is bad and it's making me feel hella stupid so I just need a kind soul to tell me exactly what to do. If it helps at all, I'm trying to make this object glossy and I'm following a Youtube tutorial to learn how to do that.  I had this problem with 2.70 and just updated to 2.80 because I figured some of you might tell me to update, but the issue persists!  And tbf (again), it seems that I might have trouble following tutorials now because 2.80 looks so different from 2.70!  Haha! Here's a screengrab of what happened when I pressed Shift + A in 2.70 (very similar to 2.80).  Here's a screengrab of what happened when I tried to search for "Shader" within that search function in 2.70.  And here's what happens when I try to search for "shader" in the search bar in 2.80 (literally the same as in 2.70; I don't know why I thought updating would fix this.  I feel so stupid right now!)  Sorry & thanks in advance.  I'll answer whatever questions you have to the best of my ability, but I'm apparently an idiot so I may not know how to find what you're asking me for and anyway I'm assuming this'll be as simple as a few clicks or keystrokes.  I really appreciate it!! EDIT:  Whoever closed this question, the link provided uses v2.70 and I'm using 2.80 so everything looks completely different and I'm a complete beginner so I don't know what they're telling me to click!  So it doesn't help me at all!  I'm really frustrated and would appreciate it if you'd tell me how to do that in 2.80!  :^)

In Blender 2.7 we could change material nodes in composting. They removed it in Blender 2.8, where can I find it??


I'm reading Goldstein's Classical Mechanics and he defines a constraint on particles having radii $\mathbf{r}_i$ to be holonomic if it can be written as $f(\mathbf{r}_1, \mathbf{r}_2, \dots , t) = 0$. He then says that an example of a non-holonomic constraint would be particles constrained to the exterior of a sphere: $r^2 - a^2 \ge 0$.  However, this could be rewritten as $\mathbf{1}_{\left\{\mathbf{r}\mid \:|r|^2 < a^2\right\}}(\mathbf{r}) = 0$, where $\mathbf{1}$ denotes an indicator function. As such it seems to me that the given example is a holonomic constraint. What am I missing?

and other sources define holonomic constraints as a function  $$ f(\vec{r}_1, \ldots, \vec{r}_N, t) \equiv 0, $$  and says the number of degrees of freedom in a system is reduced by the number of independent holonomic constraints.  I could take multiple such constraints $f_1, \ldots, f_m$ and formulate them as single one that is fulfilled if and only if all $f_i$ are fulfilled:  $$ f = \sum_{i=1}^{m}{\lvert f_i \rvert}. $$  This combined $f$ would obviously reduce the number of degrees of freedom by $m$ instead of $1$.  Alternatively, to avoid the absolute value, I could use a sum of squares  $$ f = \sum_{i=1}^{m} f_i^2 $$  instead. Where is my error in reasoning?


I am using a linear regression model to determine the effect of diet score at baseline as predictor of weight at follow up where:  lm(weight_followup ~ Diet_Score*weight_base)  When I center my predictor variables I get the following:     However, the main effect changes when I do the same un centered:   From clinical knowledge, the second set of results (uncentered) makes more sense, as Diet Score (aka quality) weight at follow up goes down.   Not sure what to use, as some posts suggest that if using continous predictors where 0 is not in the data range than predictors should centered.  All suggestions welcome. Its a large dataframe of N = 3000.

I have a question related to multiple regression and interaction, inspired by this CV thread:    When checking for a moderation effect I do center my independent variables and multiply the centered variables in order to calculate my interaction term. Then I run my regression analysis and check for main and interaction effects, which may show the moderation.  If I redo the analysis without centering, apparently the coefficient of determination ($R^2$) does not change but the regression coefficients ($\beta$s) do. That seems clear and logical.  What I do not understand: The p-values of the main effects change substantially with centering, although the interaction does not (which is right). So my interpretation of main effects could change dramatically - just determined by centering or not. (It's is still the same data, in both analyses!)  Can somebody clarify? - Because that would mean that the option to center my variables would be mandatory and everybody should do it in order to get the same results with the same data.    Thanks a lot for distributing to that problem and your comprehensive explanations. Be assured that your help is very much appreciated!  For me, the biggest advantage of centering is to avoid multicollinearity. It is still quite confusing to establish a rule, whether to center or not. My impression is, that most of the resources suggest to center, although there are some "risks" when doing it. Again I want to put out the fact, that 2 researchers dealing with the same material and data might conclude different results, because one does centering and the other does not. I just read some part of a book by Bortz (he was a Professor and kind of a Statistics Star in Germany and Europe), and he does not even mention that technique; just points out to be careful in interpreting main effects of variables when they are involved in interactions.  After all, when you conduct a regression with one IV, one moderator (or second IV) and a DV, would you recommend to center or not?


I have a GET request to a jsp page. The contents of the JSP page is below:  <%@page language="java" import="java.sql.*,java.util.*" %> <%@page import="javax.servlet.*, java.util.*,java.util.Date, java.text.*"%> <jsp:useBean id="workM" class="test.concept" scope="page" /> <jsp:useBean id="userM" class="test.learning" scope="page" /> <jsp:useBean id="checkM" class="test.check" scope="session" /> <% if (checkM.checkUser()) //For auto loading user's most used search engine. Note: Only if the difference between top two is very big {     String user_id = checkM.getUser();     ResultSet RS6=workM.executeQuery("select top 1 searchEngineUsed,count(*) as number from UserSearchEngineSearch where user_id='"+user_id+"' group by searchEngineUsed order by number desc;");     while (RS6.next())     {          String name = RS6.getString("searchEngineUsed");         if (name.equals("google"))         {             out.print("1");         }         else if (name.equals("yahoo"))         {             out.print("2");         }         else if (name.equals("bing"))         {              out.print("3");         }         else if (name.equals("baidu"))         {              out.print("4");         }         else if (name.equals("yandex"))         {             out.print("5");         }         else if (name.equals("askcom"))         {             out.print("6");         }         else //by default just display google         {             out.print("1");         }     } } else //user not login {      out.print("1"); } %>   However, the content of the GET webpage is contains 5 lines of new line followed by a 4 (which means "baidu" was selected). How do I remove the 5 lines of new line spacing?

How can I strip out extra whitespace from jsp pages' output?  Is there a switch I can flip on my web.xml?  Is there a Tomcat specific setting?


I have a simple two lines of code but fail to understand what is actually happening.       s = 'We\'re' + 'Here'     print(s[4::2])   The result is just eee. I fail to see how the [4::2] is working to cause the code to print eee.

I need a good explanation (references are a plus) on Python's slice notation.   To me, this notation needs a bit of picking up.   It looks extremely powerful, but I haven't quite got my head around it.


If you became a US citizen, but have not yet got an American passport, can you fly from the US to the UK using your British passport?

I am a dual citizen. I have both a US passport and a non-US passport. I live in the US. My US passport is currently being processed for renewal. I am unsure whether I will receive my passport in time for a trip that I have scheduled. Could I use my non-US passport to leave the US and return? I have never entered the US with my non-US passport. There is no immigration leaving the US but I still need to scan my passport for ticketing. Will the airline refuse me a ticket? I know that in this situation returning with a non-US passport can be problematic as well, but will I be able to leave at all? Note that I am traveling to a country which neither of my passports are from.


Why doesn't my program not registering the value of the sting variable? When I run the program, it all goes fine, but when I get to the part where I type in the planet, the pathway goes directly to the invalid choice, and not the actual decision.   import java.util.Scanner; public class Planet  {  public static void main(String[] args)  {     //Import the scanner     Scanner keyboard = new Scanner(System.in);      //Create variables     double weight = 0;     String planet = "";     double result = 0;       //Ask for user's weight     System.out.println("What is your weight on Earth?");     weight = keyboard.nextDouble();      //Open menu for planets     System.out.println("\nChoose a planet...\n\nMercury\nVenus\nMars\nJupiter\nSaturn\nUranus\nNeptune\nPluto");     planet = keyboard.next();       //Calculate weight     if (planet=="Mercury")     {         result = (weight * .37);     }     else if (planet=="Venus")     {         result = (weight * .88);     }     else if (planet=="Mars")     {         result = (weight*.38);     }     else if (planet=="Jupiter")     {         result = (weight*2.64);     }     else if (planet=="Saturn")     {         result = (weight*1.15);     }     else if (planet=="Uranus")     {         result = (weight*1.15);     }     else if (planet=="Neptune")     {         result = (weight*1.12);     }     else if (planet=="Pluto")     {         result = (weight*.04);     }     else       {         System.out.println("Invalid choice.");     }      //Output weight     System.out.println("Your weight is " + weight + " on Earth. Your weight is " + result + " on " + planet + ".");   }   }

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


What's the difference, if any, between the noun author and writer

In my area of work the word author as a verb has become quite common. However, it seems to have a subtly different meaning than plain vanilla write. For example, one does not write software unit tests; one authors them.  Can anyone offer a clear distinction between the two words? Has author as a verb become a common usage outside of the field of computer software?


Let $f:D\rightarrow\mathbb{R}$ be continuous (i.e. it is continuous at each point in D). Define $|f|:D\rightarrow\mathbb{R}$ by $|f|(x)=|f(x)|$. Prove that $|f|$ is continuous. Intuitively this makes sense and you can write the proof as follows: Let $\phi:f(x)\forall x<0$ and $\theta:f(x)\forall x\geq0$. Since $f$ is continuous, we know that $\phi$ and $\theta$ are continuous. Now if $\phi$ is continuous, then so is $-\phi$, meaning $-f(x)$ is continuous for all $x<0$. It then follows that $f(x)$ is continuous for all $x\geq 0$. Thus, $|f|$ is continuous. But I want to know if it is possible to prove continuity of this function using either of the definitions of continuity: Deinitions:  Let $f:D\rightarrow\mathbb{R}$. $f$ is s-continuous at $x\in D$ provided that for any sequence $\{x_n\}$ with $\lim_{n\rightarrow\infty}x_n=x$ then $\lim_{n\rightarrow\infty}f(x_n)=f(x)$.  Let $f:D\rightarrow\mathbb{R}$. $f$ is $\epsilon\delta$-continuous at a point $x\in D$ provided that for any $\epsilon>0$, there exists a $\delta>0$ such that $|y-x|<\epsilon$ implies $|f(y)-f(x)|<\epsilon$.

