I am a $12^{th}$ class student in India. I am quite new to these interesting concepts. And, I think I've learnt about electrostatics, magnetism, Maxwell's equations very thoroughly. But, my books doesn't convey satisfactory information about how $c$ is calculated. It just simply that: using Maxwell's equations, $c=\frac{1}{\sqrt{\mu\epsilon}}$.  Also, I've been reading many questions asked about light and photons on this site, stating even the electric wave and magnetic wave are out of phase (which sometimes seems obvious to me), but I lack systemetic resources to learn about them.  I just need some help like how the velocity was calculated or even some resources.  Probably, this part is more opinion based but can someone please also suggest some good resources to learn these things (free). I heavily rely on sites Khanacademy  [Clarification after two answers used the differential form of  Maxwell’s equations:]  The main problem is the equations taught to me are different which I find elsewhere:    thnx to @Elio Fabri

Having just finished physics 2, I've been (slightly) exposed to showing that light is a wave with speed $1/\sqrt{\mu _0 \epsilon _0 }$ using the differential forms of  though this is the only derivation I've come across. Can you show the same thing using the integral forms? My first thought is that it may be more difficult since the wave equation is often given as a differential equation.   Note: I have not taken vector calculus (or even multivariable), and do not have sufficient mathematical (or even physical) background to explicitly do the derivation. I'm merely asking for a hopefully understandable solution or a source to the solution.


When determining the convergence of an alternating series does an inconclusive Ratio/Root test imply the other will be inconclusive as well? Is there a relationship between the results of these two tests? Or when solving problems involving infinite series should you use each test to see if there is an absolute convergence. Please comment any recommended resources to read further on this subject. ~Thanks

I am a little bit confused regarding the meaning of the phrase :" Root test is stronger than ratio test", and was hoping you will be able to help me figure it out. As far as I can see here:  The limit from the ratio test is greater or equal the limit from the root test . So, my first question is-  is there any example of a series $\Sigma a_n$ such that the limit from the ratio test is exactly 1 (i.e.- inconclusive), but the limit from the root test is less than 1? (i.e.- convergence can be proved by using the root test but not by using the ratio test ) If not, then is it correct that this phrase is the meaning of "stronger" is when the limit from the ratio test does not exist? (as in the classic example of a rearranged geometric series)  Hope you will be able to help.   THanks !   related posts:


I have just acquired a new laptop, ASUS ROG Strix GL503VD and i have some problems and i hope you can help me.  So i have installed the latest version of windows 10 pro (1709) and i am having major spikes even when i'm not in games, just browsing around. I noticed that these spikes come from GPU usage which goes to 100% very briefly as you can see in the image.    Also at times i have black screen which looks like the driver is reloading, yet i am up to date with all the drivers (I'm using GTX 1050 4gb and installed the latest drivers with nVidia Xperience). I noticed that the process taking up 100% of GPU is System. Could this be a windows problem ? If so, would a downgrade help ?  My specs are : Video : NVIDIA Geforce GTX 1050 4GB, CPU : Intel Core I7-7700HQ, RAM : 8GB

I have noticed that from some time my system is freezing and its probably caused by the high CPU usage which is caused by the system process.  All applications I'm running is the Skype, TeamSpeak and Chrome so it definitely shouldnt eat that amount of CPU.  You can see the problem itself and running processes in the screenshot below:    Sometimes CPU usage is reaching 90%, but the average usage is like 40-65%.  My PC parameters:   Windows 8 (customer preview) Intel Core i3 - 2350M 8 GB RAM   I'd appreciate any help attempt! Regards.  --UPDATE--  As the user below posted a great answer, I have noticed that the process that is eating the most CPU in the system is called Arthurx.sys, simple google tells that it's a TPLink driver (an wifi adapter, I have bought like 2 weeks ago!) drivers has been installed from the Windows MSDN, but also tried to install the drivers from the attached CD, but it doesn't help. From the system start, it is using like 5% of the CPU only, but after 2-4 hours of working it is growing up and reaching 40-60% of the CPU usage.  Device name: TPLink WN722N


Let $f,g: V \rightarrow W$ be linear operators. Prove that $r(f + g) \leq r(f) + f(g)$   Note: r = rank  My idea was to use matrix representation and to prove that the rank of matrix C ($C= F+G$) can't be bigger than the sum of $r(F) + r(G)$,but to use that idea I must prove that $r(f) = r(g)$ which I don't have an idea how to do. Other idea was to prove that $(f+g)(v) = f(v) + g(v)$ but also with no luck.

Let A,B be in $M_{mxn}(\mathbb{R})$  Prove that if rank(A + B) = rank(A) + rank(B), then col(A) ∩ col(B) = {0}  I started with a proof by contradiction, since we know that rank(A + B) ≤ rank(A) + rank(B). I assume that if rank(A + B) < rank(A) + rank(B), then col(A) ∩ col(B) = {0}. I realize that we don't have to do the > case. However I am a little confused on how to show col from rank.


There seems to be two different steps in the Ubuntu Server 14.04 installation that involve encryption. The first asks if I want to encrypt my home directory:     The second has an option for encrypted LVM:     Are these two different encryption procedures? If I do both is my drive doubly encrypted? Why would I do one and not the other?  I don't think this is a duplicate of  because that solution does not explain why there are seemingly two encryption steps being offered.

Does encrypting my home folder make my computer more secure? Do I have to enter my password more if my home folder is encrypted? What else should I know about encrypting my home folder?


I'm not sure if this is a stupid question, but here goes anyway... I have only recently started learning PHP and Javascript and I'm reasonably proficient. One of the reasons I'm so proficient is because I LOVE Stack Overflow and find most of the solutions to my dilemmas here.   But I've found that I never get the chance to ask a question because it has normally been asked many times before and when I go through the unanswered questions to try and help someone else, they are generally WAY over my head.  So I'm not sure how to get more privileges. I can't even vote up answers that I like or that helped me. I can't comment to thank someone for their solution. It is most tragic and demoralising... How do I change the situation?

From "6 Simple Tips to Get Stackoverflow Reputation Fast" at codexon.com:   Be the First to Answer. Even at the cost of quality. Use Downvotes and Comments Strategically Use obnoxious in-your-face formatting and lists. Be Aware of the 200 rep/day Limit Edit, But Don’t Edit Too Much Associate your other accounts   Courtesy of . Agree? Disagree? Walnuts? Cantaloupe?


I am still leaning Javascript and I encountered twice a behavior I didn't expect. I would like to understand why it happens and what I should learn to understand it better. : I tried to call a function using a file input filelist as argument. Right after I call my function, I set to null the file input value. In my function, I use a callback that can't get back my fileList since the file input is reseted. What I don't understand: I expected the file list object to be somehow "copied" once it was sent to the function. Why changing the original object affects the callback? Second case: I use a JSON object called values to store, well, values. I iterate on a collection and update a name field of my values object using the iteration index before inserting the values object inside another JSON object. See the code: var myBaseName = "file" _.each (myCollection, function(file, i){     values.name = myBaseName  + " - " + i     console.log(values.name); //here the name appears correctly,                                //i.e. "file - 0", "file - 1"...     values.size = file.size,     values.type = file.type,     allFiles[i]=values;  }); console.log (allFiles);//here the name appears as the last set,                         //i.e. if my collection has 2 objects;                         //they both appear as "file - 1"  What I don't understand: Why is it updating and not simply copied? This is, I expect, the same kind of mechanism than in my first case. I used to code in .net and I never encountered such a behavior. I expected a json object to be some kind of enhanced string.

The primitive types (number, string, etc.) are passed by value, but objects are unknown, because they can be both passed-by-value (in case we consider that a variable holding an object is in fact a reference to the object) and passed-by-reference (when we consider that the variable to the object holds the object itself).  Although it doesn't really matter at the end, I want to know what is the correct way to present the arguments passing conventions. Is there an excerpt from JavaScript specification, which defines what should be the semantics regarding this?


Can I use Xubuntu 4.12 on a Intel  Celeron B800 processer on a laptop computer, the 14.4 Trusty Tahr or what Linux Os will work on a Aspire Laptop with a Intel Dual core B800 Processor with 1.5Ghz 2GB DDR3 memory 500 GB HDD

I'm thinking about installing Ubuntu Desktop, but I don't know what flavor is the best for my system. What are the minimum and recommended hardware requirements? What kind of CPU? How much memory? Should I have Hardware Acceleration? What flavor should I use?  This is an attempt of a canonical answer. My answers have the "official  requirements", the recommended are a mix of official sources and opinion based (along with the answer it's told the source). You can comment or edit if you feel that the information is obsolete or incomplete. It is a good rule of thumb that any system capable of running Windows Vista, 7, 8, x86 (Intel) OS X will almost always be a lot faster with any Ubuntu flavor even if they are lower-spec than described below.


% used PGFPlots v1.14 \documentclass[margin=0.5cm]{standalone} \usepackage{pgfplots} \usepackage{pgfplotstable}  \usepackage[scaled]{helvet} %Paquete para letra helvetica parecida a letra arial \usepackage[T1]{fontenc} \renewcommand\familydefault{\sfdefault} %Renombrar comando para hacer efecto la letra helvetica  % use this `compat' level or higher to be able to use absolute values for % the `bar width' \pgfplotsset{compat=1.7} \begin{document}  \pgfplotstableread{ fila    especie abundancia 1   Orisup  50.2 2   Agepho  6.4 3   Corcor  6.2 4   Stumag  5.2 5   Xenbai  5 6   Aphult  3.4 7   Spipas  3.4 8   Empalb  2.2 9   Turmig  2 10  Junpha  1.8 11  Pascae  1.2 12  Sitcar  1.2 13  Chavoc  1 14  Cyaste  1 15  Tactha  1 16  Melfor  0.8 17  Anadia  0.6 18  Colaur  0.6 19  Hirrus  0.6 20  Butjam  0.4 21  Haemex  0.4 22  Mellin  0.4 23  Pipmac  0.4 24  Tyrvoc  0.4 25  Ardher  0.2 26  Eupneo  0.2 27  Molate  0.2 28  Poescl  0.2 29  Psamin  0.2 30  Spinot  0.2 31  Spipsa  0.2 32  Steser  0.2 33  Toxcur  0.2 34  Troaed  0.2 }\mytable \begin{tikzpicture}[font=\tiny] \begin{axis}[ ylabel={Número de individuos}, xticklabels from table={\mytable}{especie}, xtick=data, major x tick style = transparent, %--------------------------------------------- % to make the bar plot look good ... % ---------- % ... provide the used axis limits ... % (using `\coordindex' means `xmin' always starts from 0) xmin=0, xmax=34,  % <-- this needs to be adjusted manually each time % provide a suitable `bar width' in absolute values. % This makes the plot independent of axis `width' % (this also only have to set once, because the increment is always 1) bar width=0.8, % ... and enlarge them by an absolute value which satisfies your needs % (this should be larger than half of the `bar width' so that the %  bars at the axis limits are fully shown) enlarge x limits={abs=0.6}, %------------------------------------------------- ymin=0, ymax=51, ybar, xticklabel style={ anchor=north west, align=left, rotate=60, %font=\itshape,%\fontsize{4pt}{baselineskip}\selectfont, inner sep=-0.8cm, %outer sep=0.7cm, xshift=-0.3cm %yshift=0cm }, ] \addplot table [y=abundancia, x expr=\coordindex] {\mytable}; \end{axis} \end{tikzpicture} \end{document}

I made a plot but it's not at all what I want. There are two things I'm having trouble with: 1.) The bars should be at the bottom, but there's a space between them and the x-axis. 2.) E1/E4, E2/E5 and E3/E6 should have the same color.  Here's a picture of how it is and how I want it below:   And here's my code:  \documentclass{standalone} \usepackage{pgfplots,pgfplotstable} \begin{document} \begin{tikzpicture} \begin{axis}[ symbolic x coords={E1, E4 (dyn.), E2, E5 (dyn.), E3, E6 (dyn.)}, xtick=data, width=\linewidth, height=6cm ] \addplot[ybar,fill=blue, bar width = 1cm] coordinates {     (E1,   8)     (E2,  15)     (E3,   50)     (E4 (dyn.), 4)     (E5 (dyn.), 17)     (E6 (dyn.), 40)  }; \end{axis} \end{tikzpicture} \end{document}   I hope you can help me. Thanks.


