Let $a$, $b$, $c$ be integers. Show that if $a$ and $b$ are coprime   and $a$ and $c$ are coprime then $a$ and $bc$ are coprime.   My approach:  Suppose that $a$ and $b$ are coprime, $a$ and $c$ are coprime but $a$ and $bc$ are not coprime. This implies $gcd(a,b)=1$, $gcd(a,c)=1$ and that $\exists$ $d$ $\in$ $\Bbb N$ such that $gcd(a,bc)=d$ where $d>1$. Since $d>1$ then $\exists$ $p$ a prime number such that $p|d$.  We know that $p|d$ and $d|a$, this implies $p|a$. Also, $p|d$ and $d|bc$, this implies $p|bc$. By Euclid's lemma, we have two cases:  Case 1: $p|a$ and $p|b$, this implies $gcd(a,b)\ge p$. Since $p\ne1$, we have contradiction.  Case 2: $p|a$ and $p|c$, this implies $gcd(a,c)\ge p$. Since $p\ne1$, we have contradiction.  Since these cases are collectively exhaustive, then we have contradiction and $a$ and $bc$ must be coprime.  Is this approach sound? Is there an easier way?


Guys, I just wonder if people are allowed to have civilized discussion (on any IT topic) on this forum without actually being accused of starting a row. I'm asking this question for a reason that few days I've asked few questions referring to VM, JIT etc. and compared them to C++ way and despite the fact that I've explained myself that I'm not starting any agro with anyone, that I'm really just genuinely curious, my post was first closed and then removed. I'm asking: What's wrong with asking nonstandard questions which sometimes my be quite difficult to answer? Thanks


Using the same secret key for encryption and authentication in a Encrypt-then-MAC scheme

Is it a weakness to use a single shared secret for protecting messages using a Encrypt-then-MAC scheme?    Assuming a system is using AES-256-CBC and a SHA1-HMAC and the same secret key for both operations.  Upon intercepting one of these messages and attacker could brute force this secret key by trying to solve the HMAC or by successfully decrypting the first block of the ciphertext.  Performing  a decryption on a single block of AES-256 should be a lighter operation than performing a SHA1-HMAC on a potentially large message.  Therefore AES-256 is ideal for a massively parallel brute-force attack and the use of the SHA1-HMAC doesn't hurt the system.  Is this approach sound, or is there an attack that has not been taken into consideration?


Two ethernet ports on motherboard. How can I get double the bandwidth?

Direct Question:  My evga classified motherboard has two ethernet ports.  I want to use them simultaneously to improve the speed of a remote connection.  (Yay for programming remotely).  How do I do this?  At present /etc/network/interfaces:  auto lo eth0 eth1  iface lo inet loopback  iface eth0 inet static address 192.168.1.202 netmask 255.255.255.0 gateway 192.168.1.2  ifrace eth1 inet static address 192.168.1.201 netmask 255.255.255.0   What should I change? Is there a package I need to install to bond the two channels.  Background: I do a lot of remote computing both from home to office and office to home.  But (to take my ISP out of the equation), let's frame the question as if I'm really just interested in maximizing the file transfer rate between two computers on the same (local) network.  Both boxes have dual ethernet motherboards.  Using a simple Linksys WRT54GS as a 5 port switch (ignore wireless and isp) -- how do I maximize the transfer rates between the computers?  Please Note: I'm not interested in load balancing -- Correct me if I'm wrong, but I want to bond the two channels together so that the box appears as if it has one connection that's twice as fast.


When should someone be a coauthor instead of being in the acknowledgements?

We had a master's student working on our project.  He set up a database for us, and wrote some of the initial code with me in a pair programming session.  At one point, he had more commits to the repository than any of the other students working on the project.  Then he went to do an internship for the summer, and after that my advisor did not want to keep him on the project for some reason, even though I thought he was friendly and easy to work with.  My advisor chose not to list him as a coauthor, and put him in the acknowledgements section instead.  However, there was another guy (a professor) who didn't write any code at all, and wasn't there throughout most of the project, but he wrote the introduction and related work sections for us, and he got listed as a coauthor, even though he probably did a day's worth of work on the project (maybe two).  In fact, my advisor gave him the coveted last author position, even though my advisor came up with the idea and directed the whole project.  What determines who gets put as a coauthor, and who gets put in the acknowledgement sections?


Proof matrix $A=\begin{bmatrix} 1 & 1 \\ 0 & 1 \end{bmatrix}^n , \text{ when } n \in \mathbb{N}$

Problem   Find generalitazion for matrix A exponents, when $n\in\{1,2,3,\dots\},n \in \mathbb{N}$    $$A^n=\begin{bmatrix} 1 & 1 \\ 0 & 1 \end{bmatrix}^n , \text{ when } n \in \mathbb{N}$$  Proof generalization by induction.   Attempt to solve   By computing a set of $A$ exponent's $n\in \{\ 1,2,3,4 \}$. It is possible  to form generalization that is applicable for set $n\in \{1,2,3,4 \}$  $$ A^1=\begin{bmatrix} 1 & 1 \\ 0 & 1 \end{bmatrix},A^2=\begin{bmatrix} 1 & 2 \\ 0 & 1 \end{bmatrix},A^3=\begin{bmatrix} 1 & 3 \\ 0 & 1 \end{bmatrix},A^4=\begin{bmatrix} 1 & 4 \\ 0 & 1 \end{bmatrix} \dots A^n =\begin{bmatrix} 1 & n \\ 0 & 1 \end{bmatrix} $$   Induction proof   Induction hypothesis  Assume expression is valid when $n=k$  $$ A^k = \begin{bmatrix} 1 & k \\ 0 & 1\end{bmatrix} $$  Base case  When $n=1$ $$ A^1=\begin{bmatrix} 1 & 1 \\ 0 & 1 \end{bmatrix} $$ which is valid by definition.   Induction step  When $n=k+1$  $$ A^{k+1} = \begin{bmatrix} 1 & k+1 \\ 0 & 1\end{bmatrix}$$  $$ A^{k+1}=A^kA^1 $$  By utilizing induction hypothesis we have  $$ \implies A^{k+1}=\begin{bmatrix} 1 & k \\ 0 & 1\end{bmatrix}\begin{bmatrix} 1 & 1 \\ 0 & 1 \end{bmatrix} $$ By utilizing matrix multiplication we have $$ \implies A^{k+1} \begin{bmatrix} 1\cdot 1 + k\cdot 0 & 1 \cdot 1 + 1 \cdot k \\ 0 \cdot 1 + 1 \cdot 0 & 0 \cdot 1 + 1 \cdot 1 \end{bmatrix} $$ $$ \implies A^{k+1}=\begin{bmatrix} 1 & k+1 \\ 0 & 1 \end{bmatrix} $$  $$ \tag*{$\square$} $$     EDIT   The point of posting this was to have comment on if my solution seems correct or not. If you can notice something that doesn't look right, let me know !


In a question I am doing it says:     Show explicitly that the function $$y(t)=\frac{-gt^2}{2}+\epsilon t(t-1)$$ yields an action that has no first order dependency on $\epsilon$.   Also my textbook says that     [...] if a certain function $x_0(t)$ yields a stationary value of $S$ then any other function very close to $x_0(t)$ (with the same endpoint values) yields essentially the same $S$, up to first order of any deviations.   I am confused about the first order bit? In the first case does it mean that $\frac{\partial S}{\partial \epsilon}=0$ or that it does not depend of $\epsilon$ but may take some other constant value. In the second case does it mean likewise or something different, please explain?


I have been trying to understand "wave-particle duality" and other cases related to it. I am currently a college level student. I have few question which I am not getting answers clearly.   In double slit experiment, A particle behave like a wave, then how is "wave-particle duality" explained? I mean, If the particle behave like wave, then is it generating a wave or behaving as a wave? Is that wave going horizontally through slits (Double Slit Experiment) or vertically up and down or in which direction/axis the particle is vibrating to have a specific frequency?  How does light behave as waves in it? and how does observer modify the experiment?  I may be thankful to you, If you clear my problems. I have read the theories on Wikipedia and other informational sites and tried to understand it.


Bash Automation without asking for password

How do I automate this without being ask for password every time it loops?  #!/bin/sh for k in 2 3 5 10; do     sudo ldconfig ########  # password asking here everytime     python experiments.py  done


"apt-get update" fails with "Malformed entry in list file" error

After logging in as root, I input apt-get update, and it gives me:   E: Malformed entry 51 in list file /etc/apt/sources.list (URI parse) E: Malformed entry 1 in list file /etc/apt/sources.list.d/docker.list (Component) E: The list of sources could not be read.   What's wrong with it?  Seeing many related answers I input the code: sudo -H gedit /etc/apt/sources.list  then it shows:  # deb cdrom:[Ubuntu 16.10 _Yakkety Yak_ - Release amd64 (20161012.2)]/ yakkety main restricted  # See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to # newer versions of the distribution. deb http://us.archive.ubuntu.com/ubuntu/ yakkety main restricted # deb-src http://us.archive.ubuntu.com/ubuntu/ yakkety main restricted  ## Major bug fix updates produced after the final release of the distribution. deb http://us.archive.ubuntu.com/ubuntu/ yakkety-updates main restricted # deb-src http://us.archive.ubuntu.com/ubuntu/ yakkety-updates main restricted  ## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu ## team. Also, please note that software in universe WILL NOT receive any ## review or updates from the Ubuntu security team. deb http://us.archive.ubuntu.com/ubuntu/ yakkety universe # deb-src http://us.archive.ubuntu.com/ubuntu/ yakkety universe deb http://us.archive.ubuntu.com/ubuntu/ yakkety-updates universe # deb-src http://us.archive.ubuntu.com/ubuntu/ yakkety-updates universe  ## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu  ## team, and may not be under a free licence. Please satisfy yourself as to  ## your rights to use the software. Also, please note that software in  ## multiverse WILL NOT receive any review or updates from the Ubuntu ## security team. deb http://us.archive.ubuntu.com/ubuntu/ yakkety multiverse # deb-src http://us.archive.ubuntu.com/ubuntu/ yakkety multiverse deb http://us.archive.ubuntu.com/ubuntu/ yakkety-updates multiverse # deb-src http://us.archive.ubuntu.com/ubuntu/ yakkety-updates multiverse  ## N.B. software from this repository may not have been tested as ## extensively as that contained in the main release, although it includes ## newer versions of some applications which may provide useful features. ## Also, please note that software in backports WILL NOT receive any review ## or updates from the Ubuntu security team. deb http://us.archive.ubuntu.com/ubuntu/ yakkety-backports main restricted universe multiverse # deb-src http://us.archive.ubuntu.com/ubuntu/ yakkety-backports main restricted universe multiverse  ## Uncomment the following two lines to add software from Canonical's ## 'partner' repository. ## This software is not part of Ubuntu, but is offered by Canonical and the ## respective vendors as a service to Ubuntu users. # deb http://archive.canonical.com/ubuntu yakkety partner # deb-src http://archive.canonical.com/ubuntu yakkety partner  deb http://security.ubuntu.com/ubuntu yakkety-security main restricted # deb-src http://security.ubuntu.com/ubuntu yakkety-security main restricted deb http://security.ubuntu.com/ubuntu yakkety-security universe # deb-src http://security.ubuntu.com/ubuntu yakkety-security universe deb http://security.ubuntu.com/ubuntu yakkety-security multiverse deb http yakkety main   # deb-src http yakkety main deb http://dl.openfoam.org/ubuntu yakkety main # deb-src http://dl.openfoam.org/ubuntu yakkety main # deb-src http://dl.openfoam.org/ubuntu yakkety main # deb-src http://security.ubuntu.com/ubuntu yakkety-security multiverse   Please explain to me how to remove this malformed line - line 51 is deb http yakkety main 6th from the end.