$(i)$ Given a function $f:E \rightarrow \mathbb{R}$ define $|f|:E \rightarrow \mathbb{R}$ by $|f|(x)=|f(x)|$ for $x \in E$ show if $f$ is continuous at $c \in E$ then so is $|f|$.        $(ii)$ Now the converse is not true, find $f$ such that $|f|$ is continuous but $f$ is not.


My marketing dept. devised a scheme for visuals that includes occasional occurences of characters (glyphs) rendered in non-solid colours to go beyond simple gradients. My question is: is there any way I could make a font from, say, a given .otf and a picture containing the colour movement? (The font itself is proprietary I believe, but that's hopefully not essential here.)  Here's an example:    I have not tried anything because I don't really know where to start. I think there'd be a way with pgf/tikz for individual cases.

I'm using tikz to attempt to make a book cover, and I have a "wallpaper" image that looks like leather (not that I've handled that many leather-bound books). I'm using the node command to place text over the top of it, but none of the colors I've experimented with look decent.  Can I use an image of gold-leaf as the fill/stroke for the text? Or for that matter, for the path lines as well?  I've tried googling for this, but I can't figure out a set of keywords non-generic enough to pull back useful results.


Ryan et al. (2005) added that in-depth assessment of the family was important, and this could be best achieved by considering all points of view and by exploring a broad range of family functions, including how they had been communicating, solving problems, allocating roles and responsibilities, engaging emotionally with each other, and setting rules and expectations (as cited in Keitner, 2005).  or   Ryan et al. (2005) added that in-depth assessment of the family is important, and this is best achieved by considering all points of view and by exploring a broad range of family functions, including how they communicate, solve problems, allocate roles and responsibilities, engage emotionally with each other, and set rules and expectations (as cited in Keitner, 2005).

I know the past tense carries the past tense in every dependent clause, but referring specifically to places or to things that are eternal, like the Earth, seems a bit weird and therefore we sometimes (I believe incorrectly) say     He didn't know that New Jersey was actually on the East Coast.   Because it still is. Or     He thought the Earth was round.   So is it square now?  Logically speaking, would you consider the use of past tense here a bit confusing in a day-to-day speech in these examples? Would you instinctively opt for using the present tense?


I am using UI with multiple buttons and I need to start background task on button click and report back to main thread + update UI when the task is finished.  This is currently part of my code:  private void button1Click(object sender, EventArgs e)     {         button1.Text = "Starting";         button1.Enabled = false;         button1Worker.RunWorkerAsync();     }      private void button1worker_DoWork(object sender, DoWorkEventArgs e)     {         toolStarter.startTool("button1");     }      private void button1worker_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)     {         button1.Text = "Autoruns";         button1.Enabled = true;     }   This solution works as intended / expected, however the same code is repeated for 15 different buttons and that seem to be wrong to me.  Can you recommend some other way to do the same thing?  I did try ThreadPool queue but did not manage to update UI after task finished.

Which is the simplest way to update a Label from another Thread?   I have a Form running on thread1, and from that I'm starting another thread (thread2).  While thread2 is processing some files I would like to update a Label on the Form with the current status of thread2's work.   How could I do that?


I need to exclude a bunch of paths from a find command. For example:  find "$(pwd)" -not \( \  -path "*/.git"\  -o -path "*/.git/*"\  -o -path "*/.vscode"\  -o -path "*/.vscode/*"\  -o -path "*/node_modules"\  -o -path "*/node_modules/*"\  -o -path "*/Image"\  -o -path "*/Image/*"\  -o -path "*/Rendered"\  -o -path "*/Rendered/*"\  -o -path "*/iNotebook"\  -o -path "*/iNotebook/*"\  -o -path "*/GeneratedTest"\  -o -path "*/GeneratedTest/*"\  -o -path "*/GeneratedOutput"\  -o -path "*/GeneratedOutput/*"\  -o -path "*/*_files" \) -type d   However, I want to read these paths from a text file instead of listing them all on the command-line. How can I do that?

I am on Linux (Ubuntu) and I am would like to exclude certain directories (like .hg) when I am doing a  find | less     I tried the following to exclude the .hg directory from listing, but does not seem to work.  find -type d \( ! -iname \.hg \) find -type d \( ! -name \.hg \) find -type d \( ! -iname .hg \)   How do I exclude .directory in a find command


When searching for answers on , I noticed a weird little framed box pop up in the results list:    The box turns out to be a MathJax box, and the code being displayed happens to be Perl code; apparently the $ sigils in the Perl code snippet are somehow interpreted as MathJax delimiters in Markdown, even though the code fragment is nested inside a code block. It therefore seems that the truncated preview text is insufficiently escaped.

When searching on a site with  enabled (), I saw some  rendering issues: (and currently it's also in the )        Even though the LaTeX rendering is fine when opening the :        The LaTeX code is:  $f(n) = \begin{cases} 0,  & \text{$ \omega<0, \omega=1, \omega>3 $} \\[2ex] -\omega + 1,  & \text{$ 0\le\omega<1 $} \\[2ex] \omega^2 - 1,  & \text{$ 1< \omega \le 2 $} \\[2ex] 3 \omega,  & \text{$2 < \omega \le 3 $} \end{cases}$


I created some models in web ui like this:   But when I want to get all models information in rest api, it shows that "NullPoiterException".   ps: The api to import file is ok.

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


Every time I see a different preposition for the word square, I wonder whether I do not understand it or there is a mistake.     On 10 October [1939] they gathered everyone on the brewery square, which belonged to Mr Tejla.   Looking it up in dictionaries I found that square mostly collocates with in in terms of BrE. When it comes to AmE it's on. How about at, which also refers to place but not specific?

As a foreign English speaker who never really studied too much English grammar other than the basics at high school, I often struggle to decide what is the correct preposition to use in certain phrases.   At is perhaps the easiest choice to identify, but I find it more difficult to determine when to use on or in.  I know things are on the table or in a box. I’m in a house at street XX,YY.   But are there any rules or ways to find (discounting uncommon exceptions) when to use each form?


I tried looking up information about this and couldn't find anything, so I decided to post this. Basically, if you look over my profile on Personal Finance & Money Stack Exchange, you will notice that I have an answer with a given amount of upvotes, let's say N. And then, when you look at my profile from another community, on Meta for example, that same answer will appear in Top Network Posts with N+1 votes. It also shows N+1 when I check my Top Answers on the Stack Exchange network profile. The reason is because, at some point, I had received N+1 upvotes on that answer, and the account of one of them was deleted, as explained by the reputation change. It seemed to have updated everything, except these two places. I think the same would apply for downvotes too, but I don't want to make assumptions. Is this a known minor bug?

There is already a question  which is posted around a month ago (which was fixed). My question reports a similar issue of showing inaccurate scores along with another bug.   A couple of answers in the Top Answers in my network profile are showing incorrect score.         As we can see they are showing a score of 10. But as of writing this question, the score of both the answers is 9.  and  both have a score of 9 instead of 10.  Even though the current score is 9, both these answers reached a score of 10 a few months ago and I was awarded  for both.         The vote was removed either when a user was removed or there was an unupvote. As far as I can tell, I don't remember an unupvote notification in the achievement box from these answers. My guess is the votes are removed when user accounts were deleted.   So, I suspect the score of answers in Top Network Posts is not updated either when there is an unupvote or a vote thrown away due to account deletion.   Is this the right reason why score is inaccurate? Can this be fixed?


I am working on Ubuntu 16.04, I accidentally deleted the entire limits.conf entry.  Is there any way to recover it?

I would like to restore LightDM to its default state, because for some reason /etc/lightdm/unity-greeter.conf is now an empty file.  Deleting /etc/lightdm/unity-greeter.conf and then running sudo apt-get install --reinstall unity-greeter doesn't create a new config file as you might expect.   How can I restore a missing config file?


I have been taught that an electron has a wave-particle duality nature and an electron behaves as a wave when traveling.  I do also know that a wave is some kind of vibration, either it be a vibration of a vector field, or of a particle.   My questions is: If an electron behaves as a wave and a wave means some sort of vibrations, then what "kind" of vibration is/describes an electron?

I am a n00b to physics. What physics I know comes from high school and popular science books.  At school we were taught about atoms and what make up atoms, but we weren't actually told what the particles were!  So sure an atom has electrons orbiting around a nucleus made of protons and neutrons, but what exactly is an ?  And if we don't know, how can we fire them from guns, like they do in experiments ... etc  Any clarification on this would be great.


In the following code I can access information in a notebook tab, in this case, the flag variable of the tab frame. This can be useful in several situations; in my case, when I drop one of the tabs. But it is perhaps easier to exemplify by binding to the NotebookTabChanged event, like so: import tkinter as tk from tkinter import ttk import random   class FrameA(ttk.Frame):     def __init__(self, parent, flag=0):         ttk.Frame.__init__(self, parent)         self.flag = flag         self.label = ttk.Label(self, text="This is Frame A!\nThe flag is {}".format(self.flag))         self.label.pack()   class FrameB(ttk.Frame):     def __init__(self, parent, flag=1):         ttk.Frame.__init__(self, parent)         self.flag = flag         self.label = ttk.Label(self, text="This is Frame B!\nThe flag is {}".format(self.flag))         self.label.pack()   class App(tk.Frame):      def __init__(self, parent):         tk.Frame.__init__(self, parent)          self.notebook = ttk.Notebook(parent)         self.notebook.bind("<<NotebookTabChanged>>", self.tab_changed)         self.tabs = []         for i in range(6):             frame = random.choice([FrameA, FrameB])             j = random.choice(range(30))             self.tabs.append(frame(self.notebook, flag=j))             self.notebook.add(self.tabs[-1], text="Tab {}".format(i))          self.notebook.pack(expand=True, fill='both')      def tab_changed(self, event):         i = self.notebook.index(self.notebook.select())         print("{}".format(self.tabs[i].flag))   if __name__ == '__main__':     root = tk.Tk()     root.geometry('500x200+300+300')     App(root)     root.mainloop()  It could also be helpful to have access to which class (FrameA or FrameB) was used in the definition of the selected tab. Can that be done?