I  am from Turkey.  I live in Nigeria and residency. It is difficult to get Nonimmigrant visa from Nigeria. I have valid visas for The UK and Schengen ara and I will be visiting  the UM and , France  and Germany. Can I apply for the USA visa from these countries  since I don’t have residency. My reason is to apply from another country is I got refused once when i wanted to travel with my students after then I travelled another country again this year I travelled to the UK . My students want to visit to the USa but my company is not willing to allow me coz last time all got visa but me that is why it damaged school’s reputation .that is why , first i have to get visa then i can organize my students

Possible Duplicate:          Can British passport holders apply for a B2 USA visa from other countries, if they are living there? Or do they have to go back to Britain to apply for it?


the program is to count the frequency of each word in a sentence. This is the source code:  import java.io.*; import java.util.Scanner; class Dictionary {   String key;   int val;   public Dictionary()   {     key="";     val=0;   }  void insert(String k)   {     key=k;     val=1;      System.out.println("\nInserted key with value: "+k);   }  void update()   {     val++;   }  String retkey()  {    return key;  }  int retval()  {    return val;   }  public void display()   {     System.out.println("Word = "+key);     System.out.println("Number = "+val);   } } class stack {   Dictionary D[]=new Dictionary[50];   int n;   int top;   public stack(int N)   {     n=N;     top=-1;   // D=new Dictionary[n];   }   public void push(String p)   {     top++;     System.out.println("pushing "+p+"\n top=="+top);     D[top].insert(p);     System.out.println("\ntop="+top);   }   public void check(String p)   {     int i=0,flag=1;     String q="";     if(top==-1)     {       System.out.println("top=-1");       push(p);       flag=0;     }     else     {      for(i=0;i<=top;i++)      {        q=D[i].retkey();        if(q.equals(p))          {            D[i].update();           flag=0;          }         else         flag=1;      }     if(flag==1)      push(p);     }    }  public void print()  {    D[top].display();  } } public class Wrdcnt {   public static void main(String[] args)throws Exception   {   //  Dictionary D[]=new Dictionary() ;     String st="";     String p="";     System.out.println("Enter String: ");     Scanner in= new Scanner(System.in);     st=in.nextLine(); /*    no of words*/     int n=count(st);     int j=0;     System.out.println("No of words: "+n);     stack stck =new stack(n);     for(int i=0;i<=st.length();i++)      {       if(i==st.length())        {         p = st.substring(j,i);          System.out.println(""+p);          stck.check(p);          System.out.println("Checking done for word: "+p);                                     j=0;         break;        }                if(st.charAt(i)==' ')         {          p = st.substring(j,i);          System.out.println(""+p);          stck.check(p);          j=i+1;          System.out.println("Checking done for word: "+p);                   }      }   }   public static int count(String s)   {     int w=0;     for(int i=0;i<s.length();i++)      {            if(s.charAt(i)==' ')                {                    w++;                }      }    return (w+1);   } }   output:     Enter String:   Roses are red   No of words: 3   Roses   top=-1   pushing Roses   top==0   Exception in thread "main" java.lang.NullPointerException          at stack.push(Wrdcnt.java:51)            at stack.check(Wrdcnt.java:61)            at Wrdcnt.main(Wrdcnt.java:117)

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?


Question:     Let $k$ be give the postive integers,Find the highest power of $2$ which divides the numerator of   $$H_{k}=1+\dfrac{1}{3}+\dfrac{1}{5}+\cdots+\dfrac{1}{2k-1}$$   I found some case when $k=2$,then $$H_{2}=1+\dfrac{1}{3}=\dfrac{4}{3}$$,because the numerator $4$ havethe highest power of is $2$  when $k=3$,then $$H_{3}=1+\dfrac{1}{3}+\dfrac{1}{5}=\dfrac{23}{15}$$because the numerator $23$have the highest power of is $0$  when $k=4$,then $$H_{4}=1+\dfrac{1}{3}+\dfrac{1}{5}+\dfrac{1}{7}=\dfrac{176}{105}$$because the numerator $144$ have the highest power of is $4$  So I conjecture this problem answer is $2V_{2}(k)$.then How to prove？

I'm playing with p-adic valuations, and find that the odd harmonic sums, $\tilde{H}_k=\sum_{i=1}^{k}\frac{1}{2i-1}$, has 2-adic valuation $||k^2||_2=2||k||_2$.   E.g.) $\tilde{H}_4=\frac{176}{85}$ has $||\tilde{H}_4||_2=||176||_2=4=2||4||_2$.  $\tilde{H}_6=\frac{6508}{3465}$ has $||\tilde{H}_6||_2=2$. $||\tilde{H}_8||_2=||\frac{91072}{45045}||_2=6$. $\cdots$  How can I prove this?  (Some simple observation I have tried: As , $||H_k||_2=||H_{2k}||_2+1=||\frac{1}{2}H_k||_2$. Thus ultrametric ineq for $\tilde{H}_k=H_{2k}-\frac{1}{2}H_k$ doesn't help at all, yielding trivial result $\tilde{H}_k\in \mathbb{Z}_2$.)  (That $||\tilde{H}_k||_2=2||k||_2$ for odd $k$ is almost trivial, so the problem can be reduced to show $||\tilde{H}_{2k}||_2=||\tilde{H}_k||_2+2$, still have no idea)  (I've checked this holds up to $\sim 1000$ using Mathematica, and Mathematica spits the result almost immediately for $n\sim 1000$ and takes about a minute for $n\sim 10000$. )   For anyone interested : I've used the following Mathematica code, try it yourself  a = Table[    IntegerExponent[      Numerator[HarmonicNumber[2 n] - HarmonicNumber[n]/2], 2]/2, {n,      10000}]; b = Table [IntegerExponent[n, 2], {n, 10000}]; NonNegative[Min[a - b]]


I accidently pinned my own message. I managed to unpin it, but it still remained as starred.  When I try to unstar the message I get a message saying that I can not star my own message, and the message remains starred.  So there are two issues here:   The error message is incorrect, and; It is not possible to unstar the message.    Here is a screenshot:    FWIW, I am the room owner.

Some months ago, I linked to  in the CSS chat room and  in case anybody who cared happened to drop by:  In case anybody else noticed that  questions are now highlighted a little differently, I'm actively investigating this; here's the meta thread  It was unpinned quite some time ago by one of the other room owners. I don't need it anymore anyway since the issue has been . I notice, however, that it's still visible in the starred list, with the only regular (not pinned) star being my own:  When I try to click on the star to unstar it, chat thinks I'm trying to do otherwise and simply tells me I can't star my own messages. I can easily delete this message, but I'd very much like to unstar it instead, thankyouverymuch.


I'm using a standard square collision in my 2D game. The player shoots little balls, and when they hit any wall it should bounce.  The problem is that I know when it hits a wall but I don't know if the collision happened on the side or top/bottom of the wall.  Here's my collision algorithm (pseudo code):  If A.x < (B.x + B.width) AND B.x < (A.x + A.width) AND A.y < (B.y + B.height) AND B.y < (A.y + A.height) Then a collision happened   Is it easy to detect if the collision happened on a side or top/bottom? If yes how should I do it?

I am writing a breakout clone (my first game) and am totally stuck as to how I figure out which side of the brick was hit.  I have a collision detection method that looks like this:  DetectCollision(Object a, Object b)     x = distance(a.x, b.x);    y = distance(a.y, b.y);     if (x is smaller than the combined width &  y is smaller is than combined height {        return true;    } return false;     This works totally fine, but I need to know the side of the collision, and location relative to the center in order to respond properly.  I've spent the past few days snooping around but am lost.


I know it shouldn't be this hard but I am having trouble anyway. I tried using $F_D(t)=\mathbb{P}(|X_2-X_1|\leq t)=\mathbb{P}(-t\leq X_1-X_2\leq t)$ and sketching the unit square $[0,1]^2$ but to no avail, I can't seem to find a formula that fits.

Let $X$ and $Y$ be independent random variables, uniformly distributed in the interval $[0,1]$. Find the CDF and the PDF of $|X - Y|$?  Attempt Let $Z = |X - Y|$, so for $z \geq 0$, the CDF $F_{Z}(z) = \mathbf{P}(Z \leq z) = \mathbf{P}(|X - Y| \leq z) = \mathbf{P}(-z \leq X - Y \leq z)$, which is where the algebra becomes confusing. Since they are independent, the joint pdf of $X$ & $Y$ is simply 1, as long as $(X,Y)$ belong to the unit square. The solution suggests a plot the event of interest as a subset of the unit square and find its area. Any hints?


