When I use residue theorem I have problems to determine the poles in the unit circle. I've tried $\cos \theta = \frac{z^2+1}{2z}$, $\sin \theta = \frac{z^2+1}{2iz}$, $\sin^2\theta=\frac{1}{2}(\cos(2\theta)-1)$ and $\cos^2\theta=\frac{1}{2}(\cos(2\theta)+1)$ to help me but I couldn't make it. Thanks for helping

I want to prove:  $$\int_{0}^{2\pi}\frac{1}{a^{2}\cos^2t+b^{2}\sin^{2}t}dt=\frac{2\pi}{ab}$$  by the deformation theorem of complex variable.  Then I consider a parameterization $\gamma:[0,2\pi]\rightarrow A$, traveled in the opposite direction of the clock hand, of the ellipse (in $\mathbb{C}$):  $$\frac{x^2}{a^2}+\frac{y^2}{b^2}=1$$  I thought of searching for a function $f:A\rightarrow \mathbb{C}$ (analytic in $A$) and a curve $\lambda:[0,2\pi]\rightarrow A$ (homotopic to $\gamma$) and use the deformation theorem:  $$\int_{\gamma}f = \int_{\lambda}f$$  But I can not find a function $f(z)$ that meets what I need, can you help me to find the f?   P.D: Necessarily I have to use the theorem of deformation


A bit disappointed to see     ... since I have put quite a lot of effort and time answering the question also received 55 rep points from it so I can't understand the reason it was removed.   After some discussion in the comments section and some tips from @Molot and @Gnat, I'd like to ask a favor from our moderators; please see the revision history as I believe the question may have got poorer through the editing. I honestly can't remember the question in the original form. All it takes is a simple verification to conclude one of the below two points:   If there were no significant changes made to the question I will accept the fact that I shouldn't have answered that question in first place and try to improve my judgement skills in future.  If the question got poorer through editing I'd like to ask for the removal to be reversed.     Was the user removed? Please, explain to me why was this deleted?  Some have said that the question was really poor. In the format  yes I do agree it was quite poor, but was it poor enough that it needed to be deleted?

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 .


The force required to stretch a spring varies with the distance as shown in the figure. If the experiment is performed with the above spring of half the length, the line OA will:   (a) shift toward F-axis  (b) shift towards X-axis  (c) remain as it is  (d) become double in length  If we cut the spring into half the length, the new force constant $K_{new}=2K_{org}$.  Since force is proportional to force constant(the new one). So the force must have doubled. So the line OA should shift to F. But the answer in the book is given to be (b). Can anyone explain this.

I've always been taught that the spring constant $k$ is a constant — that is, for a given spring, $k$ will always be the same, regardless of what you do to the spring.   My friend's physics professor gave a practice problem in which a spring of length $L$ was cut into four parts of length $L/4$. He claimed that the spring constant in each of the new springs cut from the old spring ($k_\text{new}$) was therefore equal to $k_\text{orig}/4$.   Is this true? Every person I've asked seems to think that this is false, and that $k$ will be the same even if you cut the spring into parts. Is there a good explanation of whether $k$ will be the same after cutting the spring or not? It seems like if it's an inherent property of the spring it shouldn't change, so if it does, why?


When I enter rendered mode it looks like this:  When I enter CPU render device it looks fine. Is it a GPU issue or a software issue?

I don't know why but now, when i go in material preview or rendered (in solid mode it works fine), my object is entirely gray, or invisible idk, because it has the same color of the background. I've been working for days on this project without having this issue, it suddenly showed up. I tried opening other old projects and suddenly they all do the same so i guess it is some blender program setting that applies for all the projects, but idk how it happened cuz i didn't change anything :/, anyone got any tips?


When I try to search for available snap packages over proxy connection:  snap find atom   I get the following error:  error: Get        https://api.snapcraft.io/api/v1/snaps/search?confinement=strict%2Cclassic&fields=anon_download_url%2Carchitecture%2Cchannel%2Cdownload_sha3_384%2Csummary%2Cdescription%2Cbinary_filesize%2Cdownload_url%2Clast_updated%2Cpackage_name%2Cprices%2Cpublisher%2Cratings_average%2Crevision%2Csnap_id%2Clicense%2Cbase%2Cmedia%2Csupport_url%2Ccontact%2Ctitle%2Ccontent%2Cversion%2Corigin%2Cdeveloper_id%2Cdeveloper_name%2Cdeveloper_validation%2Cprivate%2Cconfinement%2Ccommon_ids&q=atom&scope=wide:        proxyconnect tcp: tls: oversized record received with length 20527   My question is not a duplicate of   because my config for https proxy is already:  https_proxy=http://127.0.0.1:3128/

I know how to configure APT to use a web proxy. But what about snap?


I'm trying to get a menu option styled to-do list that allows a user to select what they wish to do. When I run the code it allows me to input once, then when it returns and I want it to wait for userInput a second time for them to navigate again, it throws a NullPointerException. I've tried various ways to solve this. public class ToDoListApplication {          Scanner scanner;     String input;          public ToDoListApplication() {         System.out.println("Starting Application\nType 'Help' for Options\nPlease Select an Option..");         scanner = null;         menu();              }          public void menu() {         input = null;         if (input == null) {             input = userInput();         }         methodSelector(input);              }               public String userInput() {         scanner = new Scanner(System.in);         if (scanner.hasNextLine()) {             input = scanner.nextLine();         }          scanner.close();             return input;     }          public void methodSelector(String userInput) {                  if (userInput.equalsIgnoreCase("help")) {             helpMethod();         } else {             System.out.println("unknown string");         }              }          public void helpMethod() {         System.out.println("Command 'Add': Add To-do item to list.\nType 'Remove': Remove Item from List.\nType 'Count': See how many items in list.\nType 'Find': Locate specific item by name.\nType 'Print': See all items in list.");         menu();     } }

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?


Find the value of $a$ and $b$ if $( x + 1 )$ and $( x -2 )$ are factors of $ax^3 - 4x^2 + bx - 12$. This is regarding polynomials.   Thank you

Find the value of $a$ and $b$ if $x+1$ and $x−2$ are factors of $ax^3−4x^2+bx−12$      Attemption $$ \begin{cases} f(-1) = -a - b - 16\\ f(2) = 8a + 2b - 28 \end{cases} $$ But then when I plug in $$b = 28 - 8a$$. Then I get $$-a -(28- 8a) - 16=0$$$$a = 34/7$$  In the book it says $a = 10$ and $b = -26$. So I am stumped. Please help


How do I make the word Virgo transparent so it shows the background of this image (background is obviously transparent)? I am using Photoshop.   I tried grouping layer 2 and the text layer and changing the blending mode options but it didn't work.

I'll start by saying I'm an enthusiast and amateur Photoshop User, and any help is much appreciated.   I have a simple PSD file containing 2 layers, an image and a font overlay. The underlying background is transparent. What I'm looking to do is place the font over the image, but remove it in a way that the font is "cut out" of the image with the transparent background visible.


I am very new to mocking framework, and my work needs mocking framework to finish unit testing. In the current code base i could see above 3 frameworks are being used in different places for unit testing. So, which one should i go for in the above 3 frameworks ?

What's the best framework for creating mock objects in Java? Why? What are the pros and cons of each framework?


Let $a, b, c$ and $d$ be positive numbers such that $a+b+c+d =4$, prove that  $$ \frac{4}{abcd}  \ge  \frac{a}{b} + \frac{b}{c} + \frac{c}{d} + \frac{d}{a} $$  I am supposed to prove my using AM-GM, so I tried  $$ a + b+ c+ d \ge 4(abcd)^{1/4} $$ $$ 1 \ge abcd$$    also by AM GM  $$\frac{a}{b} + \frac{b}{c} + \frac{c}{d} + \frac{d}{a} \ge 4 $$ The only way I get the desired result is by dividing the first inequality by second and cross multiplying, but two inequalities can't be divided without sign change.

Let $a, b, c$ and $d$ be positive real numbers such that $a+b+c+d = 4$. Prove that $$\frac4{abcd} \geq \frac a b + \frac bc + \frac cd +\frac d a .$$   How can I approach this using only the ? Are there any other methods that do not involve the AM-GM inequality?


In the book, Solving Mathematical Problems: A personal perspective (written by Terry Tao), he discusses a problem named (on Analytic Geometry Chapter, page 79):     Problem 5.4 (Taylor 1989, p. 34, Q2). In the centre of a square swimming   pool is a boy, while his teacher (who cannot swim) is at one corner   of the pool. The teacher can run three times faster than the boy can swim,   but the boy can run faster than the teacher can. Can the boy escape from   the teacher? (Assume both persons are infinitely manoeuvrable.)   A picture can be drawn as below, with the boy at O and the teacher at an arbitrary corner, say A.   His solution as is (extremely paraphrased) starting from O, let the boy swim towards BD. Let the boy stop (at say X) when the teacher is at Y (A < Y < B) and AY = 3OX. Now tricking the teacher, make a straight dash towards CD.  I am having a much different solution (restricting the boys movement to a straight line).      Putting the square in Cartesian plane with O as the origin and and the teacher at D (Not A). Assuming the square is of lenght $2k$, the teachers coordinate is $( k, -k)$. Now, lets suppose the boy makes a dash to a point on AB (say P $(x, k)$ ) and reaches faster than the teacher. So to go to P, the teacher has to move in D->B->P, with a total distance of $3k-x$. The boy should go $\sqrt{x^2 + k^2}$. Now from the ratio of the speed of the two, it reduces to solving the inequality $\sqrt{x^2 + k^2} < \frac{3k -x}{3} = k - \frac{x}{3}$, which solves to $\frac{-3k}{4} < x < 0$.    So a straight dash to a bit left of the midpoint of AB is also probably a correct answer, isn't it ? [My main point of asking is not to check the answer numerically, which can be done by a sleeping baby with its left hand, but the method's correctenss]

I'm struggling with the following problem from Terence Tao's "Solving Mathematical Problems":     Suppose the teacher can run six times as fast as the   boy can swim. Now show that the boy cannot escape. (Hint: Draw an   imaginary square of sidelength 1/6 unit centred at $O$. Once the boy leaves   that square, the teacher gains the upper hand.)   Here $O$ is the center of the swimming pool. This question is a follow up on the previous one, which is solved in the affirmative in the text     (Taylor 1989, p. 34, Q2). In the centre of a square swimming   pool is a boy, while his teacher (who cannot swim) is at one corner   of the pool. The teacher can run three times faster than the boy can swim,   but the boy can run faster than the teacher can. Can the boy escape from   the teacher? (Assume both persons are infinitely manoeuvrable.)     My attempt:  Since the boy can always swim back into the small square of sidelength 1/6 centered at $O$, I can't see how to apply the hint properly. Also, since the student's path need not even be smooth (it was taken as a polygonal chain in the previous question) I'm having difficulties writing data down clearly.  Any help would be appreciated. Thanks.