How do I find out a name of class that created an instance of an object in Python if the function I am doing this from is the base class of which the class of the instance has been derived?  Was thinking maybe  might have helped me out here, but it doesn't seem to give me what I want. And short of parsing the __class__ member, I'm not sure how to get at this information.


A java.lang.NullPointerException occurs when a Java application or Java applet has been badly coded. Typically, the Java program (and consequently, the programmer) attempted to access the reference or handle to a Java object that did not exist  I have  gone round in circles reading . I have made two minimal files  - Two.java will compile.   public class Two {    public static int width;    public static int height;     public static void main(String[] args) {      int width = 320;      int height = 100;        System.out.println(width + "," + height);    }  }   One.java in eclipse will print the string intwo to console. My question is if it will print, Why is it null? I am trying to  convert  the string to int so I can do  math with it. In real life there is a lot more than two  numbers arriving in.  import java.io.IOException; import java.io.BufferedReader; import java.io.InputStreamReader;  public class One {   public static int width;   public static int height;    public static void main(String[] args) throws IOException, InterruptedException {     Process p = Runtime.getRuntime().exec("java -jar Two.jar");     BufferedReader is;     String intwo;     is = new BufferedReader(new InputStreamReader(p.getInputStream()));      while ((intwo = is.readLine()) != null)       System.out.println(intwo); // Prints to console      String[] items = (intwo).split(","); //java.langNullPointerException     int[] results = new int[items.length];      for (int i = 0; i < items.length; i++) {       results[i] = Integer.parseInt(items[i]);     }     System.out.println(results[1]);   } }


Suppose $f: \mathbb{R} \to \mathbb{R} $ is continuous at $x = 1 $ and $g: \mathbb{R} \to \mathbb{R} $ continuous at $y = f(1) $. Then $g \circ f $ is continuous at $x = 1 $ Attempt: Let $\epsilon > 0$ be given. We can find $\delta', \delta'' $such that if $|x - 1| < \delta' $, then $|f(x) - f(1) | < \epsilon $ and we also have that $|f(z) - f(1) | < \delta'' $ implies $| g( f(z) ) - g( f(1)) | < \epsilon $ Isn't this just the proof? It is obvious that feel confused trying to write the proof nicely. IS this a correct proof ?

Suppose $f$ and $g$ are functions such that $g$ is continuous at $a$, and $f$ is continuous at $g(a)$. Show the composition $f(g(x))$ is continuous at $a$.  My idea: Can I go straight from definition and take $\delta=\min\{\delta_1,\delta_2\}$, where $\delta_1$ is used for the continuity of $g$ at $a$ and $\delta_2$ is used for f being continuous at $g(a)$. In my proof I just treat $g(a)$ as a point when referring to the composition. So it goes like this:  Proof: Given $\epsilon>0$, take $\delta=\min\{\delta_1,\delta_2\}$. Then $0<|x-g(a)|<\delta$ which implies $|f(g(x))-f(g(a))|<\epsilon$.


Our infant son threw me wife's phone. Since then the top 1 cm row of the screen is no longer responsive to touch. The display works perfectly, but touching it has no effect. Because of that she can no longer swipe down the notification tray in portrait mode. She has to open some app, rotate to landscape orientation, and swipe down.  Some apps which do not rotate or reorients the buttons in such a way that it is always in unresponsive zone are impossible to use. We can use split screen as the last workaround sometimes.  Anyway. I was wondering if there is any app for Android which force the whole OS to render in the responsive region only. I can manually select the responsive rectangular region. (Buying a new phone or changing the screen is not an option right now.)

I have Star N7189 (5.5") with the lower zone of touch screen dead     The menu and back buttons don't work,but the physical home button works.   I tried to press hard on the edges of the screen, I tried to apply a twist from the short sides as if it were nothing but a wet towel. I did the hard reset but it did not work.  Sometimes pressing dead area, the phone takes it as menu button  As well as replacing the screen what other methods can I try? Is there any app, launcher or trick to resize the screen usable only to the working area?  P.S. a few hours after leaving it in airplane mode suddenly the touch had this problem but I do not remember if I inadvertently placed something heavy in that area of the cell.


I've only seen the MGF used when it takes 0 as it parameter and then derived for the nth moment.  What does the MGF tell us when the parameter is other than 0?

In most basic probability theory courses your told moment generating functions (m.g.f) are useful for calculating the moments of a random variable. In particular the expectation and variance. Now in most courses the examples they provide for expectation and variance can be solved analytically using the definitions.   Are there any real life examples of distributions where finding the expectation and variance is hard to do analytically and so the use of m.g.f's was needed? I'm asking because I feel like I don't get to see exactly why they are important in the basic courses.


i'm new to android and here passing data from one fragment to anther but getting an error  CallFragment callFragment=new CallFragment(); textView=v.findViewById(R.id.editText); text=textView.getText().toString();  Bundle bundle = new Bundle(); bundle.putString("name", text);  callFragment.setArguments(bundle);  FragmentManager fragmentManager=getFragmentManager(); fragmentManager.beginTransaction().replace(R.id.fragment_container,callFragment).commit();

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


I have 4 tables that have 2 columns each.  'Column 1' is the 'One'  'Column 2' is the 'Many'  Column 1 has several different ID's that i need to group somehow and build a delimited string of all the 'Columns 2' values.  I need to do this for every distinct 'Column 1' value.... is this possible?  So for example i have this table..  DECLARE @tblDeadsData TABLE (     [ID] INT IDENTITY(1,1) NOT NULL,     [ContainerID] INT NULL,     [DeadsID] INT NULL     )   It is already populated with data, i need to build a delimited string of ALL the [DeadsID] for each [ContainerID], and then these delimited string need to be placed into this table (the DeadsDataTable Data goes into the tblLastMerge.DeadsIDList in this case)..  CREATE TABLE tblLastMerge(     [ID] INT IDENTITY(1,1) NOT NULL,     [FeedLotID] INT NULL,     [ContainerID] INT NULL,     [ContainerName] VARCHAR(40) NULL,     [IsMergeTargetContainer] BIT NULL,     [PurchaseIDList] VARCHAR(1000) NULL,     [DeadsIDList] VARCHAR(1000) NULL,     [RailersIDList] VARCHAR(1000) NULL,     [FeedBillIDList] VARCHAR(1000) NULL     )   ***************************EDIT********************************* in regards to the duplicate post.........Concatenation is not delimited!!!!!! no wonder when i did a search for my problem i did not see this post..... i do think you should link these 2 post though as i found an answer much more simplified compared to the (supposedly) original post

I'm trying to migrate a MySQL-based app over to Microsoft SQL Server 2005 (not by choice, but that's life).  In the original app, we used almost entirely ANSI-SQL compliant statements, with one significant exception -- we used MySQL's group_concat function fairly frequently.  group_concat, by the way, does this: given a table of, say, employee names and projects...  SELECT empName, projID FROM project_members;   returns:  ANDY   |  A100 ANDY   |  B391 ANDY   |  X010 TOM    |  A100 TOM    |  A510   ... and here's what you get with group_concat:  SELECT      empName, group_concat(projID SEPARATOR ' / ')  FROM      project_members  GROUP BY      empName;   returns:  ANDY   |  A100 / B391 / X010 TOM    |  A100 / A510   So what I'd like to know is: Is it possible to write, say, a user-defined function in SQL Server which emulates the functionality of group_concat?   I have almost no experience using UDFs, stored procedures, or anything like that, just straight-up SQL, so please err on the side of too much explanation :)


I have looked around the internet for methods of having big redstone delays (Up to 5 or 7 minutes), and multiple of these delays in a row, each delay sending a redstone signal to a command block then activating another long redstone delay (Not a loop).  The problem is that I don't want to use a whole lot of repeaters connected between different command blocks, as this would take too long and take up a lot of space. The amount of time also does not need to be too accurate.  What I have found is that many of the solutions I have tried to find are loops (Like Etho's Hopper Timer), and instead of a constant loop I want a redstone delay, like a bunch of repeaters, but more compact.  Anything easy to set up via redstone is preferred but I'm open to using scoreboards.  Edit: I slightly edited Yeet's suggestion so that the command kills the minecart, sand, and also gives an output.

I found 11 questions like this on gamingSE already, but none of them have proper and up-to-date answers. So I'm creating this Q&A:  How do you either activate a command x seconds/minutes/hours/… in the future or every x seconds/minutes/… in a loop?  Repeating command blocks and ticking functions execute 20 times per second, redstone is  in many situations and most of the extremely fancy solutions, like falling blocks in cobwebs, have broken over time or are needlessly complicated.


This year the LIGO experiments have found evidence of Gravitational waves. In their experiments two black holes merge and give rise to huge ripples in spacetime. Now after the discovery, every scientific seminar I attended on the subject says that this opened up a new era of Gravitational wave astronomy. My question:   Astronomy is usually referred to the observational study of universe, galaxies and stars. Given the gravitational waves we detect are anyway very feeble, I was wondering how is it possible to infer anything related to the structures of universe from these waves?