If $a, b>0$ and n is a positive integer, prove that: $(1+\frac{a}{b})^n+(1+\frac{b}{a})^n\ge 2^{n+1}$ I solved it in the following way: $(1+\frac{a}{b})^n+(1+\frac{b}{a})^n \ge (2\sqrt{\frac{a}{b}})^n+(2\sqrt{\frac{b}{a}})^n=2^n((\frac{a}{b})^n+(\frac{b}{a})^n)$ It is enough if $(\sqrt{\frac{a}{b}})^n+(\sqrt{\frac{b}{a}})^n\ge2$ If $n=1$: $\sqrt{\frac{a}{b}}+\sqrt{\frac{b}{a}}\ge2$ $\frac{a}{b}+\frac{b}{a}+2\ge 4$ which holds true. If it holds true for $n=k$: If $b\ge a$: $(\sqrt{\frac{a}{b}})^k+(\sqrt{\frac{b}{a}})^k$ $(\sqrt{\frac{a}{b}})^{k+1}+\sqrt{\frac{a}{b}}*(\sqrt{\frac{b}{a}})^k\ge 2$ $(\sqrt{\frac{a}{b}})^{k+1}+(\sqrt{\frac{b}{a}})^{k-1}\ge 2$ And since $b\ge a$ We have that the original proposition holds true for k+1. Similarly, we prove that it is true if $a\ge b$. Hence because of induction, it holds true. Could you please show some other methods of solving this question easier?


$h\mid (3a + 5b)$, prove $h\mid a$ and $h\mid b$

I have this homework question.  "For any integer $a$ and $b$, prove that $\gcd(a,b) = \gcd(3a+5b,11a+18b)$."  I know that if $ g = \gcd(a,b)$   and   $h = \gcd(3a+5b,11a+18b)$   then   $g = h$   iff $g \leq h $ and $h \leq g$.  I successfully proved that $g \leq h$.   Now, to prove that $h \leq g$, I need to prove that $h\mid (a,b)$, but I can't seem to find how I should prove this.  $\because h = gcd(3a+5b,11a+18b) \Rightarrow h \mid (3a+5b)$   From here I'm stuck on how to get $a$ and $b$ seperate.   Any hint would be very helpful.   Edit: Since this question was marked duplicate and I was given these ,, links to check, I did check them and didn't find my answer because all of these questions have given that $gcd = 1$, whereas my question doesn't tell if $gcd = 1$ and furthermore these questions are a bit complex for me to understand since I'm a new learner of number theory.


Looking for a book where a girl wakes up in an android body after Earth is destroyed

The novel is about a girl who wakes up in an android body after Earth is destroyed by a mysterious species who eradicate technology. The new society she finds herself in prohibits technological advances to prevent future discoveries. The story outlines her efforts to lead mankind into a new era of technological discovery beginning with black powder and sailing.


Functional equation, $f(x) f(y) = f(x + y) + xy$

$$f(x) f(y) = f(x + y) + xy$$  I found by substitution that $f(0)=1$, and that either $f(1)$ or $f(-1)$ or both are equal to zero. I tried to do casework on the $f(1)$ and $f(-1)$, but don't know how to find every solution for $f$. Hints? Any way to prove that a solution is the only one?


Help me please to prove that matrix exponential which defined as:  $e^{A}=\sum\limits_{k=0}^{\infty }\frac{A^{k}}{k!}$ converges for all matrix $A$  Thanks beforehand.


Re Exporting complete data from Google Earth to QGIS

I am trying to export Google Earth searches as a KML file to QGIS. How come all existing locations of a search (e.g. Walmart) in the United States only shows select locations. I'm doing a project on food deserts and want to include all major chains and their locations in the U.S.


I was looking at coreutils and found this as one of the files included as part of coreutils:  /usr/bin/[. What is [ and what does it do? It is an executable. I just don't know what it does or how to use it. $ file /usr/bin/[   /usr/bin/[: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), dynamically linked (uses shared  libs), for GNU/Linux 2.6.15, stripped    When I try to run it, I think it is defaulting to the bash built in line expansion. Instead of actually running the file. $ "/usr/bin/[" /usr/bin/[: missing ‘]’ $ /usr/bin/\[ /usr/bin/[: missing ‘]’


If $\lim f(x)$ exists and $\lim g(x)$ do not, when $x$ approaches $a$ , why $\lim[f(x)+g(x)]$ does not exist?

If  $\lim f(x)$ exists and $\lim g(x)$ do not, when $x$ approaches $a$, why $\lim[f(x)+g(x)]$  does not exist?  need some help over here, to prove the above statement


It was done with the help of John, Sam, and "me"—or "myself"?

Which is correct: "It was done with the help of John, Sam and me" or "It was done with the help of John, Sam and myself"


HAProxy returns error if server goes down before health check has occured

Let's say I have web01 in my list of backend servers, and web01 goes down.  It will take a few seconds for HAProxy to notice the server is down (depending on the health check interval and how long the timeout is) and take it out of rotation.  If a request comes in before that's happened, the client will end up receiving a 503 Service Unavailable error.  What I'd like to happen is to have HAProxy automatically re-try that same request again on another server.  I realize the request would end up being really slow, but it would end up resulting in a success rather than an error.  Is there a way to configure HAProxy to retry the HTTP request on another server instead of erroring out?  Ideally, I don't ever want a client to receive an error if there's any working servers in the cluster.  Here's my haproxy.cfg:  global         maxconn 4096         debug  defaults         mode    http         contimeout      5000         clitimeout      50000         srvtimeout      50000  frontend http-in         bind *:80         acl service1 path_reg ^/service1/         acl service2 path_reg ^/service2/         use_backend service1 if service1         use_backend service2 if service2  backend service1         server web01 127.0.0.1:85 check         server web02 127.0.0.1:86 check         reqrep ^([^\ :]*)\ /service1/(.*)     \1\ /\2  backend service2         server web03 127.0.0.1:87 check         server web04 127.0.0.1:88 check         reqrep ^([^\ :]*)\ /service2/(.*)     \1\ /\2


All of my Firefox add-ons have been disabled suddenly, how can I re-enable them?

All of my Firefox extensions were spontaneously and simultaneously disabled (converted to Legacy status) a few moments ago.  How can I re-enable them? Firefox 66.0.3 (64-bit)


Allow user to install from unknown sources on Android 5.0

I have Nexus 10 and have 2 users on it. On Android 4.4 both Users could install application from unknown sources.  After upgrade to Android 5.0 admin user has Security-Unknown Sources  flag is "on" but secondary User has this flag greyed and disabled.  How can I switch it on?


Looking for a YA book about a boy that learns to use powers from an adept in a weird house that appears abandoned from the outside

I am looking for a YA book about a boy who learns to use powers from a mind-adept, in a seemingly abandoned house. The adept helps him open his mind by using a cube. One of his powers, I believe, is to go into dreams of people that  he knows. He helps his young female neighbor friend by doing this, opening a door in her mind. He tries to open the mind-door of a local older bully, but finds out the young man can't be helped because he has been abused mentally and physically. I don't believe the book I read is past 1995. It might have the word "adept" in it.


Why did my Sourdough starter stopped rising?

Ok so I started my starter (no pun intended) a few days ago. I got a recipe that said I should keep it at room temp and feed it once a day with 1/2 cup of any flour (I used whole wheat) and 1/4 cup of water. I live in a place over the sea level, near a mountain and it was a pretty warm weather when I started.  So this is what I did:  Day 1: 1 cup flour, 1/2 cup of water, got a thick consistency. Leave it on top of the fridge. Day 2: I see some bubbles on the bottom, get rid of half the mix and feed. Day 3: I see a few bubbles on the top, a lot of bubbles on the bottom and it rise a considerable amount. I get rid of half, feed and keep on with my day. Day 4: It did not rise or have as much bubbles as before. The weather changed a bit, not as hot but still warm. Still got rid of half and feed. Day 5: No change whatsoever, still some bubbles on the bottom but nothing on the top nor it rise. The weather changed, today it's cold and raining.   Everyday it got a vinegary smell which I read is supposed to happen.   I feel like my dough predicted the weather haha. Anyway, what should I do now? Do I keep on feeding it? How long until I know that it didn't work and should start a new one?


How to input two arguments with getopts?

I am writing a simple bash script. My script installs . The problem is I can't add two arguments. I want to write something simple like this:  ./ppa.sh -i ppa:chris-lea/node.js nodejs   I tried this,  but doesn't read the second argument 'nodejs'...  #! /bin/sh  # Install/add PPA or Program   while getopts ":i:e:" option; do  case $option in   i)    echo received -i with $OPTARG ang='sudo apt-add-repository'    ;;   e)    echo received -e with $OPTARG ang='other line'    ;;   :)    echo "option -$OPTARG needs an argument" exit    ;;   *)    echo "invalid option -$OPTARG"  exit    ;;  esac  # done     if [ "`echo $OPTARG | cut -d ':' -f1`" == "ppa" ]; then echo 'is a ppa'     $ang $OPTARG ; sleep 2s && sudo apt-get update; clear         sudo apt-get -y install $OPTARG2     fi done


I have a 12 volt power supply rated at 250 amps for my landscape lights. If I switch to led's with little current draw will the power supply still draw 250 amps or only what is required of the connected led's?


I want to completely mute specific sounds (not all). Using /stopsound is a quite imperfect way of doing so, because then there's fractions of the "muted" sound(s) sometimes still "slipping through" causing them to not be completely muted. Does anyone know if it is possible to completely mute them, and if so, how?  (Resourcepack may be used, as long as you can tell me how to remove/replace a sound already existing in the game)  Edit: I need an explanation on what to do, I have searched for how to do sound files in resourcepacks, but I need to know how to add sounds (as in, I don't know what name to use for a specific sound in the game). I want all crossbow sounds, music and player sounds all to be muted. But in all 1.14 resourcepacks that I have found up until now, none have sound files for crossbows, usually none at all actually.  In short, I need to know how to name the sound files.


What's the relationship between the Monster's planet and Earth?

In Pixar's Monsters films (Monsters Inc. & Monsters U), the Monsters living on an Earth-like planet that is clearly not Earth.  Via their special doors, they're able to come to Earth.  It's unclear to me though how their planet and Earth are related.  Is the Monsters' planet in a parallel dimension?  Is it elsewhere in the same universe?  Is the Monsters' planet Earth in the far future ala Planet of the Apes?  How are Earth and the Monsters' planet related/connected?


Bayesian and frequentist reasoning in plain English

How would you describe in plain English the characteristics that distinguish Bayesian from Frequentist reasoning?