What explains the difference in impact velocity of meteors if they all come from roughly the same distance from the Sun (Asteriod Belt) ? I know the velocity of the Earth itself factors in, but is there anything else?

Is the speed of a meteor through our sky because of the speed of the earth's axis  rotation, or because the meteor is speeding towards us at that speed?


I've searched this topic already and found similar question.  But it was not fully answered.  Actually I know the Möbius transformation of form  $\frac{z-a}{1-\bar a z}$ is the automorphism of unit disc and interchanges $0$ and $a$.  But if I want it to change two arbitrary points in the disc. The above mapping fails.  Then how does the mapping which satisfies the condition on the title look like?  I'd like to see the mapping itself. (I mean like $f(z)=z$)

Let $a$ and $b$ be distinct points in the unit disk $D$. Show that there exists a conformal automorphism $f$ of $D$ that interchanges $a$ and $b$; that is, $f(a) = b$ and $f(b) = a$.  Idea: we know that $g(z)=\frac{\alpha-z}{1-\bar{\alpha}z}$ interchanges $0$ and $\alpha$ and by composition we can find out the map $f(a) = b$ for any $a$ and $b$ in the unit disk $D$. But how can I get the other way by the same map? Thanks.


In several posts I read about issues of specific versions of apt-mirror.  How do I find out the version? I did not see anything in the man page and it has not command line options, also no --help.

I would like to know how to get the version information of an installed program that doesn't have the      --version or -version   method implemented.


When I click nav order the page is automatically closed. This is my logcat:      E/AndroidRuntime: FATAL EXCEPTION: main Process: com.udaya.smartfoodserver, PID: 12671 java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.lang.String.equals(java.lang.Object)' on a null object reference at com.udaya.smartfoodserver.Common.Common.convertCodeToStatus(Common.java:15) at com.udaya.smartfoodserver.OrderStatus$1.populateViewHolder(OrderStatus.java:54) at com.udaya.smartfoodserver.OrderStatus$1.populateViewHolder(OrderStatus.java:49) at com.firebase.ui.database.FirebaseRecyclerAdapter.onBindViewHolder(FirebaseRecyclerAdapter.java:184)

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 a problem with solving the convergence of $\sum_{n=1}^{\infty }\frac{(-1)^{[\sqrt{n}]}}{n}$ where $[a]$ means floor function of $a$. I've already made the first thep and rewrote it with the $\sum_{n=1}^{\infty }(-1)^{n}\sum_{k=n^2}^{(n+1)^2-1}\frac{1}{k}$, which converges if and only if the previous one converges. Now I want to use Leibniz criterion, but I cannot prove that the second sum in the previous expression is monotonic. Does anyone know how to do it? (I cannot use Riemann integral, we haven't defined it yet)


I get the error  mlabel command not found   I tried using sudo apt-get install mlabel, but it said unable to locate package mlabel.  Any ideas how to get this working?

Simple enough question: is there some shell command (or GUI method) I can use that, given the path to a file on my system, tells me what package put it there? Assuming the file did in fact come from a package, that is.  Bonus question: what if it's a file that isn't installed on my system? Is there, say, a website that will let me look up a file and see what packages, if any, provide it?


Just watched , a movie inspired by , and occurring in Hong Kong. Being a movie on a non-english country, usually one of two things happen:  Movie is (almost) entirely in english Movie is entirely in foreign language  With american actors, the first option was the obvious go-to. In these cases, it is frequent to show the characters starting to speak the foreign language (just for a couple of sentences), and then switch to English. The idea is to convey to the user that they are speaking another language but that it is understandable to the characters, just like English is to the viewers. In fact, sometimes the opposite is done, where characters speak foreign languages without subtitles to give the viewer the sensation of hostility or confusion (see  or ). However, in Ghost in the Shell,  only speak in Chinese (or Japanese?), while all others go for English. Why? It doesn't seem that they are both speaking the same foreign language. The Asian actor is the only one speaking constantly in Chinese. Subtitles appear on his lines, so the viewer is meant to understand them, just like the characters. Is the language used meant to be literally interpreted (e.g., they are actually speaking English and Chinese to each other)? Or is there some perspective being conveyed to the viewers? In the former, why would the Public Security Section 9 speak English most of the time? In the latter, why this approach with only specific characters speaking the foreign language?

Throughout the live action version of Ghost in the Shell, Chief Aramaki spoke only in Japanese the whole time, whereas nearly every other character spoke in English. Is there an in-universe or production reason for this?


the error is pointing to this requestQueue.add(stringRequest). Everytime i run this app in actual device, it crashes. i declared my Volley requestQue right after service declaration.  public class SmsService extends Service {          public RequestQueue requestQueue;         public StringRequest stringRequest;   stringRequest = new StringRequest(Request.Method.POST, smsurl, new Response.Listener<String>() {                 @Override                 public void onResponse(String response) {                     Log.e("Debug", response);                  }             }, new Response.ErrorListener() {                 @Override                 public void onErrorResponse(VolleyError error) {                     Log.e("Debug", "No Internet Connection!!");                  }             }){                 @Override                 protected Map<String, String> getParams() throws AuthFailureError {                     HashMap<String, String> hashMap = new HashMap<String, String>();                     hashMap.put("email",email);                     hashMap.put("targetname",targetname);                     hashMap.put("smstype",smstype);                     hashMap.put("phone",phone);                     hashMap.put("contactname",contactname);                     hashMap.put("body",body);                     hashMap.put("date",date);                      return hashMap;                 }             };             requestQueue.add(stringRequest);


I built this site with Angular 10: https://fireflysemantics.com/ And when the top level domain is visited it reroutes to this: https://fireflysemantics.com/welcome However There's no link to that from anywhere within the app, so I don't think Google has any way of indexing that page. What would be the best way of telling Google to index the page.  From my research it seems I could do something like this:    Welcome to example!   <app-root></app-root>   Thoughts? Also any thoughts on the max number of links that this would work with and any other approaches?

I built a site with Angular 10. When the home page is visited it reroutes to this /welcome. However There's no link to that from anywhere within the app, so I don't think Google has any way of indexing that page. What would be the best way of telling Google to index the page.  From my research it seems I could do something like this:    Welcome to Example!   <app-root></app-root>   What is the max number of links that this would work with and any other approaches?


I just bought this China-made tablet, Flytouch, and it has Ice Cream Sandwich installed on it.  Is there anyway to install Jelly Bean? I Googled some and couldn't find a good source. Do you know any? thanks

Android 4.1 (Jelly Bean) was announced at Google I|O 2012 on June 27, 2012.  (You can review  at the official Android Developer's site.)  Of course, not all devices will get this update right away and others won't get it at all. Each manufacturer and carrier often choose to add their custom modifications which tend to delay the official release.  When will each device get Android 4.1, either officially or unofficially, if ever?  See also:


using System; using System.Collections.Generic; using UnityEngine; using Oxide.Core.Libraries.Covalence; namespace Oxide.Plugins {     [Info("AutoNoClip", "Test", "1.0.20")]      class AutoNoClip : RustPlugin     {         void OnUserConnected(IPlayer player)         {         player.Command("noclip");         player.Command("menu");         }     } }  This is my first plugin for the Rust video game and I'm getting this error in console

I can't get to the bottom of this error, because when the debugger is attached, it does not seem to occur.  Collection was modified; enumeration operation may not execute  Below is the code. This is a WCF server in a Windows service. The method NotifySubscribers() is called by the service whenever there is a data event (at random intervals, but not very often - about 800 times per day). When a Windows Forms client subscribes, the subscriber ID is added to the subscribers dictionary, and when the client unsubscribes, it is deleted from the dictionary. The error happens when (or after) a client unsubscribes. It appears that the next time the NotifySubscribers() method is called, the foreach() loop fails with the error in the subject line. The method writes the error into the application log as shown in the code below. When a debugger is attached and a client unsubscribes, the code executes fine. Do you see a problem with this code? Do I need to make the dictionary thread-safe? [ServiceBehavior(InstanceContextMode=InstanceContextMode.Single)] public class SubscriptionServer : ISubscriptionServer {     private static IDictionary<Guid, Subscriber> subscribers;      public SubscriptionServer()     {                     subscribers = new Dictionary<Guid, Subscriber>();     }      public void NotifySubscribers(DataRecord sr)     {         foreach(Subscriber s in subscribers.Values)         {             try             {                 s.Callback.SignalData(sr);             }             catch (Exception e)             {                 DCS.WriteToApplicationLog(e.Message,                    System.Diagnostics.EventLogEntryType.Error);                  UnsubscribeEvent(s.ClientId);             }         }     }          public Guid SubscribeEvent(string clientDescription)     {         Subscriber subscriber = new Subscriber();         subscriber.Callback = OperationContext.Current.                 GetCallbackChannel<IDCSCallback>();          subscribers.Add(subscriber.ClientId, subscriber);                  return subscriber.ClientId;     }      public void UnsubscribeEvent(Guid clientId)     {         try         {             subscribers.Remove(clientId);         }         catch(Exception e)         {             System.Diagnostics.Debug.WriteLine("Unsubscribe Error " +                      e.Message);         }     } }


I have high quality scans of my leg, I am trying to print a 1/4" thick shell for it.  I assumed it would be something with the extrude function, but I cannot figure it out.  Anyone have a little walk through or willing to explain the steps to a complete newb?  Basically, I want the outside of my scan mesh to become the inside of my print model, with uniform thickness all around my calf and under my foot.  Many thanks for any help you can offer.

I'm using blender to make a basic model of my house and I want to hollow out the inside of the house so that the walls are slightly thicker and there are normals facing both ways, I'm not really sure how to can achieve this. I think it's called shelling?    Also, has anyone got any tips on working on the interior of buildings, because I find it nearly impossible to do so :/


I had applied for a visit visa (business) to appear for my PLAB 2 exam on 21 June 2019. I had to attend practice classes from an academy in Manchester for which I had attached the invitation letter; my duration was 15 days to prepare my exam in a better way. I had mentioned the cost of my trip to be £1500 and my brother sponsoring me for £3000 (my entire trip).   My rejection letter stated that I was going with my mother, when I had nowhere in my form or cover letter mentioned that I am going with my mother, because I was going alone. I had shown that my brother is my financial sponsor as I didnt have enough funds in my account. I had attested all the documents of my brother but somewhere in my form I made a mistake where I wrote the total money I have is £3000, but I had only £1200 in my account. I thought we had to write the total amount, so I put my brother's sponsor money, which was supposed to be £3000; he hadn't transferred it into my account, it was in his account only.  I made one more mistake in the form where they asked how much is the cost of travel to you personally. I wrote £1500 but I think I had to write nil there.   I don't know how to proceed now. Should I transfer £3000 into my account from my brother's account and get a bank statement proving the source of income? I don't have enough money in my account despite bring employed since Nov 2018 with a salary of £700 per month, as I had to make some big transactions such as booking my PLAB 2 exam (£830£), etc.  I have already booked the exam for £830 and I don't have much time left.

