Let's take two inductors: one has its peak current (say, Io) flowing through itself and the other has no current through itself. Now if these two inductors are joined in series in a closed circuit, the first inductor will try to keep the current at Io while the second one will try to keep it at zero.  To solve this, I created an analogy between inductor and mass. When two masses with different velocities collide, the inertia of each mass tries to keep its velocity unchanged. Thereafter we use principle of conservation of linear momentum and value of coefficient of restitution to find the final velocities of the two masses. But here, in case of inductors, I do not know which physical quantity is analogous to linear momentum and hence I can not continue any further.  My Physics teacher told me that we need to equate the total magnetic flux in the inductors before and after joining them but he did not give any reason behind doing so.  So my questions are:   Why is the total magnetic flux, before and after joining the inductors, equal? Since I tried creating analogy between collision of two masses and joining two inductors, will there be energy loss in the latter case? And is there any quantity analogous to the coefficient of restitution on which the magnitude of loss of energy depends?   PS:   By loss of energy, I mean reduction in energy stored in the inductors. The actual question that I was solving is this:  I do not need a solution of this question. This question is just for reference.   Edit: There are two other questions similar to my question (I tried searching for related questions before asking my own question but could not find one):          As for the first one, I have not been yet taught about terms such as Inverse Laplace transformation and parasitic interwinding capacitance. Hence I can't grasp what is being discussed there.   The second question has a greater similarity to my question (as I have also asked about reason behind conservation of magnetic flux) but there is only one answer to that question which does not tell why flux is conserved. Hence my question doesn't have an answer there too.   Moreover, I have also asked about analogy between mechanical system and electrical system which neither of the above two questions have talked about. And I have already got an answer here which has solved the question using that analogy.

My teacher said that after switch is shifted (after very long time), $\phi_i = \phi_f$ $\implies i_oL  = i3L \implies i = \dfrac{i_o}{3} $ where $i_o$ is $\dfrac{\varepsilon}{R}$  So the initial current in the circuit after switch is shifted is $\dfrac{i_o}{3}$  But, I really didn't understand why the flux should be conserved in this case i.e. why  $\phi_i = \phi_f$. I would like to know about this concept and the reasons involved.   $\phi_i$ and $\phi_f$ are the total flux in both inductors immediately before and immediately after the switch is shifted?


I thought '30-day' and '30 days' are right. But, when I typed 30 days plank challenge, all subject was written as 30 day. Can I use 30 day instead of 30 days? It's tricky! Please help me.

Recently, while skimming through an article I came across a sentence which is as follows.  The five minute walk will connect you with life.  My rationale says it should have been "five minutes" and not "five minute". Kindly advise where am I going wrong?


In JDBC getConnection is a static method which returns object of Connection Interface? The getConnection method is defined in DriverManager class as a blank body as follows:  @CallerSensitive public static Connection getConnection(String url, String user, String password) throws SQLException {     // compiled code }   I am not getting how it is working? What happens when we return an object to interface? How Connection interface using this object?  How it is using this object for statment in the below line:  Statement s= c.createStatement();   Again how things are working internally in above line?  I want a deeper explanation basically how interface and classes work together to things like this. I know what an interface is, how it is implemented by the classes. It is used to support multiple inheritance and to provide security. But how are these concepts related in this example?

I have seen this mentioned a few times and I am not clear on what it means. When and why would you do this?   I know what interfaces do, but the fact I am not clear on this makes me think I am missing out on using them correctly.   Is it just so if you were to do:  IInterface classRef = new ObjectWhatever()   You could use any class that implements IInterface? When would you need to do that? The only thing I can think of is if you have a method and you are unsure of what object will be passed except for it implementing IInterface. I cannot think how often you would need to do that.   Also, how could you write a method that takes in an object that implements an interface? Is that possible?


I want to check whether the authorized user/not in SERVLET. Login.html  <!DOCTYPE html>   <meta charset="ISO-8859-1"> <title>Login page</title>

 <form action="Check.java" > USERNAME:<input type="text" value="name">

 PASSWORD:<input type="password" value="password">

     &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp<button style="color: #ff3399">SUBMIT</button> </form>     Check.java  import java.io.*;   import javax.servlet.*;   import javax.servlet.http.*;     public class Check extends HttpServlet {    public void doPost(HttpServletRequest request, HttpServletResponse response)           throws ServletException, IOException {        response.setContentType("text/html");       PrintWriter out = response.getWriter();        String n=request.getParameter("name");       String p=request.getParameter("password");        if(p.equals("servlet")){           RequestDispatcher rd=request.getRequestDispatcher("servlet2");           rd.forward(request, response);       }       else{           out.print("Sorry UserName or Password Error!");           RequestDispatcher rd=request.getRequestDispatcher("/Login.html");           rd.include(request, response);       }         }   }     WelcomeServlet.java  import java.io.*;   import javax.servlet.*;   import javax.servlet.http.*;    public class WelcomeServlet extends HttpServlet {        public void doPost(HttpServletRequest request, HttpServletResponse response)           throws ServletException, IOException {        response.setContentType("text/html");       PrintWriter out = response.getWriter();        String n=request.getParameter("name");       out.print("Welcome "+n);       }    }   Web.xml  <?xml version="1.0" encoding="UTF-8"?> <web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0">  <display-name>REALPROJECT</display-name>  <servlet>       <servlet-name>Check</servlet-name>       <servlet-class>Check</servlet-class>     </servlet>     <servlet>       <servlet-name>WelcomeServlet</servlet-name>       <servlet-class>WelcomeServlet</servlet-class>     </servlet>       <servlet-mapping>       <servlet-name>Check</servlet-name>       <url-pattern>/servlet1</url-pattern>     </servlet-mapping>     <servlet-mapping>       <servlet-name>WelcomeServlet</servlet-name>       <url-pattern>/servlet2</url-pattern>     </servlet-mapping>      <welcome-file-list>      <welcome-file>Login.html</welcome-file>     </welcome-file-list>   </web-app>    MY ERROR ARE:  HTTP Status 500 -   type Exception report  message   description The server encountered an internal error that prevented it from fulfilling this request.  exception   java.lang.NullPointerException     Check.doPost(Check.java:17)     javax.servlet.http.HttpServlet.service(HttpServlet.java:650)     javax.servlet.http.HttpServlet.service(HttpServlet.java:731)     org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)   note The full stack trace of the root cause is available in the Apache Tomcat/7.0.70 logs.

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 code below is supposed to loop through several webpages, each one determined by the value of i, and the console.log(url); line should list every URL from those webpages. Instead, the code only lists the URLs when "i" is on its final iteration (i=0) and thus it only retrieves URL's from the final webpage it requests (http://fakeURL.com/0) - the number at the end of the URL represents "i".  How can I make the console list URL's from all iterations (when i = 45, 30, 15, and 0) instead of only the final iteration (when i = 0)?   for(i = 45; i >= 0; i -= 15)  {     var xhrs = new XMLHttpRequest();                                         xhrs.open("get", 'http://fakeURL.com/' + i, true);     xhrs.onload = function()     {                    var doc2 = xhrs.response;             $(doc2).find('a').each(function()             {                     var url = $(this).attr('href');                 console.log(url);              });      }     xhrs.responseType = 'document';     xhrs.send(); }   EDIT: Below is my actual source code (unsimplified) after doing what Teemu suggested. Now 'i' is always -15 for every request the for-loop makes with the XMLHttpRequest:  var url; var title; function ajaxCall (x, y) {     setTimeout(function ()     {         var xhrs = new XMLHttpRequest();                                             xhrs.open("get", 'http://fakeURL.com/' + i, true);         xhrs.onload = function()         {                    var doc2 = xhrs.response;             $(doc2).find('a').each(function()             {                                                            var x = $(this).attr('href');                 var y = $(this).text();                  console.log(x);                 console.log(y);             });          }         xhrs.responseType = 'document';         xhrs.send();     }, Math.random() * 1000 + 1000); }  for(i = 45; i >= 0; i -= 15)  {        ajaxCall(url, title); }   Any idea why 'i' is always -15?  EDIT 2: I didn't follow Teemu's solution correctly in the code above. Here is the fixed version for future reference:  var i; function ajaxCall (x) {         var xhrs = new XMLHttpRequest();                                             xhrs.open("get", 'http://fakeURL.com/' + x, true);         xhrs.onload = function()         {                    var doc2 = xhrs.response;             $(doc2).find('a').each(function()             {                                                            var url = $(this).attr('href');                 var title = $(this).text();                  console.log(url);                 console.log(title);             });          }         xhrs.responseType = 'document';         xhrs.send(); }  for(i = 45; i >= 0; i -= 15)  {        ajaxCall(i); }

How would you explain JavaScript closures to someone with a knowledge of the concepts they consist of (for example functions, variables and the like), but does not understand closures themselves?  I have seen  given on Wikipedia, but unfortunately it did not help.


I have a CEL-TEC F5A headset. The spec says:      Bluetooth 4.0, profiles: Headset, Hands free, A2DP, AVRCP/HSP/HFP   It plays nicely with High Fidelity Playback (A2DP sink) profile.  When I want to switch audio input to the headset's microphone, the output profile automatically changes to Headset Head Unit (HFS/HFP) and the quality is terrible - like 8bit sound or something. When I switch it back to A2DP, the input is back to desktop mic.  I've read few of other questions and seems A2DP is expected not to support input, right? But the HFP part in HFS/HFP is High Fidelity Playback I guess? That sounds like it could work as a headset and still not sound like 1950's phone.  How could I simplify switching between the profiles so that it is HFS/HFP when I talk and A2DP when I listen? E.g. as a push-to-talk.  Ubuntu 17.10, no sound customization IIRC, everything latest.   My output:  $ pactl list cards Card #0         Name: alsa_card.pci-0000_00_03.0 ...  Card #4         Name: bluez_card.00_19_5D_25_6F_6C         Driver: module-bluez5-device.c         Owner Module: 30         Properties:                 device.description = "F5A"                 device.string = "00:19:5D:25:6F:6C"                 device.api = "bluez"                 device.class = "sound"                 device.bus = "bluetooth"                 device.form_factor = "headset"                 bluez.path = "/org/bluez/hci0/dev_00_19_5D_25_6F_6C"                 bluez.class = "0x240404"                 bluez.alias = "F5A"                 device.icon_name = "audio-headset-bluetooth"                 device.intended_roles = "phone"         Profiles:                 a2dp_sink: High Fidelity Playback (A2DP Sink) (sinks: 1, sources: 0, priority: 10, available: yes)                 headset_head_unit: Headset Head Unit (HSP/HFP) (sinks: 1, sources: 1, priority: 20, available: yes)                 off: Off (sinks: 0, sources: 0, priority: 0, available: yes)         Active Profile: a2dp_sink         Ports:                 headset-output: Headset (priority: 0, latency offset: 0 usec, available)                         Part of profile(s): a2dp_sink, headset_head_unit                 headset-input: Headset (priority: 0, latency offset: 0 usec)                         Part of profile(s): headset_head_unit   The problem here is not that the microphone does not work, but rather that the audio quality worsens when it is activated.