LIGO has announced the detection of gravitational waves on 11 Feb, 2016. I was wondering why the detection of gravitational waves was so significant?   I know it is another confirmation of general relativity (GR), but I thought we had already confirmed GR beyond much doubt. What extra stuff would finding gravitational waves teach us? Is the detection of gravitational waves significant in and of itself, or is there data which can be extracted from the waves which will be more useful?


Is folder /.cache/google-chrome safe to delete ?  would it affect the surfing experience on chrome?

I want clean up cache file or row data which is created by the Google chrome during playing video's form youtube as well as other site task. During cleanup I want to protect my history and cookies.  Where does Google chrome store cache data in Linux?  Is it possible that we manually delete cache files of Google chrome? But during delete that files we at least save our browsers history.   Note:- I am using standard account privilege.


I'm trying to fix my screen brightness problem, and I have checked some answers given on this site. I found out that I may have to use some command like this:  ls -la /sys/class/backlight/intel_backlight/ > lslabacklight    The problem is, while running this either with sudo or entered as super user su, I get an error saying permission is denied.  sudo ls -la /sys/calss/backlight/intel_backlight/ > lslbacklight bash: lslbacklight: Permission denied   How do I make it work? I got the idea of doing this from .

When using sudo to allow edits to files, I regularly get 'permission denied'.  For example, my mouse is jittery and sluggish, so I want to disable polling:  sudo echo "options drm_kms_helper poll=N">/etc/modprobe.d/local.conf   I'm prompted for a password, and then get:  bash: /etc/modprobe.d/local.conf: Permission denied   So I tried to do a temporary change to disable polling by using:  sudo echo N> /sys/module/drm_kms_helper/parameters/poll   Yet again the system responded with:  bash: /sys/module/drm_kms_helper/parameters/poll: Permission denied   Any ideas?


I've created a MATLAB class, something like:  classdef myclass    properties       x_array = [];   end    methods     function increment(obj,value)        obj.x_array = [obj.x_array ; value);     end   end end   The problem is, the property x_array is never modified when I invoke the increment() function: ex:  >>s = myclass >>increment(s,5)  >>s.x_array ans = []   I did some research, and I reached a conclusion that this is because of MATLAB using Lazy Copy for objects, making my class inherit the HANDLE class should have solved this, but it didn't, does anybody know why this is happening? And if extending the handle class is indeen the solution, isn't this the right way to do it:  classdef myclass < handle   or are there any extra steps?

I am trying to create a MATLAB class with a member variable that's being updated as a result of a method invocation, but when I try to change the property within the class it (apperently, from what I understood from MATLAB's memory management) creates a copy of the object and then modifies it, leaving the original object's property untouched.  classdef testprop       properties           numRequests=0;       end       methods           function Request(this, val)               disp(val);               this.numRequests=this.numRequests+1;           end       end   end     .  >> a=testprop; >> a.Request(9); >> a.Request(5);   >> a.numRequests    ans = 0


I'm wondering whether I should use "can" or "could" in the following.     How can / could I concentrate with you breathing down my neck all the time?   I'd appreciate your help.

What is difference between  Could you sell your old computer to me, seeing (that) you have no use for it. Can you sell your old computer to me, seeing (that) you have no use for it.  Can I use either one of them? Which one is grammatically correct or if both are, what is the difference in meaning?


On macOS, after you find a file using Finder, how do you get the file path? I tried right clicking on the file in Finder, but nothing happens. Usually in any other folder right clicking works, but not in Finder.

I look for a file in finder, finder finds it.  But, I'd like to find it's full path. How do I do that?


Is there a problem with Stack Overflow when extremely useful, massively upvoted/favorited questions get closed?  I'm specifically thinking about   That question currently has 155 upvotes and is on 250 favorites lists. I found it tremendously useful in getting up to speed on the bash tricks that everyone should know, and now the question has been closed because it's "subjective."  I know Stack Overflow only wants to provide answers to questions that have a clear best answer, but if people find this way of using the site to be very useful, why not modify the rules of SO?  As an aside, where is one supposed to go to get answers to questions that can present novices with a list of the most important things to know about a new tool/technology, to get a solid foundation of the most important tricks of the trade?  EDIT: Here is a list of a bunch of similar questions:

I'm on SO pretty much every day researching something to do with programming, and over the last month or two, I find I'm growing frustrated and a little disgusted at how many interesting questions have been closed as "not a good fit" or "too subjective".  I think there is a confusion between "subjective" and "calls for judgement". To me one of the most valuable things about SO is the tremendous breadth and depth of experience of the members, and experience translates into smart decisions and advice, and that advice cannot always be asked for, or expressed in terms of, bald facts and data.  It's going to be 'subjective'.  I don't think SO should be Wikipedia. I think that if I could ask a question to a group of skilled programmers sitting around a table at lunch, and get interesting, valuable answers, then I don't care whether the question or the answers are 'subjective', I think that question should equally well be fair game for Stack Overflow.  I would like to see a mechanism whereby people who vote to close a question lose reputation when somebody expresses interest in that question or its responses.  How can I, or can I, influence this aspect of SO?


Let $a_n$ be a series. For any sub sequence $a_{n_k}$, exists sub sequence $a_{n_{k_l}}$ that converge to L.  Prove or disprove that $a_n\to L$.  My try: Let $a_{n_k}=(-1)^n$, thus $a_{n_k}$ has two sub sequences that converge (one to 1, one to -1), but $a_{n_k}$ has two partial sums, thus $a_n$ has at least two partial sums, therefore not converging to L.  I saw a proof of the statement, but it's not clear and there are some assumptions which are seem wrong to me.  Please prove or disprove the statement.  Thank you!

Is the following true? Let $x_n$ be a sequence with the following property: Every subsequence of $x_n$ has a further subsequence which converges to $x$. Then the sequence $x_n$ converges to $x$.  I guess that it is true but I am not sure how to prove this.


I just dropped my iPhone in the toilet bowl but took it out after about 3 seconds. It's now totally off and wont turn back on!  Aside from cleaning it and keeping it in rice, is there any other way to fix it? Or is it just gone?  It's out of warranty.

So yesterday I dropped my iPhone into the toilet, it was literally submerged for less than 15 seconds and after taking it out I left it in my airing cupboard overnight to dry. Today the phone seems to be completely functional other than a very dark screen (changing brightness won't help).   Was wondering what the best course of action would be and if this is fixable.


I have already 5 drives in my PC. I want to install ubuntu replacing of win 7 on drive c without touching other drives. But how?

I would like to see a full how-to guide on how to install Ubuntu.


Let $p$ is an odd prime and $G$ is a group which has $2p$ elements. Show that there exists at least one element with order $p$.  I tried showing in 2 parts as $G$ is cyclic and not cyclic, but I couldn’t show it for not cyclic groups. I think I must do something different. Could you please help me in the easiest way becasue we have learnt only elemantry theorems and definitions?

I want to show without using Sylow theorem that     Any group of order $2p$ has a subgroup of order $p~$($p$ being a prime)   My attempt: Since $|G|=2p,$ even $\exists~a\neq e\in G$ such that $a^{-1}=a.$ Then $H=\{e,a\}\leq G.$ Let $S$ be the set of all left cosets of $H$ in $G.$ Now $S$ forms a group w.r.t. the composition $g_1Hg_2H=(g_1g_2)H.$ The mapping $\sigma:S\to G:gH\mapsto g$ is an $1-1$ homomorphism. Then $S\simeq\sigma(S)\leq G.$ Thus $G$ has a subgroup of order $p.$  Please tell me whether I'm right!     I'm skecptical as I didn't use that $p$ is prime.


I am trying to render . I have a few scripts. But it says     to build and the render the cursor set you'll need python-pil and x11-apps installed.   I am not sure which commands to use to install them. Any help will be great.  I have 18.04 fully updated.

I went to  for installing Pillow since the original PIL is a discontinued project and so now not so good to use. But, in the table support for Ubuntu 16.04 LTS is unmentioned. It appears neither in , or in .     Further, just installing pillow is said to be not enough. There are some dependencies that should be installed first which is also unmentioned for Ubuntu 16.04 LTS. Would the installation steps for Pillow for python 3 given for 14.04 LTS be OK for Ubuntu 16.04 LTS?  If not, How do I install pillow in 16.04 LTS for Python 3.6? (There is support for Python 2.)


Here's what I currently see on chat.se:    Badge text has lost its indentation, some icons are bottom-aligned instead of top-aligned, and the rep-change number sometimes floats above the text.  SE sites aren't affected; this is what I see on Meta.SE:    I think I saw normal behavior in chat 12-24 hours ago.  A  was reported last week, but it was fixed in the meantime and has now broken again.

The padding in the chat top bar (seen in non-room views, e.g. ) is off under "My Communities" list, and achievements dialog:        and...        and...        Affected browsers/OS:   Chrome latest stable version (65.0.3325.181) under Windows 7 and 10 (Arch)Linux. Firefox   Do also note that the top bar itself is still following the old design.  Can this please be fixed?


I am not sure how to deal with this Question:  Show, that the sequence $(a_{n})_{n \in \mathbb{N}}$ converges towards the limit $a \in \mathbb{R}$, exactly when every subsequence $(a_{n_{k}})_{k \in \mathbb{N}}$ of $(a_{n})_{n \in \mathbb{N}}$ owns itself a converging subsequence $(a_{n_{k_{j}}})_{j \in \mathbb{N}}$ towards $a$.  To show:   $PS(a_{n}):=$ the set of all subsequences of a given sequence.  $$a_{n}\rightarrow a \Leftrightarrow \forall a_{n_{k}} \in PS(a_{n})\; \exists \; a_{n_{k_{j}}} \in PS(a_{n_{k}}): a_{n_{k_{j}}}\rightarrow a$$  It is easy to show the "$\Rightarrow$" direction, as every subsequence of a given converging sequence, converges towards the same limit.  But what about "$\Leftarrow$"?