Many of the UK visa refusals we see here share a common pattern and the prevailing reasons refer to V 4.2 (a) and (c).    I do understand that, while the applicants may describe very different individual circumstances, there's a consistent pattern and, broadly, fall into specific categories:    Credibility (lifestyle, lack of ties, visit history, lies & omissions) Funding (insufficient funds, provenance of funds, funds parking) Sponsorship (family, friends, employer)   Question: What most commonly triggers a UK visa refusal where V 4.2 (a) and (c) are given as the grounds?  Secondarily: Given that there is a clear pattern, to what extent are these refusals predictable? Does sponsorship make a difference? Is there a set of personal circumstances, however abstract, where a refusal is all but guaranteed? For example, why do those we see here on TSE who sought entry for the PLAB or British Army appear to be refused with a common theme? Is there a uniform shortcoming or is it just discrimination?   PLAB: What is about applications for a visa, for the purpose of sitting the Professional and Linguistic Assessments Board (PLAB) exam, that seem to invite refusals. After all, the test is given so that international medical graduates can show that they qualify to practise medicine in the UK. The first part, PLAB 1, can be taken in centres outside of the UK. However, PLAB 2 can be taken only in the UK. Why can't you can't get a visa just to sit the exam, promising that you'll leave immediately after?    British Army: Since Commonwealth citizens are eligible to apply online to join, even those who don't reside in the UK, why is it so difficult to get a visa just to attend an interview to see whether you are suitable? Even with an invitation from the Army, such visa applications seem to be unsuccessful. Isn't a career in the British Army a valid reason?     Lastly:  After such a refusal, what approaches would increase the chance of a successful application?


One gotta love the Stack Exchange's registration system; It's so easy and efficient. Creating an account here takes only 2 steps if you have an account in one of the web giants (Google, Facebook etc.)       et viola!  My question is how? Could anyone link me to some sources on how to achieve this epic registration system?  Thanks.

What tools and technologies are used to build the Stack Exchange Network?  See also:


Honestly, I'm just not sure where to start at all. I've just been staring at this for a while

Show that if $a, b$ and $c$ are integers with $c|ab$ then $c|(a,c)(b,c)$.  Now $(a, c)$ and $(b, c)$ would both divide $c$ since it's the gcd, but how would I show $c$ divides their product, and $(a,c)(b, c) \geq  c$ and not the other way around?


I accidentally typed cd // instead of cd .. and something weird happened. The directory // doesn't exist, what's going on here exactly.  root@root:/var/www/html# cd // root@root://# pwd // root@root://# cd .. root@root://#

I mistakenly typed cd // instead of cd /. To my surprise, current directory showed up as //.   What is that directory? Why does it exist?  apple@snipped $ pwd /home/apple apple@snipped $ cd / apple@snipped $ pwd / apple@snipped $ cd // apple@snipped $ pwd // apple@snipped $ cd /// apple@snipped $ pwd /


I haven't used the bounty system before, but I understand that people place part of their rep points on to a question that has not been answered yet. But I believe that for the points to be given, the OP must give the answer the tick. If this is so, can people not just ask a question, place a bounty on to it and get the correct answer; but not give the answer the tick. Thus keeping their points. Isn't this a flaw in the system, or is this intentional?

It's possible to offer and award bounties of reputation on questions.   What is a bounty? How can I find questions that have a bounty attached? How do I start a bounty? When can I start a bounty? Why is the system requiring me to choose a bounty amount that's higher than the minimum? Can I use Markdown formatting in the bounty remarks? Can I edit the remark? How long is the bounty period? How do I award a bounty? Can I award a bounty to my own answer? Can I award a bounty to an old answer? If I offer a bounty on someone else's question, can I award the bounty to their answer? After awarding the bounty, can I remove it or move it to another answer at a later time? What happens if there's no answer after the bounty period? What happens if I feel my question is still unanswered? What is automatic awarding? Are bounty awards exempt from the 200 points/day reputation limit? How does Community Wiki mode affect bounties? How does user deletion or post dissociation affect bounties? Can I award a bounty to an answer from a deleted user or one where the author was dissociated? Can I offer a second bounty after the first one has expired? Can I raise my bounty? What happens if a bounty question is closed or deleted? Why can't I vote to close or migrate a bounty question? What happens if I delete my account while I have an active bounty? Do I keep an awarded bounty when I delete my answer? What happens if a question where I awarded a bounty later gets deleted or migrated? Can I cancel my bounty? Can I affect / divide / share part of my bounty to two (or more) users? How many outstanding bounties can a single user have?      See also:  in the Help Center


Compressing a gas (or reducing its temperature) can form "agglomerations" in the form of liquid drops and solid grains.  But if there's only one particle in the system, can it be assigned with a phase (based on the given temperature and pressure), or is phase meaningless (i.e. arbitrary) in this case? In particular, in colloids of nanoparticles, is there any purpose in specifying the phase of the nanoparticles in the colloid?

I was studying a book about thermodynamics of nanosystems and I got stuck with this question in my mind which I couldn't find an answer for.  For instance, does a single water molecule have a state, like being liquid or something? Or is one molecule of TiO2 solid or gas? I would appreciate if anyone could clarify this.  I should state that I am not considering a macromolecule in my case.


Given a finite group $G = \{a_1 ,a_2,...,a_n\}$ and $\mathbb{C}[G]$ the respective group ring, $\mathbb{C}[G] = \{\sum z_ia_i : z_i \in\mathbb{C} , a_i\in G\}$.  Defining $K_i := \sum_{a_k\in cl_G(a_i)} a_k$ , when $cl_G(a_i)$ the conjugacy class, means $K_i =a_1a_ia_1^{-1} + a_2a_ia_2^{-1} +...+a_na_ia_n^{-1}$.   I wish to show that $(K_1 ,K_2 ,...,K_n)$ spans Z($\mathbb{C}[G])$. I had already shown that for $a_i \in Z(\mathbb{C}[G])$, $K_i = \{a_i\}$ thus $a_i = 1\cdot K_i$, as needed.  But I failed to show the other direction, means that for $w\in span_\mathbb{C}(K_1,K_2,...,K_n)$ then $w$ commutes with any element of $\mathbb{C}[G]$, means $w\in Z(\mathbb{C}[G])$.

There is already a similar post, that has an answer to my question, but it is quite short and I don't get it... So I am trying to show that  \begin{align} \{e_K |~ K \subset G~ conjugacy~ class \} \end{align} is a basis for $Z(\mathbb{Z}[G])$. Serre even writes "one immediately checks that the $e_K$ form a basis", but even reading the other post  I don't see that...  My approach to this is:  Be $x \in Z(\mathbb{Z}[G])$, which is equivalent to: $x = gxg^{-1}$ for all $g \in G$. Writing  $x = \sum\limits_{h \in G} \lambda_h h$, we get $x = \sum\limits_{h \in G} \lambda_h ghg^{-1}$. I don't really know how to go on at this point. I mean, I know that when $a,b \in K$ (same conjugacy class) you get $\sum\limits_{s \in K} \mu_s s = \mu\sum\limits_{s \in K} s$, since \begin{align} a = hbh^{-1} \Rightarrow \mu_a = \mu_b ~\forall a,b\in K \end{align} So all elements in the same conjugacy class have the same scalar.  But from here I don't really know how I can generate the $x = \sum\limits_{h \in G} \lambda_h ghg^{-1}$ with the $e_K$ ...  I would be really thankful, if someone could give me quite a basic proof that even I understand...


It hasn't explicitly been taught to me what the rules are after speech, especially regarding capitalisation.   "Hello?" called June to the yellow figure. "Hello?" Called June to the yellow figure.   I'm pretty sure #1 is correct, but should the second one be corrected?

I recently learned that I have developed a consistent, but entirely wrong approach to punctuating direct speech in fiction. I am in the unenviable position of trying to relearn.  Previously I wrote such things as:     "I'm done." She said.   when the quoted speech was definitely, absolutely the end of a sentence. So now I know I need.     "I'm done," she said.   This follows the rule that a period is only allowed when the end of the spoken sentence is also the end of the sentence in the narrative. For example:     "I'm done." She slammed the door on the way out.   So, it now looks odd to me when there are multiple sentences in the speech:     "I can't take her. I'm done," she said.   Can you reassure me that is correct, or give the correct form? Please don't suggest rewriting the sentence to put 'she said' in the middle - I'm aware of that: I'm specifically asking about the punctuation rules.  The other odd case is speech ending with an ellipsis. Do sentence terminating ellipses (four periods normally) become:     "I can't take her. You know, ...," she said, nodding towards Jane.   If so, are non-terminating ellipses dealt with the same way?     "I can't take ...," she nodded towards Jane, "any more!"   or can non-terminating ellipses be used unadorned?     "I can't take ..." she nodded towards Jane, "any more!"   I'd be very grateful if you could point me at references as well as answers. For the record I am a British writer writing for both British and US publication, so any variation is also interesting to me!


I need to ask a question related to the approaches and apt technology stack architecture for my web application. Think of it like a code review for my architecture diagram. But, I am not sure whether it is a question for Server Fault or Code Review or Super User.

Bjarne Stroustrup once mentioned in one of his bigthink interviews that one of the greatest problems most programmers have is not finding or using the right libraries.  On stackoverflow and programmers, I've observed a trend towards questions like "I want to do this, is there a [library | programming language] for that", or "I have these {n} [library | language] candidates for my project; which one would yield me the least amount of headache given these requirements".   Since questions like these aren't exactly programming questions in the sense of "this code should do this, but it does this, why?", they are often (though not always) being closed as "not constructive" because they do not have a definite answer (which is true, and according to the FAQ they would be off-topic on both stackoverflow and programmers).  Nonetheless, I think library questions are valid, and that it is helpful for any programmer to receive independent input from experienced programmers (at least it helps me a lot every time I browse through one of those closed questions, which I found through google). Does anyone agree that posting library choice questions should be explicitly allowed on either stackoverflow or programmers?