This could be quite a dumb question though, I would like to ask is there a way to retrieve the oldMap of a trigger in a @future method? In the below code please refer the collection "oldReportsMap", Can I refer the old map of the record Ids? BELOW CODE IS THE EXSISTING ONE AND NEED TO MAKE GENERIC FOR MULTIPLE OBJECTS /*  * Populate acount fields on creation of the Report record.  */ public class updateAccountFields implements Triggers.Handler {     public void run(){                  if (!(Trigger.isAfter && Trigger.isInsert)) { return; }                  List<Report__c> triggerReports = (List<Report__c>) Trigger.new;         Set<Id> reptIds = new Set<Id>();                  for (Report__c report: triggerNewReports) {              reptIds.add(report.id);         }          // process accounts fields         if (Test.IsRunningTest()) {             processUpdateAccountFields(reptIds);         } else {             processUpdateAccountFieldsFuture(reptIds);         }              } }  @future public static void processUpdateAccountFieldsFuture(Set<ID> reptIds) {     processUpdateAccountFields(reptIds); }  /*  * Populate account fields on creation of the Report record.  */ public static void processUpdateAccountFields(Set<ID> reptIds) {        Set<Id> acctIds = new Set<Id>();          Map<Id, Report__c> reports = new Map<Id, Report__c>([SELECT Id, ReceivedDate__c, DueDate__c, Account__c FROM Report__c WHERE id IN: reptIds]);          // retrieve the related accounts     for (Report__c report: reports) {          acctIds.add(report.Account__c);     }          Map<Id, Report__c> oldReportsMap = new Map<Id, Report__c>([SELECT Id, ReceivedDate__c, DueDate__c, Account__c FROM Report__c WHERE id IN: ????]);          for(Id reptId :  oldReportsMap.keyset()){         ... some more code...     }     .... Some more code/logic.... }  Thanks  UPDATE:  Unfortunately serialization doesn't work for me it takes considerable amount of time to serialize the old object, and I have an sObject which could be a standard object or a custom object depends on the sObjectType. eg: our account object has 943 fields at the moment. I do not want to serialize all account object's fields just to track one field change. so far what I could see is, according to my scenario, there is no way of accessing oldMap since it is not in the trigger context when at a future call.  I found that there is an idea to for an functionality for apex. please note that our org gets updates for multiple objects via webservice API and this could update considerable number of records at a one call, which leads to a timeout the service request due to above mention issue.  Thanks all for your support!

I am trying to copy records from one org to other via web services. I am calling a class which has logic written into a trigger. But @ future method is not taking sObject  list as a parameter. Can someone suggest me an alternative?  The Code:  public class webServicesTriggerClass   {     @future public static void webServicesMethod(list<MyFriend__c> mfList)     {         partnerSoapSforceCom.Soap sp = new partnerSoapSforceCom.Soap();       partnerSoapSforceCom.LoginResult lr = sp.login('hitesh.kumar.singh@accenture.com.varun','4Rajyavardhan');      soapSforceComSchemasClassNiralaapp.SessionHeader_element ses = new soapSforceComSchemasClassNiralaapp.SessionHeader_element();      ses.sessionId = lr.sessionId;       soapSforceComSchemasClassNiralaapp.MyFriendsDetailSoapApi vNapp=new soapSforceComSchemasClassNiralaapp.MyFriendsDetailSoapApi();      for(MyFriend__c mf:mfList)       {        string  s1= mf.myEmail__c;        string  s2=mf.friendName__c;         string  s3=mf.friendEmail__c;        string  s4=mf.aboutFriend__c;        integer i1=Integer.ValueOf(mf.age__c);        boolean result=vNapp.addFriendDetails(s1,s2,s3,s4,i1);        system.debug('################' +result);           }     }    }     Trigger-->  trigger webServicesTrigger on MyFriend__c (after insert)     {      webServicesTriggerClass.webServicesMethod(trigger.new);    }     Error--    Error: Compile Error: Unsupported parameter type LIST at line 3 column 30


I dual booted Ubuntu alongside my windows 8. After installing windows 8.1 I lost grub and it boots straight into 8.1 and i have a watermark that says "secureboot isn't configured correctly". But I've been wanting to uninstall Linux for a while to reclaim memory for my steam games on windows, the only thing that keeps holding me back is the thought of dealing with grub. But since windows 8.1 knocked it out, what would happen if I just deleted my Linux partitions and reallocated that memory? And what's the watermark all about?

I have absolutely no experience with Linux, and I desperately need to get my computer back up and running again with Windows.  How do I remove Ubuntu and reinstall Windows?    Editor's note: many of the answers are about removing Ubuntu from dual-boot but keeping Windows (which is a bit complicated), while other answers are about removing Ubuntu from single-boot (which is easy: basically just format the disk while installing Windows). The question as written is ambiguous between dual-boot or single-boot.


I have been looking on the internet for a solution to my problem. I had a flight delay of over 6 hours at Paris CDG, and for my complaint form I need to know the exact departure time of my flight, but I do not remember exactly.   Is there a website where I can know that?   For example: Flight AF0422 the 4th March 2014.   Thanks a lot! I hope this is the place to ask this kinds of questions, if it isn't forgive me and would be grateful for suggestions of where to find the info.

I'm looking for some old flight stats as Flightaware provides me for the last 4 months. However, I'm looking for flights from the past 5 years. Is there any database that is capable of doing so?  For example, I'm interested in KLM1964 on January 5, 2012.  Specifically, statistics including departure/arrival times, and aircraft type.


I would like to get a copyrighted song, convert into a 8 bit song and use it in my game. Is that legal?

Background: I'm making a retro style game for both fun, and an unofficial contest.   I have bought a song, song X. However, I then found notation for song X, and all the instruments. So basically, it's a program recreating song X in a sense.  I took the notation, and used another program to make it sound like a chiptune does (just for the fun of it, and it sounds good :P). However, I would like to use this in my game. It's non-commercial, but is this allowed? I would've said yes, because I'm not actually using the original, copyrighted song.  I think the main point is can I:   Use the music with no reference to the author Use the music with a reference, since it's non-profit. Not use the music at all since the melody and rhythm is copyright.


I have intuitively guessed that the answer should be 1 as $x\to +\infty$. How do I formally prove this? Also how do I evaluate the limit as $x\to -\infty $.  UPDATE: Based on the answers below, I have managed to do the following. $$ \lim_{x\to\infty} \frac{\ln (1+e^x)}{x} \\ = \lim_{x\to\infty} \frac{\ln e^x(\frac{1}{e^x}+1)}{x} \\ = \lim_{x\to\infty} \frac{x +\ln (\frac{1}{e^x}+1)}{x} \\ = \lim_{x\to\infty} 1+ \ln (1+\frac{1}{e^x})^\frac{1}{x} \\ $$ How do I proceed proceed from here?

Show that $$\lim_{x \to \infty} \frac{\log(1 + e^x)}{x} = 1$$ How do I prove this? Or how do we get this result? Here $\log$ is the natural logarithm.


Suppose that $f:X\to Y$ and $g:Y\to Z$ are functions. If both $f$ and $g$ are one-to-one, then $g\circ f:X\to Z$ is one-to-one.  I believe the converse would be written: Suppose that $f:X\to Y$ and $g:Y\to Z$ are functions. If $g \circ f: X \to Z$ is one-to-one, then both $f$ and $g$ are one-to-one.  I cannot come up with a counterexample and I believe the converse is also true. Any thoughts.

Can anyone come up with an explicit example of two functions $f$ and $g$ such that: $f\circ g$ is bijective, but neither $f$ nor $g$ is bijective?  I tried the following: $$f:\mathbb{R}\rightarrow \mathbb{R^{+}} $$ $$f(x)=x^{2}$$  and  $$g:\mathbb{R^{+}}\rightarrow \mathbb{R}$$ $$g(x)=\sqrt{x}$$  $f$ is not injective, and $g$ is not surjective, but $f\circ g$ is bijective  Any other examples?


According to the hard drive disk space analyzer , the folder  C:\Program Files\WindowsApps is taking up a ton of storage space. Most of the folders there are from pre-installed software, mostly games. I want to delete the unneeded folders.    I was able to enter the WindowsApps folder, which previously I didn't have permission to enter. I updated my permissions to have everything except Special permissions (which I doubt is needed).    When I try to delete one of the folders I'm asked for Administrator permission, which I approve. Then, however, I'm told I need permission from myself to make changes to the folder.    One thing I noticed was that there was a difference in the security groups between the WindowsApps and the folder I'm trying to delete: the one I'm trying to delete has a Users (DESKTOP-WWWWWWW\Users) group which only has Read and Special permissions permissions.  When I tried to use the terminal to delete the folders it output Access is denied after me confirming that I wanted to delete each folder.   How can I delete folders in the WindowsApps directory?  Edit: Version 10.0.17134, Build 17134. I was looking at Add/Remove Programs as well as the Control Panel menu for programs.

Lately, I've been quite annoyed at the fact that I can't edit files in C:\Program Files\WindowsApps folder. I've used the takedown command, in elevated CMD, and changed permissions, to allow admins to have full control (I am an admin), and changed owner to Administrators. I can delete files/folders, yet, whenever I try to edit files, or add files, I get the error message "Access is denied." How do I enable creating files and editing files in WindowsApps?


Having to sit through a 20 min video to get information which could be put a 5 min video.

Example 1 - When reviewing résumés I don't want someone to use 1.5 pages to describe one job.   Example 2 - When a person uses excessive description to answer a simple question.


This should be a simple problem, yet I'm having trouble seeing the answer. Given two Riemannian metrics related by a conformal transformation $e^{2\sigma(x^{i})}$ . The relationship between them is simply:  $$\bar{g}_{\mu\nu}=e^{-2\sigma(x)}g_{\mu\nu}$$  Yet when it comes to the sphere $S^{3}$ and the flat space $R^{3}$, I know they are conformally related, and yet I can't find a way to write them in the above form. I'm supposing it may have to do with the fact that $R^{3}$ has had a point removed (ie. one point compactification). Is there actually a way to write this? As an aside I study physics, but would like to understand the deeper mathematical relationships that are often “swept under” the proverbial rug.

I am considering the unit sphere (but an extension to one of radius $r$ would be appreciated) centered at the origin. Any coordinate system will do, though the standard angular one (with 1 radial and $n-1$ angular coordinates) would be preferable.   I know that on the 2-sphere we have $ds^2 = d\theta^2+\sin^2(\theta)d\phi^2$ (in spherical coordinates) but I'm not sure how this generalizes to $n$ dimensions.  Added note: If anything can be discovered only about the determinant of the tensor (when presented in matrix form), that would also be quite helpful.


How to prove Euler's theorem using Lagrange's theorem?      If $a$ and $n$ are relatively prime then $a^{\phi(n)}\equiv 1 \pmod n$   Wikipedia says that it can done and that $\phi(n)$ is the order of the multiplicative group of integers modulo $n$. But I'm not sure how to proceed with the proof. Any ideas/hints?

From A Classical Introduction to Modern Number Theory by Ireland and Rosen, page 33:     Corollary 1 (Euler's Theorem). If $(a,m) = 1$, then $a^{\phi(m)} \equiv 1\,(m)$.      Proof. The units in $\mathbb{Z}/m\mathbb{Z}$ form a group of order $\phi(m)$. If $(a,m) = 1$, $\bar{a}$ is a unit. Thus $\bar{a}^{\phi(m)} = \bar{1}$ or $a^{\phi(m)} \equiv 1\,(m)$.   If I'm interpreting this correctly, this proof implicitly uses the fact(?) that if $G$ is a group and $x\in G$, then $x^{|G|}=1$, where $1$ is the identity element of $G$.  If this is indeed true, can someone explain why? (I have had no prior exposure to group theory.)


I am new to stats and this is a silly question, but I just cannot see how ANOVA is related to general linear models.  I am learning about GLM and all the materials I found are saying that ANOVA is a kind of general linear model. for example:   I can see how GLM is extended from multiple linear regression, but ANOVA is just the ratio: "variance between" over "variance within". How is it GLM?