I'm trying to use my headphones with my Ubuntu 13.10. My headphones are Nokia BH-905i, which can be connected via Bluetooth or green+pink wires.  If I use bluetooth, voice quality is terrible or microphone doesn't work. If I try to choose "Headset" option from In and Out tabs in Sound Settings, they're disabling each together.  In Out tab, I'm using "High sound quality A2DP", because it betters voice quality.  How could I get my microphone working? Sound out works fine.


I would like to animate a jet of smoke as in  (from the movie Interstellar). Here's a short preview:    Note the important elements are:   The smoke is translucent The smoke is very fast at the exhaust The smoke is turbulent and its "radius" increases away from the source, becoming more turbulent The smoke has quite a well defined "contour" - it is not washed out, but ends abruptly in sort of sharp turbulent blades towards the end   I would also like to be able to toggle the jet on and off via a parameter that can be keyframed, simulating the jet firing/shutting off.  So far, I can get a washed out (4 not satisfied) and fairly uniform (3 not satisfied) jet of smoke using pretty much the default Quick Smoke properties together with a particle system flow source. However, I am unable to get the rich turbulent texture of the smoke in the above video. I also do not know how to turn the smoke on/off efficiently such that when it is "off", render time is fast (I don't want to just set the material to nothing, because the physics simulation will then still take up a lot of time).

I would like to simulate a stream of water like the one in the picture, but I don't know how to simulate the fast-moving, white water. Should I use particles to simulate foam or is it much better to concentrate in the material properties? Thanks


How do you turn this off browser suggestions on html input?

How do you disable autocomplete in the major browsers for a specific input (or form field)?


Hello I tried to modify and add mesh to an object that already has smooth shading. I can't figure out how to smooth only the new part of the mesh I just added. If I smooth shade the whole object again I will just add unnecessary vertices to the whole object.   Are there any alternatives to splitting the new part of the object mesh into a separate object and smooth shading as a separate object and reintroducing it to the mesh?

I unwrapped the whole mesh, but one face is always black, I tried CtrlN and ShiftCtrlN but there is no change.  in the 2d editor "View > UV Local View" isn't selected  you can get the blend here :


What do you call the sequences of letters that produce phrases when read letter by letter? Examples include "CU" for "see you", "IC" for "I see" and so on.

XS sounds like excess, B4 sounds like before, XLNC sounds like excellency, etc.  What are these wordplays called?


As shown from figure my thesis title. I want to increase or decrease the size to adjust the title in two or three rows. I have tried by putting \Huge, \Large, \tiny and many more command but no change occurs. please give me any good suggestion? The tex file also sent.  \begin{document}  \title{\vspace{-2in} \textbf{Development of a Pulsed Laser Deposition System and the Growth of Fluoride Thin Film}}  \author{ By\\  \Large \vspace{-0.1in}\textbf{Maisum Ali}\\ \small \vspace{+0.4in}\textbf{(PPHF13E020)}\\ \vspace{-0.4cm}\textsc{A thesis submitted in the partial fulfillment} \\ \vspace{-0.4cm}\textsc{of the requirement for the degree of}\\ \vspace{-0.4cm}\textsc{Master of Philosophy}\\ \vspace{+0.3in}\textsc{in Physics.}\\ Supervised by\\ \vspace{+0.3in}\textbf{Dr. Muhammad Anwar-ul-Haq}\\ \vspace{+0.3in}\includegraphics[scale=0.67]{UoSlogo}\\ \vspace{-0.4cm}\textsc{Department of Physics}\\ \vspace{-0.4cm}\textsc{University of Sargodha}\\ \vspace{-0.4cm}\textsc{Sargodha, Pakistan} } \date{\textbf{2016}}    \maketitle

The standard titlepage is quite simple. I am looking for a very  and need help customizing my title page.  It should match the  classicthesis doctoral thesis template  Below a minimal working example:   \documentclass[12pt,a4paper,footinclude=true,twoside,headinclude=true]{scrbook} \XeTeXinputencoding iso-8859-1 \usepackage[marginparsep=8pt,left=3.5cm,right=3.5cm,top=3cm,bottom=3cm]{geometry}  \usepackage[parts,pdfspacing,dottedtoc]{classicthesis}    \frontmatter  \begin{document}     \pagestyle{scrheadings}        %this is the place to set up my cover sheet.       %*******************************************************      % Abstract     %*******************************************************    %\renewcommand{\abstractname}{Abstract}    \pdfbookmark[1]{Résumé}{Résumé}   \begingroup    \let\clearpage\relax    \let\cleardoublepage\relax    \let\cleardoublepage\relax       \chapter{Résumé}     Résumé de la thèse en français\dots      \vfill      \chapter*{Summary}   Résumé de la thèse en anglais\dots    \endgroup             \vfill     \end{document}


Say have a simple class as follows:  class Test:     some_attributes      def first_method():         pass      def second_method():         pass   Now lets say I have put the list of methods in a list like so: methods=['first_method', 'second_method']  The question that has perplexed me is: How can I call the methods using the list above in a for loop. The scheme I want is like this:  for method in methods:     Test.method   I have tried:  for method in methods:     'Test.{}'.formats(method)   and  for method in methods:     vars()['Test.{}'.formats(method)]   How can I achieve this concept?

What is the best way to go about calling a function given a string with the function's name in a Python program.  For example, let's say that I have a module foo, and I have a string whose content is "bar". What is the best way to call foo.bar()?  I need to get the return value of the function, which is why I don't just use eval. I figured out how to do it by using eval to define a temp function that returns the result of that function call, but I'm hoping that there is a more elegant way to do this.


I am having no luck getting youtube-dl installed on my 20.04 system. Here's what I have tried:  sudo apt-get install youtube-dl RESULT: The command executes OK, but when I try to download anything I get errors. I checked the version: $ youtube-dl --version 2020.03.24 $ which youtube-dl /usr/local/bin/youtube-dl  I assume I got an old version of youtube-dl because Ubuntu's repo is out-of-date?   So, searching for solutions led me to try this:  pip3 install --upgrade youtube-dl This attempt being a . But first - removed the apt-installation using sudo apt-get remove youtube-dl But when I check to verify the version, I remain stuck at the old version! $ youtube-dl --version 2020.03.24  So let's move that out before trying something else: $ pip3 uninstall youtube-dl Found existing installation: youtube-dl 2020.11.26 Uninstalling youtube-dl-2020.11.26:   Would remove:     /home/walker/.local/etc/bash_completion.d/youtube-dl.bash-completion     /home/walker/.local/etc/fish/completions/youtube-dl.fish     /home/walker/.local/lib/python3.8/site-packages/youtube_dl-2020.11.26.dist-info/*     /home/walker/.local/lib/python3.8/site-packages/youtube_dl/*     /home/walker/.local/share/doc/youtube_dl/README.txt     /home/walker/.local/share/man/man1/youtube-dl.1 Proceed (y/n)? y   Successfully uninstalled youtube-dl-2020.11.26  Whoa!? I just un-installed the current version!  sudo snap install youtube-dl Aka , which went as follows: $ sudo snap install youtube-dl youtube-dl 2020.11.17+gitd65d891 from Joe Borg (joeborg) installed $ youtube-dl --version bash: /usr/bin/youtube-dl: No such file or directory $ which youtube-dl /usr/local/bin/youtube-dl    Which leaves me confused and bewildered beyond repair. I have used youtube-dl for over a year now & installed on macOS & Debian systems - with no problems. I know Ubuntu is different, but... this is confusing. How do I fix this?

I use youtube-dl to download videos for watching later offline. Usually, it works fine. However, due to frequent changes on the video sites, it sometimes requires a quick update. It wasn't a problem before on 13.04 but after upgrading to 13.10, I get  # youtube-dl -U It looks like you installed youtube-dl with a package manager, pip, setup.py or a tarball. Please use that to update.   I tried updating it via apt-get but there is no new package. So the app's update mechanism has been disabled and the maintainers aren't keeping up, what is the solution? How do I update it?  And why was it changed at all? It was updating a package manager version just fine in raring.   I'm already running into compatibility problems.   $ youtube-dl "http://vimeo.com/55784152" [vimeo] 55784152: Downloading webpage [vimeo] 55784152: Extracting information ERROR: Unable to extract info section; please report this issue on https://yt-dl.org/bug . Be sure to call youtube-dl with the --verbose flag and include its complete output. Make sure you are using the latest version; type  youtube-dl -U  to update.   QUICK UPDATE:  As requested,  # type youtube-dl youtube-dl is hashed (/usr/bin/youtube-dl)  # apt-cache policy youtube-dl youtube-dl:   Installed: 2013.08.29-1   Candidate: 2013.08.29-1   Version table:  *** 2013.08.29-1 0         500 http://pl.archive.ubuntu.com/ubuntu/ saucy/universe amd64 Packages         100 /var/lib/dpkg/status


There's a user who frequents the same tag as I do on Stack Overflow, and I consistently see him giving either bad advice, or advice that's not relevant to the question or just says "no you're doing it all wrong, do this instead" where the this is not best practice. It's not the worst, but it's far from good.  Unfortunately the tag I frequent doesn't get much voting traffic (and generally has a lot of new users, some of whom don't know the difference between a good answer and this person's answers and some of whom don't vote or mark answered) so I can't just post a competing answer and expect the community to magically solve the issue of the other user's answer quality. Plus I don't always have time to write a better/more-detailed answer, and sometimes I don't have enough confidence in my domain knowledge to propose an answer (though I know that this other user is at least somewhat wrong/bad).  My question is - what do I do in this situation? Once or twice I've voted this user's answers down when they've been particularly bad. Earlier today I commented on one of his answers saying that it didn't really answer the question asked (as well as posting my own answer giving a really detailed discussion of what can be done) and got a snarky "well I could give all the details like you did but then he's not learning" response back (I admit maybe I went over the top and gave an almost copy-and-pastable answer, but this guy's answer was completely rubbish and did not answer the question).  There doesn't seem to be a way to flag a user for an in-depth moderator overview, and I'd rather not waste the smallish rep I have (600ish) downvoting 90% of this person's answers.  I'm really new to SO myself (only because particularly active a couple of weeks ago) so I don't know the conventions or whether I'm caring too much. Any advice would be appreciated. I can give concrete details on request (examples and explanations of the user's bad answers, the snarky comment to me (which I flagged as non-constructive, by the way)) but thought I'd ask in the abstract first.  FYI the user is not a troll, but I feel that they think they know more than they do. They're probably trying to be helpful like most of us here, but the majority of their answers are just plain bad/confusing. They probably don't even realise it. However, it appears that they take criticism badly, and I certainly don't want to go around commenting on all the answer I find bad explaining why, especially when I have lower rep than they do.  Slightly related:

I have been regularly coming across a new user recently; let's call "him" Bob?  Bob is absolutely convinced of his correctness on every topic. So convinced that he answers questions using completely invalid syntax because he knows how to solve a similar problem.  Commenting on the answer and pointing out the flaws sometimes results in a constructive response but more regularly not. Any downvotes (I haven't) normally results in a semi-unconstructive comment about '"experts"' or a small lecture on how people shouldn't downvote answers where someone was trying to help and that people should learn some manners.  So far, this has degenerated once, with a different user, and the community expressed themselves by downvoting more than usual.  I obviously don't know the particulars of the banning algorithm but it seems unlikely that Bob will be answer banned. He currently has 73 answers, 6 with a positive score and 6 with a negative. Five have been accepted, one an answer with positive score, which means only 10 of Bob's answers have been considered "helpful". People seem to be more wary of downvoting answers than questions, so Bob has escaped the worst. A significant minority of answers I would normally downvote as they're just wrong, but I can't and won't do that.  I am becoming extremely wary of commenting that Bob's answers are incorrect as I can't be bothered to have an argument over it. When combined with the volume of incorrect answers this is detrimental to the site. If wrong answers keep getting posted that people are unwilling to downvote or comment that they are incorrect then they stay around. I can't flag the answers as  they're just technical inaccuracies.  Is there anything that an ordinary user can/should do in this situation? Bob is obviously acting in good faith and I don't think that he should be punished for doing so.  I am deliberately not posting Bob's identity as I'd rather Bob wasn't picked on.


Take the following ~/test.sh script as an example:  #!/bin/bash  sudo -u ${SUDO_USER} cp ~/.profile ~/.profile.bak  cat <<EOF >>/home/${SUDO_USER}/.profile export HELLO="Hello StackExchange" EOF  sudo -u ${SUDO_USER} source ~/.profile  sudo -u ${SUDO_USER} cp ~/.profile.bak ~/.profile sudo -u ${SUDO_USER} rm ~/.profile.bak   I then run it like this:  User@MACHINE:~$ sudo bash test.sh User@MACHINE:~$ echo $HELLO   I was expecting Hello StackExchange to be printed on the terminal, but a blank line was printed instead.  If I understand what's happening correctly, the source ~/.profile command is not being applied to my current shell. So how I can source changes done to files like .profile to the current running shell from a script without having to logout and log back in? Is this even possible?  P.S: Assume test.sh is always ran with sudo and never without it. The script above is just an example, but I use sudo -u ${SUDO_USER} command when I need certain commands to run as the user who invoked the script and not as root.

On Slackware, using sbopkg permits one to build a package from source. Repos is not big as Debian, but it's nice.  Some software can use environment variables, for example on the VICE c64 emulator, if the variable FFMPEG is set to yes, it will enable ffmpeg recording the emulator.  I tried to use  $ export FFMPEG=yes; sudo sbopkg -B -i vice   but ffmpeg is disabled.  Instead I had to use  $ su - $ export FFMPEG=yes $ sbopkg -B -i vice   which works.  How to use environment variables with sudo?


I've noticed that my C++ programs compile fine whether I use ::size_t or std::size_t.  I can use them interchangeably with no issues at all, so it seems like one of them is a typedef for the other.  As an example, consider the following code which uses the global size_t (this is the whole file, no usings and other stuff):  #include <iostream> int main() {     ::size_t x = 100;     std::cout << x << std::endl; }   The next code uses the size_t in std:  #include <iostream> int main() {     std::size_t x = 100;     std::cout << x << std::endl; }   Both compile fine and outputs 100 as expected.  I was under the impression that everything in the standard library is put in namespace std, but clearly this isn't the case.  Why is this so?  Note: the same goes for ptrdiff_t, intN_t and uintN_t too.

In some code I've inherited, I see frequent use of size_t with the std namespace qualifier.  For example:  std::size_t n = sizeof( long );   It compiles and runs fine, of course.  But it seems like bad practice to me (perhaps carried over from C?).  Isn't it true that size_t is built into C++ and therefore in the global namespace?  Is a header file include needed to use size_t in C++?  Another way to ask this question is, would the following program (with no includes) be expected to compile on all C++ compilers?  size_t foo() {     return sizeof( long ); }


Hey anyone know about a function in C# that converts numerical value in to words Like If I give Input: 53904 Then the output should be: FIFTY THREE THOUSAND NINE HUNDRED FOUR ONLY

Is there a library or a class/function that I can use to convert an integer to it's verbal representation?  Example input:     4,567,788`   Example output:     Four million, Five hundred sixty-seven thousand, seven hundred eighty-eight


While using minted I can change font size () on each individual place using the fontsize=\footnotesize:  \begin{listing} \inputminted[fontsize=\footnotesize]{javascript}{file.js} \end{listing}   Can I set this once for the entire document?

I'm using minted package. My problem is \usepackage[nodisplayskipstretch]{setspace} \setstretch{1.5} line. I do need this line stretch, but I don't want it to affect code sources generated by minted. How can this be done? Also, I would like to be able to change font size used by code listings independently from rest of document. I think I want 10 or 11pts for code listings and 12pt for rest of the text.  \documentclass[12pt,a4paper]{mwrep} \usepackage{minted} \usepackage[nodisplayskipstretch]{setspace} \setstretch{1.5} \begin{document} \begin{minted}{java} public class Foo {   public static void main(String[] args)   {     for(int i=0; i<10; i++)     {       System.out.println(i);     }   } } \end{minted} \end{document}


One of Important conclusions of Einstein's Theory of Relativity is that we cannot cross or break the speed limit set by the laws of physics that is the speed of causality   consider this scenario:      suppose I somehow built a spaceship and is able to reach 99.99.......% the speed of light. After achieving this much speed i somehow turned on the boosters on my shuttle.   will I be able to cross the limit by turning on the boosters if no what will actually happen to spaceship and where will the work-done by the boosters go. can expect to be in another universe having different laws and speed limits.

The title says it all.  If I was on a bus at 60 km/h, and I started walking on the bus at a steady pace of 5 km/h, then I'd technically be moving at 65 km/h, right?  So my son posed me an interesting question today: since light travels as fast as anything can go, what if I shined light when moving in a car?  How should I answer his question?


Over at , on the list of sites,  is still listed as "Cognitive Sciences" and the image is scrambled:  Can we fix that?

This has , and it's happened again, all because Cognitive Sciences recently was renamed , with a change to the URL. The first thing that needs to be fixed is the name should be changed, as it uses has the old name. The second problem, due to the URL changing from cogsci.stackexchange.com to psychology.stackexchange.com is that the icons are broken. These are the right URLs: https://cdn.sstatic.net/Sites/psychology/img/apple-touch-icon.png https://cdn.sstatic.net/Sites/psychologymeta/img/apple-touch-icon.png  These problems affect both the Psychology & Neuroscience main and meta site listings. And it's not just one page either: the problems are seen , on the , and on the . It's currently also affecting Writers Writing, which has been . It also currently


While reading a textbook on Physics, I came across this :     Mass is a universal constant. It does not depend upon the position of the body on the Universe but it changes with speed of the body.   It's just two contrasting statements with no further explanation. Maybe the author left it to our curiosity but I can't even find out how mass changes with time. Thanks P.S : This is not a homework question.

I learned recently that when an object moves with a velocity comparable to the velocity of light the (relativistic) mass changes. How does this alteration take place?


I have Ubuntu 16.04LTS and today, I was experiencing very slow resume. So, I ran systemd-analyze blame And the results were:  20min 58.054s apt-daily.service  1min 3.335s sendmail.service      38.761s mysql.service      27.554s systemd-rfkill.service      18.918s NetworkManager-wait-online.service      12.038s ModemManager.service      10.571s dev-sda8.device       9.204s wpa_supplicant.service       8.921s accounts-daemon.service       7.911s grub-common.service       7.187s apport.service       7.162s irqbalance.service       7.062s networking.service       7.038s ondemand.service       6.770s systemd-logind.service       6.743s speech-dispatcher.service       6.706s sysstat.service       6.646s lm-sensors.service       6.639s alsa-restore.service       6.511s gpu-manager.service       6.493s avahi-daemon.service       6.480s pppd-dns.service       6.476s rsyslog.service       6.473s systemd-user-sessions.service       6.234s snapd.autoimport.service       5.940s systemd-fsck@dev-disk-by\x2duuid-09E2\x2d89F7.service       4.419s apparmor.service       3.475s NetworkManager.service       3.330s plymouth-read-write.service       2.191s lightdm.service       2.038s systemd-udevd.service       1.959s polkitd.service       1.857s plymouth-start.service       1.727s mnt-27EDE16A355CF599.mount       1.237s systemd-modules-load.service       1.180s keyboard-setup.service       1.130s apache2.service       1.124s systemd-tmpfiles-setup-dev.service        988ms systemd-timesyncd.service        924ms bluetooth.service        871ms systemd-journald.service        784ms console-setup.service        699ms upower.service        656ms dev-mqueue.mount        582ms systemd-update-utmp.service        527ms udisks2.service        487ms systemd-backlight@backlight:intel_backlight.service        479ms ufw.service        463ms kmod-static-nodes.service        455ms sys-kernel-debug.mount        421ms systemd-tmpfiles-clean.service        418ms systemd-udev-trigger.service        402ms systemd-tmpfiles-setup.service        398ms colord.service        376ms systemd-journal-flush.service        325ms fancontrol.service        302ms thermald.service        280ms phpsessionclean.service        232ms systemd-random-seed.service        198ms dev-hugepages.mount        189ms dev-sda9.swap        173ms logmein-hamachi.service        172ms systemd-sysctl.service        167ms resolvconf.service        167ms setvtrgb.service        166ms dns-clean.service        146ms boot-efi.mount         96ms rc-local.service         74ms systemd-remount-fs.service         68ms rtkit-daemon.service         31ms user@1000.service         13ms snapd.socket          9ms systemd-update-utmp-runlevel.service          6ms ureadahead-stop.service          4ms sys-fs-fuse-connections.mount          2ms plymouth-quit-wait.service   And, the Results of systemd-analyze critical-chain were:  The time after the unit is active or started is printed after the "@" character. The time the unit takes to start is printed after the "+" character.  graphical.target @1min 57.100s └─multi-user.target @1min 57.100s   └─cups-browsed.service @5min 30.739s     └─cups.service @5min 30.738s       └─basic.target @24.702s         └─sockets.target @24.702s           └─snapd.socket @24.676s +13ms             └─sysinit.target @24.606s               └─apparmor.service @20.167s +4.419s                 └─local-fs.target @19.979s                   └─media-Windows-D.mount @4min 44.168s                     └─dev-sda3.device @17.200s   What can I do to solve the problem? Please help!