Is there a Map implementation in Java that will use case-insensitive String matching for the key, but also supports the null key? I know that  new TreeMap<String, String>(String.CASE_INSENSITIVE_ORDER)   supports case-insensitive matching of String keys, but it doesn't support the null key.

I'm implementing compareTo() method for a simple class such as this (to be able to use Collections.sort() and other goodies offered by the Java platform):  public class Metadata implements Comparable<Metadata> {     private String name;     private String value;  // Imagine basic constructor and accessors here // Irrelevant parts omitted }   I want the natural ordering for these objects to be: 1) sorted by name and 2) sorted by value if name is the same; both comparisons should be case-insensitive. For both fields null values are perfectly acceptable, so compareTo must not break in these cases.   The solution that springs to mind is along the lines of the following (I'm using "guard clauses" here while others might prefer a single return point, but that's beside the point):  // primarily by name, secondarily by value; null-safe; case-insensitive public int compareTo(Metadata other) {     if (this.name == null && other.name != null){         return -1;     }     else if (this.name != null && other.name == null){         return 1;     }     else if (this.name != null && other.name != null) {         int result = this.name.compareToIgnoreCase(other.name);         if (result != 0){             return result;         }     }      if (this.value == null) {         return other.value == null ? 0 : -1;     }     if (other.value == null){         return 1;     }      return this.value.compareToIgnoreCase(other.value); }   This does the job, but I'm not perfectly happy with this code. Admittedly it isn't very complex, but is quite verbose and tedious.  The question is, how would you make this less verbose (while retaining the functionality)? Feel free to refer to Java standard libraries or Apache Commons if they help. Would the only option to make this (a little) simpler be to implement my own "NullSafeStringComparator", and apply it for comparing both fields?  Edits 1-3: Eddie's right; fixed the "both names are null" case above  About the accepted answer  I asked this question back in 2009, on Java 1.6 of course, and at the time  was my preferred accepted answer. I never got round to changing that until now (2017).  There are also —a 2009 Apache Commons Collections one and a 2013 Guava one, both posted by me—that I did prefer at some point in time.  I now made the clean  the accepted answer. That should definitely be preferred if on Java 8, and these days Java 8 should be available to nearly all projects.


With macOS Sierra pushing Siri as a very cool new feature, the behaviour of my (wired) Apple earbuds has changed.  When I give it a single tap, the music will pause or play, which is normal.  However, I'm also used to double-tapping to advance to the next song, like on my iPhone.  That feature is gone.  Also, on the first tap, the "Enable Siri?" dialog comes up: I decided to disable Siri as I don't use it much and the additional battery drain (that I may be making up) doesn't seem worthwhile to me.  How can I disable this dialog and revert my iTunes behaviour back to what I'm used to?

I have installed macOS Sierra.  I often work on my Mac while on the go, and then I play music using iTunes over my EarPods connected via the mini-Jack plug.  The button allows me to pause the music, but now in Sierra, every time I press it, I am asked whether I want to allow Siri.  Refusing will simply bring the window up again when I press the button.  I don't want to use Siri on Sierra.  At all.  How can I prevent it from trying to activate when I press play/pause on my EarPods?  Added after reading comments: When I enable Siri, Siri doesn't activate when I press the button, unless I press it really long.  But when I disable Siri entirely, it asks whether it's allowed to activate every time I press the button, even if it's just a short click.


I have a requirement where I need to run a task for every 5 seconds, but only between specific times (like between 1:30 and 2:30 tomorrow).  I looked at celery, but a normal task cannot be executed repeatedly in celery and the periodic tasks cannot be dynamically scheduled.  I also looked at APScheduler, but that doesn't support running it as a 'daemon' and scheduling tasks from outside.  Any idea what I could use to make this happen?  Edit: Should have mentioned this earlier, I need to do this during a web request, like a background task.

I want to repeatedly execute a function in Python every 60 seconds forever (just like an  in Objective C). This code will run as a daemon and is effectively like calling the python script every minute using a cron, but without requiring that to be set up by the user.  In , the solution appears to effectively just  for x seconds. I don't need such advanced functionality so perhaps something like this would work  while True:     # Code executed here     time.sleep(60)   Are there any foreseeable problems with this code?


I am running a dual boot setup of windows and Ubuntu and I wanted to install Manjaro KDE Chain of events that lead me into this mess 1.To get rid of Ubuntu I deleted it's partition and now I am stuck with grub rescue prompt "directory not found" 2.To get rid of grub rescue I followed the steps in this  involving the removal of ubuntu folder in the EFI directory 3.Achivement: got rid of grub rescue 4.Now to install the OS I wanted to try(Manjaro) I made a bootable live usb using , plugged it and tried to boot from it and again guess what! grub rescue 5.just to make sure there is no problem with the live USB, I made a bootable USB of Ubuntu to check 6.geuss what it worked fine and I was able to install Ubuntu but if I plug in any another OS other than Ubuntu grub rescue shows up unknown file system only a live usb with ubuntu is able to boot and any other usb with other os prompts grub rescue help!!! I really want to get rid of grub rescue and try manjaro

I had Ubuntu 12.04 Beta installed on my computer. When 12.04 was finally released, I made a bootable USB Flash Drive using Startup Disk Creator.  Then I decided to check if this drive works properly and to reinstall the system on my desktop. I must add, my desktop behaves a bit strange when it comes to bootable USB's, it recognizes them as HDD.  In BIOS I changed priority of boot so USB Flash Drive (recognized as HDD) was first. Successfully booted, I installed Ubuntu. Everything worked fine, but...  Now I cannot boot from my real HDD. Every time I want to boot, I put the USB Flash Drive into my computer, boot, safely remove it and everything works.  What do I need to do to repair boot?


How can 2 objects be added through a js function without using 'join' that the result output below is true? This is the code that I have now:   var twoObjs = function(obj1, obj2) {  return obj1 + obj2; // does not work };  twoObjs("dog", "ball");  var output = mergeObjs({dog: "Max"}, {toy: "mouse"});  console.log(output.cat === "Max") console.log(output.toy === "mouse")

I need to be able to merge two (very simple) JavaScript objects at runtime.  For example I'd like to:  var obj1 = { food: 'pizza', car: 'ford' } var obj2 = { animal: 'dog' }  obj1.merge(obj2);  //obj1 now has three properties: food, car, and animal   Does anyone have a script for this or know of a built in way to do this?  I do not need recursion, and I do not need to merge functions, just methods on flat objects.


Recently I started remaking an old game on Unity. Basically I want to remake an old RPG that was released for Playstation 1. I'm not ripping anything from the old game, all the assets are being created by me. I'm creating everything from the scratch, music, 3D models, gameplay however I will keep the (copyrighted ?) names, I will try to create the characters and maps/levels as they were in the original version of Playstation 1 but with better graphics.  I'm not planning on selling it or adding in on a platform like Steam (for obvious reasons, copyrights etc), just giving it for free. But I wanna know when I will finish the development, can I share the game on public with other people so they can download it?  Can the company that made the original game sue me/fine me because of copyrights reasons even though I'm not planning on selling for money?  tl;dr Remake an non-profit game of PS1 from the scratch, can the company that holds the copyrights of the game sue me/fine me?

Most games build on other games' successes and many are downright clones. Where is the limit of imitation before legal issues come into play? Is it down to literary or graphic work like characters and storyline that cause legal problems, or can someone actually claim to own gameplay mechanics?  There are so many similar clone games out there that the rules are probably very slack or nonexistent, but I'd like to hear the views of more experienced developers / designers.


I want to recreate this Kate Moss, Life Is A Joke image with a friend (and later photoshop in a moustache). I'm unfamiliar with beauty/studio photography. The hair and make up I can wing.  Am I right in thinking one top down soft light; and maybe a 85mm lens?  Edit: I got my lighting answer from this detailed post

I often hear the term 'Butterfly Lighting' used when discussing high-fashion and glamor photography. How do I set up Butterfly Lighting, and when do I use it?


Here is my main. All I am trying to do is create an object of the class file, this is probably a very noobish question so sorry, just need to know what I'm doing wrong.  #include <iostream> #include "Player.h"  using std::cout; using std::cin;  int main() {     cout << "Hello and welcome to the student adventures game.\n";      Player player1(); }

Is there any good reason that an empty set of round brackets (parentheses) isn't valid for calling the default constructor in C++?  MyObject  object;  // ok - default ctor MyObject  object(blah); // ok  MyObject  object();  // error   I seem to type "()" automatically everytime. Is there a good reason this isn't allowed?


I have two Lua functions that manipulate their arguments in different ways, and two new ConTeXt macros defined to let me use them. I tried to nest them together, but they seem to also be consuming and manipulating the macro calls themselves, not just their outputs. In one nesting order this causes incorrect output, and in the other order it causes a fatal error during typesetting. This is the MWE: \startluacode     userdata = userdata or {}          function userdata.lastWords(s)         context(s:sub(s:find(" ") + 1))     end          function userdata.changeCase(s)         context(s:upper())     end \stopluacode  \define[1]\ChangeCase{\ctxlua{userdata.changeCase([==[#1]==])}} \define[1]\LastWords{\ctxlua{userdata.lastWords([==[#1]==])}}  \starttext  \LastWords{One Two Three A}\par % => "Two Three A" \ChangeCase{One Two Three B}\par % => "ONE TWO THREE B" \LastWords{\ChangeCase{One Two Three C}}\par % => "One Two Three C", wrong output %\ChangeCase{\LastWords{One Two Three D}}\par % uncomment for fatal error  \stoptext  The problem with C is that \LastWords consumes all of \ChangeCase{One Two Three C} and therefore strips off \ChangeCase. This means the first word is not being removed, and the string isn't up-cased either. The problem with D is that it changes the case of \LastWords, so it fails with a fatal error because \LASTWORDS is not a macro: ! Undefined control sequence  l.1 \LASTWORDS              {ONE TWO THREE D}  Both of these should be consuming only the output of each other, not consuming each other's macro calls. I don't know how to define them that way though. (The MWE version of \ChangeCase is boring, I know. My real Lua code is attempting more interesting case changing, but this stub illustrates the core problem: that the Lua code is being passed the macro names too.) I'm new to using Lua in ConTeXt and I'm not really familiar with the internals of ConTeXt. Maybe there's an obvious thing I'm missing or doing wrong. My fallback is to give up on separating these macros and define an ad hoc \LastWordsChangeCase macro just for this use. That's a bit gross but will work for this project. I want to be able to make robust Lua macros in the future though, and these ones are unexpectedly fragile. I must be doing something wrong. The documentation for Lua on the ConTeXt wiki is basic and doesn't seem to cover this. I have no idea what search terms to try on the wiki or the mailing list that might illuminate this problem. How do I make this work as intended?