How are they all versions of the same basic statistical method?


am trying to follow the instructions in developer.android website to install android studio in my Backbox 4.10 .  uname -a result:  Linux backbox 4.10.0-37-generic #41~16.04.1-Ubuntu SMP Fri Oct 6 22:42:59 UTC 2017 x86_64 GNU/Linux   i tried to install these libraries which are required for 64bit:  sudo apt-get install libc6:i386 libncurses5:i386 libstdc++6:i386 lib32z1 libbz2-1.0:i386   but it gives the next result:   Reading package lists... Done Building dependency tree        Reading state information... Done  libc6:i386 is already the newest version (2.24-17).  libc6:i386 set to manually installed.  Some packages could not be installed. This may mean that you have requested an impossible situation or if you are using the unstable distribution that some required packages have not yet been created or been moved out of Incoming. The following information may  help to resolve the situation:   The following packages have unmet dependencies:    lib32z1 : Depends:libc6-i386 (>= 2.4) but it is not going to be installed   libncurses5:i386 : PreDepends: libtinfo5:i386 (>= 5.9-3) but it is not going to be installed      Depends: libtinfo5:i386 (= 5.9+20140118-1ubuntu1) but it is not going to be installed      Recommends: libgpm2:i386 but it is not going to be installed  E: Unable to correct problems, you have held broken packages.   == I tried to use fixbroken and install -f. I tried all the methods i know , always there's dependencies and broken packages ...

After upgrading from 10.04 to 12.04 I am trying to install different packages.  For instance ia32-libs and skype (4.0).  When trying to install these, I am getting the 'Unable to correct problems, you have held broken packages' error message.   Output of commands:  sudo apt-get install -f Reading package lists... Done Building dependency tree        Reading state information... Done 0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.   After running this:  sudo dpkg --configure -a foo@foo:~$ sudo apt-get install -f Reading package lists... Done Building dependency tree        Reading state information... Done 0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.


I would like to know if there are easier ways to navigate to specific sections of manual pages such as Examples or Options  I currently resort to piping man to regex find and retrieve statements.  For example to find the entry for the -f option in the grep manual I use this statement:  man grep | grep -A 2 -e '-f'  Is there a better way to use man? I've been able to find scant info on the -S option but perhaps I'm going down the wrong rabbit hole.

I finally got fed up when wanting to read about bash's read and it's -s option with man bash. I found the right spot eventually (around line 4500), but it was a frustrating as usual, since both /read and even /\s-s\s searches have way too many matches.  So, the question is: How can I read long man pages efficiently, or get same information in other ways, locally? As a specific example, how to reach the relevant documentation after seeing read -s pwd in a shell script? A good answer could be a shell script snippet, or hint about some tool and how it is used, or something else entirely, as long as it helps in finding the right spot to read.  Note: I'm not tagging with  because I want the question to be about man page reading in general, even though that quite possibly is the most commonly encountered humongous man page.


One of my biblatex entries causing a Overfull \hbox message. The result looks like this    The question is how I could handle errors like this? Removing the date/eventdate field or shorten the title is not possible.  This is the mwe for the result above.  \documentclass{scrartcl} \usepackage{filecontents} \begin{filecontents}{\jobname.bib} @InProceedings{Paulicke2019a,   author       = {Denny Paulicke and Christian Buhtz and Karsten Schwarz and Katrin Wedler and Dietrich Stoevesandt and Patrick Jahn},   title        = {Technische Assistenzsysteme in der Pflegeausbildung},   subtitle     = {Eine Online-Erhebung},   eventtitle   = {20. Jahrestagung EbM-Netzwerk 2019 - EbM und digitale Transformation in der Medizin},   eventdate    = {2019-03-22},   venue        = {Berlin},   organization = {Deutschen Netzwerks Evidenzbasierte Medizin e. V. (DNEbM)},   publisher    = {German Medical Science GMS Publishing House},   doi          = {10.3205/19ebm059},   eprint       = {nbn:de:0183-19ebm0591},   eprinttype   = {urn},   year         = {2019}, } \end{filecontents}   \usepackage{xltxtra} \usepackage{microtype}  \usepackage{csquotes} \usepackage{polyglossia} \setdefaultlanguage[spelling=new]{german}  \usepackage{hyperref} \usepackage[     backend=biber,     style=apa,     sortlocale=auto,     language=german ]{biblatex} \addbibresource{\jobname.bib} \DeclareLanguageMapping{german}{german-apa} %\DefineBibliographyStrings{german}{andothers = {{et\,al\adddot}}}  \begin{document} \nocite{*} \printbibliography \end{document}

This question continues my .  I have to use weird margins and line spacing for my academic wirting. MWE:  \documentclass[                pagesize,                usegeometry = on,                DIV = calc,% for the line spacing, KOMA-Script manual, page 40                ngerman               ]{scrartcl}  \usepackage[             left = 25mm,             bottom = 20mm,             right = 45mm,             top = 20mm            ]{geometry} \usepackage[onehalfspacing]{setspace}% for the line spacing, KOMA-Script manual, page 40 \usepackage{             babel,             csquotes            } \usepackage[             backend = biber,             sortlocale = auto,             sorting = nyt,             style = ext-authoryear-comp            ]{biblatex}  % for the line spacing, KOMA-Script manual, page 40: \AfterTOCHead{\singlespacing} \KOMAoptions{DIV = last} % adjusting the bibliography \AtBeginBibliography{\renewcommand*{\mkbibnamegiven}{\textsc}}% small caps for the author name \AtBeginBibliography{\renewcommand*{\mkbibnamefamily}{\textsc}}% small caps for the author surname \DeclareFieldFormat{biblabeldate}{#1}% year without the surrounding brackets \DeclareDelimFormat[bib]{nameyeardelim}{\addcomma\space}% comma before the year % changes the type @online \DefineBibliographyStrings{german}{                                    urlfrom = {verfügbar unter},                                    urlseen = {zuletzt geprüft am}                                   } % changes the format of the fields url and urldate \DeclareFieldFormat{url}{\bibstring{urlfrom}\addcolon\space\url{#1}} \DeclareFieldFormat{urldate}{\mkbibbrackets{\bibstring{urlseen}\addcolon\space#1}} \renewbibmacro*{url+urldate}{% changes the default order of the fields url and urldate                              \usebibmacro{urldate}%                              \newunit                              \usebibmacro{url}%                             }  \begin{filecontents}{\jobname.bib}    @ONLINE{Chemie,           EDITOR   = {LUMITOS GmbH},           LOCATION = {Berlin},           URL      = {http://www.chemie.de/lexikon/Kerosin.html},           TITLE    = {Kerosin},           URLDATE  = {2018-06-22},          }  \end{filecontents} \addbibresource{\jobname.bib}  \begin{document}    Text. Text. Text. Text. Text. Text. Text. Text. Text. Text. Text. Text. Text \autocite{Chemie}.   \printbibliography  \end{document}   The result:    How can I improve the breaking?  Thank you for your help and effort in advance!


Let $f:(0,\infty)\to \mathbb{R}$ be a differentiable function and $F:(0,\infty)\to \mathbb{R}$, $F(x)=\frac{1}{x}\int_0^x f(t)dt$. Prove that $f$ is monotone if and only if $F$ is monotone. I could prove the "$\implies$" part by only using $f$'s continuity (I just made the substitution $t=xs$ and used $f$'s monotony). For the "$\impliedby$" I don't really have many ideas. I tried to differentiae $F$, but to no avail. I also tried to start from the definition of monotony, but I couldn't relate $F$'s monotony to $f$'s.

Let $\omega:\mathbb{R}_+\to\mathbb{R}_+$ such that $\omega(0) = 0$ and $\xi(s) = \frac{1}{s}\int\limits_{0}^s \omega(t)dt$ is nondecreasing, i.e., $\forall s,s': s\leq s'$, $\xi(s)\leq \xi(s')$. Show that $\omega(t)$ is nondecreasing a.e., i.e. find a function $w(t)$ such that $w$ is nondecreasing and $\omega = w$ a.e.  I was able to show the reverse implication easily, that if $\omega$ is nondecreasing then $\xi$ is nondecreasing. This way seems more difficult.


light not passing through a transparent object in eevee, is this just a limitation with eevee or am i missing something, I actually have a car model and i want the light to go through the windshield, but the windshield is just casting shadow. why????

Using Eevee, I'm trying to simulate a light bulb. I have a sphere with glass material and inside it, I have a Point light. But the light is not passing through the glass:  However, if I disable the sphere object, the light is working:   How to make the light inside a bulb lamp pass through glass (using Eevee)? Here my test project:


I have been recently trying to solve a continued product of cosines:     If $x=2\pi/2009$, then evaluate   $$\cos x \cos 2x \cos 3x \cdots \cos 1004x$$   I have found formula for this which says product of this series is $\pm(1/2^n)$.   I'm recently in 11th, so please try to give this proof according to my knowledge

Evaluate $$ \prod_{r=1}^{7} \cos \left({\dfrac{r\pi}{15}}\right) $$  I tried trigonometric identities of product of cosines, i.e, $$\cos\text{A}\cdot\cos\text{B} = \dfrac{1}{2}[ \cos(A+B)+\cos(A-B)] $$ but I couldn't find the product. Any help will be appreciated. Thanks.


I wrote 3 reviews for an app, one of them showe up once and the others never did.  This app is almost useless and I feel that others should know that.  So why isn't my review appearing?  It's negative, but professional.

I have an app that's been out for a couple of weeks. Its not exactly selling like hot cakes yet, but I'm pretty sure I've gotten a rating or a review by now. But nothing shows when viewing either in iTunes or directly on the AppStore on the iPhone.  Is there a standard delay as to when ratings/reviews show up, that Apple imposes, especially for new apps? Or do you think there is some problem with Apple's system?


Do we need the 'the' in this sentence?  While some have argued that pastels are better because they calm people down, others suggest that lively colors are (the) best because they make people happier.  The task suggests that the 'the' shouldn't be used, but I don't know how to explain it. How does the use of the article change the meaning of the sentence?

Do both have the same meaning? Or they are subtly different? Example sentence:  What was (the) best? To go left or right, up or down?   it says that both are exactly the same. But I wonder if that's really the case.


Is 65 minutes enough to connect in FRA with Lufthansa Business class ticket coming from JFK going to Beirut? It looks like gates yesterday were Z62 arrival from JFK- and B33 to depart to BEY

I am traveling from Chennai to Atlanta. M first flight is to Frankfurt reaches at 8 30 AM. My second flight is scheduled at 10 45 AM.   Will the two hours transit time enough for boarding my second flight.  What should be my do's and dont's?  Update  Its more than enough. I was able to make it without any tension.