My boot is horribly slow, and I don't know why.  $ systemd-analyze  Startup finished in 10.975s (kernel) + 49.732s (userspace) = 1min 708ms $ systemd-analyze blame           34.971s apt-daily.service          20.590s snapd.refresh.service          17.113s grub-common.service          16.033s apport.service          16.027s networking.service          15.894s ondemand.service          15.860s irqbalance.service          15.655s speech-dispatcher.service          11.695s ModemManager.service           9.772s accounts-daemon.service           8.626s NetworkManager-wait-online.service           8.058s systemd-logind.service           8.053s bluetooth.service           7.944s gpu-manager.service           7.896s alsa-restore.service           7.892s pppd-dns.service           7.882s rsyslog.service           7.860s avahi-daemon.service           7.844s dev-sda1.device           7.842s systemd-user-sessions.service           7.648s lightdm.service           7.610s teamviewerd.service           6.445s apparmor.service   Also, during boot-up, I see a message that says something like:  device descriptor read/all, error -62 ata1 softreset failed (device not ready) #most of the times error loading journal #(sometimes) Test WP failed, assume Write Enabled Asking for cache data failed     #most of the times Assuming drive cache: write through   apt-daily.service slows the boot the most. Any idea on how to tackle that?  I have Ubuntu MATE 16.04.


Let $y∈ℝ$, $y>−1$ and $y≠0$. Show that for $k∈ℕ$, $k>1$ we have $(1+y)^k > 1+ky$.       I've been trying to solve this for the last two hours and still don't really have any idea on how to do it.

I'm asked to used induction to prove Bernoulli's Inequality: If $1+x>0$, then $(1+x)^n\geq 1+nx$ for all $n\in\mathbb{N}$. This what I have so far:  Let $n=1$. Then $1+x\geq 1+x$. This is true. Now assume that the proposed inequality holds for some arbitrary $k$, namely that $$1+x>0\implies (1+x)^k\geq 1+kx,~\forall~k\in\mathbb{N}\setminus\{1\}$$ is true. We want to show that the proposed inequality holds for $k+1$. Thus multiplication of $(1+x)$ on each side of the above inequality produces the following result: $$(1+x)(1+x)^k\geq (1+kx)(1+x)\implies (1+x)^{k+1}\geq 1+x+kx+kx^2\cdots\cdots\cdots$$  I'm not sure where to go from here.


I am using Ubuntu 18.10 with Gnome Desktop on a UHD laptop display. My system's fonts have generally been tweaked using the font scaling in Gnome Tweak Tools, but this has had no effect on OpenSCAD which has an unreadably small interface font.  How can I change the font size without effectively lowering the screen resolution (e.g., without using Settings>Devices>Display>Scale>200%).

My laptop has a 15-inch 4k display. Almost everything works perfectly, but some applications don't scale and are too small to use. Some examples: Hipchat, Ardour, Steam, Gimp, etc.   Is there a way for me to solve this? I've seen to use xrandr to set DPI before running the app, but that seems to have no effect (or I'm doing it wrong.)  If I could fix this one problem I'd have everything working perfectly.  Also, I'm using Gnome, but the issue was the same in Unity.


Specifically, British people go "to hospital", while American English speakers say "to THE hospital".  We say, "go to school", so why not "got to hospital"?

Why do British speakers omit the article in constructions like "go to hospital" or "go on holiday"? Pretty much all American speakers would rephrase those as "go to the hospital" and "go on a holiday", I think. Is there any good reason, or forgotten sense behind those words that might explain why the articles are ommitted?  Are there other common constructions other than those two that the British use that drop the article?  EDIT: I just realized per Kosmonaut's comment that Americans do much the same thing with a few nouns, so this isn't all that special.   Do grammaticists designate nouns that can have their article dropped with anything, i.e. do they have anything in common?


I frequently see static keyword with variables and with methods. Why we use static with main(String args[]) method in java ? Can anybody explain me the role of static in easy terms. So i can understand it better

To be specific, I was trying this code:  package hello;  public class Hello {      Clock clock = new Clock();      public static void main(String args[]) {         clock.sayTime();     } }   But it gave the error      Cannot access non-static field in static method main   So I changed the declaration of clock to this:  static Clock clock = new Clock();   And it worked. What does it mean to put that keyword before the declaration? What exactly will it do and/or restrict in terms of what can be done to that object?


i need to simulate a click event on a select element to show the options. i found this  but it don't work in chrome and firefox. In safari it works.   this is my code:  $(document).on('keypress', function (e) {     if(e["keyCode"] == 13){          //Bei Enter-Eingabe das Dropdown öffnen         var elem = $('#select');         if (document.createEvent) {             var e = document.createEvent("MouseEvents");             e.initMouseEvent("click", true, true, window, 0, 0, 0, 0, 0, false, false, false, false, 0, null);             elem[0].dispatchEvent(e);         } else if (element.fireEvent) {             elem[0].fireEvent("onmousedown");         }      } });   how i can solve this problem for chrome and firefox ?

How can you programmatically tell an HTML select to drop down (for example, due to mouseover)?


I am using Ubuntu 18.10. Sometimes, when some program has just crashed, a window pops up saying the following: "Sorry, Ubuntu 18.10 has experienced an internal error. Send problem report to the developers?" Then there are three buttons: "Show details", "Don't send" and "Send".  If I click "Show details" then it does show details nicely, for example that "gjs-console crashed with SIGABRT" and lots of other info. It seems like a good idea to send this to the developers, so I click "Send". Then the window is closed. I do not get any confirmation that anything was actually sent. I would have liked to get some confirmation like "OK, problem report sent successfully" or something but there is no such confirmation so I am a little worried that something went wrong when I clicked the "Send" button.  My questions:   Is anything actually sent to the developers? Is there any way for me to verify that something was actually sent? Can I even see the details of the resulting automatically generated problem report in a public bug tracking system somewhere?   EDIT: according to an answer here:  it should be possible to see the resulting bug report by going to  but that does not work for me -- that page just says "There are currently no open bugs." So I am still not sure if any problem report was really sent and if so, where did it end up.  EDIT 2: this seems related also:  but after reading that I still don't know how to verify if a problem report was really sent.  EDIT 3: in /var/log/syslog there are a few lines mentioning "whoopsie" saying for example "Uploading /var/crash/_usr_bin_gjs-console.1000.crash." and "Sent; server replied with: No error" which sounds good. Also, the file /var/crash/_usr_bin_gjs-console.1000.crash does seem to contain all the collected error report info.

How can I find my Bug-report that I submitted from the Desktop on launchpad?  I have found a partial solution to my own question:  The program that sends the Bug-reports from the desktop is called apport. It doesn't requires a launchpad account. The service whoopsie submits the Bug-Report directly to the server daisy.ubuntu.com (I'm not sure if those bugs actually appear on launchpad publicly.)  But I found my Bug-Report on my Harddisk in /var/crash/ .  From there I can copy and paste parts of the file to my opened bug on launchpad. Thanks for your tips.  Original question:  I had a severe bug, and I found someone with the same problem in launchpad. After I found a temporary fix I was able to submit the bug with the ubuntu-bug-reporter.  How can I find this ubuntu-bug-reporter generated bug-report in launchpad? I would like to combine those two bug-reports (mark as duplicate). Because the generated one has all the debug information and the other one has the description of this bug.


I'm in a pretty simple "CS Math" course for year 1 Comp Sci, and I came across this: Disprove, $x^2 + y^2 = z^2$, such that $x, y, z$ are primes I thought of this as, if n is a prime, then prime factorization of n must be: $n = z*1$ $n^2 = (z*1)(z*1) = (z)(z)$  So I tried to derive a contradiction:  Assume $x, y, z$ are primes such that $x^2 + y^2 = z^2$ Then: $x^2 = z^2 - y^2$  Then: $x^2 = (z-y)(z+y)$ #Contradiction, prime factorization of $x^2$ must be uniquely represented. But then I noticed that this statement is true if $z-y = 1$ and $z+y = x^2$, So: Then: $y = -1+z = y = z-1$  Because: $x^2 + y^2 = z^2 $  Then: $(z-1)(z-1) + z+y = z^2$ Then: $z^2 - 2z + 1 + z + y = z^2$ Then: $z^2 - z + y + 1 = z^2$ # subtract $z^2$ from both sides  Then: $-z + y + 1 = 0$ Then: $y = -1 + z$ #Loop??  I remember reducing this to $x + y = z$, which I think is false?  EDIT: Thought of this: z - y = 1 Then: z = y + 1 Then z must be 3, y must be 2  Because: z is greater than y by 1, since z is a prime and y is a prime, z and y must be 3 and 2 respectively since no other prime number is 1 apart because one of them would be even if greater than 2, and any even number has at least 3 divisors (2, the even number, and 1) thus not a prime. Then: $x^2 + 2^2 = 3^2$ ,Because $2^2 = 4, 3^2 = 9$ Then: $x^2 = 9 - 4$ Then: $x = \sqrt5$ Contradiction: x is a prime, but sqrt(5) is not a prime!  Is this a solid evidence proof in that can I say that only prime numbers 1 apart are 2 and 3? I'm pretty sure there is a more simpler and intuitive way to prove this, are there any other ways to prove this via contradiction?

Suppose $a$, $b$ and $c$ are three prime numbers.   How to prove that $a^2 + b^2 \neq c^2$?


I'm following as tutorial and once I inserted a Landscape object a whole lot of settings for the landscape came up on the left side of my screen.  I've somehow lost these setting and I can't find it. I may of accidentally pressed a button or something.

When you first add a cylinder, you have the option to change the number of vertices, etc, but once you do anything else in blender, it seems you no longer can edit those parameters.   Is there a setting anywhere or an add-on that allows these parameters to be edited later on? If not, how easy would such an addon/feature be to create for anyone reading this?


Show that:  \begin{align*}   a \cos \theta + b \sin \theta = \sqrt{a^2+b^2} \cos (\theta - \varphi) \end{align*}  fyi, the context is in studying the differential equation:  \begin{align*}   y''(t) + c^2 y(t) &= 0 \\ \end{align*}  which has general solution:  \begin{align*}   y(t) &= a \cos (ct) + b \sin (ct) \\ \end{align*}  My textbook says that this can easily be transformed into, where $\varphi \in \mathbb{R}$:  \begin{align*}   y(t) &= \sqrt{a^2 + b^2} \cos (ct - \varphi) \\ \end{align*}

I don't understand this. These identities are given in the online notes for MIT's 18.01 calculus class. It's related to taking the sum of two trig functions and transforming them into a single trig function. I can use the formulas to do this, but I am having trouble finding anything on the internet to use a proof for my understanding.  Thanks for any responses!  EDITED (added after the first answer):  Sorry, the identity goes like this:  $A\sin{k(x-c)}=a\sin{kx}+b\cos{kx}$ ,  with the relationships  $a=A\cos{kc}$ , $b=-A\sin{kc}$ , $A=\sqrt{a^2+b^2}$ , and $\tan{kc}=-b/a$


Write $1,2,\dots,n^2$ into a $n\times n$ square grid. If $u,v$ are adjacent, call $\max_{u,v}|u-v|$ the maximal distance of this grid. So what is the minimal maximal distance? I feel like that it is $n$, the construction is to write $1,2,\dots,n^2$ in order, but I do not know how to prove it, and I cannot find any results on it either.