The interaction of TeX and Lua can be quite delicate at times.  While the former has category codes and tokens, the latter has escape sequences and datatypes.  Mixing the disparate concepts of these two worlds can lead to unexpected behaviour which favours common errors, known as gotchas. In the community wiki answer below you can find an overview of the common mistakes that people make when getting to grips with LuaTeX.


In 3D math I always see matrices with one additional dimension. For example, in 3D graphics, matrices are always 4x4 and in 2d they are 3x3 matrices. Can anyone explain why?

Following recommendation of  answer I've recently read the series of articles of Wolfire about linear algebra. I'm somewhat familiar with matrices and I came to a conclusion that vector and a matrix multiplication is in fact multiplication of 2x2 and 2x1 matrices:  \begin{equation*} \begin{bmatrix} a & c \\ b & d \end{bmatrix} \qquad \begin{bmatrix} x \\ y \end{bmatrix} \end{equation*}  In  the author reveals that to accomplish translation in addition to rotation we need to add a row and a column to the translation matrix:     If we want to translate by a vector (e,f), we can just tack it onto our change-of-basis matrix like this:   \begin{bmatrix} a & c & e\\ b & d & f\\ 0 & 0 & 1 \end{bmatrix}   And then we add an extra  to the end of each position vector like this:   \begin{bmatrix} x\\ y\\ 1 \end{bmatrix}   P.S. I edited the direction of the vector to make it comply with matrix multiplication conditions.  The 1 at the third row of the vector is totally understandable: to multiply 2x3 matrix we need a 3-row matrix.  What I didn't get here is why we need extra row for translation matrix? I can't see any difference in multiplication (except for the useless 1):  \begin{equation*} \begin{bmatrix} a & c & e\\ b & d & f\\ 0 & 0 & 1 \end{bmatrix} * \begin{bmatrix} x\\ y\\ 1 \end{bmatrix} = \begin{bmatrix} ax + cy + e\\ bx + dy + f\\ 0 + 0 + 1 \end{bmatrix} \end{equation*}  \begin{equation*} \begin{bmatrix} a & c & e\\ b & d & f\\ \end{bmatrix} * \begin{bmatrix} x\\ y\\ 1 \end{bmatrix} = \begin{bmatrix} ax + cy + e\\ bx + dy + f\\ \end{bmatrix} \end{equation*}  So the same question for 3D matrices, just it's easier to convey with a 2D case


So, I have Ubuntu One on my mac, and is synced with the Ubuntu One website. I have folders within folders, within folders, and so on. If I needed to (If, I got a new computer, for example), would it be possible to download everything from the website in a big compressed file (zip, tar.gz, 7z, etc.)? If not, how would I go about downloading all of the files from the website to my hard drive?

I just installed Ubuntu 14.04, and Ubuntu One isn't installed by default and their download page says it comes pre installed, which doesn't help with anything.  I wanna move all my files from Ubuntu One to Dropbox, but downloading one file at a time from the browser and upload it again to dropbox will take way too long.  Is there any way to get Ubuntu One on Ubuntu 14.04? or somehow download all files from the Ubuntu One website?  I see they updated their site:


I have a requirement to create subscriber third party API. So here is a requirement before callout:  I need to do callout for getting the inventory name from thirdparty before creating subscriber. Then I need to get the value of subscriber then pass it to create a subscriber.  I'm getting a error in test class  System.CalloutException: You have uncommitted work pending. Please commit or rollback before calling out. Please help me because it's a production issue.Any help will be really appreciated. Thank you in advance Thanks Akshit Jain

So I have a method that takes as a parameter an Id of a object and uses it to make an external callout.  Unfortunately I can't seem to figure out any way to test it.  @isTest static void sometimes_salesforces_sucks() {    My_Object__c foo = new My_Object__c(Name='test');    insert foo;    MyClient client = new MyClient();    MyMockResponseGenerator mockResponse = new MyMockResponseGenerator();    Test.setMock(HttpCalloutMock.class,mockResponse);     Test.startTest();    client.bar(foo.Id);    Test.stopTest(); }    says that using start/stop test should work, but it doesn't work for me


I am in search of a term that describes movement, or practice of motor skills, as a factor of laterality. Would "kinesiological" be appropriate? I'll leave my two previous questions down below; hopefully it can shed more light. Thank you so much!

I recently asked a question about the cause of motor laterality:  I understand that there can be genetic factors, epigenetic factors, or environmental factors. But in terms of continuous practice of motor skills, what type of factor will that be? Physical factors? Thank you!


I am frying green tomatoes. The recipe calls for kosher salt. Can I use iodized salt or sea salt instead?

The roasted chicken recipe I'm following of course calls for kosher salt, but I don't have any, and getting some is out of the question.  I have sea salt and table salt on hand.  Can I substitute one of those instead, and if so, what is the proper ratio of the kosher salt the recipe calls for to either sea salt or table salt?


For $C[0,1]$ the space of all continuous functions $f:[0,1]\to\mathbb{R}$, Show that, in $C[0,1]$, the functions with $f(\mathbb{Q})\subseteq \mathbb{Q}$ are dense. I'm having trouble understanding what dense means in relation to functions, so am not sure how to answer this! Any help would be appreciated :)

I am trying to prove the following:  In $C[0,1]$ the functions that preserve the rationals (i.e. $f(\mathbb{Q})\subseteq \mathbb{Q}$) are dense.  So far, I have not made much progress- I am aware that $A$ is dense in $B$ iff $A$ has non-empty intersection with each open set $U$ in $B$ but am not sure how to apply this definition. I have also thought about showing that the closure of $X$ (where $X$ is the set of functions that preserve the rationals) is equal to $C[0,1]$ by a double-inclusion proof but I have also made no progress with this approach. Am I on the right track or should I change my approach?


helo; we start again. computer has an EOL (14.04) ubuntu and I would like to run a Supported Version. everything tried so far has come to naught, including LinuxMint. A fresh install is the desired option. right then, we have managed to put the 'installation stuff' onto a USB, and can hold f12 on start up. This leads to a Boot Menu, which offers Options 2:, 4:, 5: and 6: [usb] option 6 chosen. "  Missing parameter in configuration file. Keyword: path gfxboot .c32: not a COM32R image boot:  " repeat repeat for a few minutes until it seems to stop repeating. quite apparently it's gobbledygook and makes no sense to me There must be a way to make this happen! patience is useful, Please can someone help. Thank you.

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


The sum of the series  $1+\frac{1+2}{1!}+\frac{1+2+3}{3!}+....$ equals?  The answer is $\frac{3e}{2}$.  But I dont Know How?  I have tried following:  $1+\frac{1+2}{1!}+\frac{1+2+3}{3!}+....$=$\sum\limits_{n=1}^{\infty} \frac{n(n+1)}{2n!} $  I know that sequence of partial sum $S_n$=$1+\frac{1+2}{1!}+\frac{1+2+3}{3!}+....+\frac{n(n+1)}{2n!}$ and $\sum\limits_{n=1}^{\infty} \frac{n(n+1)} {2n!}$ converges to same point.  Now how to find $S_n$ converges to which point?

Deteremine the sum of the series $$\frac{1}{1!}+\frac{1+2}{2!}+\frac{1+2+3}{3!}+ \ldots$$  So I first write down the $n^{th}$ term $a_n=\frac{\frac{n(n+1)}{2}}{n!}=\frac{n+1}{2(n-1)!}$.  So from there I can write the series as $$1+\frac{3}{2}+\frac{4}{2\times 2!}+\ldots +\frac{n+1}{2(n-1)!}+\ldots $$  I am quite sure I can do some sort of term by term integration or differentiation of some standard power series and crack this. Any leads?


I am using the Stack Overflow data dump (located at ) for research that involves looking at the popularity history of posts, and I have a question regarding view counts.  The dump contains a Votes.xml file with information on when a vote has been cast and to which post, which allows one to construct a time series of post score over time for all posts. Is there a similar thing available for post view counts? As far as I checked, the only data available on view counts is the count in Posts.xml for questions, which is the current (at the time of the snapshot) total view count - there seems to be no history available.

An interesting addition to the data dump would be the daily/hourly/whatever view counts for the websites. This could be used to see what happened to SO when proposal X came out, what time of day is the most active (if it was hourly), what day of the week is the most active, activity to question ratio, and many other things.   Before you say "What about Users.Views and Posts.ViewCount?", they aren't usable since they only list the total, not the breakdown of when it happened. The only statistics you could draw are monthly, which is useless.  If your worried about size, then your exaggerating what I'm asking. Daily is tiny, only 7 rows for an entire week. Hourly is a bit bigger, 168 rows per week. Considering other tables are millions of rows long, this won't affect size at all considering the growth.


I have a simple piece of code that tries to give a convenience to file in Python.  class File:     def __init__(this, *args):         this._file = file(*args)      def __del__(this):         this._file.close()  def createCallForwarder(method):     return lambda obj,*args: method(obj._file, *args)  _dict = file.__dict__ for (k,v) in zip(_dict.keys(), _dict.values()):     if not (k.startswith('__') and k.endswith('__')):         if v.__class__.__name__ == 'method_descriptor':             File.__dict__[k] = createCallForwarder(v)  # get the repr method File.__repr__ = createCallForwarder(dict_proxy['__repr__'])   If i change File to inherit from object, it does not let me assign the methods.   Why is it different?

What is the difference between old style and new style classes in Python?  When should I use one or the other?


Suppose there is a rigid body in space and one single force is acting on it and the force does not pass through the center of mass. I would like to ask why the torque on a body is always the force times perpendicular distance to the center of mass if there is no supporting point on that body? What's the principle behind that?

Assume there is a rigid body in deep space with mass $m$ and moment of inertia $I$. A force that varies with time, $F(t)$, is applied to the body off-center at a distance $r$ from its center of mass. How do I calculate the instantaneous acceleration, rotational acceleration, and trajectory of this object, assuming it starts from rest?