How can we find $x′ = Ax$ for the matrix   \begin{pmatrix}3 &1 &0\\ 0& 3 &0\\ 0& 0& 2\end{pmatrix}

$x′ = Ax$  where $$A = \begin{pmatrix} 3&1&0\\ 0&3&0\\ 0&0&2 \end{pmatrix} $$ what is the logic to solve such type of equations?  I found that $det(A-λI) = (3-λ)^2(2-λ)=0$, so the eigenvalues are 3 and 2


We have just built the official website for our company, but it is not listed in the results returned by google even if users input the full name of our company. Instead,the search results are all news reports about our company from other media outlets and very dated.

This is a general, community wiki  question and answer pair intended to address any questions   concerning the reasons a site or specific site contents do not appear   in search engine results.      If your question was closed as a duplicate of this question and you   feel that the information provided here does not provide a sufficient   answer, please open a discussion on .   My site (or specific pages on my site) is not appearing in search engine results.  Why isn't my content indexed and what can I do about it?


I would like to ask how can I use Tetration notations in this page    in TeX, LaTeX  It seems to me it does not support Tetration symbols??

I am trying to put two subscripts at the left and right of a character. For example, something like:  _{t} p_{x}  where p is in the middle. How do you do this?


Currently, when you follow a link to a chat room, you'll automatically join the room. This means, everyone in the room sees who's just entering that room.  For me personally, this is almost never the desired behaviour. I want to read the contents of the room, joining a room is an entirely separate decision for me. I almost never join a room unless I intend to participate in the discussion.  This behaviour is for one surprising, I don't think everyone expects that they'll be publicly joining a particular chat room just by following a link. This is made even worse by the "convert comments to chat" function, which leaves chat links scattered on the main sites. I can't just read the converted comments, I have to join the chat because it's the only link there (unless I manually try to find the room). For me this means that I never actually follow the links to chat unless it's something really important to me.  Joining a chat room is an active action to me, not something that should automatically happen without the user's consent. It has privacy implications, other users get notified that you're looking at that chat room at that specific point in time. It can also provoke reactions, suddenly I'm greeted by someone I don't know because they noticed I entered that room. As I'm a moderator they might also suspect that there is some kind of trouble which caused me to enter that room.  Following a link to a chat room should not automatically make you join that room. The easiest way would be to just redirect to the transcript, but that could be confusing for people that aren't familiar with SE chat. The other option would be to still go to the live chat page, but without joining chat. So the bar at the bottom would have a big "join this chat room" button instead of the message box.

There are  regarding how users should be treated when they join a chat room:   If you join a chat room, you've signed on to be addressed by random people and bots. It's expected that you may be pinged by anyone or anything. If you join a chat room, you're lurking. Until you talk, you've only dipped your toes into the water.   I'm in camp #2, and the main reason is that joining a chat room is very lightweight. It happens as soon as you click the big link in the room description. I'm not too happy that (provided that you're logged into chat and have enough reputation to talk) clicking the big link makes you appear in a very visible manner into the list of participants in the room.  I wouldn't mind as much if joining a chat room was truly an active decision, if it wasn't something that happened as soon as you wanted to have a look. (Yes, there's a link to the transcript, but it's rather small and hidden.)  Changing the main link to the transcript would solve the problem — browsing the transcript is discreet. However, I don't think this is an acceptable solution, because it would make actually joining the room — a common action — too much work.  What I propose instead is the following:   When you click on the main link in a room description, the display is similar to what it is now when you don't have the reputation to participate in the room (or aren't logged in at all). You get to see messages appearing in real time, and the screen layout is the same as if you were in the room. The bottom part of the screen should show a message like “click here to participate” (I'm not hung on the wording). If you click, you get to join the room, with your avatar appearing in the participant list. If you start typing, then “send” button and the other buttons appear, and posting a message also joins the room. If you've talked in a room recently, clicking on the main link for that room directly makes you an active participant.   The first click is merely clicking on a link whose text is the room name, which doesn't hint that this is an active, public action, so it doesn't have any effect that's visible to other people. The second click clearly tells the user that he's about to participate, and participating in a chat is by definition public since others may talk to you.  This provides a lightweight way to make joining a chatroom less accidental than it is now. It solves the problem of users being jumped on as soon as they click the link to a chat room: now they won't be jumped on until they deliberately jump in.


I am pretty sure I've asked questions on 100 days at Christainity.SE, and since I have the silver "Inquisitive" badge, I'm pretty sure my question quality is good.  And yet, I don't have the Socratic badge.  How can I see what my question score is, and the number of days I've asked questions, preferably without having to use the data explorer or the API?

These badges were only recently added to StackExchange. I would like to know if there is any way I can find out how many more questions I should ask to get these badges.   For e.g. like the counters for the review-related badges:


I believe it is correct to add the abstract to my TOC but I don't know how.  talking about adding the abstract chapter to the TOC. I'm using Lyx and if I output to .tex file this is what I see.  \documentclass[english]{report} \usepackage[T1]{fontenc} \usepackage[latin9]{inputenc} \setcounter{secnumdepth}{3} \setcounter{tocdepth}{3}  \makeatletter %%%%%%%%%%%%%%%%%%%%%%%%%%%%%% User specified LaTeX commands. \usepackage{babel}  \makeatother  \usepackage{babel} \begin{document}  \title{My Title}   \author{My Name}  \maketitle \tableofcontents{} \begin{abstract} %% This isn't a chapter!   My Abstract isn't a chapter.    Abstract is created with begin{abstract} unlike in questions I LINKED to and have been marked as a duplicate. In that example abstract is a chapter. Does this affect the correct use of getting my Abstract into the TOC?       Assuming that the abstract and acknowledgement contents is typeset using a \chapter*{...},    Well it isn't, So what do I do in my case?

I followed Mike's solution from my first question:    My next question is how to add entries (for the abstract and acknowledgements pages) into the table of contents.


Is there a way to export a null's position/rot/scale data from an animation and use it later for comping in After Effects?  Thanks

How can I export a 3D object from blender to adobe after effects without using cinema 4D. And in what format?


Suppose $f$ is a complex polynomial in $z$ and $\bar z$. Assume that $\frac{\partial f}{\partial z} = 0$ and $\frac{\partial f}{\partial \bar z} = 0$.  How do you prove that $f$ here MUST be a constant polynomial?  Thanks in advance!!!

There is an exercise in Function Theory of One Complex Variable by Greene & Krantz that is very similar to a Proposition in the book, but I am having trouble getting to the conclusion.      Let $f : \mathbb{C} \to \mathbb{C}$ be a polynomial. Suppose further that $$\frac{\partial f}{\partial z} = 0$$   and $$\frac{\partial f}{\partial \bar z} = 0$$    for all $z \in \mathbb{C}$    Prove that $ f \equiv$ constant.    Now, part of the proposition (1.3.2) proves that if $p$ is a polynomial, $$p(z, \bar z) = \sum a_{lm}z^l \bar z^m$$ with $\frac{\partial f}{\partial \bar z} = 0$, then $\frac{\partial ^{l + m}}{\partial z^l \partial \bar z^m}p$ evaluated at zero is $l!m!a_{lm}$.  Is this the constant that $f$ equals? It doesn't seem like I've used the hypothesis, or reached the conclusion!  Maybe I should use the definition of the partial... $$\frac{\partial f}{\partial z} := 1/2 (\frac{\partial }{\partial z} - i \cdot \frac{\partial }{\partial z})f$$  Any hints would be greatly appreciated.


I'm using VirtualBox Version 6.1.8 r137981 and trying to get full screen desktop working. I believe I need to install VBoxGuestAdditions. I have Oracle VM VirtualBox Extenstion Pack 6.1.8r137981 added to the Extensions in Oracle VM VirtualBox Manager. In Oracle VM VirtualBox under Devices I select Insert Guest Additions CD Image and run it.  I get:   I read to check uname -r & it returned 3.10.0-1127.el7.x86_64  Also ls /usr/src/kernels* returned 3.10.0-117.8.2.el7.x86_64  yum list shows:   I read the post, but I haven't been able to resolve my problem.  How can I resolve the above errors and get Virtual Box Guest Additions installed correctly?

I try to install VirtualBox Guest Additions on a CentOS 7 VM.  I installed the prerequisites via  sudo yum install perl gcc dkms kernel-devel kernel-headers make bzip2   then I "inserted" the Guest Additions CD image and the Guest Additions auto runner came up and ran.  However the Guest Additions installation errored out with     VirtualBox Guest Additions: Kernel headers not found for target kernel 3.10.0-1062.el7.x86_64.   For closer examination I issued the following commands in the Terminal shell of the VM:  $ ls /usr/src/kernels/ 3.10.0-1062.18.1.el7.x86_64   and  $ uname -r 3.10.0-1062.el7.x86_64   Notice the ddition caharcters 18.1 in the installed headers copared to what the kernel reports. I guess that is the reason why he Guest Additions installation fails.  How can I fix this and install the Guest Additions?    A few more details:   OS Version: CentOS 7.7.1908 Guest Additions Version: 6.1.6 EPEl Repo URL:


Can anyone tell me what this type of repetitive use of two words together in a phrase is actually called? For example:    "What it is, is..."

This is a phrase I've heard many people use, and it sounds wrong to me; e.g.:     The thing about that is, is that she might take it the wrong way.   It seems to treat "The thing [...] is"—the entire phrase—as the subject of the sentence. Of course, even if that were allowed, the comma placement would still be questionable.  I'm curious to know:   Is there a name for this wording? Is it specific to a certain dialect? Is its etymology known?


I've started using the Lib GDX AssetManager instead of the "normal" way to import textures. However, when experimenting with it, I quickly encountered a NullPointerException error. Here is the code:      assets = Generals.getAssetManager();     assets.load("Characters/c.pack", TextureAtlas.class);     assets.finishLoading();     TextureAtlas atlas = assets.get("Characters/c.pack", TextureAtlas.class);     atlas.findRegion("PriestOverworld3");     Array<TextureRegion> frames = new Array<TextureRegion>();     Texture testtex = new Texture("Characters/c.png");     TextureRegion test = new TextureRegion(testtex);     for (int i = 0; i < 3; i++) {         System.out.println(i);         frames.add(new TextureRegion(getTexture(), i * 16, 0, 16, 16));     }     playerStasis = new Animation<>(0.2f, frames);   I get a NullPointerException at the line  frames.add(new TextureRegion(getTexture(), i * 16, 0, 16, 16));   The error:  Exception in thread "LWJGL Application" java.lang.NullPointerException     at com.badlogic.gdx.graphics.g2d.TextureRegion.setRegion(TextureRegion.java:82)     at com.badlogic.gdx.graphics.g2d.TextureRegion.<init>(TextureRegion.java:53)     at Project.sprites.Player.<init>(Player.java:55)   TextureRegion:  // TextureRegion.java:53 setRegion(x, y, width, height); ... // TextureRegion.java:82 float invTexWidth = 1f / texture.getWidth();

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 looked at all info on gov website but although you can make an appointment for an express passport the option is not there if passport is lost. Also where should I go in London. Address please?