Suppose we write each number from $1$ to $n^2$ in an $n\times n$ grid exactly once. Prove there are two adjacent cells such that the absolute value of their difference is not less than $n$.   I think it should be a pigeonhole problem, but the work I did so far was basic observations like if we assume all differences are less than $n$, then neither of $1,2,\dots,2n-2$ could be in the row or the column $n^2$ is placed.  Any hints would be appreciated.


Since java is pass by value.In below code we are passing a value to appendStringMethod not a reference, then why in main method we get HelloWorld not just Hello after calling appendStringMethod() in main.   public class test {     public static void main(String args[]) {          StringBuilder str = new StringBuilder("Hello");         appendStringMethod(str);         System.out.println(str);     }      static void appendStringMethod(StringBuilder s) {         s.append("World");     } }   However in below code, values are not swapped.  public class Mock {   public static void main(String args[]) {     StringBuilder str1 = new StringBuilder("Hello");     StringBuilder str2 = new StringBuilder("World");     swap(str1, str2);    System.out.println(str1);    System.out.println(str2);     }    static void swap(StringBuilder s1, StringBuilder s2) {    StringBuilder s= s1;    s1=s2;     s2=s1;    } }

I always thought Java uses pass-by-reference. However, I've seen a couple of blog posts (for example, ) that claim that it isn't (the blog post says that Java uses pass-by-value). I don't think I understand the distinction they're making. What is the explanation?


I bought this ipad second handed I already disabled it bt after connecting it to a wiffi its says "This iPad is currently linked to an Apple Id sign in with the Apple ID that was used to set up this ipad" is there anywway i can get pass through that.

I bought a used iPhone 4.  The previous owner re-set the phone, but did not remove the device from their iCloud.  It is asking me for their iCloud information when I try to set-up the phone.  I don't have contact with the previous owner anymore.  Is there a way to remove the device from their iCloud so I can use a new one?


I am trying to identify a book that I read in the mid 1980's. Some details:   It was a graphic novel, or comic. All black and white, if I remember correctly. The main character was a human, though I believe all of the other characters were anthropomorphized animals. There was a cat-woman who acts as a kind of mentor/mother to the main character, along with some varied animal "children".   I believe the main character's name was Phaedrus, or a variation of this.   The main character flies a spaceship shaped like a falcon, and arrives on the animal planet as a stranger, looking for something specific that I can't remember.   There is a metal sphere that, when opened, has a simple pattern inside: a single concentric circle with a cross extending through it to the edges of the sphere.   There is a human-sized earthworm that appears in the background of panels early in the story, but becomes a vital part of the story later on, eventually merging with the main character.   It's incredible that despite all of these details, I can't seem to find anything via Google. I've even gone so far to return to the library that I remember checking it out from as a child, but they no longer have the book.  Thank you for your help, this has been bugging me for years now.

When I was a kid(early 1990s), I read a graphic novel from the local library that I have been unable to find or identify.  Here are the clues:   It's from the 1970s or 1980s, from what I remember of the art style. It felt like one of those strange sci-fi / fantasy mixes that were common in the 70s. It was black and white. The main character's soul becomes detached from his body and takes the form of a giant(human-sized) earthworm. The earthworm goes off and does its own thing. Our hero sometimes sees the earthworm in the distance, and at some point goes hunting for the thing, through forests and wastelands. The earthworm-soul thing was only ONE part of the comic's storyline. There was other stuff, but for the life of me, I can't remember what.


I'm interested in running a Hexcrawl Sandbox style game in pathfinder. The hexes would dictate what range of CR the encounter tables would contain. What I'm wondering is at what CR magic items start becoming a major factor in the balance. And in what way do these issues affect the game.   There will be spell casting classes allowed for PCs and there will be magic items out there to be found and so I am apprehensive to call it "low magic".   Where this style of game will differ is in how gold and magic won't be awarded for each and every encounter by the virtue of it being an encounter. Wealth and magic as a reward won't be a guarantee for facing an encounter.  If players find through exploration some ancient ruins and choose to face the risks inside it then they could find wealth and magic. Though if the players don't find such locations, or choose to play it safe and not enter, they might end up facing many battles with wolves and spiders and gain enough experience to start levelling up without having found magic items or large sums of money.  Additionally there won't be spell casters in the towns capable of crafting magic items should the players find wealth.  Because of these structures there is a chance but not a guarantee that the players will get magic items. It is far more likely that players will gain experience faster and more consistently than magic items.  This is why I'm interested in the relationship between CR and magic items. But I'm not interested in "rebalancing" encounters or rebalancing the classes. I'm curious to hear about people's experiences with this relationship and specifically when the balance issues become apparent and in what ways they impacted game play.   I would like to see if it is feasible to do with pathfinder, but I'm starting to lean towards dnd 5e as its encounters aren't balanced with magic items in mind (from what I understand).  Thanks in advance for your thoughts!

Recently, my players and I got kind of bored with the fact that Pathfinder relies heavily on magic items than martial prowess for fighting classes. I realize and accept the fact that spellcasters are more powerful than petty sword fighters in Pathfinder, but my players usually prefer fighters, rangers or rogues not spellcasting classes.  So, we came up with the idea of playing a low-magic campaign. Here are the terms;   No spellcasting classes for players. This includes paladins, rangers, bards etc. But archetypes that replace spells(such as skirmisher archetype for ranger) is ok. No magical items except for very rare and powerful artifacts that will serve a specific purpose. There will be spellcasters in the world, but, again very rare and they will probably be the villains of the story. Alchemy exists, as well as special materials such as cold iron, mithral etc. There will be magical creatures, such as undead, demons, devils.   The main purpose here is that, I want my players to feel competent when they kill a horrific creature, I want them to feel they killed it because of teamwork and tactics, not because they had the right magical item combinations.  Of course, with this comes several concerns on balance of the game.   How should I handle healing between encounters? Refilling 30 hp can last a long time, even with the help of Heal skill. How should I balance encounters? Challenge Ratings assume access to magical items and magical items improve at an exponantial rate so maybe treat the party level as -1 for every four levels they have(against the magical creatures or those rare spellcasters of course)? Example; Party level 1-4 = -1 Effective party level, Party level 4-8 -2 Effective party level etc when determining Challenge ratings for "magical encounters". Without magic, Armor Class does not scale, however attack rolls do. At some point, attack rolls will be automatic hits and I don't like that prospect without magic or healing to aid the players. This will make fighting defensively, or feats like Dodge or Combat Expertise more important but I feel, they won't be enough. How should this be handled? And finally, without magic, everyone will be a fighter of one kind or another.  What are your thoughts on replacing Fighter-level Requirements on feats like Weapon Specialization with Character level?   P.S; The question may be too broad and not have only one definitive answer from one person only, but every idea helps and I will combine those ideas while creating the campaign.  Thanks in advance.


I want to know how to make the taskbar at the bottom of the screen disappear.    This taskbar appeared after I installed some theme. How can I make that taskbar disappear?  I thought this was editable in gnome-tweak-tool, but I can't find the relevant tab.  (It's not the Dock that's installed by default in Ubuntu)  OS: Ubuntu 17.10 Artful Aardvark

How do I disable "Workspace dock" (a bottom panel with the list of open windows and a workspace indicator-cum-switcher), the one that is over "Plank" in the screenshot below?    I'm using Ubuntu 17.10.


Starting from yesterday, all emails sent from our server are being rejected by Gmail and Hotmail.  Everything was working properly until now.  Here are the error messages received:  Gmail  Failed Recipient: email@gmail.com Reason: Remote host said: 550 5.7.1 [server IP 1] Our system has detected an unusual rate of 5.7.1 unsolicited mail originating from your IP address. To protect our 5.7.1 users from spam, mail sent from your IP address has been blocked. 5.7.1 Please visit http://www.google.com/mail/help/bulk_mail.html to review 5.7.1 our Bulk Email Senders Guidelines. el7si1434447wib.69 - gsmtp   Hotmail  Failed Recipient:address@hotmail.com Reason: Remote host said: 421 RP-001 (BAY0-MC3-F30) Unfortunately, some messages from [server IP] weren't sent. Please try again. We have limits for how many messages can be sent per hour and per day. You can also refer to http://mail.live.com/mail/troubleshooting.aspx#errors.   I do know the point of those messages - they both blocked our server because it might be sending out spam.  However, I don't understand what exactly could have caused this.     Was someone spamming Gmail/Hotmail addresses from our server?   Did some of the recipients report our emails as spam? Any other possibilities?   I'm honestly not sure where to look at first.  Thanks!

This is a  about Fighting Spam.   Also related:                    There are so many techniques and so much to know about fighting SPAM. What widely used techniques and technologies are available to Administrator, Domain Owners, and End Users to help keep the junk out of our inboxes?  We're looking for an answer that covers different tech from various angles. The accepted answer should include a variety of technologies (eg SPF/SenderID, DomainKeys/DKIM, Graylisting, DNS RBLs, Reputation Services, Filtering Software [SpamAssassin, etc]); best practices (eg mail on Port 25 should never be allowed to relay, Port 587 should be used; etc), terminology (eg, Open Relay, Backscatter, MSA/MTA/MUA, Spam/Ham), and possibly other techniques.


I've got a couple switches controlling an exterior light which is not directly visible from either switch. That causes issues if, for instance, I am leaving during daylight hours and know I will be returning after dark and want to have the light on. I need to flip the switch and then check to see if the light is on (or check, then switch) which is inconvenient (there's a similar issue checking to turn if off during daylight hours).  Ideally, I'd like to use something like the Lutron dimmer system where tapping the top always turns it on and tapping the bottom always turns it off. I don't need a dimmer function so I'd rather not pay for one. Alternatively, switches that had an LED indicator to show when the circuit is energized would work. Are there any products available that would provide either feature? For various not-very good reasons, mostly having to do with laziness, I don't want to use a motion sensor or light sensor and just leave it "on" permanently.  Thanks.  Colin

Have some carriage lights outside my garage that can be turned on from inside the house. It's common that the switch will get flipped and the lights will stay on when they're not wanted.  Is there some way I can add an indicator to the light switch so I can know if the light is on?  Note: the carriage lights are on a 3 way switch.