A quickie...  I needed a 1uf non polarised cap for a circuit which I didn't have so I found info that said I could join the + of two polarised caps and connect the two - terminals into the circuit to create a non polarised electrolytic cap.  I understand I should not exceed the reverse breakdown voltage in either direction and that the capacitance will be halved but are there any other issues (I also understand electrolytics are leaky)  Bash me by all means

There was some discussion on this question        which I don't see as being conclusively resolved:   "turns out that what might LOOK like two ordinary electrolytics are not, in fact, two ordinary electrolytics." "No, do not do this. It will act as a capacitor also, but once you pass a few volts it will blow out the insulator." 'Kind of like "you can't make a BJT from two diodes"' "it is a process that a tinkerer cannot do"   So is a non-polar (NP) electrolytic cap electrically identical to two electrolytic caps in reverse series, or not?  Does it not survive the same voltages?  What happens to the reverse-biased cap when a large voltage is placed across the combination?  Are there practical limitations other than physical size?  Does it matter which polarity is on the outside?  I don't see what the difference is, but a lot of people seem to think there is one.  Summary:   As posted in one of the comments, there's a sort of electrochemical diode going on:     The film is permeable to free electrons but substantially impermeable to ions, provided the temperature of the cell is not high. When the metal underlying the film is at a negative potential, free electrons are available in this electrode and the current flows through the film of the cell. With the polarity reversed, the electrolyte is subjected to the negative potential, but as there are only ions and no free electrons in the electrolyte the current is blocked. —    Normally a capacitor cannot be reverse-biased for long, or large currents will flow and "destroy the center layer of dielectric material via electrochemical reduction":     An electrolytic can withstand a reverse bias for a short period, but will conduct significant current and not act as a very good capacitor. —    However, when you have two back-to-back, the forward-biased capacitor prevents a prolonged DC current from flowing.  :     For circuit positions when reverse voltage excursions are unavoidable,   two similar capacitors in series connected “back to back” ... will create a   non-polar capacitor function ... This works because almost all the circuit voltage   is dropped across the forward biased capacitor, so that the reverse   biased device sees only a negligible voltage.   :     The oxide dielectric construction that is used in tantalum capacitors   has a basic rectified property which blocks current flow in one   direction and at the same time offers a low resistance path in the   opposite direction.


I was thinking about how I would go about calculating the time taken for a swing to swing from one side to the other, assuming that there only exists a gravitational force and discarding all other forms of resistance/friction.  The best way to demonstrate this scenario is with this image:      The black line is the movement of the swing. For now I'm only interested in knowing how long it takes from $(-x, h)$ to the middle $(0, 0)$. This is my attempt to solve this problem.  I know that $\frac{1}{2}mv^{2} = mgh_\text{max} - mgh$, solving for $v$ gives  $$v = \sqrt{2g(h_\text{max} - h)}.$$  Since,  $$\omega = \frac{v}{r} = \frac{\sqrt{2g(h_\text{max} - h)}}{r},$$ in order to make this practical, for the sake of simplicity lets plug in a few numbers. Let the highest point be $2m$, therefore the radius is also $2m$ and the gravitational acceleration is $9.8\,\text{m/s}^2$ this reduces the equation to  $$ w(h) =   \frac{\sqrt{19.6(2 - h)}}{2}. $$ The maximum angular velocity is when $h=0$, $w(0) \approx 3.13\,\text{rad/s}$.  I also thought about this in another way:  $$w(\theta) = \omega_\text{max}\sin(\theta) = 3.13\sin(\theta)$$  Angular velocity is $\omega = \mathrm{d} \theta/\mathrm{d} t$, this is where I'm stuck. I've attempted to solve many differential equations but they don't have a solution. I've also tried to think about $\sin(\theta)$ as $\sin(kt)$ or $\sin(kh)$ where $k$ is just some constant, but nothing seems to work.  Probably the easiest one that comes to mind is  $$ \int_{\pi}^{\frac{3}{2}\pi}\frac{1}{3.13\sin(\theta)}\,\mathrm d\theta = \int_{0}^{t}\,\mathrm dt, $$ this however is undefined.  What have I done wrong? How could I solve for the time taken?

Do you have access to any scientific experiment which gives the period of a pendulum when the angle is $90^\circ$:     says $T$ varies to about $18\%$ up to $90^\circ,$ so for a seconds pendulum the complete period would be roughly $2.36.$    I d'like to know the ratio at $90^\circ$ with a good approximation, and the span it can vary in relation to air friction, if the bob  is not massive.  Also, I'd like to know the max. speed of the bob at $P_0$ and how it compares with the speed of same ball sliding without friction on a circular surface, would it be the same?      What I am trying to understand here is rather complex, I'll try to explain:  If the block is placed on an air-track or other frictionless surface, the block would acquire a certain speed, momentum and KE in the opposite direction, right? same amount of momentum is lost by the bob and we can find speed loss.    Isn't the same amount of speed lost by the bob when it is attached to a pendulum?  Is this an important factor or may be the most important factor (more relevant than air friction or friction at the pivot) for the increase of the period when the angle is greater than $30^\circ$?  I figured out that this factor can account for about one third of the $18\%$ increase, can you give a more accurate value?   What I am suggesting is that this (loss of horizontal momentum, which is made clear when the bob is not attached to a rod but slides on a block) is the most important factor that makes the actual period increase when the starting point deviates on the vertical direction.


I have a total of .  I am hoping to power these as well as a  with a 3.7V lithium rechargeable battery.  I was just wondering how I would go about calculating the resistors needed for these RGB's?   I'm confused because I've seen this example of using 150ohm for Red and 100ohm for Blue and Green.    I guess I'll have to eventually get my head around resistance. There's a great app called Circuit Playground, but I wasn't 100% sure on what the forward voltage and supply voltage (Vf) meant.

I have a simple circuit:    The max rating (current) of the LED is 30mA.  How can I work out what the resistance of the resistor needs to be? By using ohm's law I found it to be \$3V/0.03A = 100 \Omega\$. However using software called , and trial and error I got the minimum possible resistance to be 36Ω. However, if I use a 35Ω resistor, then the LED breaks. Is the software wrong, or (more likely) am I doing something wrong?


I find myself unable to vote on comments or flag them for moderator attention in the .  However, there are some comments that need upvoting (and one that needs flagging, too). Could this be fixed, please?  Others don't seem to have this problem, as there are some upvoted comments on the current nominations. FWIW, I get this error in the JavaScript console:     getQuestionId could not find an id   (occurs with both Firefox 9.0.1 and a virtually untouched but up-to-date Chrome installation)

An  over on Ask Ubuntu. There is currently one nomination with 4 comments (one of which is mine). However, I can't upvote any of the last three - clicking the upvote arrow doesn't do anything.  Popping open the Chrome Inspector reveals nothing - no errors, no network requests, nothing.  I am using Chrome 16.0.912.77 m.


I want to ask reasons for swp file for instance generated by vim increasing its size automatically.  What could possibly be the reasons / factors of size being increased?

As part of the program I wrote, I constantly read and write data from files. I noticed that as part of doing so, I am inadvertently creating swap .swp files.  What do you think is going on? What would cause swap files to appear if you had to reproduce the problem?


There is an element like this in my DOM:
 whatever
   And I get its text as well like this:  var elValue = $(".myClass1").text();   Now I want to avoid selecting that element when it looks like this:
 whatever
   So, the scenario is: get the value of div.myClass1 when that element doesn't have myClass2 class name. How can I do that?

In jQuery I need to do an if statement to see if $this doesn't contain the class '.selected'.  $(".thumbs").hover(function(){  $(this).stop().fadeTo("normal", 1.0); },function(){ $(this).stop().fadeTo("slow", 0.3);  });   Basically when this function is run (on hover) I don't want to perform the fades if the class '.selected' has been appended to the div, this will mean that the image will be at full opacity to signify that it's selected. Searched on Google to no luck even though it's a simple question of how to use an IF statement...


In English Question format is  Question world (Wh- , How) + Auxiliary + subject + Object?  a) How are you feeling now?  b) How you are feeling now?  Which one is correct to ask in above Question?

I always get confused between these two sentences:     Why are you making noise?      Why you are making noise?   Could anyone put light in the differences between the two?


What is $$\int \frac{1}{\sqrt{25-x^2}}$$ WolframAlpha says $\sin^{-1}(\frac{x}{5})$ while I got $\frac{1}{5}\sin^{-1}(\frac{x}{5})$. What is correct? Thanks in advance.

Somewhere in the provided answer:   $$\int \frac{1}{\sqrt{2-x^2}} dx = \sin^{-1}{\frac{x}{\sqrt{2}}}$$  How did they get that? What I have:   $$\frac{1}{\sqrt{2-x^2}} = \frac{1}{\sqrt{2(1-\frac{x^2}{2})}} = \frac{1}{\sqrt{2} \sqrt{1-\frac{x^2}{2}}}$$  $$\frac{1}{\sqrt{2}} \int \frac{1}{\sqrt{1-(\frac{x}{\sqrt{2}})^2}} = \frac{1}{\sqrt{2}} \sin^{-1}{\frac{x}{\sqrt{2}}}$$  So I have an extra $\frac{1}{\sqrt{2}}$ ... I probably had some stupid mistakes?


I was reading in the comments of this question: , and came across the term 'signal-to-unicorn ratio' and I have been unable to find out what it means.  Can anyone explain it?

Catchphrases and concepts that spread from person to person are known as [memes], which, courtesy the Internet, can now explode across the Earth like a highly contagious virus (hence "going viral"). As with their real-life counterparts, some infectious diseases are global (pandemic), while others are endemic to specific regions. Stack Overflow, and now even more predominantly Meta Stack Exchange, have seen more than their fair share of these pathological social constructs spread through the user base. They are now ingrained units of our collective culture as SOpedians (a term which I hate, by the way). Just as travelers' immune systems can be assaulted by new diseases in new places, new users are increasingly likely to be miffed by an ingrained meme and left sitting scratching their heads. I therefore propose that this space be used to document the memes endemic to Stack Exchange's culture. Each meme should be listed in a separate answer and I hope that we as a community will be able to provide greater context to each one. Please actually explain each meme in a way understandable to those not already in the know. Especially considering that a lot of these memes aren't really understandable to newer users who weren't around in the early years of the network, or are based on system features that no longer exist.  On other Stack Exchange sites          [memes]:


Let B be a set, and let * be a binary operation in B. Suppose * satisfies the associative law. Let  $$P=\{b \in B : b * w = w * b \quad\forall\, w \in B\}$$  Prove that P is closed under *.

Here is the problem:  Suppose that $*$ is an associative binary operation on a set $S$. Let  $$H:= \{a \in  S\mid a * x = x * a \mbox{ for all }x\in S\}.$$  In other words, $H$ is consisting of all the elements of $S$ that commute with every element in $S$.  Show that $H$ is closed under $*$.


Is there a way (I know this is very specific but hang with me) to press Ctrl+v+1 to copy the last thing on your clip board and Ctrl+v+2 for the thing after that and so on and so forth? I know that there are widgets and thing you can get, but I think that this would be way easier.