How to solve java.lang.StackOverflowError

This is the first time I got this error.  This code basically gets the sum of each item sold in a particular date.  Any tips on resolving this problem? Thanks.          Statement statement = connection.createStatement();        String query = "SELECT itemcode, SUM(quantity) AS 'Total Sales Per Day' "                + "FROM sales "                + "WHERE real_pur_date = '" + date + "' "                + "GROUP BY itemcode ";        ResultSet rs = statement.executeQuery( query ); // this line gets the error / exception        while( rs.next() ){            Vector row = new Vector();            row.add( rs.getString( "itemcode" ) );            row.add( rs.getInt( "Total Sales Per Day" ) );            dailyData.add( row );        }        statement.close();    Exception in thread "AWT-EventQueue-0" java.lang.StackOverflowError at com.mysql.jdbc.Util.handleNewInstance(Util.java:431) at com.mysql.jdbc.ResultSetImpl.getInstance(ResultSetImpl.java:383) at com.mysql.jdbc.MysqlIO.buildResultSetWithRows(MysqlIO.java:3140) at com.mysql.jdbc.MysqlIO.getResultSet(MysqlIO.java:491) at com.mysql.jdbc.MysqlIO.readResultsForQueryOrUpdate(MysqlIO.java:3118) at com.mysql.jdbc.MysqlIO.readAllResults(MysqlIO.java:2288) at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2709) at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2677) at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2627) at com.mysql.jdbc.StatementImpl.executeQuery(StatementImpl.java:1556) at posinventory.Controller.StatisticEngine.getDailyData(StatisticEngine.java:20) at posinventory.Statistic.refreshTableDailyStat(Statistic.java:36) at posinventory.Statistic.refreshTableDailyStat(Statistic.java:37) at posinventory.Statistic.refreshTableDailyStat(Statistic.java:37) at posinventory.Statistic.refreshTableDailyStat(Statistic.java:37)


Can I implement a SaaS infrastructure with Juju?

My aim is to implement software as a service using cloud computing. Can we use Juju for implementation of Software as a service? We can deploy MySQL and Wordpress using Juju. But I want to install other applications (e.g matlab etc) on my server and want to give access for those applications to client.


Is it possible to redirect a command's output to cd? For example, I searched for a directory using locate and got the path to it. Now, instead of writing a cd path, can I redirect the locate output to cd?  I tried this:  $ locate Descargas | grep Descargas$ /home/oliver/Descargas $ locate Descargas | grep Descargas$ | cd $ locate Descargas | grep Descargas$ > cd $ locate Descargas | grep Descargas$ < cd /home/oliver/Descargas $    No luck. This probably isn't particularly useful, but I'm curious.


Evaluating an integral by substitution and special functions

How can I evaluate this integral? $$\int_{0}^{1} \frac{dx}{\sqrt{{1+x^4} }}$$ I tried using the substitution $x=\mathrm{e}^{-u}$ but I got nowhere.


Why normal acceleration doesn't bring a change in speed?

Suppose There's a particle of mass m moving with speed $v_{0}$, at certain moment a force starts acting on it (centripetal force) and it start uniform circular motion  Now every other reference states that centripetal force only brings about change only in direction  But plugging-in things in the equations paint a different picture  suppose  normal/centripetal acceleration = $A$  then $|v| = \sqrt{v_{0}^2+\frac{(A t)^2}{1}}$  we can certainly see that factor of $t$ will bring change in magnitude of velocity   Secondly, why the velocity is always tangential to the circle, but how can we mathematically show such? Intuitively for me if there's constant acceleration toward a certain then at some point of time, the body should 'slack' and fall toward the direction of acceleration   Here' a picture for a reference:


Is there a visual web editor based on bootstrap?

Bootstrap is a great framework, and I want know if there is a tool that gives you the possibility of dragging html components, re-sizing and moving them, changing colours, all while generating the bootstrap html code.  I don't want to use Dreamweaver because you need to go and add classes and IDs to the html, which could be a pain sometimes.


Every proper normal subgroup of a $p$-group contains non-trivial central elements

How do I prove the following statement?     Let $G$ be a $p$-group, $H$ - its normal subgroup, $H\neq \{e\}$. Then the center of $G$   $$ Z(G)=\{a\in G\ \ |\ \ \forall x\in G\ \ ax=xa\} $$   has non-trivial intersection with $H$, i.e. $H\cap Z(G) \neq \{e\}$.   As far as I understand, this is about finding central elements in a normal subgoup. Maybe there is some straightforward way to construct such an element (using inner automorphisms, for instance...)?


Why synchrotron uses RF field and not static field to accelerate electrons?

In synchrotrons electrons lose energy while emitting light so accelerating fields are used to boost up their speed back to >99% of light speed.  Why RF (time varying) fields are used for accelerating electrons? Why not constant field?  In  it is said that the energy gain from a varying field is: $$\Delta W = q V_0 T \cos\phi = \Delta W_{\text{DC}} T \cos\phi$$  where $\Delta W_{\text{DC}}$ is the the energy gain from a static DC field and $T$ is the transit time factor, $T = \frac{\beta\lambda}{\pi L} \sin\frac{\pi L}{\beta\lambda}$.  But isn't $T\cos\phi$ always smaller than 1?


I can't open my ipad mini. Please send help :((

I have jailbroken my ipad mini months ago. 2 weeks ago i decided to erase all data. I didnt turn off anything i just went to general and deleted all data. I waited for my ipad to restart but it didnt. Its been days now, but still i cant open my ipad. Only an apple logo appears with a bar below that doesnt seem to have any progress. I did everything, charged my device, waited until its battery is dead then charge it again but same apple logo appears. What do I do? :(


I have created a program which searches for files in a source folder. If it finds any file, it processes that file and moves it to a destination folder, then looks for a new file in the source folder. It has to keep on checking the source folder for a file.  I have used a thread to look for files in the source folder. The problem I am facing is whenever any exception is thrown during file processing, the thread gets stopped. I want the thread to be running even if an exception is thrown. It has to move the file that caused the error to some other folder and look for a new file in the source folder. How can I make the thread keep on running?  Eg:  public void run() {     try {         searchfile();     }     catch(Exception e) {         e.printStackTrace();     } }  public void searchfile(){   ... }     Update :   I should be more clear in my question. Actually there are 4 source folders and 4 destination folders. I have to perform the same operation in each source & destination pair. So i have created 4 threads in one class and do the operation in separate class.  class MainClass {    public static void main(String[] args){       for(int i=0;i<4;i++){          SearchClass search = new SearchClass();          Thread thread = new Thread(search);          thread.start();      }    }    }  class SearchClass {    public void run() {    try {       searchfile();    } catch(Exception e) {       e.printStackTrace();    } }  public void searchfile(){ ... } }   All the thread wont stop running eventhough it caught any exception in middle. How can i do that?


Show that $G$ is a group if the cancellation law holds when identity element is not sure to be in $G$

Having already read through , however in Herstein's Abstract Algebra, I was required to prove it when we're not sure if identity is in the set.  If $G$ is a finite set close under an associative operation such that $ax=ay$ forces $x=y$ and $ua=wa$ forces $u=w$, for every $a, x, y, u, w\in G$, prove that $G$ is a group.  How to show it then? I have no idea what to do at all.


Difference between declaring variables before or in loop?

I have always wondered if, in general, declaring a throw-away variable before a loop, as opposed to repeatedly inside the loop, makes any (performance) difference?  A (quite pointless) example in Java:  a) declaration before loop:  double intermediateResult; for(int i=0; i < 1000; i++){     intermediateResult = i;     System.out.println(intermediateResult); }   b) declaration (repeatedly) inside loop:  for(int i=0; i < 1000; i++){     double intermediateResult = i;     System.out.println(intermediateResult); }   Which one is better, a or b?   I suspect that repeated variable declaration (example b) creates more overhead in theory, but that compilers are smart enough so that it doesn't matter. Example b has the advantage of being more compact and limiting the scope of the variable to where it is used. Still, I tend to code according example a.  Edit: I am especially interested in the Java case.


Is there difference in range in dual band routers

My home router shows two things -  Connect to a 2.4 GHz Wifi Connect to a 5 GHz Wifi I found the range of 5 GHz lower than that of 2.4 GHz Is that normal or something wrong with the router configuration?  Like right now when I am typing this question the 2.4 GHz shows 2 points or sometimes 3 points of signal strength whereas the 5 GHz shows just 1 point.  And sometimes even gives trouble loading websites.


How to start a "Workflow 2010" with CSOM in Sharepoint Online

I am creating a workflow that sends an email to internal & external users. Since, in sharepoint Online, workflows are not allowed to send emails to external users. It is not the case in "workflow 2010", so I created a "workflow 2010" and attached it to the site collection through "Sharepoint Designer 2013".    Now here is my SendEmail workflow, is there a way I could start this workflow from my Sharepoint Addin (Office 365) i.e JavaScript solution  Thanks


In C++ what are the benefits of using exceptions and try / catch instead of just returning an error code?

I've programmed C and C++ for a long time and so far I've never used exceptions and try / catch. What are the benefits of using that instead of just having functions return error codes?


How do I get Notepad++ to associate a file type with a language?

I have associated .wxs files with Notepad++. So far so good. However, it doesn't remember that it should use XML syntax highlighting. How do I associate a file-type with a Language?


Find the exact value of    $$\tan^{-1}\left(\frac{1}{2}\right)+\tan^{-1}\left(\frac{1}{5}\right)+\tan^{-1}\left(\frac{1}{8}\right)$$   How do you solve this problem? I don't know what trigonometric properties or identities may help with it.


GetSQLValueString - What is this function for, generated by Dreamweaver?

What is GetSQLValueString for? And if there is a difference for PHP7, what difference does this function make? What happens if I don't use it? Can anyone help me understand this better? if (!function_exists("GetSQLValueString"))  {     function GetSQLValueString($theValue, $theType, $theDefinedValue = "", $theNotDefinedValue = "")      {         if (PHP_VERSION < 6) {             $theValue = get_magic_quotes_gpc() ? stripslashes($theValue) : $theValue;         }          $theValue = function_exists("mysql_real_escape_string") ? mysql_real_escape_string($theValue) : mysql_escape_string($theValue);          switch ($theType) {             case "text":             $theValue = ($theValue != "") ? "'" . $theValue . "'" : "NULL";             break;                 case "long":             case "int":             $theValue = ($theValue != "") ? intval($theValue) : "NULL";             break;             case "double":             $theValue = ($theValue != "") ? doubleval($theValue) : "NULL";             break;             case "date":             $theValue = ($theValue != "") ? "'" . $theValue . "'" : "NULL";             break;             case "defined":             $theValue = ($theValue != "") ? $theDefinedValue : $theNotDefinedValue;             break;         }         return $theValue;     } }  After that, there is a section that uses this function. if($cod_u > 0){         $updateSQL = sprintf("UPDATE usuario SET cod_id=%s, nome=%s, sexo=%s   WHERE cod_u=%s",             GetSQLValueString( utf8_decode($_POST['cod_id']), "int"),             ....