I'm making a poker game and I have a class which contains a std::map to assign a value for every card on the poker deck referring to its name. I tried to put it as a component of another class as static member, since I have to assign a value every time a card is created, but for some reason when I try to access to it I get compiler error undefined symbol or duplicated symbol.  My partial solution have been declaring the class container as a global variable outside a class scope, but I know it's a bad practice , and if not there is anyway my doubt.  extern Baraja baraja;   For some reason when I declare this as static member or static const member, happens that I cannot access to the values of the std::map or I get compiler error undefined symbol or duplicated symbol so as I have searched in web documentations and cannot find a reason or solution I have this question.  How to correctly create, initialize and access to a static member of a class?

What is the best way to initialize a private, static data member in C++?  I tried this in my header file, but it gives me weird linker errors:  class foo {     private:         static int i; };  int foo::i = 0;   I'm guessing this is because I can't initialize a private member from outside the class.  So what's the best way to do this?


I looked around, and most questions deal with why you would use virtual, what polymorphism is and so on.  I am having a problem in my program and I want to know WHY the child function is not being called and how to actually CALL the child function in this situation.  I can emulate my problem:  #include <string> #include <iostream> #include <vector>  class BaseA {   public:   BaseA(const std::string &n)     : name(n)   {   }    virtual void print() const   {     std::string str("");     str += name;     std::cout << str << std::endl;   }    protected:   std::string name; };  class BaseB : public BaseA {   public:   BaseB(const std::string &n, const std::string &v)     : BaseA(n), value(v)   {   }    void print() const   {     std::string str("");     str += name;     str += ' ';     str += value;     std::cout << str << std::endl;   }    private:   std::string value; };  int main() {   std::vector<BaseA> vec;   vec.push_back(BaseA("cat"));   vec.push_back(BaseB("cat", "kitten"));    for(BaseA &obj : vec)     obj.print();    return 0; }    Why is the output: cat cat? How do I change the output to "cat cat kitten " using BaseB::print()?

Someone mentioned it in the IRC as the slicing problem.


I am a newbie in C and I stumbled on this c-structure:  typedef struct {    int dog;    int cat; } FOO;  typedef struct {    int  id;    FOO* pRow[0] } BAR;   I know basic c and c++ but I have no idea the motivation of the following line: "FOO* pRow[0]".  If the author wants to define a pointer to an array of FOO, then he/she should just define it as "FOO* pROW", right? Why does pROW[0] stands for in this case then?  Please enlighten me. Thanks!

I am working on refactoring some old code and have found few structs containing zero length arrays (below). Warnings depressed by pragma, of course, but I've failed to create by "new" structures containing such structures (error 2233). Array 'byData' used as pointer, but why not to use pointer instead? or array of length 1? And of course, no comments were added to make me enjoy the process...  Any causes to use such thing? Any advice in refactoring those?  struct someData {    int nData;    BYTE byData[0]; }   NB It's C++, Windows XP, VS 2003


I have a Repo (called Repo1) and another separate Repo, which has branches in it (REpo2). What I am trying to do is fold changes made in the master branch of Repo2 into Repo1   Is there a way to merge across multiple Repos? or can I only merge between branches of the same Repo?

Let's say I've got a setup that look something like  phd/code/ phd/figures/ phd/thesis/   For historical reasons, these all have their own git repositories. But I'd like to combine them into a single one to simplify things a little. For example, right now I might make two sets of changes and have to do something like  cd phd/code git commit  cd ../figures git commit   It'd be (now) nice to just to perform  cd phd git commit   There seems to be a couple of ways of doing this using submodules or pulling from my sub-repositories, but that's a little more complex than I'm looking for. At the very least, I'd be happy with  cd phd git init git add [[everything that's already in my other repositories]]   but that doesn't seem like a one-liner. Is there anything in git that can help me out?


Is there any Proof of the Principle of Superposition? Is it just a principle or is it verified experimentally?

In the theory of electromagnetism (EM), why is the principle of superposition true? Can we read it off from Maxwell's equations directly?  Does it have any limit of applicability or is it a fundamental property of nature?


This question is dedicated to a better understanding of a card: .  The Gather entry has the following ruling.     "Unlike a face-down creature that was cast using the morph ability, a manifested creature may still be turned face up after it loses its abilities if it's a creature card."   I would like to know its exact meaning, and possible use. Thank you!

Related to : The question specifies morphs, but I wondered if this was true for Manifest as well? As Manifest is not an ability on the card, does  prevent it from being turned face up for its mana cost?


I have a 100 line text file. I want to extract lines 50 to 70 inclusive. How can I do this? My Google skills are failing me and man cut doesn't seem to have the answer - perhaps I need a different tool.

I have file with 200 lines.  I need to extract lines from 10 to 100 and put them into a new file.  How do you do this in unix/Linux?  What are the possible commands you could use?


If $\gcd(a,b) =1$. Why does $\gcd(a+b,ab)=1$ ?  I know that if $\gcd(a,b)=1$ then there exists $u$ and $v$ where $au+bv=1$. But I can't seem to relate it to $a+b$ and $ab$.

I need to prove that:   If $\gcd(a,b)=1$, then $\gcd(a+b,ab)=1.$  So far I used what's given so I have:  $ax+by=1$ (I wrote the gcd of a and b as a linear combination)  and   $(a+b)u+ab(v)=1$ (I also wrote this as a linear combination)  where do I go from here?


I was trying the code to check the time taken by stream() and parallelStream() for the same operation.   Code 1  List <String> list = new ArrayList < String > ();  for (int i = 1; i <= 30000; i++) list.add("a"); for (int i = 1; i <= 20000; i++) list.add("b"); for (int i = 1; i <= 10000; i++) list.add("c");  //part 1 long start = System.currentTimeMillis(); Map <String, Long> countListSequence = list.stream()     .collect(Collectors.groupingBy(e -> e, Collectors.counting())); long end = System.currentTimeMillis();  System.out.println("Time taken in by stream() " + (end - start) + " millisec data " + countListSequence);  //part 2 long start1 = System.currentTimeMillis(); Map <String, Long> countListparallel = list.parallelStream()     .collect(Collectors.groupingBy(e -> e, Collectors.counting())); long end1 = System.currentTimeMillis();  System.out.println("Time taken by parallelStream() " + (end1 - start1) + " millisec data " + countListparallel);   Output 1  Time taken in by stream() 109 millisec data {a=30000, b=20000, c=10000} Time taken by parallelStream() 16 millisec data {a=30000, b=20000, c=10000}   But if I changed the order first use parallelStream() then stream() like  Code 2  //part 1 long start1 = System.currentTimeMillis(); Map <String, Long> countListparallel = list.parallelStream()     .collect(Collectors.groupingBy(e -> e, Collectors.counting())); long end1 = System.currentTimeMillis();  System.out.println("Time taken by parallelStream() " + (end1 - start1) + " millisec data " + countListparallel);  //part 2 long start = System.currentTimeMillis(); Map <String, Long> countListSequence = list.stream()     .collect(Collectors.groupingBy(e -> e, Collectors.counting())); long end = System.currentTimeMillis();  System.out.println("Time taken in by stream() " + (end - start) + " millisec data " + countListSequence);   Output 2  Time taken by parallelStream() 109 millisec data {a=30000, b=20000, c=10000} Time taken in by stream() 15 millisec data {a=30000, b=20000, c=10000}   My question is that why the second part stream() in Code 2   is taking less time then parallelStream() showing different behavior from Code 1?  Not only in the case of stream() and parallelStream() I also tried the same situation with stream() and stream() .I got the same situation with that also, second stream is taking less than first stream.  Code 3  //part 1 long start1 = System.currentTimeMillis(); Map <String, Long> countListparallel = list.stream()     .collect(Collectors.groupingBy(e -> e, Collectors.counting())); long end1 = System.currentTimeMillis();  System.out.println("Time taken by stream() 1 " + (end1 - start1) + " millisec data " + countListparallel);   //part 2     long start = System.currentTimeMillis(); Map <String, Long> countListSequence = list.stream()     .collect(Collectors.groupingBy(e -> e, Collectors.counting())); long end = System.currentTimeMillis();  System.out.println("Time taken in by stream() " + (end - start) + " millisec data " + countListSequence);   Output 3  Time taken by stream() 1 107 millisec data {a=30000, b=20000, c=10000} Time taken in by stream() 14 millisec data {a=30000, b=20000, c=10000}   Second print showed less time then first.So does stream calculated data reuse itself if I would believe that how could it be possible because the object created countListSequence and countListparallel are different.I am confused here how the second part in each code sample take less time then first part. Am I miising something about streams here?  Thanks

How do you write (and run) a correct micro-benchmark in Java?  I'm looking for some code samples and comments illustrating various things to think about.  Example: Should the benchmark measure time/iteration or iterations/time, and why?  Related:


Are these capacitors аffected by the temperature changing or not?