I have a program named Log. I want to run log, but normally I have to go to ~ directory and use the command ./Log . How would I make it so that I can use the command Log to do the same thing, from any directory? Would I have to add it to /usr/bin? Thanks!  this is my ~/.profile file:  # ~/.profile: executed by the command interpreter for login shells. # This file is not read by bash(1), if ~/.bash_profile or ~/.bash_login # exists. # see /usr/share/doc/bash/examples/startup-files for examples. # the files are located in the bash-doc package.  # the default umask is set in /etc/profile; for setting the umask # for ssh logins, install and configure the libpam-umask package. #umask 022   # if running bash if [ -n "$BASH_VERSION" ]; then     # include .bashrc if it exists     if [ -f "$HOME/.bashrc" ]; then     . "$HOME/.bashrc"     fi fi  # set PATH so it includes user's private bin directories PATH="$HOME/bin:$HOME/.local/bin:$PATH"  alias log=/home/sqidman310/Log

I'd like to know if there is a way to run  program/shell script without typing full path:  /opt/idea/bin/idea.sh


So basically, I'm making a website with a form inside a modal. After that form submits the data to script.php, whatever script.php sends back is appended to the modal body like so:  // Function to submit data to php $("#formModificarArticulo").on("submit", function(e) {      var postData = $(this).serializeArray();     var formURL = $(this).attr("action");      $.ajax({         url: formURL,         type: "POST",         data: postData,         success: function(data, textStatus, jqXHR) {             $('#divModificarArticulo .modal-header .modal-title').html("Resultado");             $('#divModificarArticulo .modal-body').html(data);             $("#submitFormModificar").remove();             reloadDataTable();         },         error: function(jqXHR, status, error) {             console.log(status + ": " + error);         }     });      e.preventDefault(); });  $("#submitFormModificar").on('click', function() {     console.log("Submit presionado");     $("#formModificarArticulo").submit(); });   So, basically, when the user sends data using the form inside the modal, the modal changes to show something along the lines of "Data sent to server successfully".  After the result from script.php is showed to the user and the user closes it, the modal is supposed to revert back to its original state with the form. This is the function where that magic happens:  // Function to reset modal (function(){      var template = null;      $('#divModificarArticulo').on('show.bs.modal', function (event) {         if (template == null) {             template = $(this).html();         } else {             $(this).html(template);         }          $('#divModificarArticulo').modal({ show: false});     })  })();   The thing is, I can send data pressing the Submit button on the form, the modal brings me the back the results from the server and when I open the modal for a second time the form is back to its original state. For some reason, however, when I press the Submit button for a second time, it doesn't do anything. It's like it's not even pressed.  I'd really appreciate if someone could help me out.

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


Then the expression will be  $$|z|+\frac{2}{|z|}\ge 2$$  Solving the quadratic inequality   $$|z|\ge1+i$$ and $$|z|\le1-i$$  I don’t know how to solve further. Please help  Thanks!   this is the corrected version of an identical question asked by me. I am sorry for the inconvenience caused


Does QGIS - through one of its rich algorithms library - allow for reduction of raster DSM/DEM resolution? I want to speed up the analyses and reduce effect of detailed raster on results readability.   The problem lies in the detail level of the raster. Input dsm was made based on the uav survey (output format: .tiff), so its size (area) is not large, but very, very detailed. This makes results of every analysis run on it difficult to view - i.e. QGIS calculates the aspect for every bump even 10 cm high, or streams for catchments for completely irrelevant areas.

I'm not much of a GIS user, but I've got a big ascii file that I'm trying to convert into a   lat  long  data x1   y1     d1 x1   y2     d2 x1   y3     d3 x2   y1     d4 ... etc   format, so that I can work with it in R.  I've got global national identifier data (i.e.: which country occupies what grid) at 2.5 arc-minute resolution, but I want to coarsen it into half-degree, because that is the resolution of the rest of my data.  I could do so in R if the file weren't so large -- its 3.9GB and I can't read it into memory.  A NetCDF file would obviously be ideal for me, but I can't find a netcdf version of the data I want.  The data is categorical -- country identifiers.  What I want to do is simple to take each 12x12 block of gridcells, evaluate that N=144 matrix, and return the country that appears the most times.  (I'd also like it to ignore NA values, unless all values are NA).  This would be easy enough in R if I could only open the darn text file.  So I opened QGIS, but there doesn't seem to be any obvious way to "coarsen" a raster.    Is there one?    Then it occured to me that I could convert the data to vector, and then convert it back to raster, specifying the resolution that I want.    BUT is there a way to do so that would allow me to specify that each gridcell should be .5x.5 degrees, going from -180 to 180 and -90 to 90?    This seems like a pretty gross hack.    Is there a better way?    I've decided that it makes more sense for me to just make the file into a netcdf using a remote machine with the memory for it.


I wish to prove the following by contradiction:     Let $f:[0,1]\rightarrow[0,1]$ be a continuous function. Prove that there exists $x\in [0,1]$ such that $f(x)=x$.   Proving this directly, one would have to define a new function $g(x):=f(x)-x$ and prove that there exists $x\in [0,1]$ such that $g(x)=0$ using Intermediate Value Theorem, hence $f(x)=x$. But I'm struggling to elaborate a proof by contradiction.  My approach is as follows. Suppose by contradiction that it does not exist $x\in [0,1]$ such that $f(x)=x$. Then for all $x\in [0,1]$, $f(x)\neq x$. Then $f(x)>x$ or $f(x)<x$ for all $x$. This is where I'm not sure if it's correct.  If $f(x)>x$ for all $x\in [0,1]$, let $x:=1$. Then $f(1)>1 \implies f(1)\notin [0,1]$ which is a contradiction because $f$ was defined in $[0,1]$  If $f(x)<x$ for all $x\in [0,1]$, let $x:=0$. Then $f(0)<0 \implies f(0)\notin [0,1]$ leading to the same contradiction as above.  I'm skeptical because my contradiction does not involve $f$s continuity. Is the proof correct? If not, how can I approach this by contradiction? Thanks.

Be a continuous function $f:[0,1] \rightarrow [0,1]$.  Show that there is a $\zeta \in [0,1]$ with $f(\zeta)=\zeta$ ($\zeta$ is called fixed point).  Consider the function $g:[0,1] \rightarrow [-1,1]$, $g(x):= f(x)-x$.  $g$ is continuous.  Because of $f(0),f(1) \in [0,1]$ is $g(0)\geq0$ and $g(1)\leq 0$.   Because $f(0)$ has a value between $0$ and $1$, $f(0)\geq 0$.  $g(0) = f(0)-0= f(0) \geq 0 - 0 = 0$.  Because $f(1)$ has a value between $0$ and $1$, $ f(1) \leq 1 $.  $g(1)=f(1)-1 \leq 1 - 1 = 0$ $\Leftrightarrow g(0)\geq 0$ and $g(1)\leq 0 $  After the IVT: $\exists \zeta \in [0,1]:g(\zeta)=0 \Leftrightarrow f(\zeta) = \zeta $  $\zeta$ is a fixed point of $f$. $\Box$  My questions are:  Is this proof done in the correct way or have I missed something?  Is there something I can improve?


While studying Newtonian mechanics, we are concerned with only three laws of motion that describes force and it's relations. But when we switch to rotational dynamics, we are presented with torque and moment of inertia as being the rotational analogue of force and mass. With no laws other than Newton's laws describing motion of this type. How, did we actually arrived at the idea of torque and moment of inertia from force and other related concepts?

Since Newton's laws are defined for point particles, I'd like to derive some laws of motions for rigid bodies only by considering a rigid body as a system of particles such that the distances from every particle to every other particle doesn't change with time. I think I derived that the force applied on one particle of a rigid body must be the same for every other particle of the rigid body in one dimension by the following:  Consider two particles on a line $P_1$ and $P_2$ both with masses $dm$ and positions $x_1$ and $x_2$. Let's say that a force $F_1$ acts on the particle $P_1$. By Newton's second law we get: $$F_1 = dm\frac{d^2x_1}{dt^2}$$ By the definition of a rigid body, the distance between $P_1$ and $P_2$ doesn't change with time. Define $r$ as this distance ie. $r = x_1 - x_2$. Therefore: $$\frac{dr}{dt} = 0$$ Taking the derivative of both sides we further get that $$\frac{d^2r}{dt^2} = 0$$ $$\frac{d^2(x_1 - x_2)}{dt^2} = 0$$ $$\frac{d^2x_1}{dt^2} = \frac{d^2x_2}{dt^2}$$ By Newton's second law this is the same as: $$\frac{F_1}{dm} = \frac{F_2}{dm}$$ (where $F_2$ is the force acting on $P_2$), and since $dm \ne 0$ finally: $$F_1 = F_2$$  These steps can be done for arbitrary amount of particles, and so we get that in one dimension, if a force is applied on one of the particle of a rigid body, every other particle of the rigid body experiences the same force.  The problem is that I cannot do a similar proof for two dimensions by defining the distance $r = \sqrt{(x_1 - x_2)^2 + (y_1 - y_2)^2}$, but I'm sure that it can be done, and that if done torque, moment of inertia and center of mass would arise. Can someone do a similar proof for two dimensions, if it can be done like this at all?


Long time ago, I read a story which in retrospect I'd classify as Lovecraftesque in style, though I doubt it was one of HPL's own works (it doesn't match any of HPL's stories I've read long afterwards). I don't remember the title nor the author thereof. It had the following elements:   One of the characters managed to escape from an eldritch temple of sorts, but had an urge to return, crawling back on his arms and legs in his sleep. I remember the character described as having sores on his limbs, but I don't remember if it was in the process of praying, escaping, or trying to return. The temple was a giant well-like hole in the ground, with a spiral staircase and niches in the walls. The eldritch entities that demanded worship were normally invisible; it took drinking some special substance to begin seeing them, but the effect of that was lasting. The entities' shape included a vermiform body, though I'm not sure if it had any limbs; IIRC they also included a sphere or halo or something like that on top. The events of the story were taking place during some expedition through wilderness or at least deep foreign land. I'm inclined to believe that the story dates back to the 90s at the latest, and is likely older than that. I'm not sure what was the date within the story, but it was probably no later than the traditional Lovecraftian era.   What story might this be?