Trouble opening plist files in text editor

From Finder, I can preview a plist file without any difficulties. For example, using Quick Look with ~/Library/Preferences/com.apple.Safari.RSS.plist I get a nice preview of its contents:     However, if I then try to open the file, either with TextEdit, or any other editor (I've tried SublimeText, TextMate, Vim, Nano, and Coda 2 so far), the encoding appears to be off:  bplist00Ò_"FixedRefreshesInBackgroundSettings_(com.apple.PreferenceSync.ExcludeSyncKeys ¡ 2]^����������������������������`   Here's what it looks like if I open it with TextEdit:     I've tried changing the encoding in Sublime Text and other apps, but that doesn't help.  Any thoughts?  I'm running 10.8.4.


Should possessive 's be used when there is no possession in the strict ('this is John's property') sense involved?

I was trying to write “I was using the lecture's flow of logic”, as to say that I was following the logic that was in the lecture. But I am corrected by a spell-checker.   I tried to google it, but this leads me to another much more silly question. How do you call that “..'s” that designates ownership / association? I really did try to google it, but since “'s” is such a bad search term, and any formation for "What do you call that 's you add to designate ownership" I could think of, yielded anything but the answer I was looking for.   So my question is twofold.    What is the name of that 's thing? I guess it is not the "ownership 's" :) Is it perhaps called officially the ‘possessive s’? Is saying "lecture's" (pertaining to the lecture) valid English grammar? Or is it valid grammar but people just don't say it this way?


I am trying to prove Boole’s inequality  $$P\left(\ \bigcup_{i=1}^\infty A_i\right) \leq \sum_{i=1}^\infty P(A_i).$$  I can show it of any finite $n$ using induction. What to do for $\infty$ ?


Due to curiosity, it made me wonder what is outside of the universe, is it a new chemical or just empty space?  But empty space have protons appearing and disappearing in it, it basically still has something in it.  (It might have something to do with string theory.)


Why doesn't the review list update automatically?

Referring to the first image below,   What I have seen and found easier to implement is the functionality which updates the THE YELLOW CIRCLED AREA, and it could update the THE RED CIRCLED AREA in a similar way.  This might not be exact duplicate of , for which I have .  In the Review page, the list of the recent reviewers is updated automatically, but the list of questions/answers available for review is not updated. Why?  Don't you think it should be added?      Note: I don't want this type of solution:      People who are giving this solution must see this image too:      This already has this type of button, so there isn't any need to use the Check again button.  My question is concerned with the other page.


Using sed, how do you print the first 'N' characters of a line?

Using sed what is an one liner to print the first n characters?  I am doing the following:  grep -G 'defn -test.*' OctaneFullTest.clj  | sed ....


A linear operator between $C[0,1]$ and $C[0,1]$ defined as $Tf = f + \int f$; Show $T$ is an isomorphism

Define a linear operator $T:C[0,1] \to C[0,1]$ as follows: $$Tf(x) = f(x) + \int_0^x f(u)du$$ It is easy to show that $T$ is a bounded linear operator. The statement also (1) claims that $T$ is one-to-one and onto, and (2) asks to compute $T^{-1}$. (Hence $T$ is an isomorphism due to a corollary of Open Mapping Theorem)  I need help to prove $T$ is onto: given any $g \in C[0,1]$, how to decompose it into a sum between a continuous $f$ and its antiderivative. I have trouble decomposing $g(x)=|x|$, not to mention bizarre functions like Weierstrass function. It seems impossible.  Thanks in advance for help!


Set every label node to his north west position

Is there a way in order to set every label of every single node to his north west position?


How can I make my PHP script run at a certain time everyday?

I have a PHP script that checks my database's code for validity. How can I have this run everyday at a certain time so then I can just have it run on autopilot.


Create a Date with a set timezone without using a string representation

I have a web page with three dropdowns for day, month and year. If I use the JavaScript Date constructor that takes numbers, then I get a Date object for my current timezone:  new Date(xiYear, xiMonth, xiDate)   Give the correct date, but it thinks that date is GMT+01:00 due to daylight savings time.  The problem here is that I then pass this Date to an Ajax method and when the date is deserialised on the server it has been converted to GMT and so lost an hour which moves the day back by one. Now I could just pass the day, month, and year individually into the Ajax method, but it seems that there ought to be a better way.  The accepted answer pointed me in the right direction, however just using setUTCHours() by itself changed:  Apr 5th 00:00 GMT+01:00    to  Apr 4th 23:00 GMT+01:00   I then also had to set the UTC date, month and year to end up with  Apr 5th 01:00 GMT+01:00   which is what I wanted.


I have some text file (for example json). I can use head order for the reading of the first lines. For example:  head -n 100 file.json   get me 100 first lines back. What is Linux order, which I can use to read some general lines somewhere in file? For example from the line 500 to the line 700.


How to increment in vim under windows (where CTRL-A does not work...)

While CtrlX works fine in vim under windows, CtrlA selects all (duh).  Is there a way to increment a number with a keystroke under windows?


How to add reputation to stack overflow answers?

I am new to stack overflow and i don't know how to add/mark reputation or points to those who answered a question in stack overflow. Can anyone give me steps? Thanks.


An English word which needs a prefix to be plural

Can you suggest a word in the English language which needs a prefix to be converted to a plural form?


US Green card holder with Indian passport expiring in 4 months planning a short weekend trip by road to Canada

I am a US Green card holder with an Indian passport expiring in 4 months planning a short weekend trip by road to Canada next month.  Will I be allowed to enter Canada considering my passport won't meet the "valid passport" criteria of 6 months?


I have a question about prime order group.  answer by amWhy says that:      It follows that any group of order 5 (and any group of prime order) must be generated by a single element and is hence, cyclic.    I understand previous part but this. If any group of prime order must be generated by a single element??


How to delete my own question to prevent new comments and answers?

I have recently asked a question where I wanted to scrape data from Google maps, but it turns out it's ethically wrong. I would have liked to delete my question, but as other people have spent time on it, I am not allowed to delete it. I would like to delete the question now, so nobody can comment/answer the question.


Is there a graphical way to get an RGBA value from a pixel in an image?

Is there a free way possible to open an image in a PC environment, click on the image, and obtain the RGBA value on the pixel that you clicked? I'm looking for a way to do this in a PC Windows environment.   Edit: This question asks specifically about RGBA, which is not addressed at the marked duplicate .  I don't believe any of the answers there have a way to obtain an alpha value. (RGBA as opposed to RGB).


Is it alright to use multiple h1 tags on the same page, but style them differently?

I have a webpage that I use h1 tags multiple times within various DIVs and I style h1 for each div to be the appropriate size.  For example...  #content h1 {   font-size:22px; }  #left-nav h1 {   font-size:14px; }  #content .recent-news h1 {   font-size:16px; }   Is this alright? I am worried about SEO.  What is the best way to go about this? Or am I worrying about nothing?


Continuous function whose inverse is not continuous

Suppose $f:\mathbb{R}^n\to\mathbb{R}^n$ is bijective and continuous. Is it possible that $f^{-1}$ is not continuous?  I can prove that for $n=1$ it is not possible, i.e. if $f:\mathbb{R} \to \mathbb{R}$ is bijective and continuous then $f^{-1}$ has to be continuous.  I also know that one can easily construct an example of a function $f : \mathbb{R}^2 \to S$, for some $S\subset\mathbb{R}^2,$ such that $f$ is bijective and continuous but $f^{-1}$ is not continuous. But this is different from what the above question is demanding.


I am trying to create a custom service and call it from a controller that is being used on a route. I use simple code, so I think I am missing something  The membership service:    Controller:   services file:   routing file:   The error I get:     RuntimeException: Controller   "Drupal\hsbxl_members\Controller\Test::test()" requires that you   provide a value for the "$container" argument (because there is no   default value or because there is a non optional argument after this   one). in Drupal\Core\Controller\ControllerResolver->doGetArguments()   (line 165 of   /var/www/drupalvm/web/core/lib/Drupal/Core/Controller/ControllerResolver.php).   So it seems the ContainerInterface $container is missing when the controller is being initiated. But how do i do this? Confused.  Cheers! Tom


is my profile page on Stack Overflow. I have accounts on all 104 Stack Exchange sites including the newest ones. But the profile page is showing only 101 accounts instead of 104. Is this a possible bug? I must also add that all those accounts are quite old. EDIT  page on Stack Exchange shows all the 104 accounts, so I believe none of the accounts were deleted.


Given is an $n \times n$ matrix $M_n$ with the following structure — $$M_n = \left( \begin{array}{ccccc} a_1 & 0 & \dots & 0 & b_1 \\ b_2 & a_2 &  &  & 0\\  & \ddots & \ddots &  & \vdots \\  &  & b_{n-1} & a_{n-1} & 0\\  &  &  & b_n & a_n\end{array} \right),$$ with $a_i$ and $b_i \in \mathbb{R}$ where $i \in \{1,\dots,n\}$.  Is there a name for this specific type of matrix? The non-zero entries in each row are shifted one position to the right compared to the previous row, which reminds me of a circulant matrix (though in that case, the rows share the same values, which is generally not the case for $M_n$).  Is there a short/fast way (i.e. not just using ) to compute the determinant of this type of matrix?   It might help to consider an example, so here's $M_5$: $$M_5 = \left( \begin{array}{ccccc} a_1 & 0 & 0 & 0 & b_1 \\ b_2 & a_2 & 0 & 0 & 0\\ 0 & b_3 & a_3 & 0 & 0\\ 0 & 0 & b_4 & a_4 & 0\\ 0 & 0 & 0 & b_5 & a_5\end{array} \right) = \left( \begin{array}{ccccc} a_1 &  &  &  & b_1 \\ b_2 & a_2 &  &  & \\  & b_3 & a_3 &  & \\  &  & b_4 & a_4 & \\  &  &  & b_5 & a_5\end{array} \right)$$


an 84MB Volume /dev/loop0 popped up and I don't know what it is or why it popped up

So, out of nowhere a 84MB Volume /dev/loop0 popped up. I don't know what it is or why it is there. I did recently install dropbox, Kdenlive, and VLC Media Player. Could one of those programs have caused this? Should I worry? I'm new to Linux. Should I get rid of this Volume, and if so how do I do that?


How to compute the following set of the matrix?

Let $Z$ be the matrix   $$Z = \begin{pmatrix} 1 & 2\\ 3 & 4 \end{pmatrix}$$  And the set $\text{Commu}(Z) = \{B ∈ M_{2\times2} | ZB = BZ\}$.  What is the set $\text{Commu}(Z)$? Isn't it just $\{ Z^{-1} , I\}$?  Thank you.


On a web form, what should happen when the user presses the ENTER key?  I'm writing a sign-up form - name, email, password, sign-up button: the usual sort of thing. Since I'm using JavaScript, and the page does not use the <form...> tag, I have complete control over what happens with each key press. I can make it change the focus, submit the data to the server, validate the field contents, whatever. But what should it do?  Things I'm wondering: should ENTER take the user to the next field (as per TAB key)? Should pressing ENTER while focus is on the final field submit the form?


How to limit the asynchronous job running in salesforce

I am using Queueuable Interface in trigger like this, System.enqueueJob(new testobjectmethod(trigger.new,trigger.oldMap))  My Queueuable class: public class testobjectmethod implements Queueable,Database.AllowsCallouts {        test__c[] newList;        Map<id,test__c> oldMap; public testobjectmethod(test__c[] newRecords,Map<id,test__c> oldRecords){        newList = newRecords;        oldMap  = oldRecords; } public void execute(QueueableContext context) {         Handlerclass.test(newList,oldMap);     }  }  Daily in 24 hours period , it is running more times, whenever the record operation performes asynchronously.while scheduling new job interface, i am facing the error - we ran into an error “You have exceeded the maximum number (100) of Apex  scheduled jobs” How to overcome this error?