I am a UK citizen. I have lost my passport and planned to travel by Eurostar from London to Paris in five days' time. The quoted time for a fast-track replacement passport is "within 1 week" of an appointment.    When can I book the appointment? I.e., could I book one at 9am this morning, for midday? Could I book one for the evening (after 5pm) or would I have to wait until the next working day? How likely is it that the new passport could arrive within less than a week? If I collect in person rather than it being posted, could I minimise the time to get one? Is there any other way to minimise the time? E.g. if I have a scan of my old passport, and/or it was found by the police and returned to the passport office and cancelled? If I pay a premium?


I am trying to understand the best way to find the conjugacy classes of $S_3$. What I am doing to find these is first consider what elements would be in the center of the group $Z(S_3)$. Then, after that, I try finding the conjugacy classes for each element of $S_3$ that is not in the group. Namely, I try finding the conjugacy class of 2 cycles, so for $(12)$ and after that I try finding the conjugacy class for 3 cycles like $(123)$. Doing all the work of computing the conjugacies, I found taht the conjugacy class of $(12)$ is $\{(12),(13),(23)\}$ and the conjugacy class of $(123)$ is $\{(123),(132)\}$. Now my question is, is there a more efficient way to find these conjugacy classes, without computing all the conjugacies? For instance for the group $A4$, I think this approach is not efficient and definitely harder to apply. Thanks!

Is there a systematic way of finding the conjugacy class and centralizer of an element? Could the task be simplified if we are working with "special groups" such as $S_n$ or $A_n$? Are there any intuitive approaches? Thanks.


My Skype beta version 5.3.0.1 Not working, when I open this in Ubuntu 14.04LTS its showing below message:  Sorry, this version of Skype is not supported anymore.  Any help would be great appreciated.

Skype for Linux Beta shows the following message when running the application. Is there a new version of Skype for Linux?  Sorry, this version of Skype is not supported anymore.   How can I get it work?


I have this segment of python code. I want to have a global variable called filetext. However, it does not work as intended, I want to modify the filetext variable in the first method and then use this in the second method.  filetext = "x"  def method1():      filetext = "heyeeh"  def method2():     print(filetext)   This yields "x". How come, and how can I overcome this?

The following code works as expected in both Python 2.5 and 3.0:  a, b, c = (1, 2, 3)  print(a, b, c)  def test():     print(a)     print(b)     print(c)    # (A)     #c+=1       # (B) test()   However, when I uncomment line (B), I get an UnboundLocalError: 'c' not assigned at line (A). The values of a and b are printed correctly. This has me completely baffled for two reasons:   Why is there a runtime error thrown at line (A) because of a later statement on line (B)? Why are variables a and b printed as expected, while c raises an error?   The only explanation I can come up with is that a local variable c is created by the assignment c+=1, which takes precedent over the "global" variable c even before the local variable is created. Of course, it doesn't make sense for a variable to "steal" scope before it exists.  Could someone please explain this behavior?


So I am currently experementing with Sockets and I want to have 3 ports open for client sockets to connect to. So this works if I manually add my threads. Thread t = new Thread(() => SyncServer.StartListening(new IPAddress(new byte[]{127,0,0,1}), port)); t.Start(); Thread t2 = new Thread(() => SyncServer.StartListening(new IPAddress(new byte[]{127,0,0,1}), port + 1)); t2.Start(); ....  But I want to do it a bit cleaner so I tried with a for loop List<Thread> threads = new List<Threads>(); for(int i = 0; i<3;i++) {     Thread t = new Thread(() => SyncServer.StartListening(new IPAddress(new byte[]{127,0,0,1}), port + i));     t.Start();     threads.Add(t); }  The socket server does fully work but when I work with threads and add them manually. If I work with a for loop, the socket server with the port becomes unavailable. Probably because the thread is stopped and I fail to understand why. Note: SyncServer is a static class and StartListening is a static method. If I use a for loop, they always get the latest portnumber (in this case 11003).

I met an interesting issue about C#. I have code like below.  List<Func<int>> actions = new List<Func<int>>();  int variable = 0; while (variable < 5) {     actions.Add(() => variable * 2);     ++ variable; }  foreach (var act in actions) {     Console.WriteLine(act.Invoke()); }   I expect it to output 0, 2, 4, 6, 8. However, it actually outputs five 10s.  It seems that it is due to all actions referring to one captured variable. As a result, when they get invoked, they all have same output.  Is there a way to work round this limit to have each action instance have its own captured variable?


It's the weirdest thing, all of a sudden on macOS Catalina when I try to use my 1password shortcut option + command + \ it for some reason gets mapped to command + c. I checked here:  and it really weird that the c key gets pressed when I am literally typing option + command + \. Here's a video:    What might be causing this??

TL;DR, somehow ⌘⌥\ has become aliased to ⌘C on High Sierra (possibly earlier). I cannot for the life of me determine the source of this.  I first noticed this when invoking 1Password Mini began producing a system bell tone. I finally started to dig into the problem today. In the Keyboard preference pane, there are no conflicts with the ⌘⌥\ shortcut. So I disabled the shortcut in 1Password Mini. Tested, and system bell still sounds. When I attempted to re-add the shortcut, I get the following:    To be clear, this dialog displays when I carefully type ⌘⌥\ — I am not typing ⌘C.  So something has apparently aliased ⌘⌥\ as ⌘C. I have tested this further. If I highlight text, click on the Edit menu, and type ⌘⌥\, I briefly see the Copy item flash, and text is copied to the clipboard.  Any ideas? This is driving me nuts. I've quit all other applications, including menu items. I've checked the Keyboard Shortcuts preference pane for conflicts. And everything has come up short.  Update: I've installed Key Codes from the App Store, and even this application indicates I'm pressing ⌘C! However there's some slight differences that might provide useful information for debugging:  ⌘⌥\:    ⌘C:    Update 2:  As additional information, this happens with both an external Apple Wireless Keyboard as well as the internal keyboard on the MacBook Pro.  Update 3:  This is the full log from Key Codes, including modifier keys being pressed, up to and including pressing the \ key. It indicates immediately after the \ key is pressed (which it identifies as the c key), the c key is released and a modifier change is made as well (despite no keys actually having been released).


I have ubuntu 16.04, want to play games,  But nvidia driver is not installed, Should I install the driver for better performance or Intel Graphics will cope up with it?   In additional drivers nvidia is not showing up! But when I run lspci the graphic card is there!    If I have to install the driver, which version is stable?

I have NVIDIA Geforece 7025 / nForce 630a integrated gfx card on my UBUNTU 12.04.And I have 4 options in Additional drivers:    NVIDIA accelerated graphics driver (version 173)   NVIDIA accelerated graphics driver (post-release updates)(version current updates)  NVIDIA accelerated graphics driver (version current)[Recommended]  NVIDIA accelerated graphics driver (post-release updates)(version 173 updates)   I am currently using the First option.  My Problem is there I can't update the version 173 to the latest version of drivers using xswat PPA. Whenever I do it and reboot but the NVIDIA xserver sttings always shows me the same version.  Which option would allow me to update my drivers to the current version?


what is the difference between :  String s1;   And  String s1 = new string();   How does the memory operate?

While looking at online code samples, I have sometimes come across an assignment of a String constant to a String object via the use of the new operator.  For example:  String s; ... s = new String("Hello World");   This, of course, compared to  s = "Hello World";   I'm not familiar with this syntax and have no idea what the purpose or effect would be.  Since String constants typically get stored in the constant pool and then in whatever representation the JVM has for dealing with String constants, would anything even be allocated on the heap?


Yesterday I made a question on Chess Stack Exchange as a guest user (ChessNoob - ) People answered and I'd like to accept one of the answers (the one made by user1583209) but I can't because it seems I already have another account registerd with the same email (the one I'm using now). Maybe the solution to this kind of loop would be to add a check on the emails when posting as a guest?  Returning to the original question, how can I accept an answer if I made a question as a guest?

I accidentally posted a question without being logged in. Is there a way to associate that question with my account?   For more information, visit "" in the .   a.k.a. How can you link a registered account to a cookie-based account? a.k.a. How do I merge an unregistered account with a registered account a.k.a. Merging users a.k.a. How do I associate anonymous questions I’ve asked with my registered account? a.k.a. Is there a way to claim an unregistered user? (in case anyone searches with those terms)


I have a HashMap<Long, Date> forecastedEndDates. It is in a field class named Card. In my JUnit test I want to assertEquals my Date and a Date from the map, but  on   date1 = card.getForecastedEndDates().get(95L);  line, it givens me a null pointer exception. I have declared and initialized the date as:  Date date1 = new Date()  I can't go and change Date to Calendar or Time, because it is too big of a project. I have a suspicion that there is a format mismatch. When I println Date.getTime(), I get 1538473954932 and when I do:   Card card = new Card(); card.getForecastedEndDates().get(95L);  I get: Tue Oct 16 03:16:34 EEST 2018   I fill in the map with:  Map<Long, Date> forecastedEndDates = new HashMap<Long, Date>();     forecastedEndDates.put(50L,          Date.from(LocalDateTime.now(ZoneOffset.UTC)              .plus(Math.round(forecast.getSimulation().getMedian() * DAY_IN_MILISECONDS), ChronoUnit.MILLIS)              .toInstant(ZoneOffset.UTC)));   The 50L is the key and the Date is value

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've been scratching my head for hours, and am completely lost. I have ubuntu installed on a separate drive, and 5 other drives I use with windows 7. I ran Boot-Repair with "Recommended Repair" and came across this error:   GPT detected. Please create a BIOS-Boot partition.   I also created a bootinfo summary, which can be viewed here:   I have no idea how to create a BIOS-Boot partition, or where to begin.   How can I change the grub boot order so I can choose to boot into Windows 7 or Ubuntu?

Since I updated Windows to 8.1 my Grub menu disappeared. I ran Ubuntu using Live USB, I used Boot-Repair but something went wrong. If I click on Reccomended repair I get this error:     GPT detected. Please create a BIOS-Boot partition (>1MB, unformatted filesystem, bios_grub flag). This can be performed via tools such as Gparted. Then try again. Alternatively, you can retry after activating the [Separate /boot/efi partition:] option.   So I tried to set my sda9 (I think that it's the Ubuntu system partition, since it's ext4) with the bios_grub flag and then to run Boot-Repair again. It didn't work.  I don't know what to do. My Grub was working fine (using UEFI) before I updated Windows.  I removed the bios_grub flag. Then I used fsck and it didn't find any error. So I tried again with Boot-Repair but it always gives me the "GPT detected" error. My boot is on UEFI mode, Secure Boot is "off".  When I boot my PC with SecureBoot OFF, I can reach the GRUB menu. But it's empty (the only voice is "System Setup").  I mounted my Ubuntu system disk:  sudo mount /dev/sda9 /mnt   and the other things:  sudo mount --bind /dev /mnt/dev sudo mount --bind /proc /mnt/proc sudo mount --bind /sys /mnt/sys   I logged on the system with chroot:  sudo chroot /mnt   I re-installed grub:  grub-install /dev/sda update-grub2   But it still doesn't work.