How can I find the Temperature Coefficient of Capacitance of the following capacitor series:


Currently have the following code, where by when the button is clicked, i want it to trigger off certain events, however, nothing seems to happen. Any help would be benficial:  Appending input button:  var row = $("

").addClass("row resource").attr("resource", "new"); var label = $("").addClass("label imaged").text("New resource"); var spanEl = $("&nbsp").addClass("defaultJobType"); spanEl.append($("<input id ='setDefaultJobType' type='submit' name='Default' value='Set Default'/>"));         label.append(spanEl);   When clicked, it should go into the following code:  $("#setDefaultJobType", context).click(function() {                 clickedDefaultJob($(this));             });   Which triggers of the following:  function clickedDefaultJob($el) {             //Remove bold tags from previous job type             $("div.row.ordertype").each(function(){                    if(($(this).text()).length>0){                     $("strong").contents().unwrap();                    }                 })             //assign default bold text to selected job type             var row = $el.closest(".row");             var rowNumber = row.attr("key");             var defaultVal = row.find(".defaultVal INPUT");             var jobTypeNameEl = $el.closest(".label.imaged");             jobTypeNameEl.wrapInner("");             var value = jobTypeNameEl.text();             updateSetting("<%=Setting.SET_DEFAULT_JOBTYPE%>", rowNumber, "int");         }

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 am currently reading Einstein's relativity book and trying to wrap my head around the time dilation.   I know about some implications of the twin paradox and wanted to ask a few questions that don't make any sense in my mind, obviously because of the ignorance. Please explain.   So let's assume, that we have two people. One is inertial at a certain point in space, not affected by any massive objects. Let that point be A. The second person is moving from this point A at 99.999999999% of speed of light, assume no acceleration. The trip one-way destination is 4 light-years away and let's say that's point B.   Now we know that the $t_{moving} = \frac{t_{standing}}{\gamma}$. So the time for stationary person will go slower. Time dilation in effect.   The moving person travels from A to B and back to A. Classic problem. Comes back. In his reference $t$ is 8yrs. For a stationary person $8*\gamma$ years. The moving person factually traveled to the future and came younger.  But my problem is that the only way the stationary person observed time dilation is if for her either the moving person's speed was slower or the overall distance was larger. We know that for inertial observers the speed of light will always be constant. So it has to be the distance that becomes larger and larger for the moving person with the speed approaching to the speed of light. Which doesn't make any sence.   The $D = 8yrs * c$. If nobody is moving. For the moving person it stays the same since their clock is at 8yrs precisely when they hit the A on the way back. However, for the stationary person the distance would have to be $D = 8yrs * \gamma *c$ or the c should be smaller, which is impossible.  Please help me out.

The paradox in the  is that the situation appears symmetrical so each twin should think the other has aged less, which is of course impossible.  There are a thousand explanations out there for why this doesn't happen, but they all end up saying something vague like it's because one twin is accelerating or you need general relativity to understand it.  Please will someone give a simple and definitive explanation for why both twins agree on which twin is younger when they meet for the second time?


I've noticed multiple copies of one of my external hard drives (that i replaced recently) showing up in Disk Utility.   Does anyone know how to remove them? I no longer have the original external hard drive.

I have this external (USB) drive that can't seem to be disconnected correctly.  Whenever I eject the drive, it won't disappear from Disk Utility.  Afterwards when the drive gets re-connected again, it cannot be mounted. At this stage, I would need to reboot the Mac to get the drive to mount again.    Ejecting from the Terminal via diskutil eject /dev/disk2 returns a Disk /dev/disk2 ejected message and unmounts the disk.  However the disk still shows up both in Disk Utility and diskutil list.   Furthermore even after the USB cable is disconnected, the disk still shows in both Disk Utility lists — GUI and command line.   How can I solve this?  OS: macOS Mojave 10.14.1 (18B75)


Please refer to the "screen capture" below.  When trying to install google-musicmanager-beta via apt-get, I get a "Hash sum mismatch". Any ideas what could be wrong?  edit1: I deleted all contents of the apt cache and run apt-get update again and still not working.  sudo rm -rf /var/lib/apt/lists/*   edit2: I downloaded the .deb file shown when running apt-get install and I was able to successfully install it!  screen capture  root@chiyo-VirtualBox:~# cat /etc/apt/sources.list.d/google.list  deb [arch=amd64] http://dl.google.com/linux/chrome/deb/ stable main deb http://dl.google.com/linux/musicmanager/deb/ stable main  root@chiyo-VirtualBox:~# apt-get --quiet --yes update Hit:1 http://au.archive.ubuntu.com/ubuntu xenial InRelease Hit:2 http://au.archive.ubuntu.com/ubuntu xenial-updates InRelease Hit:3 http://au.archive.ubuntu.com/ubuntu xenial-backports InRelease Ign:4 http://dl.google.com/linux/chrome/deb stable InRelease Ign:5 http://dl.google.com/linux/musicmanager/deb stable InRelease Get:6 http://security.ubuntu.com/ubuntu xenial-security InRelease [94.5 kB] Hit:7 http://dl.google.com/linux/chrome/deb stable Release Hit:9 http://dl.google.com/linux/musicmanager/deb stable Release Fetched 94.5 kB in 1s (61.3 kB/s) Reading package lists...  root@chiyo-VirtualBox:~# apt-get --quiet --yes install google-musicmanager-beta Reading package lists... Building dependency tree... Reading state information... The following additional packages will be installed:   libqt4-opengl libqtwebkit4 The following NEW packages will be installed:   google-musicmanager-beta libqt4-opengl libqtwebkit4 0 to upgrade, 3 to newly install, 0 to remove and 0 not to upgrade. Need to get 4,362 kB/13.7 MB of archives. After this operation, 55.1 MB of additional disk space will be used. Get:1 http://dl.google.com/linux/musicmanager/deb stable/main amd64 google-musicmanager-beta amd64 1.0.243.1116-r0 [4,362 kB] Err:1 http://dl.google.com/linux/musicmanager/deb stable/main amd64 google-musicmanager-beta amd64 1.0.243.1116-r0   Hash Sum mismatch Fetched 4,362 kB in 2s (1,971 kB/s) E: Failed to fetch http://dl.google.com/linux/musicmanager/deb/pool/main/g/google-musicmanager-beta/google-musicmanager-beta_1.0.243.1116-r0_amd64.deb Hash Sum mismatch  E: Unable to fetch some archives, maybe run apt-get update or try with --fix-missing?  root@chiyo-VirtualBox:/var/lib/apt/lists$ cat dl.google.com_linux_musicmanager_deb_dists_stable_main_binary-amd64_Packages Package: google-musicmanager-beta Version: 1.0.243.1116-r0 Architecture: amd64 Maintainer: Google Music Team <googleplay-support-music@google.com> Installed-Size: 16490 Pre-Depends: dpkg (>= 1.14.0) Depends: libc6 (>= 2.16), libexpat1 (>= 2.0.1), libflac8 (>= 1.3.0), libgcc1 (> = 1:4.1.1), libidn11 (>= 1.13), libqt4-network (>= 4:4.5.3), libqtcore4 (>= 4:4 .8.0), libqtgui4 (>= 4:4.8.0), libqtwebkit4, libstdc++6 (>= 4.6), libvorbisfile 3 (>= 1.1.2), xdg-utils (>= 1.0.2) Conflicts: google-musicmanager Replaces: google-musicmanager Provides: google-musicmanager Section: net Priority: optional Filename: pool/main/g/google-musicmanager-beta/google-musicmanager-beta_1.0.243 .1116-r0_amd64.deb Size: 4361868 SHA1: 8a8e9434f3ccb778c761f983ec1196ad4a4701c0 MD5sum: 4537c0f2bdf57eee7d576b7b0a42d083 Description: Google Music uploader.  Google Music Manager is a simple application for adding the music files on your computer to your Music library.

When I check for updates, I get a "Failed To Download Repository Information" error.   This is what comes up under details:   W: Failed to fetch gzip:/var/lib/apt/lists/partial/us.archive.ubuntu.com_ubuntu_dists_natty_main_source_Sources  Hash Sum mismatch,  E: Some index files failed to download. They have been ignored, or old ones used instead.


I'm trying to write a program to count up and down the musical scale. Unfortunately, I have ran into a problem. I need a way to check if the input value is one of the notes on the musical scale. If it is, turn it into a number for later calculations. If not, display an error and ask again. I tried to do this and it puts me in an infinite loop even when i give a valid note. Any help? My code:      package music;  import java.util.Scanner;  import javax.swing.JOptionPane;  public class musicc {     public static void main(String[] args) throws Exception {         int noteid;         noteid = musicc.getNoteId();     }      public static int getNoteId() {         String note = "0";         int returnValue = 0;         note = (String)JOptionPane.showInputDialog(null,"What note do you want to start on?",JOptionPane.PLAIN_MESSAGE);          while (note != "A" && note != "B" && note != "C" && note != "D" && note != "E" && note != "F" && note != "G") {             JOptionPane.showMessageDialog(null, note + " is not a valid note! Try again.", "Invalid note!", JOptionPane.ERROR_MESSAGE);             note = (String)JOptionPane.showInputDialog(null,"What note do you want to start on?",JOptionPane.PLAIN_MESSAGE);         }         switch(note) {         case "A":return 1;          case "B":return 2;         case "C":return 3;          case "D":return 4;          case "E":return 5;          case "F":return 6;          case "G":return 7;          }         return 0;            } }

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


I have a disturbing problem for a few weeks now ... One of my three DNS-servers (running bind9 as slave of a Plesk DNS master) is getting spammed with senseless DNS requests. The origin IPs of those requests are from all over the world, so I can't just drop an IP range or a whole country by iptables.  Here are a few log lines so you can see the scheme of those "attacks":  10-May-2015 11:15:54.714 client 120.87.202.161#47441: query: sjgzincrmxobabst.www.luzhiye.com IN A + (my-ip) 10-May-2015 11:15:56.252 client 111.187.196.51#41387: query: mrcf.www.330dp.com IN A + (my-ip) 10-May-2015 11:15:56.806 client 89.90.44.173#56673: query: qzwp.www.330dp.com IN A + (my-ip) 10-May-2015 11:15:57.891 client 116.93.242.237#55721: query: srapafupglkxaver.www.330dp.com IN A + (my-ip) 10-May-2015 11:15:59.611 client 123.153.92.59#20847: query: yj.www.330dp.com IN A + (my-ip)   Those requests are not really attacks because the host server is very relaxed. I tried to block the requests with iptables, but after a few minutes/hours the requested domains are changing, so I have no chance to do so.  Chain INPUT (policy ACCEPT) target     prot opt source               destination DROP       all  --  anywhere             anywhere             STRING match  "888fy.com" ALGO name bm TO 65535 DROP       all  --  anywhere             anywhere             STRING match  "taohua.me" ALGO name bm TO 65535 DROP       all  --  anywhere             anywhere             STRING match  "yymo.us" ALGO name bm TO 65535 DROP       all  --  anywhere             anywhere             STRING match  "taohuazu.cc" ALGO name bm TO 65535 DROP       all  --  anywhere             anywhere             STRING match  "taohua.me" ALGO name bm TO 65535 DROP       all  --  anywhere             anywhere             STRING match  "227x.com" ALGO name bm TO 65535   Does anyone have experience with these kind of "attack"? How to stop it? I tried to shutdown the whole server for 48 hours. After the restart there were no attacks anymore, but a few hours later they started again.  Configuration (named.conf.local / named.conf.options):  dnssec-validation auto; allow-new-zones yes; notify master-only;  auth-nxdomain no;    # conform to RFC1035 listen-on-v6 { any; };  statistics-file "/var/cache/bind/named.stats"; zone-statistics yes;  controls {         inet * port 953 allow { plesk-ip; 127.0.0.1; } keys {"rndc-key"; }; };  logging {         channel b_query {                 file "/var/log/bind9/query.log" versions 2 size 1m;                 print-time yes;                 severity info;         };         category queries { b_query; }; };   I ran a few online tests to verify again that my DNS server is not an open resolver. Successfully: No open resolver found.  Help is really appreciated!