I am trying to learn spring. So I typed up this project but on running it it gives me this error  Exception in thread "main" java.lang.NoClassDefFoundError: org/apache/commons/logging/LogFactory at org.springframework.context.support.AbstractApplicationContext.<init>(AbstractApplicationContext.java:145) at org.springframework.context.support.AbstractRefreshableApplicationContext.<init>(AbstractRefreshableApplicationContext.java:84) at org.springframework.context.support.AbstractRefreshableConfigApplicationContext.<init>(AbstractRefreshableConfigApplicationContext.java:59) at org.springframework.context.support.AbstractXmlApplicationContext.<init>(AbstractXmlApplicationContext.java:58) at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:136) at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:83) at maven.spring.trial.App.main(App.java:12) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:498) at com.intellij.rt.execution.application.AppMain.main(AppMain.java:144)  Caused by: java.lang.ClassNotFoundException: org.apache.commons.logging.LogFactory at java.net.URLClassLoader.findClass(URLClassLoader.java:381) at java.lang.ClassLoader.loadClass(ClassLoader.java:424) at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:331) at java.lang.ClassLoader.loadClass(ClassLoader.java:357) ... 12 more   I have tried many solutions given on SO already, like adding commons-logging, via maven, downloading the jar and adding it to my external Libraries.  This is a screenshot of my tree structure-      My Pom.xml:  <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"      xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"> <modelVersion>4.0.0</modelVersion>  <groupId>com.mkyong.common</groupId> <artifactId>SpringExamples</artifactId> <version>1.0-SNAPSHOT</version> <packaging>jar</packaging>  <name>SpringExamples</name> <url>http://maven.apache.org</url>  <properties>     <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding> </properties>  <dependencies>     <dependency>         <groupId>junit</groupId>         <artifactId>junit</artifactId>         <version>3.8.1</version>         <scope>test</scope>     </dependency>      <dependency>         <groupId>org.projectlombok</groupId>         <artifactId>lombok</artifactId>         <version>1.16.10</version>         <scope>provided</scope>     </dependency>      <dependency>         <groupId>commons-logging</groupId>         <artifactId>commons-logging</artifactId>         <version>1.2</version>         <scope>compile</scope>     </dependency>      <dependency>         <groupId>org.springframework</groupId>         <artifactId>spring</artifactId>         <version>2.5.6</version>     </dependency>  </dependencies>     I am running the project from my App.java  Can someone help me with this?? Thanks in advance.


How do we know that the motion of the particle in an central force field lies on a plane?

If I take r as the radial vector of the moving object and v as the velocity vector of the moving object in central force field.   Then r should be perpendicular to r×v . So that depicts that r.(r×v) = 0 . So how does this say that the particle is lying on a constant plane ?


How can I visualize the file system usage on Windows?

How can I visualize which folders and files are taking up all of the space on my hard drive?  I'm getting some conflicting reports on the size of hard drive contents. Namely what is and isn't there and what folders are actually using the space.   I need to know which of the files or folders the culprits behind all this hidden bloat. Also there should be a print option to get it on paper.


Potential drop across a wire with zero resistance

I am currently studying Circuits and it is written in my book that the Potential Drop across a wire with zero resistance is 0. If there is no potential drop then why do electrons flow through the wire since potential difference is required to generate a force on electron. The electric field inside the wire is constant (correct me if I am wrong), then the potential drop should be V = EL (here L is length travelled along the wire). Then why potential drop across a wire with no resistance is 0.


How can I fix "NO_PUBKEY 40976EAF$37D05B5"?

Best regards, I recently tried to open “Software” in Ubuntu Studio Disco Dingo 19.04, to search for an application and continuously issues the following message:  Unable to download updates: failed to refresh cache: W: GPG error: http://archive.canonical.com lucid InRelease: the following signatures couldn`t be verified because the public key is not abvailable: NO_PUBKEY 40976EAF437D05B5"


Hodge star operator and the adjoint of exterior multiplication

Given the adjoint of exterior multiplication by $\xi$, that is $\gamma: \Lambda_{p+1}(V) \rightarrow \Lambda_p(V) $,  $$\langle \gamma(v), w\rangle = \langle v, \xi\wedge w\rangle$$ for $v\in \Lambda_{p+1}(V)$ and $w\in \lambda_p(V)$. I would like to show that  $$\gamma(v) = (-1)^{np} \star(\xi\wedge(\star v))$$ where $\star$ is the Hodge star operator.   I know the basic definition of $\star: \Lambda_p \rightarrow \Lambda_{n-p}$, and  given an orthonormal basis $\{e_1,\cdots,e_n\}$ on $V$, we have the computation $$\star (e_{i_1} \wedge e_{i_2}\wedge \cdots \wedge e_{i_k})= e_{i_{k+1}} \wedge e_{i_{k+2}} \wedge \cdots \wedge e_{i_n}.$$  Also for $u,w \in \Lambda_p(V)$, we have  $$\star(w\wedge \star v) = \star(v\wedge \star w) = \langle u,w \rangle = \det(u_i, w_j).$$


Unsubscribe from answered and old questions without having them closed?

This question is a followup to 2013's  by Tom Brito.   Summary  I want to unsubscribe from notifications about some questions when they are either   already answered old   Back in 2013 the tenor of the comments was “It is not possible, by design”, but by now it is becoming a spam-problem for me.   Background  Unless I have asked a new question within the last few days, by now the majority of inbox notifications I receive are no longer relevant to me. This can be because there was already a satisfactory answer or because I asked it so long ago, that it simply has lost relevance since. Yet I still receive notifications about new answers or comments.   Obviously I wouldn't want to flag such questions for closing, as new answers may very well still be relevant to others.   The old question received  as a possible answer (as a comment). This does however seem like overkill – also I don't see how either case warrants administrator intervention.   Hence I'd appreciate an option to unsubscribe from the notifications. Since having this option unconditionally would invite poor quality questions that are quickly abandoned, prerequisites such as a minimum age of the question or having an accepted answer could be required.


I have PG server (9.0.4) installed on Debian x86. In one of my tables I use numeric(6,1):  CREATE TABLE mytable(name text, numfield numeric(6,1))   Also index created for this field:  CREATE INDEX mytable_numfield_idx ON mytable USING btree (numfield);   Everything is going fine if I use this field with real numeric value. As I see the query uses the index:  EXPLAIN ANALYZE SELECT * FROM kodiall WHERE kodgo=123.0      Index Scan using mytable_numfield_idx on mytable  (cost=0.00..8.27 rows=1   width=193) (actual time=0.085..0.087 rows=1 loops=1)      Index Cond: (numfield = 123.0)      Total runtime: 0.131 ms   But the index is ignored for some reason if I use 0.0 or NULL as condition value:  EXPLAIN ANALYZE SELECT * FROM kodiall WHERE numfield=0.0 --EXPLAIN ANALYZE SELECT * FROM kodiall WHERE numfield=NULL      Seq Scan on mytable  (cost=0.00..57.80 rows=1080 width=193) (actual   time=0.033..1.853 rows=1088 loops=1)      Filter: (numfield = 0.0)   What wrong here? Is 0.0 not a numeric value?  In real query I use LEFT JOIN with numfield and values in joined table can be NULL.


Show that the set $\mathbb{Q}(\sqrt{p})=\{a+b\sqrt{p}; a,b,p\in\mathbb{Q},\sqrt{p}\notin \mathbb{Q}\}$ is a field  I am having a little trouble proving that for each non-zero $b\in\mathbb{Q}(\sqrt{p})$, there is $d\in\mathbb{Q}$ such that $b\cdot d=1$.  My attempt:  Let $b=a_1+b_1\sqrt{p}$  Let $d=a_2+b_2\sqrt{p}$  We want $$b\cdot d=(a_1+b_1\sqrt{p})(a_2+b_2\sqrt{p})$$ $$=a_1a_2+a_1b_2\sqrt{p}+a_2b_1\sqrt{p}+b_1b_2p$$  $$=(a_1a_2+b_1b_2p)+(a_1b_2+a_2b_1)\sqrt{p}$$ $$=1$$  Am I following the right approach? What should be my next step


Why can't I install local deb files properly

I need to make a list of deb files, which allows me to install things without Internet.  As we know, when we execute apt-get install XXX, we can find some deb files at /var/cache/apt/archives/. With these deb files, we can execute apt install ./*.deb to do the installation locally (without Internet).  So here is what I've done:  sudo apt-get install pkg1 sudo apt-get install pkg2 ... ... sudo cp /var/cache/apt/archives/*.deb ~/deb/   Now, I get all necessary deb files in ~/deb.  Then, I copy ~/deb to another new Ubuntu 16.04.3 and execute apt install ./deb/*.deb.  To my surprise, I found some weird errors:  1) Some debs conflict. For example, when I execute apt install ./deb/*.deb, it says that a.deb and b.deb conflict, I have to remove one of them to finish the installation.  2) After executing apt install ./deb/*.deb, the ssh of system is broken, I have to execute apt update && apt install openssh-server openssh-client to repair it.  I can't understand why the deb files coming from official source can't be installed locally properly.


How to get players to do something without them feeling railroaded?

I'm DM'ing a play-by-post campaign and I'm at a point in the adventure where the group all meets for the first time. They've all had something stolen from them at the same time and saw a creature that took something run into a nearby alley (there's three separate parties within the play group currently, as they've only just started, so there's three separate robbers running into alleys in the marketplace).  Ideally, I want the players to have their PCs all give chase so they end up in the same part of town, all looking for the same thing. However, I don't want to railroad my players into doing this. I know I'm not supposed to take away player agency or narrate their actions for them, but the only way I could think of was to tell them that they start giving chase.  So how would you deal with this situation? And more broadly, how can I stop something like this happening again?  If it matters, we're currently playing D&D 5e.


What are the exact criteria for the "new contributor" indicator to be shown?

According to :  The new indicator works by the age of a user's first visible post. This could be a question or answer, and the association bonus won't influence the behavior. While you might not be new to our engine, everyone is new when they first join a new community, so the indicator is shown.   How old does one's first visible post have to be for the indicator to be removed?  Is the indicator status calculated on the fly when loading a post, or is it permanently attached to a post and only removed on later posts?  Finally, what happens if the first visible post gets deleted? Is the calculation still based on that post, or is it based on the next post that continues to be visible? In other words, if I posted a few years ago and later post again, and I delete my post from a few years ago, will the indicator start showing up?


In what order are replacement effects chosen with respect to damage prevention?

How are replacement effects handled in multiplayer? Here's a concrete example.   Player A, B, and C are seated around the table. It is Player A's turn. Player A has a  (double all damage), and  (prevent damage to opponents, and create 3/1 tokens instead) in play. Player A casts  (2 damage to each creature and player). Player B responds with  (prevent all damage from spell, gain life equal to damage prevented). No one has any more responses, no other permanents are in play.   What possible different life totals and 3/1 tokens are generated when the stack resolves? Who gets to make the choice(s)?  Do the possibilities change if Player B or Player C are the active player? What are  the possible results?