I am looking for a clipboard manager, but I don't want one that just keeps a list so I can select an item to bring it to the front of the clipboard, nah, that's too easy.  What I am looking for is a clipboard manager where I can assign say Ctrl+Shift+1 to paste the first item in the clipboard, Ctrl+Shift+2 to paste the second item in the clipboard ... Ctrl+Shift+9 to paste the ninth item in the clipboard Ctrl+Shift+0 to paste the tenth item in the clipboard    why? As we web developer I am often pasting alternating lines of code (remember, not all browsers support CSS3!),
...

...

...

...
   So, the ability to just sit there doing Ctrl+Shift+1 Enter    Ctrl+Shift+2 Enter    Would be a huge help,  I am using 12.10 with gnome-shell 3.6.2.  I have looked into gPaste and such, but none seem to have this feature.


I have the Samsung Galaxy S4 Mini, if i use Ubuntu on my phone, will I lose features such as SBeam? and will it be compatible with US Cellular Network?

With the announcement of the Ubuntu Phone OS I'd like to know what phone (and tablet) models are supported at this time.  Note from foss & Oli: We are making this the master question for all future "Will this work on <insert random tablet/phone/device here>?!" questions


I have filled my disk but can see games in /usr that I could delete but can't see how to do it. I am not a computer buff and have no idea what a terminal is.

Seeing there are various ways to install on Ubuntu. What are the various ways to uninstall items?  Which ways always work? How can I be sure something was uninstalled?


I am new to visual design and have already read dozens of articles about color, typography and other related things. But I can't understand how to use the elements and principles to create a professional and amazing looking layout. As I can't find anything useful which throws a light behind that layout. So, can you give some insight to it? It will be of huge help.

Thanks to the internet, graphic design and programming are becoming increasingly overlapping fields.   As a programmer, I constantly find myself needing basic knowledge of Graphic Design, but have trouble locating thorough yet concise graphic design learning resources, and instead usually find bits and pieces of knowledge applicable to the task at hand.  Can you guys offer some tips or recommend some good books, tutorials, blogs, and websites which provide a beginner level overview of web design that have been, in your experience, effective and high quality learning materials. I'm not looking for tips on how to use image editing tools, but assuming a basic grasp of those, which resources and advice will best help a new designer create professional looking designs?


(Windows 10.1 and QGIS 2.18)  I am trying to create an action for a Shapefile layer that will display an image when any of its three polygons are clicked.  I have added an "image" field to the layer's attribute table, and changed it to "File Name" type, so that each of the layer's polygons has an image associated with it.  I then went to layer properties > actions and created the action as shown in the screenshot below.    But when I tried to click on one of the layer's polygons, I got the following error:  "Unable to run command open C:/Users/******/Downloads/QGIS-Training-Data-QGIS-Training-Data-v1.0/training_manual_data/school_property_photos/rugby_field.jpg"  I tried to find what I had done wrong, but as far as I could see, I had done everything right. I tried to research but found nothing helpful. I tried to restart both QGIS and my PC but I still got the same error.

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


Currently I have Ubuntu installed on a 120gb SSD, however I also have 3 more hard drives installed in the computer, 2 x 640gb in a RAID array and a 60gb SSD   What I am trying to achieve is to use the 640gb drive to store all my documents etc, the 120gb SSD to only Ubuntu and programs and then the final 60gb SSD to back up the most important documents from the 640gb drives, this must be an incremental back up system and not replace the file each time  How can I achieve this ?

I am going to put an additional (non-USB) hard drive in my system. I already have Ubuntu on my other hard drive so I do not want to install Ubuntu on the additional drive but only use it for storage. How do I add the additional hard drive to my Ubuntu system, e.g. make Ubuntu recognize it and mount it properly?


We are debating the use of Whoever vs Whomever in this sentence "Thanks to whoever fixed this".  What is the correct form? - Thanks to whoever fixed this - Thanks to whomever fixed this!  Any explanation will be highly appreciated.

On the subject of "whoever" and "whomever", I was reading this but I am still confused:   What is the correct use of whoever/whomever in the following sentence?     I like your copy, congratulations, whoever is writing it.   Whoever? Whomever?   Is there a difference between US and UK English?


in my map i try to show hight quality markers, so i use xml markers from an svg files instead of using low png pictures, so to do that i convert the xml to bitmap with:  public BitmapDescriptor vectorToBitmap(Context context, @DrawableRes int id)  {     Drawable vectorDrawable = ContextCompat.getDrawable(context, id);     int h = Objects.requireNonNull(vectorDrawable).getIntrinsicHeight();     int w = Objects.requireNonNull(vectorDrawable).getIntrinsicWidth();     vectorDrawable.setBounds(0, 0, w, h);     Bitmap bm = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);     Canvas canvas = new Canvas(bm);     vectorDrawable.draw(canvas);     BitmapDescriptor bitmapDescriptor = BitmapDescriptorFactory.fromBitmap(bm);     return bitmapDescriptor; }   then i call this methode by:  BitmapDescriptor marker = vectorToBitmap(getActivity(),R.drawable.pin_work);   everything work fine in many devices, but sometimes i get this error  Context.getDrawable(int) on a null object reference   how can i fix this specially with LG smartphones? thank you

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?


Why the compactness of a metric/normed space and of a topology is so important as property ?  I mean I understand the importance of completeness density and separability but I don’t see the point of the importance of compactness . Thanks

I've read many times that 'compactness' is such an extremely important and useful concept, though it's still not very apparent why. The only theorems I've seen concerning it are the Heine-Borel theorem, and a proof continuous functions on R from closed subintervals of R are bounded. It seems like such a strange thing to define; why would the fact every open cover admits a finite refinement be so useful? Especially as stating "for every" open cover makes compactness a concept that must be very difficult thing to prove in general - what makes it worth the effort?  If it helps answering, I am about to enter my third year of my undergraduate degree, and came to wonder this upon preliminary reading of introductory topology, where I first found the definition of compactness.


I have the following problem. I have several points on the plain, and there is another point somewhere in the middle of them. The goal is to find angular distance between any two points.  My only thought so far is to draw a line between a central point and all the lines from the central point to all the others and see where these lines intersect the circle. If we shift the coordinates to make central point (0,0), then it becomes  x² + y² = 1 y = m*x  (m is trivial to calculate here)  x² + (m*x)² = 1  (1+m)(x²) = 1  x = ±sqrt(1/(1+m))  plus/minus is trivially resolved by seeing where the original point was in relation to the centre.  y = m*x  (Of course if the points are in vertical alignment m is undeterminant, but that is trivially resolved by setting x=0 and y to either 1 or -1).  Then i can easily through pythagorean distance find the distance of these points on the circle. But something tells me that there must be a much easier way to turn all these into a single value as projections on a circle.

Given the following image:   $\hskip{1.5 in}$   Supposing $A(100, 300)$ and $B(300, 100)$, how can I find the angle $\alpha$ between A and B?  On a side note, what's the main difference between a point and a vector? translating a point to a vector is as simple as Point = Vector? Sometimes I find articles where the terms are interchangable


I've been brought up believing that most of the words that have suffix with '-ize' or '-ized' is the American English form and the British English forms use (most of the time) '-ise' or '-ised' as the equivalent.   Two questions:  1) What is the rule, if any, around exception cases, i.e. choice of one or the other in a single form (dialect?) of English?  2) I have read recently, on Wikipedia admittedly, that the etymology of these terms is such that the correct form anyway, for all English from Greek roots, is '-ized' using the 'z'. This contradicts what I see, and what I've been brought up to know. But is that correct - it was from this site:    and the Wikipedia page.  I am not saying it is wrong, but I wanted to verify if this is the case...as I say, it runs contrary to what I know, but came across it by chance and it is a  very difficult habit to get out of. I don't want to do it (as a British person, using '-ise' all the time) to the American English version, when actually it would be wrong.  On a more pragmatic matter, I wonder if doing this is a bad idea anyway in the UK, since most people are told the 's' version is correct.  Finally, etymologically, what is the reason for this shift across, whatever the reason is? And is it something that is 'wrong' or more 'the development of language over time'.   I don't understand why America would revert to 'z' after the development of English in Britain towards 's', given that Greek is the origin. I understood British people discovered America and brought British English over there. Unless, and probably quite likely, I haven't got a clue re the history between the two nations (and this is not meant to offend, I just have a confused understanding - sorry if it does).

What is with words that have forms that end both in -zation and -sation, such as localization and localisation?  Many spell checkers recommend -zation.


Prove by induction: $A(n) = 2^n \lt\ n!$   $A(n+1) = 2^{n+1} \lt\ (n+1)!$  The expression below is true for $n = 5$.  $2^n \lt\ \frac{n!}{2}$  Then, we have:  $2^n \lt\ \frac{n!}{2} \lt\ n! \lt\ (n+1)!$  Which implies that:  $2^{n+1}  \lt\ (n+1)!$          for every $n \ge\ 5$  Is this proof correct?  Update: the case is true for $n = 4$. It's true for $n = 5$, too. I started the induction proof with $n = 5$.  Let be more clear:  $A(n) = 2^n \lt\ n!$ is true for $n = 5$.  For $n= 5$, the expression $2^n \lt\ \frac{n!}{2}$ is true too.  From the expression above, we can deduce: $$2^n \lt\ \frac{n!}{2} \lt\ n! \lt\ (n+1)!$$  $$2^n * 2  \lt\ n! \lt\ (n+1)!$$ Hence: $$2^{n+1} \lt\ (n+1)!$$  I would like to know if there is something wrong with this proof. Remember, I assumed the expression is true for $n=5$, not $n=4$ (which is true too).  Update 2: I think is neccessary to prove the expression below by induction first:  "For $n= 5$, the expression $2^n \lt\ \frac{n!}{2}$ is true too."  We don't know if it's true for  $ n\gt\ 5$

Suppose that when $n=k$  $(k\geq4)$, we have that $k!>2^k$.  Now, we have to prove that $(k+1)!\geq2^{k+1}$ when $n=(k+1)$ $(k\geq4)$.  $$(k+1)! = (k+1)k! > (k+1)2^k  \text{ (since }k!>2^k)$$  That implies $(k+1)!>2^k2$, since $(k+1)>2$ because of $k$ is greater than or equal to 4.  Therefore $(k+1)!>2^{k+1}$  Finally  we may conclude that $n!>2^n$ for all integers $n\geq4$    Solved, thank you!