This is a  about securing public DNS resolvers   Open DNS servers seem pretty neat and convenient, as they provide IP addresses that we can use consistently across our company regardless of where they are located. Google and OpenDNS provide this functionality, but I'm not sure that I want these companies to have access to our DNS queries.  I want to set up something like this for use by our company, but I hear a lot about this being dangerous practice (particularly in regards to ) and I want to make sure that we do this right. What things do I need to keep in mind when building this type of environment?


Given $A\in\Bbb C^{n \times n}$,I want to prove $\text{rank} A=\text{rank} A^H$ where $A^H$ is the conjugate transpose matrix of $A$. We only need to prove:     $\text{rank} A=\text{rank} \bar A$    where $\bar A$ is the conjugate matrix of $A$. I have tried but was not able to solve the problem.     I found a similar question here . I know rank-nullity theorem, but I have not learn any theorem about maps that preserve the dimension of nullity. How do we prove $A \to \bar A$ map preserves dimension of nullity?

I have a question about complex conjugate matrix.  Prove that for any rectangular matrix $A$,  rank $A$=rank $A^*$ where $A^*$ is complex conjugate transpose of A.


As the title suggests, I am wondering what the whole point of echo $$ is... I understand that the command echo $? returns the status of the last command that was ran and now I am stumped on what echo $$ returns... I believe it runs something related to PID's, am I somewhat correct or totally wrong?

Why does running echo $$ in bash return a number like 7190, while running echo $ only returns a $?


My book says:  A group is an ordered pair $(G, \cdot)$ where $G$ is a set and $\cdot$ is a binary operation satisfying the following axioms [emphasis mine]: $\vdots$  Why doesn't it say  A group is an ordered pair $(G, \cdot)$ where $G$ is a set and $\cdot$ is a binary operation satisfying the following propreties: $\vdots$  As far as I know, axioms are statements which we take for granted; I don't understand why the group axioms are something we have to take for granted; we already know that there exist objects (such as the set of permutations of $3$ objects) which satisfy those propreties. Even if we knew of no objects which satisfy those propreties, then perhaps the axiom should be "There exists an object which satisfies those propreties" rather the axioms being the propreties themselves.

Thus, axioms are propositions we assume to be true and we use them in an axiomatic theory as premises to infer conclusions, which are called "theorems" of this theory.  For example, we can use the  to prove theorems of arithmetic.  This is one meaning of the word "axiom". But I recognized that the word "axiom" is also used in quite different contexts.  For example, a group is defined to be an algebraic structure consisting of a set $G$, an operation $G\times G\to G: (a, b)\mapsto ab$, an element $1\in G$ and a mapping $G\to G: a\mapsto a^{-1}$ such that the following conditions, the so-called group axioms, are satisfied:   $\forall a, b, c\in G.\ (ab)c=a(bc)$, $\forall a\in G.\ 1a=a=a1$ and $\forall a\in G.\ aa^{-1}=1=a^{-1}a$.      Why are these conditions (that an algebraic structure has to satisfy to be called a group) called axioms? What have these conditions to do with the word "axiom" in the sense specified above? I am really asking about this modern use of the word "axiom" in mathematical jargon. It would be very interesting to see how the modern use of the word "axiom" historically developed from the original meaning.   Now, let me give more details why it appears to me that the word is being used in two different meanings:  As peter.petrov did, one can argue that group theory is about the conclusions one can draw from the group axioms just as arithmetic is about the conclusions one can draw from the Peano axioms. But in my opinion there is a big difference: while arithmetic is really about natural numbers, the successor operation, addition, multiplication and the "less than" relation, group theory is not just about group elements, the group operation, the identity element and the inverse function. Group theory is rather about models of the group axioms. Thus: The axioms of group theory are not the group axioms, the axioms of group theory are the axioms of set theory.  Theorems of arithmetic can be formalized as sentences over the signature (a. k. a. language) $\{0, s, +, \cdot\}$, while theorems of group theory cannot always be formalized as sentences over the signature $\{\cdot, 1, ^{-1}\}$. Let me give an example: A typical theorem of arithmetic is the case $n=4$ of Fermat's last theorem. It can be formalized as follows over the signature $\{0, s, +, \cdot\}$: $$\neg\exists x\exists y\exists z(x\not = 0\land y\not = 0\land z\not = 0\quad\land\quad x\cdot x\cdot x\cdot x + y\cdot y\cdot y\cdot y = z\cdot z\cdot z\cdot z).$$ A typical theorem of group theory is  which states that for any finite group G, the order of every subgroup H of G divides the order of G. I think that one cannot formalize this theorem as a sentence over the "group theoretic" signature $\{\cdot, 1, ^{-1}\}$; or can one?


Does the map $S^1\to P(\mathbb{R}^2)$ defined by $\vec{v} \mapsto \mathbb{R}\vec{v}$ admit a continuous section. Where:  $S^1:=\{ (x,y) \in \mathbb{R}^2 : x^2+y^2=1 \}$ denotes the circle,  $P(\mathbb{R}^2)$ denotes the projective space, and a section of a map $\pi:X\to Y$ is a map $\sigma : Y \to X$ such that $\pi \circ \sigma = id_Y$.   I believe that that it doesn't admit a continuous section, but I'm not sure since I haven't been able to prove or disprove.

Consider the map $q:S^1 \to \mathbb{R} P^1$ given by $v \mapsto \mathbb{R} v$. I want to show that this map does not admit sections. I've previously shown that $S^1$ is diffeomorphic to $\mathbb{R} P^1$ but this doesnt seem to be of much help. I've also shown that $TS^1$ is trivial, however I don't see how to use this. My only idea is that such a section wouldn't be well defined since it could go to either antipidal points when composing with $q$. Any hint or help with this would be amazing!


I am planning this character out for levels 1-20. We're starting at level one and we are continuing until we're done or dead.  I'm having some trouble deciding on my feats, and spells to maximize damage and healing output.  I understand that warpriest clerics are given armor proficiency to help make creating a 2nd edition battle medic super easy, but I'm trying to balance my character perfectly between doing damage with my deity's weapon and healing my allies. I'm having a lot of trouble judging which trade-offs to take so that I can hit harder while still being a viable healer.  As a character, I've chosen Cleric, Warpriest, Dwarf, Medium Armror, Shelyn, and Glaive.  Right now, my plans for feats are leaning toward Domain initiate with Zeal, communal healing, divine weapon, but the details are starting to get fuzzy. It's all the different numbers floating around that are confusing. I really just want to increase the amount of healing from my spells and the amount of damage from my glaive. What is the best way to balance these two paths?

I am making a Dwarf Warpriest Cleric of Shelyn wielding a Glaive. I expect to use Medium armor. I am planning this character out through level 20.   I'm looking for a build of feats, skills (if applicable) and spells that maximize my damage in melee and healing with spells. Other character choices are locked in.  If it matters, my allies in this group are: rogue, sorcerer, barbarian, monk, and fighter(longbow).   My original plan includes:    (Zeal Domain)     What Feats, Skills, and Spells (through level 20) will allow this character to do its highest DPR with a glaive and heal the most with its spell slots?


I quit my Ph.D. two years ago because of multiple reasons but largely due to my own naiveness over deciding to enroll for a Ph.D. I decided to do a Ph.D. without knowing anything about it. I wasn't prepared at all. I wrongly chose a lab that has a very poor vision for any scientific advancement. I foolishly chose a supervisor who had no idea what's going on in his lab. Once I understood this, I also became aware of my own weakness that has resulted in not getting me an ideal lab. This realization happened very lately and until now I had already developed a strong vision for my research project and my future career. And according to my plan, it wasn't that lab or supervisor who was going to help me to reach my goal. In academia, everything is connected, so if I wasn't going to be the best version of myself in Ph.D., the chances of finding a better opportunity after my Ph.D. was very less. So I decided to quit my Ph.D. and start it all over again; only this time knowing everything about a research career and how to excel in it. I wanted to become the best and for that, I had to work on myself first. So, a six month gap period was planned after leaving my Ph.D. But this gap time became much longer (because of some unfortunate circumstances); almost two years now and I have started feeling like a failure. I really want to go back and do some quality research. What is the best way to do it?  P.S. I am from India and I am talking in terms of the Indian research institute.