Why can't I loop cut all the way around the object?

How to make a loop cuts all around the object? I can select just one side and I need them all at the same time.    Here is what I need.


When answering , I came up with the following: Suppose we have a length $l$ and integrate $\frac 1 l$ over $l$: $$\int \frac {\operatorname d\!l}l=\ln l$$ Since the dimension of $l$ is length, and $\ln$ should have a dimensionless argument, this cannot be a 'good' integral in the physical sense, although it would be mathematically (omitting units). A way to solve this would be to reformulate the indefinite integral like this: for $c=-\ln (1 \text{meter})$. $$ \int \frac {\operatorname d\!l}l=\ln l+C=\ln l-\ln( 1\text{m})=\ln\left(\frac{l}{1\text{meter}}\right) $$ The question is whether the first integral given would be acceptable and how to deal with the two logarithms with bad arguments, which, when combined, aren't a problem anymore.


I am intermediate in PHP. To polish my skills I start learning Drupal 7. While learning Drupal architecture concepts, the terms hooks and bootstrapping puzzled me a lot. I read the "Pro Drupal development" book, and some documentation on drupal.org, but it is so advanced for me to learn how hooks work in Drupal to display the web page.  Can anyone tell me what hooks are in simple words?


I heard that one can construct field based on $p^n$ elements where $p$ is prime. I tried with $p = n = 2$. It seemed easy as there are 2 groups which $\{0,1,2,3\}$ can form and 1 group formed by $\{1,2,3\}$. However each time I get into contradiction. Is there anything I missed or it is not possible to form $p^n$ element group?


When I compile with LuaLaTeX and TL2016 this MWE   \documentclass{article}  \usepackage[no-math]{fontspec} \usepackage{luatex85} \usepackage{shellesc}  \setmainfont{Minion Pro}  \begin{document}  \huge{huge} \textbf{\huge{huge}}  \Huge{Huge} \textbf{\Huge{Huge}}   \end{document}   I have this .pdf.     Any help? With TL2015 all is correct. Thanks


R is a ring. $W=\left\{ x\in R|\text{x is a nilpotent}\right\}$ and $P\left( R\right) =\cap \{ P|P\unlhd A,  \text{P is prime}\}$ .How to proof  $W\subseteq P\left( R\right)$


Use World Lighting, but Render Without it

I want to render a PNG image from a scene which uses an environment texture (HDR file) to provide lighting on my materials. However, I want the render to have a transparent (alpha) background -- without the world appearing. How can I configure my render so that my materials are lit by the environment, while hiding the environment texture from the render?


My question is - I know, $0\times anything=0$ and $anything \times \infty=\infty$.  So,what is $0 \times \infty$?  I suppose it's $0$ but why not $\infty$?  If I say that area of an indefinitely long line is $\infty*0=0$,where am I wrong?  I know upto limits and basic derivatives.  Thanks.


What can I do to retrieve windows that have gone off screen?

I am having a weird issue with a machine where sometimes when a window is initialized, it will shoot off screen and out of sight. I am unable to click on it to drag it back to sight.   Are there any programs or fixes for this in Windows XP?  I know Windows and other programs like to save window locations after they close so when you reopen them they are in the spot where they were closed and I cannot see any of these windows that were closed off screen.


I'm quite new to printing graphics. I understand why crop marks are used when printing, and on the face of it, they seem quite straight-forward to use. However, when I went to trim a document I have printed using the crop marks that were added (using Illustrator), I came across an issue that has me confused.    Take the example above. If I was to trim the top of the document, using the two horizontal crop marks, then I would also remove the two vertical crop marks indicating the left and right edges of the final document. As a result, when I go to trim say the left-hand side of the document, there is no crop mark to use as a guide at the top.  My question therefore is: how is a document trimmed using crop marks such that when a cut is made in one direction (eg. horizontally) the crop marks necessary for trimming the document in the other direction (eg. vertically) are not removed? Or is there something else I am missing?


ObservableCollection that also monitors changes on the elements in collection

Is there a collection (BCL or other) that has the following characteristics:  Sends event if collection is changed AND sends event if any of the elements in the collection sends a PropertyChanged event. Sort of an ObservableCollection<T> where T: INotifyPropertyChanged and the collection is also monitoring the elements for changes.   I could wrap an observable collection my self and do the event subscribe/unsubscribe when elements in the collection are added/removed but I was just wondering if any existing collections did this already?


Recommended jobs do not align with my abilities

I'm just trying out the SE app, and while I like a lot of the features, most of the recommend jobs are for Android engineers (something I most certainly am not).  I really like Careers 2.0, but it seems the recommendation engine could use some work.


How come the diagonal of a right triangle is not the same as the total distance of the adjacent and opposite leg?

Disclaimer: This might seem like a very dumb question. But I rather ask it and learn than to never ask at all and always wonder. Also, to me it is confusing, you guys are probably much more advance in math than I am.  Let's say you have a "zig-zag step" pattern, you can show that the the total length of the diagonal zig-zag step is 20 for a 10 in by 10 in width and height. As shown in the picture. But as you make the "zig-zag" smaller and smaller the "zig-zag" total should still remain 20, but instead it seems to be $10\sqrt{2}$. I get this it is a triangle now and this is the formula for the diagonal of the triangle, but if the diagonal can really be made of this zig-zag step pattern where the zig-zag are infinitely small, shouldn't it be 20 by that logic?  I get the Pythagorean theorem and everything, but in terms of calculus a the zig zag steps can turn into a triangle by making the length of an individual zig-zag infinitely small, making infinitely many zig-zags. So why is it $10\sqrt{2}$, over $20$.


Tourist to F1 change of status within 60 days

I have a PhD place at a US university starting Aug 21 but want to visit a different university for casual research for 6 weeks from July 1. This is longer than the 30 day grace period for the F1. Can I arrive on the visa waiver program or tourist visa in July and then just stay on for the PhD? I guess I might need to change status. Will this work?  Please don’t suggest exiting and reentering, that’s too expensive.  (British masters student in UK)


how does the circuit of a basic Variable speed electric drill work?

i am trying to 'automate' the control of an electric drill motor that im taking from a garden variety Variable Speed drill (from Harbor Freight)  it has a universal AC motor which I basically undertand and a DPDT switch to reverse direction and a triac citcuit to vary speed    Question 1 . i see 4 wires going to the 'field/Stator coil(s)'. Are there 2 seperate field/stator coils here? is this to provide low/high power.  I think in theory , you only need 1 coil with 2 wires and that coil is wired in series with the brushes... is that right?   how does this circuit work with 2 coils.  Question 2 . how does this variable speed circuit work.  is the wiring diagram correct (it doesnt show a variable resistor and it doesnt show what drives the control input of the traic? why are there two switches in the thing? does switch 2 close at high speed and thus shunt around the triac?  please see the attached 4 diagrams


How to get any software update in synaptic?

Will I get any software update ever, in synaptic? For instance, synaptic has mkvtoolnix 45 where the latest stable mkvtoolnix 48 has been released. Why?


Proof for $z\neq 0$ , z is any complex number?

$\sum _{k=1}^{n}\mathrm{sin}kz=\frac{\mathrm{sin}\frac{n+1}{{2}}\cdot \mathrm{sin}\frac{nz}{2}}{\mathrm{sin}\frac{z}{2}}$ Proof for $z\neq 0$


What I'd like to do is lock the screen and have it wait a set amount of time (eg 20 mins) before it lets me log back in - so I make myself to have a break from the computer.  Is it possible to do this?   Thanks    EDIT: Thanks for the suggestions - but I don't actually want something to remind me to take scheduled breaks. More something I can click when I realise I'm getting distracted and it'll immediately lock the screen for a fixed amount of time. Or even just lock screen if I can find a way to stop it letting me log in for 20 mins or so.


How does the SNES' Mode 7 sprite perspective projection work?

I've always wanted to know how to replicate the old  graphics mode of the Super NES. It was frequently used for a pseudo-3D effect in racing games like  ().   Top Gear ⓒ Gremlin Graphics. Image credit: .    Every explanation I can find seems a little too complex for me.  In simple terms, how does Mode 7 work?


Cross-validation for timeseries data with regression

I am familiar with "regular" cross-validation, but now I want to make timeseries predictions while using cross-validation with a simple linear regression function. I write down a simple example, to help clarify my two questions: one about the train/test split, one question about how to train/test for models when the aim is to predict for different n, with n the steps of prediction, in advance.  (1) The data  Assume I have data for timepoints 1,...,10 as follows:  timeseries = [0.5,0.3,10,4,5,6,1,0.4,0.1,0.9]   (2) Transforming the data into a format useful for supervised learning  As far as I understand, we can use "lags", i.e. shifts in the data to create a dataset suited for supervised learning:  input = [NaN,0.5,0.3,10,4,5,6,1,0.4,0.1] output/response = [0.5,0.3,10,4,5,6,1,0.4,0.1,0.9]   Here I have simply shifted the timeseries by one for creating the output vector. As far as I understand, I could now use input as the input for a linear regression model, and output for the response (the NaN could be approximated our replaced with a random value).  (3) Question 1: Cross-validation ("backtesting")  Say I want to do now 2-splits, do I have to shift the train as well as the test sets?    I.e. something like:  Train-set:  Independent variable: [NaN,0.5,0.3,10,4,5]  Output/response variable:[0.5,0.3,10,4,5,6]  Test-set:  Independent variable: [1,0.4,0.1]  Output/response variable:[0.4,0.1,0.9]  (ii) Question 2: Predicting different lags in advance:  As obvious, I have shifted dependent to independent variables by 1. Assuming now I would like to train a model which can predict 5 time steps in advance -- can I keep this lag of one, and nevertheless use the model to predict n+1,...,n+5,... or do I change the shift from independent to dependent variable to 5? What exactly is the difference?


How to copy a file to multiple directories using the gnu cp command

Is it possible to copy a single file to multiple directories using the cp command ?  I tried the following , which did not work:    cp file1 /foo/ /bar/ cp file1 {/foo/,/bar}   I know it's possible using a for loop, or find. But is it possible using the gnu cp command?


Cannot connect to Wi-Fi after upgrading from ubuntu 16.10 to Ubuntu 17.04

I have just upgraded to Ubuntu 17.04. The upgrade was successful, but now I cannot connect to WiFi - I see the list of available netwroks, but when I try to connect it seems to be connecting for several seconds and then stops (the icon returns to "no connection" status). I get no error message apart from the regular "Disconnected - you are now offline" notification.  My WiFi card is "Killer E220x Gigabit".  Thanks


show sequence $a_n= \frac{1}{n+1}+\frac{1}{n+2}+...+\frac{1}{n+n}$ converges to log2  my attempt:   sequence $a_n$ is monotonic increasing 0<$a_n$<1/2   how to find limit?


Segmentation fault when trying to modify a string

This code is giving me a segmentation fault at run time.  char *str = "HELLO"; str[0] = str[2];   Please can anyone tell me why?


When is mapping $g$ to $g^{-1}$ a group homomorphism? It just means that the map maps the identity to the identity and inverses to inverses. So does that mean it's only a homomorphism if the inverse is itself?