I'm trying to remember the name of this story: Some gold panners? are in Alaska? (I remember it was cold, and or the pacific northwest) near a huge hand-shaped mountain, and see an eerie blue light in the sky, a pillar shining from beyond the mountain; it draws them hypnotically, but they resist. Coming south from the mountains and into their camp is a raving, semi-comatose man, lashed to his sled/sled-dogs. He wakes up and speaks or they see his journal, and start to read his story.   He was drawn to the legends of an ancient city in the wilderness, either for knowledge or gold, and comes from the north to its reputed location; his native guides do the stereotypical desertion in the progress, and he is left alone to enter. He finds himself at the edge of a canyon, where there are a giant set of stairs leading down. Flanking the steps are a pair of weathered statues, making warding gestures. He proceeds down, the stairs switching back and forth, passing by resting places dug into the cliff, each also guarded by statues. Protected from the wind in the canyon, these are less eroded, and he can see they are natives? At the bottom, a bridge extends out from the stairs and enters the city. The architecture is hollow tubes laid on their sides in pyramidal configurations. The landscape features mist and alien disk-shaped? vegetation. The bridge goes inside the largest structure, where there is an idol.   He passes through there, and starts exploring. Night falls, and presences stir. They are basically invisible, except for glowing lights inside them; they are slug-shaped? He tries to hide, but they capture him and chain him to the idol. His mind or soul starts to be taken by them, and they start to become visible. He reacts to the alien other with prototypical Lovecraftian revulsion. During the day, they all go away. He is fed on bowls of something like milk, which drugs or changes him, or furthers the communion. Several days go by. He determines to escape before he is too weak, breaks the chain, and crawls to the first shelter on the stairs. When night comes, his absence is noted and they shine the blue light. Only his own weakness and the protective powers of the statues keep him from succumbing to its hypnotic power and going back. In the day, he keeps climbing the stairs. Either that day or later, he makes it back to the top, and starts south. That brings us back to the present.  He is dying, and begs to be burned so that the city cannot claim him, even in death. He dies, and they burn him, and they have to burn, or melt or shun the remnants of the manacle on his wrist, even though it's made of gold? or something. And then, suitably horrified, they go back south.  I'm pretty sure the story wasn't by Lovecraft, but it was absolutely Lovecraftian, and I believe it was an entry in the mythos.  Thank you.


I’ve got windows installed on an nvme drive and I have a sata ssd that I want to install Ubuntu on without wiping out the windows drive. Can I use the “Erase disk and install Ubuntu” option? Or will this destroy my other drives?

I have gotten as far as to create the bootable usb, booting into that bootable usb and getting to the install options however i quit because I had some concerns.  I currently have a Samsung 850 evo 1tb that has win 10ninstalled. I want to dual boot with Ubuntu 18.04 by installing it on a brand new unformatted uninitialized Samsung 860bevo 250gb. Should i format the brand new ssd as a new volume in win 10 and then proceed with the Ubuntu install on this volume. What else should i do? Im a first time Ubuntu user and installer.  Any and all help is appreciated.


Provided that $x$ is positive, when does the following converge? $$x^{x^{x^{x^{...}}}}$$      I just had a talk with my friend who is taking a calculus class and he is dealing a lot with divergence and convergence stuff. His TA said that if anyone could answer this and write a proof, he or she doesn't have to come to the recitation class anymore. This drives me a lot.   So here is my work, but I don't really know if this is correct. Could anyone shed some light on this?     I haven't done any real analysis before so I'm trying to make use of   whatever I can use, and my plan is to find the critical points of $y'$   and look at the graph of $y=f(x)$. First let   $f(x)=x^{x^{x^{x^{...}}}}=y=x^y$, then I have $$ \ln{y}=y\ln{x} $$ $$  \frac{d(\frac{\ln{y}}{y})}{dx} = \frac{d\ln{x}}{dx} $$ $$  \frac{1-\ln{y}}{y^2} \frac{dy}{dx} = \frac{1}{x}$$ $$ y'=  \frac{f^2(x)}{x(1-\ln{f(x)})} $$ Now I noticed that the critical   points are $x=0$ and $f(x)=0$ or $f(x)=e$. Since   $f(x)=x^{x^{x^{x^{...}}}}$ is an increasing function, the graph of   $y=f(x)$ would go up vertically at some point as $x$ increases, and that   is when the function diverges. From these 3 critical points, $f(x)=e$   seems to make most sense. By plugging $f(x)=e$ back into $y=x^y$, it's   not hard to see that $f(x)=e$ occurs at $x=e^{\frac{1}{e}}$. So the   function converges when $x\in (0, e^{\frac{1}{e}})$   Edit: I just noticed something strange in my proof: $$ y'= \frac{f^2(x)}{x(1-\ln{f(x)})} $$ When $f(x)>e$, the denominator on the right hand side is negative. But since $f(x)$ is an increasing function, therefore, shouldn't $y'$ be positive? Now it seems to deep for me to perceive...

I got this problem from my teacher as a optional challenge. I am open about this being a given problem, however it is not homework. The problem is stated as follows. Assume we have an infinite tetration as follows $$x^{x^{x^{.^{.^.}}}} \, = \, a$$ With a given $a$ find $x$. The next part of the problem was to discuss the convergence radius of a. If a is too big or too small the tetration does not converge. Below is my humble stab at the problem.  My friend said you would have to treat the tetration as a infinite series, and therefore could not perform algebraic manipulations on it before it is know whether it converges or diverges. However my attempt is to first do some algebraic steps, then discuss the convergence radius. I) Initial discussion At the start it is obvious that the tetration converges when $a=1$ (just set $x=1$) Now after some computer hardwork it seems that the tetration fails to converge when a is roughly larger than 3. II) Algebraic manipulation $$ x^{x^{x^{.^{.^.}}}} \, = \, a$$ This is the same as $$ x^a \, = \, a$$ $$ \log_a(x^a) \, = \, \log_a(a)$$ $$ \log_a(x) \, = \, \frac{1}{a}$$ $$ x \, = \, a^{\frac{1}{a}}$$ Now, if we let $a=2$ then $x = \sqrt{2}$. After some more computational work, this seems to be correct, which makes me believe this formula is correct. III) Discsussion about convergence By looking at the derivative of $ \displaystyle \large a^{\frac{1}{a}} $ we see that the maxima occurs when $a=e$, which also seems to correspond to the inital computational work. Now I think, that the minima of $\displaystyle \large a^{1/a}$ is zero by looking at its graph, studying its derivative and the endpoints. So that my "guess" or work shows that it converges when $$ a \in [0 \, , \,  1/e] $$ VI) My questions Can my algebraic manipulations be justified? They seem rather sketchy taking the a`th logarithm and so on . (Although they seem to "magically" give out the right answer) By looking at Wikipedia it seems that the tetration converge when $$ a \in \left[ 1/e \, , \, e \right] $$ This is almost what I have, why is my lower bound wrong? How can  I find the correct lower bound?


\documentclass[a4paper, 12pt]{article} \usepackage{amsfonts} \usepackage{tikz} \usetikzlibrary{decorations.markings}  \begin{document}      \begin{tikzpicture}[scale=0.90, acteur/.style = {circle, fill=black, thick,                  inner sep=0.5pt, outer sep=0pt, minimum size=1.3mm},    decoration = {markings, mark=at position 0.5cm with {\arrowreversed[semithick]{>}}}, every label/.append style = {font=\scriptsize},      ] \node (v2) at (0,0) [acteur,label=below:$v_2$]{}; \node (v1) at (0,1)[acteur,label=above:$v_1$]{}; \node (v3) at (1,0) [acteur,label=below:$v_3$]{}; \node (v4) at (2,0) [acteur,label=below:$v_4$]{}; \node (v5) at (2,1) [acteur,label=above:$v_5$]{}; \node (v6) at (1,1) [acteur,label=above:$v_6$]{}; % \draw (v1) -- (v2); \draw (v3) -- (v6); \draw (v5) -- (v4); \draw (v1) -- (v6); \draw (v2) -- (v3); \draw (v6) -- (v5); \draw (v3) -- (v4); % \node at (-2.5,1) {\textit{$G_1$}}; \end{tikzpicture}      \begin{tikzpicture}[scale=0.90, acteur/.style = {circle, fill=black, thick,                  inner sep=0.5pt, outer sep=0pt, minimum size=1.3mm},    decoration = {markings, mark=at position 0.5cm with {\arrowreversed[semithick]{>}}}, every label/.append style = {font=\scriptsize},      ] \node (v2) at (0,0) [acteur,label=left:$v_2$]{}; \node (v3) at (1,0)[acteur,label=right:$v_3$]{}; \node (v1) at (0.5,1) [acteur,label=above:$v_1$]{};  % \draw (v1) -- (v2); \draw (v2) -- (v3); \draw (v3) -- (v1);  % \node at (-2.5,1) {\textit{$G_2$}}; \end{tikzpicture} \end{document} How I can put the following two figure side by side?

How can I put two figures side-by-side? Not two sub-figures, but two actual figures with separate "Fig.: bla bla" captions.  A figure is supposed to spread over the entire text width, but I have two figures which are narrow and long, and I need to save the space in order to withstand the pages limit.


When referring to America, one should use the definite article, "the", "the United States".  However, in some titles of posts, the definite article is omitted.       Is that some kind of grammar rule?

Given the following headline at Bloomberg.com:     Verizon Explores Lower Price or Even Exit From Yahoo Deal   My questions are:   Why in this case the definite article is omitted before Yahoo Deal? E.g., From Yahoo Deal vs From the Yahoo Deal. Why there is no article before Lower Price in this title? E.g., Explores Lower Price vs Explores a Lower Price.


While playing with a violin with my friend, they told me plucking at just any position will produce the "wrong" sound, and to achieve the sound desired for the piece you must pluck at a specific point on the string (about a half inch below where the fingerboard ends). I did not believe her, as surely plucking a string tightened to play a certain frequency and amplitude will not play a different frequency or amplitude based purely on what position on the string you pluck.   Now, playing with my guitar I realize that possibly the difference in sound is caused by a shift in the position of the wave. While it is an interesting idea, it feels wrong at a fundamental level.   So, why does playing a string instrument at different positions along the string cause different sounds to be produced?

When you energise a taut string, the following resonant modes of vibration occur:    Plotting on the frequency domain, you can see their corresponding frequencies:    But what is the underlying physical principle? Why does this happen?  Is there any way of explaining it that could be understood by a smart 15 year old?  EDIT: I'm going to give my best attempt so far. Here goes:   We can start with sympathetic resonance. Sounding a particular frequency, a pure sinewave.  And noticing the string resonates sympathetically at the frequency of each harmonic. Say this is explained and understood. Now imagine that plucking a string is equivalent to a burst of white noise, which contains frequencies all the way through the spectrum. This could be approached backwards, by starting with random frequencies and noticing that resultant wave produced looks like white noise.   If the above is scientifically correct, then it restricts the domain of the question.  I would really like to be able to understand it scientifically and also be able to explain it intuitively.  PS Images from


can I connect a 12v router directly to a 12v battery which normally will be at 13-14v (because most of the time it’ll be charging)? The router is a TP LINK Archer MR200 rated at 12V 1A

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


I am currently in Portugal (UTC timezone - , and it is 2021-01-09 11:31AM. I have asked a question yesterday, 2021-01-08, at 02:54PM  However, if one looks at the metrics under the title of the question, it says that the question was asked "Today"

Looking at , I see "asked yesterday" (which I really hate; I'd like to see an exact time specification rather than this vague one, especially in the list of questions). But it was not asked yesterday! When I hover over it to show the exact time, it shows it was actually the day before yesterday!  This snapshot was taken at 2012-03-31 15:00 UTC (plus or minus a few minutes):    Whatever different opinions you may have on the implementation, yesterday is a word with a certain meaning. Redefining it is not a good idea. At least rephrase this as "1 day ago" or something.