I am a Ph.D. dropout with a one year of career gap. I want to return to academia, but now  I have realized that it was perhaps the biggest mistake to take a gap after quitting my Ph.D. The purpose of taking a gap was to work on my communication skills and get a  new perspective on my work and my career in science. This could have been done within a period of 2-3 months but it became one year long because of my own recklessness. I allowed myself to distract from my goal and I started working on my hobby i.e. Painting. I lost myself there and completely lost track of my time. I was really enjoying everything about this new venture. I took it as a challenge to become better at my skills in painting. Eventually, I became the best in my group and got lots of appreciation. But then, I lost my interest while realizing that there was no further challenge and all there was left is to work and work while crafting your art which was never going to be perfect. It made me realize that what I actually love is to take the new challenges and work on myself. To be an artist was never a career option for me, all I wanted was to learn the skills. That's it!   While counting my achievement in science, I  realized that it was an irresponsible thing to take a gap in doing something that has nothing to do with science. Earlier I had a scholarship and a very competitive mind that has led me to get a Ph.D. position in one of the best labs in the country. Now I don't have the scholarship. I want to go back to my world of research where I was accelerating exponentially. I want to tackle the challenges of science with a new perspective and better skills. I want to be productive more than earlier and ready to take all the tough challenges.  But I feel embarrassed about my past mistake. Because of this, I come across as someone who is not sincere about her career. But I can't help it because the truth is that I did behave insincerely by losing track of my time.  I should have been conscious enough to realize the consequences. Now, what do I do? The past has gone and the vision of the present is crying for a better future. How do I make things better like before?


I want to know what is the rationale behind substitution method of integration.I'm very familiar with the following sort of integration but I don't understand why we substitute  i.e use one variable in terms of another variable. For the integral, $\int 2x\sqrt{x^2+3}\,dx$ we can use the substitution method in the following manner. If $z=x^2+3,$ then $dz=2xdx$. We have $\int\sqrt{z}dz$.  My question is that why $\int\sqrt{z}dz$=$\int 2x\sqrt{x^2+3}\,dx$? Is there rationale behind it?

I'm not entirely sure what I want to ask here, so please bear with me!  I think the explanation they give us in school for how finding the antiderivative by substitution works is: $$\int f(g(t))g'(t)dt=(Fg)(t)=F(g(t))=F(u)=\int f(u)du$$  But I never really understood the equality $F(u)=\int f(u)du$. Why can we behave as if the identity $u=g(t)$ doesn't exist, compute the integral $\int f(u)du$, and then 'substitute' $u$ in the result yielding the correct answer? In a sense, it feels like the variable $u$ switches from being 'meaningful' in $F(u)$ (where it stands for $g(t)$) and being insignificant in $\int f(u)du$, since as I perceive it the "variable name" here is meaningless and we could say $ \int f(u)du = \int f(k)dk = \int f(x)dx = ... $ all the same. Another way to ask the same thing: why $(Fg)(t)=\int f(u)du$ and not, say, $(Fg)(t)=\int f(x)dx$? Where am I getting confused?  Maybe someone can explain this better than my high school teacher? Is there a 'formal' explanation for this? Thank you a lot!


I have a problem with footnote inside parcol. I'm trying to remove the black square at the end of the text of the footnote. The text is the following:  Pro angusilis\footnote{emend. \textit{angustiis}.} mortem homines quaerentes, qui nimium utique gratulantur,[...]   and here the results, what's wrong with this?    I'm using overleaf.  Edit: As you requested here the document that reproduce the problem:  \documentclass[a4paper, 12pt, oneside]{book} \usepackage[utf8]{inputenc} \usepackage[main=italian, latin]{babel} \usepackage{paracol} \usepackage[left=3.5cm, right=3cm, top=3.5cm, bottom=3cm]{geometry} \usepackage{hyperref} \usepackage[hang, flushmargin, bottom]{footmisc}  \begin{document}  \begin{paracol}{2}     \subsection*{Commento interlineare}     this is first text\footnote{this is the footnote}     \switchcolumn     \subsection*{}     this is first text \end{paracol} \end{document}

I have already read similar questions, but they did not help.  I use \documentclass[12pt,a4paper]{book} and I would like footnotes without indention.  Using \noindent does not help. Using this package \usepackage[hang,flushmargin]{footmisc} solves the issue, but TeXstudio gives back an error and I can see a little black square at the end of the footnote, which should not appear.  EDIT:  \documentclass[12pt,a4paper]{book}  \usepackage[T1]{fontenc} \usepackage[utf8]{inputenc} \DeclareUnicodeCharacter{FB01}{fi} \usepackage[italian,UKenglish]{babel} \usepackage{paracol} \usepackage{geometry} \usepackage{microtype} \usepackage{lmodern} \usepackage[hang,flushmargin]{footmisc} \author{Bla Bla} \title{Bla Bla}  \begin{document} \maketitle \begin{paracol}{2} \noindent bla bla  \bigskip \noindent bla bla \footnote{bla bla}.  \switchcolumn \noindent bla bla  \end{paracol} \end{document}


$$\sum_{n=0}^\infty \frac{1}{n^n}$$  it's easy to see that this series converge by using ratio test, but i have no idea what this series converges to  there might be some problem with $0^0$ if that's the case, i would like to change the lowest bound to $n=1$ or $\displaystyle\sum_{n=1}^\infty \frac{1}{n^n}$  i'm just curious on how to tackle this kind of problem

Earlier today, I was talking with my friend about some "cool" infinite series and the value they converge to like the Basel problem, Madhava-Leibniz formula for $\pi/4, \log 2$ and similar alternating series etc.  One series that popped into our discussion was $\sum\limits_{n=1}^{\infty} \frac{1}{n^n}$.  Proving the convergence of this series is trivial but finding the value to which converges has defied me so far. Mathematica says this series converges to $\approx 1.29129$.  I tried Googling about this series and found very little information about this series (which is actually surprising since the series looks cool enough to arise in some context).  We were joking that it should have something to do with $\pi,e,\phi,\gamma$ or at the least it must be a transcendental number :-).  My questions are:   What does this series converge to? Does this series arise in any context and are there interesting trivia to be known about this series?   I am actually slightly puzzled that I have not been able to find much about this series on the Internet. (At least my Google search did not yield any interesting results).


I'm trying to find a proof of this:     The group  $\langle\mathbb{Z}_n,\oplus\rangle$ is cyclic for every $n$, where $1$ is a generator. The generators of the group $\langle\mathbb{Z}_n,\oplus\rangle$ are all $g \in \mathbb{Z}_n $ for which $\gcd(g,n)=1$, as the reader can prove as an exercise.   It is perfectly clear that $1$ generates all $\mathbb{Z}_n$, but I can't get myself to understand the second part or find a way to prove it. Thanks.

A cyclic group is a group that is generated by a single element.  That means that there exists an element $g$, say, such that every other element of the group can be written as a power of $g$.  This element $g$ is the generator of the group.  Is that a correct explanation for what a cyclic group and a generator are? How can we find the generator of a cyclic group and how can we say how many generators should there be?


I have the following polygons:  01060000000300000001, 01060000000400000001, 01060000000400000001, 01060000000200000001, 01060000000100000001, 01060000000200000001, 01060000000100000001, 01060000000300000001, 01060000000100000001, 01060000000100000001, 01060000000100000001, 01060000000100000001   And I'd like to merge them using:  SELECT st_union(ARRAY(SELECT geom FROM areas))   And I get: https://pastebin.com/V18JtCz8 (I should paste here but it's above the char count - if you're reading this and the link doesn't work, it's simply the output of the above)  When I plot this output, there are holes (deliberate) but I'd like to just take the outline of the polygon as the new polygon.  How would I go about this?

I try to delete the slivers that appeared when I have merged some polygons.   I have two different cases:  For the CASE 1, no problem I fill the gap with:  CREATE OR REPLACE FUNCTION sliver_killer(geometry,float) RETURNS geometry AS $$ SELECT ST_BuildArea(ST_Collect(a.geom)) as final_geom FROM ST_DumpRings($1) AS a WHERE a.path[1] = 0 OR (a.path[1] > 0 AND ST_Area(a.geom) > $2) $$ LANGUAGE 'sql' IMMUTABLE;  UPDATE merged SET geom = sliver_killer(geom,50::float);   A function that fill all the gaps smaller than x square meter.  BUT for the CASE 2, when the small gaps are "open" I can't manage to fill those gaps.   I have try something like: buffer(1) followed by buffer(-1)  but of course I obtain some rounded corners. Did someone have a true solution ?


Time is a tool we've invented to measure changes of state. What evidence do we have that it is a natural phenomenon?

This is an attempt to gather together the various questions about time that have been asked on this site and provide a single set of hopefully authoritative answers. Specifically we attempt to address issues such as:   What do physicists mean by time? How does time flow? Why is there an arrow of time?


I am trying to find the landing time of the Virgin Atlantic flight (VS27) from Gatwick to Orlando on the 2nd August 2019. I have tried to search on numerous sites but can't find one with this historic data to easily find the scheduled / landing time. Could anyone advise please?

Where can I find historical data on flights, specifically Delta international flights?  I need to find out about cancellations, diversions and any other flight data pertaining on particular route at a given time.  This source has to be official and stand up to legal scrutiny.


I'm trying to do a Welch's t-test of two sample groups which turn to have estimated variance equal to 0.  As could be seen from wikipedia page of Welch's t-test: , the formula for calculating the t-stat:  $$ t= \frac{\overline X_1 - \overline X_2}{\sqrt{\frac{s_1^2}{N_1} +\frac{s_2^2}{N_2}}} $$  contains 0 at the denominator and the t-stat could not be calculated (obviously my C++ program retuns me a NaN value...)  I need a way to handle this an calculate the t-test anyway, could you tell me how to proceed in these cases?

The formula for a one sample t-test, as given by  is  $t = \dfrac{\bar{x} - \mu_0}{s\big/\sqrt{n}}$  However, in this equation, if the sample standard deviation, $s$, is zero, $t$ will be undefined. Is there any reasonable way to get a $t$ value in this case?