I’m new to D&D and want to play with someone if anyone could introduce me to the game and invite me to your online table (is that what you call where you play D&D) I would be very greatful


I use this program in Windows that's one-box and searches all of my drives. By default it lists all files, everywhere, in a single list. Is there a Linux graphical utility that does this?


I'm looking for advice about favicons and their impacts on search engines. Recently I noticed a site which changes its favicon every time you load another page without losing overall recognition of the favicon style. I'd like to incorporate this into my site as well but am I taking any SEO risks here?


If a trait does not appear to be advantageous to organism, why does the organism have it?

Why do organisms have some traits that do not appear to have any evolutionary advantage?


Why is IEx64 not the default for x64 Windows?

I don't think I've seen any answers to this question, but I'm curious as to why, when you have a 64-bit OS installed (ex: Vista x64), IE defaults to the 32-bit version? Are there drawbacks to using the x64 version of IE (IE8, specifically)?


I'm trying to use the tikz package's foreach command in a tabular environment. I know that it is not really suited for doing this, but how would I be able to make the following command work (I think, it is obvious what it should do, and I know that there are some difficulties regarding the textbf command as well):  \newcommand{\myTable}[1]{     \begin{tabular}{p{0.35\textwidth}|p{0.65\textwidth}}         \hline         Headline 1 & Headline 2 \\         \foreach \lhs/\rhs in {#1} {             \textbf{\lhs} & \rhs \\         }         \hline     \end{tabular} }   MWE:  \documentclass{article} \usepackage{tikz}  \newcommand{\myTable}[1]{     \begin{tabular}{p{0.35\textwidth}|p{0.65\textwidth}}         \hline         Headline 1 & Headline 2 \\         \foreach \lhs/\rhs in {#1} {             \textbf{\lhs} & \rhs \\         }         \hline     \end{tabular} }  \begin{document} \myTable{{Title 1}/{Description 1}, {Title 2}/{Description 2}} \end{document}


Spring Boot - Is it possible to pass a variable defined in the controller into a model class?

As a simple example, there's a class called 'Car'. There's a method in it that takes a String variable called 'result':  public class Car {      public void move(String result) {         System.out.println(result);     }  }   Then there's the controller that uses the car class:  @Controller public class carController {      private Car myCar;      myCar.move("Vroom vroom"); }   However, when it tries to pass in "Vroom vroom", it crashes and gives the following:  Caused by: java.lang.NullPointerException: null  I debugged it and found it crashes while executing the line that calls the method with the value that needs to be passed in.  It seems you can't pass variables from a Spring Boot controller into a model class.  Here's the actual error message from my project:      Error starting ApplicationContext. To display the conditions report re-run your application with 'debug' enabled. 2020-04-15 16:54:46.331 ERROR 7388 --- [  restartedMain] o.s.boot.SpringApplication               : Application run failed  java.lang.IllegalStateException: Failed to execute CommandLineRunner     at org.springframework.boot.SpringApplication.callRunner(SpringApplication.java:787) [spring-boot-2.2.6.RELEASE.jar:2.2.6.RELEASE]     at org.springframework.boot.SpringApplication.callRunners(SpringApplication.java:768) [spring-boot-2.2.6.RELEASE.jar:2.2.6.RELEASE]     at org.springframework.boot.SpringApplication.run(SpringApplication.java:322) [spring-boot-2.2.6.RELEASE.jar:2.2.6.RELEASE]     at org.springframework.boot.SpringApplication.run(SpringApplication.java:1226) [spring-boot-2.2.6.RELEASE.jar:2.2.6.RELEASE]     at org.springframework.boot.SpringApplication.run(SpringApplication.java:1215) [spring-boot-2.2.6.RELEASE.jar:2.2.6.RELEASE]     at com.demo.coronavirus.CovidUkApplication.main(CovidUkApplication.java:13) [classes/:na]     at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_241]     at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) ~[na:1.8.0_241]     at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) ~[na:1.8.0_241]     at java.lang.reflect.Method.invoke(Unknown Source) ~[na:1.8.0_241]     at org.springframework.boot.devtools.restart.RestartLauncher.run(RestartLauncher.java:49) [spring-boot-devtools-2.2.6.RELEASE.jar:2.2.6.RELEASE] Caused by: java.lang.NullPointerException: null     at com.demo.coronavirus.controller.DisplayCasesController.lambda$0(DisplayCasesController.java:35) ~[classes/:na]     at org.springframework.boot.SpringApplication.callRunner(SpringApplication.java:784) [spring-boot-2.2.6.RELEASE.jar:2.2.6.RELEASE]     ... 10 common frames omitted


Old story about mysterious creatures at the bottom of a well that have a taste for "live turkey" (i.e. human flesh)?

Plot Summary/Details  The basic premise of this one (as best that I can remember it) is that a farmer, who has recently dug a new well, has discovered some sort of strange beings living underground near his well.  I don't remember the details of how, but they communicate through notes lowered/raised in the well's bucket.  At one point, the farmer and his wife send down a roast turkey dinner, which the beings below enjoy.  For reasons I cannot remember, the farmer either becomes angry with, or exceptionally curious about, the beings below.  He descends the well one evening, possibly armed with a shotgun, possibly not.  The chilling twist to the story comes the next day went the wife retrieves the bucket from the well.   The beings write that they really enjoyed the live turkey she sent them, and would like more.  The live turkey, of course, was the farmer, who was eaten by the creatures below.  Other Details  I remember not only reading this one as a kid, but also seeing a tv show adaptation of it.  I thought it was the old Rod Serling show Night Gallery, but I have not been able to find that particular story yet.  I also seem to remember hearing the story told at summer camp a few times, which makes me wonder if the story has its roots in some old story/legend.  Timeframe of Publication  I'd guess no later than the 1970s, probably a lot earlier.


Are periods placed inside quotes, or outside?

If, for example I have this sentence:     He started a website, SaveSandy.org, however this website is currently “Under maintenance”.   Does the period go on the outside, or the inside of the quotation marks? I've seen various newspaper and web articles with it on the inside, and on the outside.  Which one is it? And if possible, preferably give me a source, to verify your claim? Also, I'm talking about American English, not British. Thanks.


Can a force that has magnitude of an irrational number be exerted?

Can a force, which has magnitude of an irrational number or does not end (ex : 1/3), act upon any particle?  If photon of particular wavelength lambda has some energy say E, then can the photon/group of photons exert a force which is irrational in its magnitude. If yes, then how?   If the desired force is pi(3.1415...), how can this force be attained by sum of force in a finite amount of time.  pi = 3 + 0.1 + 0.04 + 0.001 + 0.0005 + 0.00009 + ....... The above sequence does not end; And if a photon can exert a finite amount at a time, we would either require infinite amount of time or infinite amount of photons to create an infinitesimally small force.   My teacher says that the forces which are of magnitude of any irrational number are exerted on bodies. And it is just the incapability of humans that we cannot image that particular magnitude.


Deleted user's posts showing in 'First Posts' queue

On Scifi.SE, a user had their account deleted this morning.  Also this morning, about half a dozen of "their" posts were in the First Posts queue.  The posts were all roughly a month old, and they all had the same disassociated user#.   one of them.  Why'd this person's posts show up in the First Posts queue?  Why do a deleted user's posts ever show up in that queue, when it's purpose is to help the community provide feedback to new users?  A deleted user is no longer a member of the community, and they're not even going to be able to act on any feedback.


Linux - Help, I'm running out of inodes!

I have a filesystem that has lots of small files. Currently about 80% of inodes are used (I checked with df -i), however only 60% of disk space is used. How can I 'increase' the number of inodes? If it was just disk space, I know that I could just increase the size of the disk (this disk is on LVM). If I increase the size of the disk, will that make me have more inodes?  I'm willing to grow the filesystem this disk is on, if that'd help.


How to directly initialize a HashMap (in a literal way)?

Is there some way of initializing a Java HashMap like this?:  Map<String,String> test =      new HashMap<String, String>{"test":"test","test":"test"};   What would be the correct syntax? I have not found anything regarding this. Is this possible? I am looking for the shortest/fastest way to put some "final/static" values in a map that never change and are known in advance when creating the Map.


Negative sign in rotation operator (quantum mechanics, angular momentum)

Schaum's Quantum Mechanics comes up with  $$\exp((-i/\hbar)\cdot \theta \cdot{\hat{L}} \cdot {\overrightarrow{n}})$$  as the formula of the rotation operator.   Other sources I see don't have the negative sign.  How did they get the negative sign in here?


Annihilator of image $T$ equals to $\text{ker}(T^*)$

Let $T:V\to W$ be a linear transformation, then $\text{Ann}(\text{Im}T)=\text{ker}T^*$.  How one could start to prove it?  Many thanks.


Is a Monk attack considered a finesse weapon attack?

Since the Monk Martial Arts feature grants the ability to choose either Str or Dex as the modifier would the unarmed and flurry of blows be considered as finesse? the mechanics are essentially the same. This question is primarily for the purpose of figuring out if the Rogue Sneak Attack will work with a Monk Unarmed strike and Flurry of blows.


Connecting to a computer inside a network

I have a network in my College which is connected to the internet. How can I access a system inside this network from the internet (WAN)? I don't have access to the gateway of the system, so port forwarding is not an option. Is there any program that could run inside my computer (which is in the network) that could then connect to a static IP address on the Internet, reverse the connection, and make me able to use ssh/telnet to access the computer?  Edit: I checked the duplicate question but still I am little bit confused. Actually in my college I have ssh non root access to a system (192.168.1.5) from within the network    Is there anyway I can access that machine through ssh from the internet?    If ssh tunneling is an option how to setup that?    Can anybody explain step by step?


Transfer Minecraft PE world from broken device

My son's tablet broke and when he gets a new one he is hoping he will be able to access all his saved worlds on his new device. Is this possible? Will the minecraft servers have his data saved if he re-installs his already purchased app?


This is from a list of problems from a local university's Integration Bee.  I have no idea how to do it, but I thought maybe someone here can explain it to me.  $$\int_{0}^{1} \frac{\ln(1+x)}{1+x^2} dx$$  The answer they have is $\frac{\pi \ln(2)}{8}$, but no clue how they got there.  Thanks!