I got an assignment from my college to create this  Now I know there might be some way, that I can copy the disassembly of my C code I created from a debugger, I guess...  If there is a way please let me know... Or atleast...  Help me with the disassembly of this code I created...  #include <stdio.h> #include <string.h> #include <stdlib.h>  //Logic loop int to_base3(int decimal_number)  {     //To return the function at the end of recursion      if (decimal_number == 0)           return 0;     //The Recursion       else         return (decimal_number % 3 + 10 *  to_base3(decimal_number / 3));  }   //Main function   int main()  {      int decimal_number;     char check[20];     //Inputting the values and checking for characters     do{                                      int flag=1;         printf("Enter the number: ");         fgets(check, 19, stdin);         //Loop to check for number or character         for(int i=0; i<sizeof(check);i++){             if(isdigit(check[i])){                 flag =0;                 break;             }             else{                 continue;             }         }         //The place where to_base3() gets called         if(flag==0)         {             decimal_number = atoi(check);             printf("Base 3 number: %d\n", to_base3(decimal_number));         }         //If flag == 1 i.e. if it's a char, then exit the loop         else             break;     }while(1);     //The final statement     printf("Thank you for using my program. Bye!");     return 0; }    Also, if you think that you can come up a shorter assembly code for this problem... Let me know...

How does one do this?  If I want to analyze how something is getting compiled, how would I get the emitted assembly code?


Let a rod move past a mark which is stationary in the reference frame $S$ with a relativistic speed, Let it take a time $t$ to do so, In the frame of a rod this will take time $t'$ and clearly due to length contraction in $S$'s frame $t'>t$. But if the rod experience's a time $t'$ then due to time dilation the time passed for an observer in the frame S will be $\gamma t'$ so here $t>t'$ which contradicts our original inequality . What went wrong here ?

Suppose we have two twins travelling away from each other, each twin moving at some speed $v$:    Twin $A$ observes twin $B$’s time to be dilated so his clock runs faster than twin $B$’s clock. But twin $B$ observes twin $A$’s time to be dilated so his clock runs faster than twin $A$’s clock. Each twin thinks their clock is running faster. How can this be? Isn’t this a paradox?


So let's say for instance I am attacking with a  and it's blocked so I use  on it because I know it will be destroyed. If I have  in play does the Zombie Card returned act as a spell cast? I was looking at rulings on Supernatural Stamina

If  or any other card states that when it is cast, does this mean that it can trigger when it returns from the battlefield? Such as Conduit of ruin is in the graveyard, I return it to the battlefield from the graveyard. Does the first ability trigger and allow me to search my library for an eldrazi card 7 or more to place on top of my library?


(edited) I am having trouble finding a single word to describe a person who likes to "celebrate". This is different from "party animal", "clubber", "reveller" or "socialite". Specifically, I am looking for a noun that is designated for such a person.  The said person has the personality that simply enjoys being with friends and likes to find occasions to celebrate, in good spirits. In addition, the said person not only goes to party, but s/he takes the initiative to propose having one to celebrate (an event/life/news...etc) whenever s/he finds the opportunity to do so.  Any help? Thanks.

I'm looking for a short word that could describe people who are always going to every event in town. It doesn't need to be an existing word, feel free to create one of your own. It can also be made of words related to events and parties. (ex: club, event, guest list, etc.)  Edit  The word will serve as a new term to describ these people in a favorable way. It will probably be used for an app name so it need to be catchy and fun. ( Preferably )


So, I know that $\cos z =4 \Rightarrow z = \arccos(4) = i\ln(\arccos 4 + \sqrt{\arccos^24  -1}) = i(\ln(\sqrt{\arccos^2 4}+ \arccos^2 4 -1) + i(\arg(\arccos 4 + \sqrt{\arccos^2 4 -1}) + 2k\pi), \ \ k \in  \Bbb Z$  But I don't know what to do next and how to find modulus and arg.

Find all roots in $\mathbb{C}$ of the equation $\cos(z)=2$ and plot them on an Argand diagram.  My solution: $\cos(z)=2$, $z=x+iy$ so we have that $\cos(x)\cos(iy)-\sin(x)\sin(iy)=2$ so $\cos(x)\cosh(y)=2$ and $\sin(x)\sinh(y)=0$ must hold. So if $\sinh(y)=0$ then $y=0$ so $\cosh(y)=1$ and so $\cos(x)=2$ which is a contradiction, therefore $x=n\pi$, for some $n\in \mathbb{Z}$ and so $\cos(x)=\pm 1$. However, $\cosh(y)>0$, so if $\cos(x)=-1$ it follows that $\cos(x)\cosh(y)<0$ and cannot equal $2$. Hence $\cos(x)=1$ so $x=2n\pi$ for some $n\in \mathbb{Z}$ and $y=\pm\cosh^{-1}(2)$ since $\cosh(y)=2$. Therefore since $z=x+iy$ $\implies z=2n\pi \pm i\cosh^{-1}(2)$, $n\in \mathbb{Z}$.  My question is, is this sufficent to answer the question $\cos(z)=2$? And if not how should I structure it using this method? Also why is it $\pm\cosh^{-1}(2)$? I don't understand this sutble point. And if I was to draw an Argand diagram would it just be on the imaginary axis at $\cosh^{-1}(2)$ every $2n\pi$?


I want to create a custom mouse pointer on Ubuntu 16.04 from icons .How do I do it?

How can I change X11 cursor and theme in the newest Ubuntu? I can't find it. Please help.


I applied for a tier 4 general student visa. Hours before my biometrics I realized I forgot to put down some countries I visited in Europe last year for travel history. My passport is stamped with these places, and I just completed my biometrics. If I cancel my application now to resubmit, will I have to redo my biometrics? Will this for sure get my visa rejected? UKVIS contact basically doesn't work and I have no answers for anything. My application support center said to call the UK embassy, but I have no idea what to do.

I just submitted my UK Standard Visitor visa application and I inadvertently answered the question Did your travel outside your country of residence? with "NO", which should be "YES" as I have plenty of foreign travels as seen in my passport.  At this moment I can't edit my application anymore. I emailed them about this.


Problem: Prove whether or not $x^2+y^2=100,003$ has any integer solutions using modulo arithmetic. My professor gave the following solution: $x^2+y^2=100,003 \equiv 3 \pmod 4$. By the previous proof verifying that no integer of the form $4k+3$ with integer $k$ is the sum of two squares. Thus $x^2+y^2=100,000$ has no integer solutions.  Why did my professor know to use modulo 4 with remainder 3 looking at the problem? I can't think of any reason to do that.

This question has already been answered . My question is, when we suppose the hypothesis is not true (proof by contradiction), namely that $4 \mid (n^2 - 3)$, we get $n^2 - 3 = 4k$ for some integer $k$ and then we have two cases. But where does the two cases come from? In addition, why does putting them into two cases work to prove the statment? My thought process would be to try to prove this statement by contradiction and somehow figure out a way to produce a contradiction similar to how $\sqrt{2}$ is proved by contradiction. Any help is great! Let me know if I need to clarify more!


What are the rest please?  Note: I flagged my own question as a duplicate.

I am not able to find a link to the twitter account of Academia SE (), for example, in the Academia SE main webpage.   Why are twitter links not included on the main site page of each Q&A site in SE?


I hear there are a total of 65,535 ports on a computer. Does this mean that the computer can communicate with 65,535 instances at the same time? (Let's assume the computer has enough power to handle network)

The socket API is the de-facto standard for TCP/IP and UDP/IP communications (that is, networking code as we know it). However, one of its core functions, accept() is a bit magical.  To borrow a semi-formal definition:     accept() is used on the server side.   It accepts a received incoming attempt   to create a new TCP connection from   the remote client, and creates a new   socket associated with the socket   address pair of this connection.   In other words, accept returns a new socket through which the server can communicate with the newly connected client. The old socket (on which accept was called) stays open, on the same port, listening for new connections.  How does accept work? How is it implemented? There's a lot of confusion on this topic. Many people claim accept opens a new port and you communicate with the client through it. But this obviously isn't true, as no new port is opened. You actually can communicate through the same port with different clients, but how? When several threads call recv on the same port, how does the data know where to go?  I guess it's something along the lines of the client's address being associated with a socket descriptor, and whenever data comes through recv it's routed to the correct socket, but I'm not sure.  It'd be great to get a thorough explanation of the inner-workings of this mechanism.


I come across an issue when rendering tree particles.  All of my trees in the attached image are from the source tree. The source tree is free of alpha mask problems. As one can see, most of them show up perfectly fine. Still, some show strange black artefacts. Which seems weird as they are part of the same particle system.  Any suggestions? I appreciate your help.  Thanks.

Using v2.73, cycles and a very simple scene: an array of cubes, no big deal.   If I set the shader's material to transparent, the cubes in the foreground do become transparent but those far away in the back do not disappear completely and this strange dark things appear (visible in rendered mode and in final renders)    I've played with the clipping distance on the viewport and camera, but I can't figure out how to make those ghosts go away...


In my main form code, I've added this:  public static ShoeStyle selectedStyle;   ShoeStyle is the name of an enum I have in a class. I want selectedStyle to contain the name of whatever I select in my combo box. Like this  private void cmbShoeList_SelectedIndexChanged(object sender, EventArgs e) {     selectedStyle = (ShoeStyle)cmbShoeList.SelectedValue;                        }   But when I run the program, it gives me the error:     specified cast is not valid.   I'm not sure how I can fix this. I've heard of the term cast before but am unfamiliar with it

What's the best way to convert a string to an enumeration value in C#? I have an HTML select tag containing the values of an enumeration. When the page is posted, I want to pick up the value (which will be in the form of a string) and convert it to the corresponding enumeration value. In an ideal world, I could do something like this: StatusEnum MyStatus = StatusEnum.Parse("Active");  but that isn't a valid code.


Consider the ring of the formal power series $k[[T_1,\ldots,T_n]]$ ($k$ algebraically closed) where $\mathfrak m$ is the maximal ideal. If $f\in\mathfrak m^2$, why $$\frac{k[[T_1,\ldots,T_n]]}{(f)}$$ is a nonregular local ring?

How can I prove this:     Let $A$ be a local regular ring with maximal ideal $\mathfrak m$ and $x \in \mathfrak m-\mathfrak m^2$. Then $A/(x)$ is a regular ring. Prove also that if $x\in\mathfrak m^2$, $x\ne 0$, the result does not hold anymore.   I don't know how to begin! Thanks to everyone who helps!  But if $d=\infty$?


When I try updating my system this error pops up.  Can anyone help?  E: Failed to fetch http://ppa.launchpad.net/pasgui/ppa/ubuntu/dists/xenial/main/binary-amd64/Packages

PPA seems to be constantly offline. Whenever I use sudo apt-get update, this error is shown:  W: Failed to fetch http://ppa.launchpad.net/ 404  Not Found   How do I fix these errors?