How can I prove that $\left(\dfrac{ n+1}{2}\right)^n$ is greater than $n!$ where $n$ is natural number greater than $1$?  My work We know that $n^n >n!$ because $n!$ is the way for filling without any repetition and $n^n$ is the way of filling without any restriction. But here I can't find relation of inequality between $n^n$ and $\left(\dfrac{n+1}{2}\right)^n$. Can I prove it this way or some other way would help? Can you prove it by some other way than mathematical induction?

Show that $$n! \leqslant \left(\frac{n+1}{2}\right)^n \quad \hbox{for all } n \in \mathbb{N}$$  I know that it can be done by induction but I always find line where I do not know what to do next.


After one of my papers was put "on hold," every single one of my new papers is being put on "on hold," many of which are ultimately rejected from Arxiv. This makes no sense to me as the same papers that are rejected are often accepted to and published in reputable, peer-reviewed journals, such as Mathematics of Computation and even the PeerJ Journal of Computer Science.  So I'm stuck; preprinting my work and making it open access is very important to me.    Because of the struggle of uploading anything at all to Arxiv, I would like to ask if there are other reputable preprinting servers (i.e. not Vixra) that cover the same subject areas: Physics, Mathematics, and Computer Science.   EDIT: Would sites such as OSF Preprints be considered reputable? My initial checking shows their papers maintain DOIs and are cited on google scholar, and the site seems fairly popular also.

While  is great, it covers only topics in physics, mathematics and computer science.  Are there any good preprint storage places for other scientific disciplines?


Why there is a Java class declaration without public or private at the beginning?  For example :   class MyClass{   // code  }

In Java, are there clear rules on when to use each of access modifiers, namely the default (package private), public, protected and private, while making class and interface and dealing with inheritance?


If we were to have the integral from a to b if some function f(x), then that integral would represent the area under the curve from a to b, now based on the properties of integrals given to us in school, we are told that changing the bounds from b to a results in the negative of the original integral. However why would it result in the negative, you would think that it doesn't matter if you go from a to b or b to a as it would result in the same area under the curve. so my question is why is the integral negative when changing the bounds?

Let us define a very simple integral:   $f(x) = \int_{a}^{b}{x}$    for $a,b\ge 0$.  Why do we have the identity $\int_{a}^{b}{x} = -\int_{b}^{a}{x}$?  I drew the graphs and thought about it but to me integration, at least in two-dimensions, is just taking the area underneath a curve so why does it matter which direction you take the sum?


I just duplicated a part of a mesh but as I select one of them, both are being selected. I learned about the 'P' hotkey, however, it's not working in my case. I'm using the latest version of Blender. I used the 'P' button for the selection menu but it's not working. Please tell me another way to do it  Project link:

I've just made a set of armor by using a male body mesh model I downloaded and selecting certain faces from the model and duplicating them to create viable armor pieces.   Since the pieces are just duplicated from the same mesh male model, then it's still part of the same object.   How do I separate the armor piece from the model to make the pieces separate?


Let $G$ denote the set of edges between vertices $1,...,N$ such that $G$ connects all vertices, i.e., for any distinct vertices $x,y =1,2,...,N$, there exists a connected paths in $G$ from $x\mapsto y$. Then how would one prove $$ \sum_{G}(-1)^{|G|} = (-1)^{N-1}(N-1)!, \quad N\ge 1 $$ where $|G|$ is the number of edges of $G$

While trying to derive some formula, I encountered the following problem. Consider the set $C_n$ of all connected graphs on $n$ vertices. What is $$ \sum_{G \in C_n} (-1)^{|G|} ? $$ In other words, if we give a graph with an even number of edges a weight of $+1$, and a graph with an odd number of edges a weight of $-1$, what is the total weight of all connected graphs?  Here is an example: when $n=3$, any two edges form a connected graph, and the complete graph is also connected, so the value of the sum is $3 - 1 = 2$.  Surprisingly, the answer is $$ \sum_{G \in C_n} (-1)^{|G|} = (-1)^{n-1} (n-1)!. $$ This can be proved using the "exponential formula" (see e.g. the freely-available generatingfunctionology). The exponential generating function of all graphs, counted according to their parity, is $1+x$ (since for $n \geq 2$, the even and odd graphs cancel). Hence the exponential generating function for all connected graphs (counted according to their parity) is $$ \log (1+x) = \sum_{n \geq 1} (-1)^{n+1}\frac{x^n}{n} = \sum_{n \geq 1} (-1)^{n+1}(n-1)!\frac{x^n}{n!}. $$  My question is:     Is there an enumerative proof of the formula $$ \sum_{G \in C_n} (-1)^{|G|} = (-1)^{n-1} (n-1)! \quad ? $$


I have a junit + powermock test which is giving me NullPointerException after execution.  Error:  Running com.ebayenterprise.publicapi.events.dao.EventLogDaoTest Tests run: 1, Failures: 0, Errors: 1, Skipped: 0, Time elapsed: 0.36 sec <<< FAILURE! - in com.ebayenterprise.publicapi.events.dao.EventLogDaoTest testGetNextEventIdSequence(com.ebayenterprise.publicapi.events.dao.EventLogDaoTest)  Time elapsed: 0.05 sec  <<< ERROR! java.lang.NullPointerException: null     at com.ebayenterprise.publicapi.events.dao.EventLogDaoTest.testGetNextEventIdSequence(EventLogDaoTest.java:27)   EventLogDaoTest.java  public class EventLogDaoTest {      private final DataSource dataSource = Mockito.mock(DataSource.class);     private final PlatformTransactionManager txManager = Mockito.mock(PlatformTransactionManager.class);     private static final long MOCK_EVENT_ID = 1001;     private JdbcTemplate jdbcTemplate;     private EventLogDao eventLogDao;      @Before     public void setup() {         eventLogDao = new EventLogDao(dataSource, txManager);     }      @Test     public void testGetNextEventIdSequence() {         when(jdbcTemplate.queryForLong("select next-seq-value from table")).thenReturn(MOCK_EVENT_ID);         long eventId = eventLogDao.getNextEventIdSequence();         assertTrue(eventId == 1001);     }  }   EventLogDao.java  @Repository public class EventLogDao extends BaseEventLogDao {      public EventLogDao(DataSource dataSource, PlatformTransactionManager transactionManager) {         super(dataSource, transactionManager);     }  }   BaseEventLogDao.java  public abstract class BaseEventLogDao {      protected final JdbcTemplate jdbcTemplate;     protected final PlatformTransactionManager transactionManager;      public BaseEventLogDao(DataSource dataSource, PlatformTransactionManager transactionManager) {         this.jdbcTemplate = new JdbcTemplate(dataSource);         this.transactionManager = transactionManager;     }  public long getNextEventIdSequence() {         long eventIdSeq = jdbcTemplate.queryForLong(SELECT_EVENT_LOG_SEQUENCE_SQL);         System.out.println("eventIdSeq = " + eventIdSeq);         return eventIdSeq;     }  }

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 am using the APK info app to know what activities' name are:    package name.v2.acyivities.SplashActivity    package name.v2.acyivities.OnBoardingChooseRegion   (...)  And then I create the DesiredCapabilities:  public AndroidDriver remoteRunningDevice() throws  Exception {      DesiredCapabilities cap = new DesiredCapabilities();     cap.setCapability("platformName", MobileConfig.platformName);      cap.setCapability("deviceName", MobileConfig.emulatorDeviceName);      cap.setCapability("platformVersion", MobileConfig.emulatorPlatformVersion);      cap.setCapability("app-package", MobileConfig.appPackage);     cap.setCapability("appActivity","MobileConfig.appPackage" +".v2.acyivities.OnBoardingChooseRegion");     cap.setCapability("noSign", true);      driver = new AndroidDriver(new URL(MobileConfig.url), cap);     driver.manage().timeouts().implicitlyWait(10, TimeUnit.SECONDS);      return driver; }   But it can't be run and result is:  java.lang.NullPointerException   How do I solve this?

is there any way to test an application which is already installed For Eg. i want to test the calculator or google map application ?  my Current Appium version is 1.3.4.1


I develop a C code on Debian. I am looking for a program to monitor memory consumption of my code in real-time. The only value I care is the maximum RAM consumption, it should hold the value even if the the program is killed (e.g. by SIGKILL) . Could anyone suggest a handy tool for it?  Normally I use top -p pidnumber, but it outputs with too much delay and if my program gets killed, it does not show the RAM consumption just before it is ended.

time is a brilliant command if you want to figure out how much CPU time a given command takes.  I am looking for something similar that can measure the max RAM usage of the program and any children. Preferably it should distinguish between allocated memory that was used and unused. Maybe it could even give the median memory usage (so the memory usage you should expect when running for a long time).  So I would like to do:  rammeassure my_program my_args   and get output similar to:  Max memory allocated: 10233303 Bytes Max memory used: 7233303 Bytes Median memory allocation: 5233303 Bytes   I have looked at memusg  but I regard that as somewhat a hack.


Noob here. I do not know why the userInput variable is not coming out in the alertbox i am creating <!DOCTYPE HTML> <html>     <head>         <title>fns</title>     </head>     <body>         <button onclick="namebox()">Enter Name</button>         <button onclick="yoyoyo()">Generate Greeting!</button>      </body>     <script>     function namebox() {         var userInput = prompt("Enter your name");     }     function yoyoyo() {         alert("Hello" + userInput);     }     </script> </html>```

What is the scope of variables in javascript? Do they have the same scope inside as opposed to outside a function? Or does it even matter? Also, where are the variables stored if they are defined globally?


I have a array as follows, and I would like to change the value of the middle entry of the second row.       array = [[0, 0, 0],               [0, 0, 0],               [0, 0, 0]]     array[1][1] = 1   expected output:      [[0, 0, 0],       [0, 1, 0],       [0, 0, 0]]   however, it seems like the value of the whole column is changed:      [[0, 1, 0],       [0, 1, 0],       [0, 1, 0]]   Why does this not work? How do I just change the value of the entry that I want?  Thanks!

I needed to create a list of lists in Python, so I typed the following: my_list = [[1] * 4] * 3  The list looked like this: [[1, 1, 1, 1], [1, 1, 1, 1], [1, 1, 1, 1]]    Then I changed one of the innermost values: my_list[0][0] = 5  Now my list looks like this: [[5, 1, 1, 1], [5, 1, 1, 1], [5, 1, 1, 1]]    which is not what I wanted or expected. Can someone please explain what's going on, and how to get around it?