Cannot access Ubuntu Server 13.10 remotely after server reboot

I've encountered a weird problem imo, and none of my co-workers have no idea why this keeps happening.  First of, I've built a little server machine for beta testing of my upcoming software & website. I installed Ubuntu Server 13.10 on the machine and openssh-server on it. The machine has only ethernet cable plugged in, no monitors or keyboards. My router uses a dhcp server but I have setuped a static ip for Server. I can remotely access it from public easily. I forwarded ssh port from my router. I did some changes to my website files and then I decided for some odd reason to reboot the server. After rebooting it, I cannot access it from public anymore. The server is currently at home and I'm away. But I managed to get physically to the server today. I plugged in a monitor to inspect in which state the server is. The server was on logon state. I checked is router working fine by connecting into wlan with my phone, and went to whatsmyipaddress.com. IP hadn't changed and connection was working. I didn't have keyboard nor my laptop with me to inspect it further. I assumed it was working because it had rebooted and internet connection was fine. When I finally made it to my laptop and tried to connect with putty it said "Network error: Connection refused". My lucky guess is that after every reboot I need to login physically on the server before ssh connections will work.  I googled and found about of autologin. Wouldn't that then be a security issue? I mean you could just make a ssh connection from every single machine with internet connection if you just happen to know the IP address, and then you could just mess everything up, am I right?  I need some suggestions what to do for this. I get to the server machine again tomorrow morning with laptop and keyboard this time so I can inspect it further. I hope you guys make up some suggestions what I should do about it. I must be able to reboot the server remotely, and then get back on it after reboot.  The best regards, Roope


sql query to check whether multiple entries exist

I have a table with the following fileds.Here table name is det Name ID A     1 B     2 C     1 D     3  I need a querry to check if multiple entry of name is there for single id. Here iam expecting result like Name ID A     1 c     1


Looking for identification of SF story where humans are the "ancient evil"

Unique short SF story where aliens being invaded by other aliens, went looking for allies (to help save their galactic empire).  While being chased by the antagonistic aliens, they encountered a barrier surrounding a solar system. They somehow managed to disable it and found a solar system where the third planet from the Sun showed signs of life. When they landed, they were received by a human girl who greeted them. The enemy ship which followed them also landed, but were destroyed by the humans easily.  Upon learning of the aliens request, the humans decided to help the aliens, and moved their entire world to follow the aliens' ship. Too late the aliens realized that these humans were the ancient war mongering race which was sealed up eons ago and they had accidentally released them.  Could someone please help to identify this title for me. Thanks.


Postfix failed because it can't set an exclusive lock

I'm trying to make a Postfix-based E-mail server. I face the following error whenever I try to launch the server:  Sep 24 12:17:39 hostname9727 postfix/postfix-script[7506]: warning: group or other writable: /etc/postfix/./master.cf Sep 24 12:17:39 hostname9727 postfix/postfix-script[7507]: warning: group or other writable: /etc/postfix/./relocated Sep 24 12:17:39 hostname9727 postfix/postfix-script[7508]: warning: group or other writable: /etc/postfix/./generic Sep 24 12:17:39 hostname9727 postfix/postfix-script[7524]: starting the Postfix mail system Sep 24 12:17:39 hostname9727 postfix/master[7526]: fatal: open lock file /var/lib/postfix/master.lock: unable to set exclusive lock: Resource temp...vailable Sep 24 12:17:40 hostname9727 postfix/master[7525]: fatal: daemon initialization failure Sep 24 12:17:41 hostname9727 postfix/postfix-script[7527]: fatal: mail system startup failed Sep 24 12:17:41 hostname9727 systemd[1]: postfix.service: control process exited, code=exited status=1 Sep 24 12:17:41 hostname9727 systemd[1]: Failed to start Postfix Mail Transport Agent. Sep 24 12:17:41 hostname9727 systemd[1]: Unit postfix.service entered failed state. Hint: Some lines were ellipsized, use -l to show in full.   postconf -M  smtp       inet  n       -       n       -       -       smtpd pickup     unix  n       -       n       60      1       pickup cleanup    unix  n       -       n       -       0       cleanup qmgr       unix  n       -       n       300     1       qmgr tlsmgr     unix  -       -       n       1000?   1       tlsmgr rewrite    unix  -       -       n       -       -       trivial-rewrite bounce     unix  -       -       n       -       0       bounce defer      unix  -       -       n       -       0       bounce trace      unix  -       -       n       -       0       bounce verify     unix  -       -       n       -       1       verify flush      unix  n       -       n       1000?   0       flush proxymap   unix  -       -       n       -       -       proxymap proxywrite unix  -       -       n       -       1       proxymap smtp       unix  -       -       n       -       -       smtp relay      unix  -       -       n       -       -       smtp showq      unix  n       -       n       -       -       showq error      unix  -       -       n       -       -       error retry      unix  -       -       n       -       -       error discard    unix  -       -       n       -       -       discard local      unix  -       n       n       -       -       local virtual    unix  -       n       n       -       -       virtual lmtp       unix  -       -       n       -       -       lmtp anvil      unix  -       -       n       -       1       anvil scache     unix  -       -       n       -       1       scache   postconf -n  alias_database = hash:/etc/aliases home_mailbox = /home/virtual/mail/ alias_maps = hash:/etc/aliases broken_sasl_auth_clients = yes command_directory = /usr/sbin config_directory = /etc/postfix daemon_directory = /usr/libexec/postfix data_directory = /var/lib/postfix debug_peer_level = 2 debugger_command = PATH=/bin:/usr/bin:/usr/local/bin:/usr/X11R6/bin ddd $daemon_directory/$process_name $process_id & sleep 5 home_mailbox = /home/virtual/mail/ html_directory = no inet_interfaces = localhost inet_protocols = all mail_owner = postfix mailq_path = /usr/bin/mailq.postfix manpage_directory = /usr/share/man mydestination = $myhostname, localhost.$mydomain, localhost, $mydomain mydomain = hostname9727.com mynetworks = 127.0.0.0/8, 10.0.0.0/24 myorigin = $myhostname newaliases_path = /usr/bin/newaliases.postfix queue_directory = /var/spool/postfix readme_directory = /usr/share/doc/postfix-2.10.1/README_FILES sample_directory = /usr/share/doc/postfix-2.10.1/samples sendmail_path = /usr/sbin/sendmail.postfix setgid_group = postdrop smtpd_banner = $myhostname ESMTP unknown_local_recipient_reject_code = 550   what is the problem? Thanks!


My laptop's fan is making a loud sound similar to buzzing and even vibrates. Could someone tell me if I just have to clean the dust inside the laptop box or I have to take it to a specialist?


Calculating the optimal number of bins for severely skewed data

I have a data set with a sample size over three million numeric values. Close to 20% are either 0 or 1, with the maximum being nearly 18500. So the data is clearly quite heavily positively skewed.  I am trying to categorize some of this data by putting it into bins of equal width, so I decided to try and find the optimal number of bins. Using the Freedman-Diaconis rule it gave me a value of 126044.0262335108, this is clearly a ridiculously large number of bins for the data.   Breaking the set into the Inter-decile range also proved fruitless giving me [0, 1, 1, 2, 3, 5, 8, 17, 47]  Reading elsewhere the square root of the sample size was suggested, this gave 1732.05081 which is more reasonable. However the method is quite crude.  I also looking into Doane's formula given . But reading up on this method it seems to have been based on an incorrect .  How should I deal with this level of skew in the data?  What is the best way to categorize this data?


Loading post like facebook on scrool to bottom

I have a page to show my product, now i want to load further posts using "infinite scroll".


Getting an error when printing the middle character of a string

When trying to print the middle character of a string using the following code: def mid(a):     return a[(len(a) + 1) / 2]      print(mid("abc"))  I get the error: TypeError: string indices must be integers  Changing it to:  def mid(a):     return a[(len(a) - 1) // 2 : (len(a) + 2) // 2]      print(mid("abc"))  outputs: b  Why does directly grabbing the middle value return the TypeError, but grabbing the 0th value and then the middle value actually work?


Make Visual Studio understand CamelCase when hitting Ctrl and cursor keys

Is there a way that I can configure Visual Studio 2008 to understand CamelCase?  Specifically, I'd like to be able to get Ctrl + right or left cursor to take me to a subsection of a variable or type name. i.e., if my cursor was at the start of this line: LongNamedExampleClass longNamed = new LongNamedExampleClass();  and I hit Ctrl + right, I'd like to jump to "Named" in the class name, rather than the start of the variable name.  If I hit it again, I'd like to go to "Example".  I hope that makes sense. I used this navigational feature in Eclipse quite a lot, and find it difficult to unlearn something so ingrained.


How do you compare two version Strings in Java?

Is there a standard idiom for comparing version numbers?  I can't just use a straight String compareTo because I don't know yet what the maximum number of point releases there will be.  I need to compare the versions and have the following hold true:  1.0 < 1.1 1.0.1 < 1.1 1.9 < 1.10


Videos requires to install plugins to play files of the following types: • MPEG-4 AAC decoder • H.264 (High Profile) decoder

i am unable to perform the task though i followed the instruction. how to handel Unable to locate package ubuntu-restricted-extras?


In my child theme's archive.php, I have the following code for displaying the title of my archive pages:      <?php         the_archive_title( '
', '
' );     ?>   But that displays my titles as "Category: Category Title" instead of simply the title without the prepended "Category: ".  My first instinct was to override get_the_archive_title() from wp-includes/general-template.  But from what I've read, apparently I'm not supposed to ever alter wordpress core stuff, even with overrides from a child theme.  So what is the best-practice way to control the output of the_archive_title()?


Detecting JavaScript errors in a UIWebView

Possible Duplicate:          I'm running into a very annoying issue developing javascript for a UIWebView in an iPhone application.  If there is an error in the javascript, it silently fails and halts execution of the function it was running.  And some errors do not happen in a desktop browser, so all appears fine.  I then run it on an iPhone and get a massive failure as the function craps out half way through, and no idea why.  I then slowly and methodically comment out various lines of code until no catastrophic failures happen, in order to pinpoint the offending line of code.  This sucks.  So is there any way at all to get a UIWebView to log or report in anyway javascript errors?  They are obviously happening, I just don't know why or how, and it's making my life hard.


Translating his/her when the original language is genderless

I'm translating a course manual but I'm struggling with something. The manual could be read by a man or a woman.  In my own language, he or she or it doesn't exist, so I'm not sure how to make my texts easier to read.     The student can meet his/her Inner Guide who opens his/her heart chakra.   The teacher guides his/her student so he/she can advance more in his/her life.   I'm going to open his/her chakra and so he/she can express his/her emotions easier.


Use Page Object vs other models for Automation in Selenium Webdriver?

I have been doing automation testing since last 2 years and I am following below ways for any website and mobile application automation testing.    Create Global Method class where I implement all test cases Create class for constant values where I put all constant values Create Utility package and Add class under it to invoke browser and webdriver I do data driven and all within global method class.   Above is easy for me and also easy to maintain as well. But When I look at Page Object Model , I got confuse because many people are saying page model object is easy to manage but how? It require to create methods for each field and becomes long time taking when we have form with 100+ fields.  I have checked page object model example .     Please help me that how can I decide that which model I should use for automation. I know it is depends in project and requirements but still I need some good hints. And Suggest other models also if suitable.


How to add line numbers to the code lines?

is it possible we have the option of adding line numbers to the beginnings of the code lines added to the questions and answers? This is a needed fonctionality especially when responding to the long code lines.  ps. This is a duplicate of . But I want to ask this feature-request again, because the question owner there accepted a response which mentions that this feature is unnecessary. I think that it is a necessary feature. His acceptantation does not reflect my needs. Please do not downvote this question because of the duplicateness. Instead of downvoting for duplicateness, you can tell me the alternative way of asking the same feature-request in your comment. Thanks.  EDIT: Hope I could explain the problem. Thanks for the downvotes.


Remove sub-folders without deleting files

I have a directory below (Before). I would like to remove the Sub-folders and move the files to the Folder (After). How can I  archive it? Thanks Before Folder  |-----Sub-folder1  |        |------ fileA.txt  |        |------ fileB.txt  |-----Sub-folder2           |------ fileC.txt           |------ fileD.txt  After Folder  |------ fileA.txt  |------ fileB.txt  |------ fileC.txt  |------ fileD.txt