I want to compare mean temperatures for three future periods (2011-2040, 2041-2070, 2071-2100) with the measures mean temperatures of 1971-2000.  My resulting shapefiles will show the difference between the simulated and measured temperatures for each period.   I want to have a classification from -1°C. to +3°C. So I would like to have manual break values like -1,0, -0,8, -0,6 and so on. But how can I realize it? For example The difference between 1971-2000 and 2011-2040 is found within a range of -0,69 and +1,88. So the the "coldest" class begins at -0,69°C.   How can I create classes which are outside of the range of the values (for example -1,0 - -0,8)? When I try to edit the break values manually, it automatically jumps back to the coldest existing value (-0,69).

I have two shapefiles representing grids with values that are symbolized with graduated colors, shown below:    You can see that the two shapefiles encompass similar ranges of data, but assign slightly different colors to ranges in these data.  I would like to symbolize the ranges in each of the two shapefiles using the same colors for the same ranges, enabling easier comparison between the files and allowing a single legend to be used.  However, when I attempt to classify the ranges with a manual interval, ArcGIS forces what should be the uppermost range to also include the minimum value from the dataset.  You can see this in the "-81.64 - 10.00" range of the left data frame, below.  This forces the entire layer to be symbolized with this color.  Essentially, ArcGIS is requiring that the minimum value in the dataset be used as a value in one of the ranges.    Is there a way to circumvent this feature?


My schema:  id:int | post_hash:str | post_body: str | is_op: tinyint(1) | parent_id:int  1 | 'dddba11f43d90117b01' | 'test post' | 1 | Null   2 | Null                  | 'test reply'| 0 | 1   This is to store forum posts and replies. How can I select post_hash and all its child posts specified by parent_id? To clarify, the idea is something like:  SELECT p.id FROM posts p WHERE post_hash = ? or parent_id = p.id   where p.id is the result of the select. It's self-referential so a subquery or join will be needed but I'm not sure how to go about this one.

Assume you have a flat table that stores an ordered tree hierarchy:  Id   Name         ParentId   Order  1   'Node 1'            0      10  2   'Node 1.1'          1      10  3   'Node 2'            0      20  4   'Node 1.1.1'        2      10  5   'Node 2.1'          3      10  6   'Node 1.2'          1      20   Here's a diagram, where we have [id] Name.  Root node 0 is fictional.                          [0] ROOT                           /    \                [1] Node 1          [3] Node 2               /       \                   \     [2] Node 1.1     [6] Node 1.2      [5] Node 2.1           /            [4] Node 1.1.1   What minimalistic approach would you use to output that to HTML (or text, for that matter) as a correctly ordered, correctly indented tree?   Assume further you only have basic data structures (arrays and hashmaps), no fancy objects with parent/children references, no ORM, no framework, just your two hands. The table is represented as a result set, which can be accessed randomly.   Pseudo code or plain English is okay, this is purely a conceptional question.  Bonus question: Is there a fundamentally better way to store a tree structure like this in a RDBMS?    EDITS AND ADDITIONS  To answer one commenter's ('s) question: A root node is not necessary, because it is never going to be displayed anyway. ParentId = 0 is the convention to express "these are top level". The Order column defines how nodes with the same parent are going to be sorted.  The "result set" I spoke of can be pictured as an array of hashmaps (to stay in that terminology). For my example was meant to be already there. Some answers go the extra mile and construct it first, but thats okay.  The tree can be arbitrarily deep. Each node can have N children. I did not exactly have a "millions of entries" tree in mind, though.  Don't mistake my choice of node naming ('Node 1.1.1') for something to rely on. The nodes could equally well be called 'Frank' or 'Bob', no naming structure is implied, this was merely to make it readable.  I have posted my own solution so you guys can pull it to pieces.


On my html page, I have a button with an onClick function window.print().  When users press this button (in Chrome) it opens the default printer interface but in the header of the page and in the footer there are some excessive information.  In header, it prints out date and index.html as the name of the html file. In footer it prints the location of index.html file on my computer (C:://...).  How to disable this and print the page as it is presented in the browser?

I got an HTML with the <body onload="window.print()">.   The question I'm trying to ask is:   Is there any way to remove the strings that the web browsers add to the printed page? Such as:   Web site from where the page was printed Page count Title of the web page Date of printing


Let $n$ be a positive integer. Then the length $\ell(n)$ of $n$, that is, the number of digits in the decimal representation of $n$, is given by $$\ell(n) = \lfloor \log_{10}(n)\rfloor + 1.$$ How can one go about rigorously proving that this holds for all positive integers?

I read recently that you can find the number of digits in a number through the formula $\lfloor \log_{10} n \rfloor +1$ What's the logic behind this rather what's the proof?


This is a book I've read a few (4-5) years ago and I do not believe it's from the Golden Age of SciFi. A guy working for the Space Survey Service (?) in charge of exploring new stellar systems stumbles upon a spaceship lost for centuries then is killed by greedy treasure hunters (?). An antiques / space souvenirs dealer finds a coffee mug and uniform patches of the long lost ship and traces them back to the Survey officer. He then buys the dead man's survey ship and is able to crack its memory banks and find the wreck which leads him to its sistership wreck orbiting around a planet where the descendants of the two ships live in complete ignorance of the rest of mankind. Thanks for your help :)

I'm trying to remember the name of a book I read, here are some details:   Main character is some sort of detective/investigator (I think) Sci-fi, takes place in distant future.  Oldest known relic is an american coin (from 2006 I think) Hired to track down whether or not a cup is authentic from a lost ship They end up finding the ship, but not the planet that it was sent to colonize. They are bringing back a bunch of relics from the ship when they decided to stay over in the space station for a bite to eat.  The shuttle carrying the relics is destroyed (they were supposed to be on it but weren't). They end up following the clues and finding the lost colonized planet which is orbiting a star which is on some sort of crazy orbit through the galaxy which is why no one was able to find it before.


I want to delete my post with a bad reputation and I am getting warnings about being blocked. Here's a link to it

What circumstances can cause a question or answer to be deleted, and what does that actually mean?    How can a post be deleted? When can't I delete my own post? Can I still see my post even after it's deleted? Can I see a list of my deleted posts? How can I undelete one of my posts? What does deletion mean for a post? How do votes to delete work? What are the criteria for deletion? What else should I know about deleted posts? If I flag my question with a request to delete it, what will happen?       For more information, see the articles about  and  in the .


I have seen arguments that we should automate all our tests, and I have seen arguments that manual testing is necessary.   I don't know which one to believe. Is it even possible to automate all tests? When people say that all tests should be automated, do they mean the kind of tests where manual testers work through a detailed test script or do they mean the kind of tests where manual testers explore the application?  How do I decide which approach is correct?

Can every test be done by automation?  Or is there anything that cannot be done by automation?


I was wondering if there was one word in English for "to read something thoroughly until one understands it well"? I am trying to translate a word which has this meaning in Chinese.  Thanks.

Sometimes we read books rather quickly and don't give them much (or any) thought, so the action 'reading' does not necessarily imply that we have given enough thoughts to any book we read.   Is there a word that describes reading a book with great care; usually but necessarily slowly over a long period of time.


I'm trying to export the file names of the files that were changed through commits in git to a txt file. How can I approach this problem? I just want the file name and I would like one file name on each line instead of all of them clumped together. Thank you in advance for the help!

I am looking for a simple Git command that provides a nicely formatted list of all files that were part of the commit given by a hash (SHA-1), with no extraneous information. I have tried: git show a303aa90779efdd2f6b9d90693e2cbbbe4613c1d  Although it lists the files, it also includes unwanted diff information for each. Is there another git command that will provide just the list I want, so that I can avoid parsing it from the git show output?


Is there a connected space $(X,\tau)$ such that $X$ has more than $2$ points and the only proper connected subsets of $X$ are the singletons?

The particular point topology on any set is connected, but on removing the particular point, the complement is discrete, and hence totally disconnected. Although this is not even $T^1$,  also has this property, and is a subspace of $\mathbb{R}^2$.   Is there an infinite connected topological space such that the complement of every point is totally disconnected? Or in other words, is there an infinite connected space such that every proper subset of at least two points is disconnected?


This is too deep in the charms since I use it constantly. I would like a tile that would either connect to the VPN or a tile that will open the network connections options within the charms menu.  I have the 8.1 preview installed so I can use Outlook to connect to my work Exchange account. This requires VPN, so this is why I will be connecting to the VPN constantly.

It was easy to create a shortcut that automatically dials a VPN connection in Windows 7 (e.g., see  ). But if I create that shortcut in Windows 8, double-clicking it opens the Networks panel (and doesn't establish the connection).  How do I create a shortcut in Windows 8 that dials a VPN connection?


If the joint p.d.f of a two-dimensional random variable $(X,Y)$ is given by:  $f(x,y) = \  \left\{ \begin{array}{ll}       2 &s.t.~ 0<x<1;~0 <y<x \\       0 &x <0~;~x>1 \\ \end{array}  \right. $  Then, what is the conditional density of $X$ given $Y$?  Attempt: $f_{X|Y}(x|y)= \dfrac{P_{XY}(x,y)}{P_Y(y)}$  As per given condition : $\int^0_1 (\int_0^xP_{XY}(x,y)~dy) dx=2$  How does one calculate $P_{XY}(x,y)$ from here.  Also, I have trouble visualizing a way to find out $P_Y(y) = \int_0^\infty P_{XY}(x,y)~ dx$  Thanks a lot for your help

$$f(x,y) = \begin{cases} 2 & 0< x< y<1  \\     0 &\text{otherwise} \end{cases} $$  I need to find   the density function of $y$ and conditional pdf of $X$ given $Y$.   My answer is coming out to be   $2y$ $\frac1y$


I've searched all of over SO but I haven't quite found exactly what I'm looking for because it's overly complicated.  I want to know why I'm getting this error (posted below).  My code seems logically correct but for reason I'm getting the null pointer exception.  Here's my HashTable.java file:  import java.util.*;  public class HashTable {     public static void lastFourDigitsStudent(Student s) {         LinkedList<Student>[] llStudent = new LinkedList[1000];          String a = s.getId().substring(4,8);         int lastFourDigits = Integer.parseInt(a);         int hashFunction = lastFourDigits % 1000;          llStudent[hashFunction].add(s);     } }   Here's the error I'm getting:  Type safety: The expression of type LinkedList[]  needs unchecked conversion to conform to LinkedList<Student>[]

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?


Please I don't need a fish I need one learn me hunting, Also I looked at all the answers, about this question on StackExchange, so would  you give us a new answer.Please

I'm trying to wrap some text around a raspberry shaped image that is placed to the right on the page. I would realy liked the text to follow the shape of the Raspberry. Is this possible?  Below is a MWE, and an image of what I have for now.  \documentclass[12pt]{scrartcl} \usepackage{graphicx,wrapfig,lipsum} \usepackage[onehalfspacing]{setspace}  \begin{document} \begin{wrapfigure}{r}{.3\linewidth}     \centering     \includegraphics[width=\linewidth]{raspberry_pi_logo}     \caption{Raspberry Pi} \end{wrapfigure} \lipsum[2]\lipsum[1]  \end{document}