I did a lab in class and the data I got might be a bit skewed (this is homework). When I graphed the speed of sound (m/s; y-axis) vs. air temp (degrees Celsius; x-axis), my graph resembled that of the graph of $y=x^3$ where it goes from concave down to concave up. Does my data contain errors or is this actually the way the graph was supposed to turn out?  Experiment: We took a Pasco Resonance tube and heated it up with a hair dryer to about 38 degrees Celsius. Then we placed a microphone near the open end (other side was closed) and used a dog clicker to make a sound right next to the microphone. The microphone recorded the sound as it went into the tube, bounced back, and came back to the microphone. The room was a standard college Physics classroom (room temp, regular pressure, humidity, etc...)

I was reading a textbook. I found that it was mentioned the speed of sound increases with increase in temperature. But sound is a mechanical wave, and it travels faster when molecules are closer.   But an increase in temperature will draw molecules away from each other, and then accordingly the speed of sound should be slower. How is it possible that the speed of sound increases if temperature increases? What is the relation of speed of sound and temperature?


I have a 4TB external Time Machine disk. There are three internal volumes totaling 3.3TB that have been actively backed up to that external drive for a few weeks.   I was troubleshooting something and moving a bunch of files around, so I briefly turned off Time Machine. When I turned it back on, it started backing up... but then it stopped later, saying "there is only 707MB available on the drive, but 3.3GB is required."   It's almost as if it refuses to overwrite the old backups. It wants to start an entirely new backup or something. How can I make it pick up where it left off without having to delete that entire backup and start anew? I don't like deleting backups!

Time Machine stopped this morning, stating it has too little disk space left. It wants to back up 200 gigs, but my local hard drive has 240 gig used and 150 gig are excluded in the Time Machine options, so this leaves 90 gigs of data at most that can be backed up, and I am pretty sure only very few files have changed (no big update or similar). So I would estimate a backup of, at most, 1 gig.  How can this happen? Any idea?


It is very rare for me to need a parenthesis without \left and \right. Is there a way to redefine the parenthesis () to being treated as if I wrote \left( and \right).  Of course, I would need another command \noleft( and \noright) or something similar to get back the original meaning.  I know I can run a Perl script before every latex compilation to achieve this, but I am looking for a LaTeX solution.

Is it possible to automatically "add" \left and \right commands in front of all brackets? The source code should be left intact, but LaTeX should interpret every pair of brackets as if they were preceded by such commands. This is because adding \left and \right commands is time consuming and makes source code longer and less readable. I considered defining new commands such as \lb and \rb for \left( and \right), but it doesn't seem very elegant to me: what if I also want to add square brackets for example?  Any ideas? Thanks.


Why would a photon striking an electron "make both recoil" as I read in an answer to another question. If the photon is massless, how can it make an electron change momentum?

As an explanation of why a large gravitational field (such as a black hole) can bend light, I have heard that light has momentum. This is given as a solution to the problem of only massive objects being affected by gravity. However, momentum is the product of mass and velocity, so, by this definition, massless photons cannot have momentum.  How can photons have momentum?   How is this momentum defined (equations)?


So we know that Voldemort's appearance became more snakelike as he made more horcruxes and dove deeper into dark magic, but why did he become more like a snake and not more like any other animal or creature?    Relate:

The nose of Tom Riddle (as a student) was fine, as I have seen in the movies. But, Voldemort's nose doesn't look like a normal human nose. What really happened?


I wrote a method(verifyUser) that checks if the user already exists in the database or not , but i get this error:     ( java.lang.NullPointerException: Attempt to invoke virtual method   'android.database.sqlite.SQLiteDatabase   com.example.testapp.DatatBaseHelper.getReadableDatabase()' on a null   object reference)   That's my ContentProvider Class:  public class TestProvider extends ContentProvider {      private DatatBaseHelper helper;     private SQLiteDatabase db;     public static final String LOG_TAG = TestProvider.class.getSimpleName();     private static final int test=1;     private static final int test_id=2;      private static final UriMatcher urim=new UriMatcher(UriMatcher.NO_MATCH);      static{         urim.addURI(Test.test.authority,Test.test.TABLE_NAME,test);         urim.addURI(Test.test.authority,Test.test.TABLE_NAME+"/#",test_id);     }     @Override     public boolean onCreate() {         helper=new DatatBaseHelper(getContext());         return false;     }      @Nullable     @Override     public Cursor query(@NonNull Uri uri, @Nullable String[] projection, @Nullable String selection, @Nullable String[] selectionArgs, @Nullable String sortOrder) {         int match=urim.match(uri);        db=helper.getReadableDatabase();          Cursor c;          switch(match){             case test:                 c=db.query(Test.test.TABLE_NAME,projection,selection,selectionArgs,null,null,sortOrder);                 break;              case test_id:                 selection= Test.test.ID+"=?";                 selectionArgs=new String[]{String.valueOf(ContentUris.parseId(uri))};                 c=db.query(Test.test.TABLE_NAME,projection,selection,selectionArgs,null,null,sortOrder);                  break;             default:                 throw new IllegalStateException("Cannot query form: " + uri);         }          return null;     }      @Nullable     @Override     public String getType(@NonNull Uri uri) {         return null;     }      @Nullable     @Override     public Uri insert(@NonNull Uri uri, @Nullable ContentValues values) {           db=helper.getWritableDatabase();          String email=values.getAsString(Test.test.EMAIL);              int match=urim.match(uri);          switch (match){             case test:           int   id=(int)(db.insert(Test.test.TABLE_NAME,null,values));                     uri= ContentUris.withAppendedId(uri, id);         }           return uri;     }      @Override     public int delete(@NonNull Uri uri, @Nullable String selection, @Nullable String[] selectionArgs) {         return 0;     }      @Override     public int update(@NonNull Uri uri, @Nullable ContentValues values, @Nullable String selection, @Nullable String[] selectionArgs) {         return 0;     }       public boolean verifyUser(String email){          SQLiteDatabase db=helper.getReadableDatabase();          Cursor c;          String pro[]={Test.test.ID};         String select=Test.test.EMAIL+"=?";         String args[]={email};          c=db.query(Test.test.TABLE_NAME,pro,select,args,null,null,null);          if(c.getCount()>0){             return true;         }          return false;     }   That's my datatbase class:  public class DatatBaseHelper extends SQLiteOpenHelper {      public static final  String DB_NAME="dress.db";     public static final int DB_VERSION=1;      public DatatBaseHelper(Context c){         super(c,DB_NAME,null,DB_VERSION);     }       private  String TABLE_CREATE= "CREATE TABLE " + test.TABLE_NAME+ "( "+   test. ID+" INTEGER PRIMARY KEY AUTOINCREMENT,"+ test.NAME+" TEXT NOT NULL,"+    test. EMAIL+" TEXT NOT NULL,"+ test.PASSWORD+ " TEXT NOT NULL);";            @Override         public void onCreate(SQLiteDatabase db) {     db.execSQL(TABLE_CREATE);         }          @Override         public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {          }           }

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?


The , and any other public access point. I'd like to make sure my apple device always uses a VPN when using Wi-Fi. That way even if an attacker were to see my data, they would only see an encrypted jumble of bits. Note that this hack can also be applied to HTTPS connections. How do I ensure that OSX automatically uses a VPN when using Wi-Fi?

I use the built-in VPN on Mac OS X 10.7.3. It's IPSec, FWIW. From time to time, it disconnects (probably an issue with my corporate server). Is there a way to get it to automatically reconnect? Sometimes I don't notice for a while, which is kinda annoying.


In a work setting, which of the following is more acceptable to say in email messages?        Thanks for your help   Thanks for your assistance

Intro  The words aid, assist, help, and facilitate are all closely related. What do you believe the differences among them might be? My best attempt to make the differences explicit follows.  My Attempt   Aid, in modern English, is more appropriate for non-human help Assist, would be help for something that someone could do themselves but because of the assistance is able to do that thing more efficiently, profitably, effectively, etc. Help, is the most generic term and can refer to any sort of support. Facilitate, is help that is necessary for a thing to be done or that improves the utility of that thing to such a degree that it would not be worth doing but for the facilitation.  In as much as facilitates is a word that refers to help that is necessary for a thing to be done, the word differs from 'enabling' in that the facilitating thing is not the only thing that could facilitate the thing in question. Whereas, the thing in question could not happen without the things that enable it to happen. E.g. In the 17th century, lumberjacks enabled logging companies to fell trees and convert them to logs, while rivers facilitated the transport of the logs to their buyers. Without the lumberjacks, the trees could not have been felled, but its conceivable they could have been transported without the river, albeit much less efficiently.    Question  What do you think are the differences among aid, assist, help, and facilitate?


I just upgraded to Ubuntu 17.04 and I'm having some problems that I didn't have before, so I would want to know if it's possible to restore Ubuntu into 16.10 without losing files and apps.

I just installed a new version of Ubuntu and I want to roll it back to the previous version.  How can I do that? Is that even possible?


Scenario 1 A series of unfortunate events has led Makoto "Edamame" Edamura to adopt the life of crime—pickpocketing and scamming others for a living. However, after swindling a seemingly clueless tourist, Makoto discovers that he was the one tricked and, to make matters worse, the police are now after him. Scenario 2 A series of unfortunate events has led Makoto "Edamame" Edamura to adopt the life of crime—pickpocketing and scamming others for a living. However, after swindling a seemingly clueless tourist, Makoto discovers that he was the one tricked , and to make matters worse, the police are now after him. I beleive it is Scenario 2 because "and" is always a coordinating conjunction.

This is a bit of a strange question because I know that there should never ever be a comma after 'and.' But what if there's a parenthetical statement/clause-thing right after it? Let me demonstrate.      She spread her arms, tilted her head back, and, closing her eyes, let the sun warm her face.    Should it be:      She spread her arms, tilted her head back, and closing her eyes, let the sun warm her face.    I feel like the ,and, looks really bulky, but I also feel it's necessary to separate the statement between the commas. Help?


I'm running Windows 8.1. I'm trying to run  (and several other similar programs) but they all fail to open because they don't recognize my version of DirectX.  I get the following error when I try to run 3D_Model_Viewer:     DirectX 9.0 installed (589824). Requires DirecX 9.0c (December 2005) or later.   and this error when I run AssimpViewer:     Failed to initialize Direct3D 9 (2)   I've run dxdiag.exe and confirmed that, in fact, DirectX 11 is the installed version, not 9.0 like the programs are saying.  What might be happening here? Can I get these programs to run under DirectX 11?

I've just installed a new game on my Windows 7 RTM machine. The game is asking me to install DirectX 9.0(c). I said 'NO' because my machine has DirectX 11 (confirmed with dxdiag). When I run the game, an error occurs informing me that d3dx9_39.dll is missing.  Is Windows 7 DirectX backwards-compatible?