I've tried removing and installing MySQL several times and I always get the same message:  Do you want to continue? [Y/n] Y Setting up mysql-server-5.5 (5.5.61-0ubuntu0.14.04.1) ... start: Job failed to start invoke-rc.d: initscript mysql, action "start" failed. dpkg: error processing package mysql-server-5.5 (--configure):  subprocess installed post-installation script returned error exit status 1 dpkg: dependency problems prevent configuration of mysql-server:  mysql-server depends on mysql-server-5.5; however:   Package mysql-server-5.5 is not configured yet.  dpkg: error processing package mysql-server (--configure):  dependency problems - leaving unconfigured No apport report written because the error message indicates its a followup error from a previous failure.                                       Errors were encountered while processing:  mysql-server-5.5  mysql-server E: Sub-process /usr/bin/dpkg returned an error code (1)     When I try to start the service, I get the following message:  Mysql command  root@falcon:~# mysql ERROR 2002 (HY000): Can't connect to local MySQL server through socket '/var/run/mysqld/mysqld.sock' (2)   Mysqladmin command  root@falcon:~# sudo mysqladmin root root mysqladmin: connect to server at 'localhost' failed error: 'Can't connect to local MySQL server through socket '/var/run/mysqld/mysqld.sock' (2)' Check that mysqld is running and that the socket: '/var/run/mysqld/mysqld.sock' exists!   When listing the files in the "/var/run/mysqld" directory I realized that it is empty.  Mysql error log:  root@falcon:~# cat /var/log/mysql/error.log ERROR: 1005  Can't create table 'tmp_db' (errno: 13) 180916 22:22:50 [ERROR] Aborting  180916 22:22:50 [Note] /usr/sbin/mysqld: Shutdown complete  180916 22:22:50 [Warning] Using unique option prefix myisam-recover instead of myisam-recover-options is deprecated and will be removed in a future release. Please use the full name instead. 180916 22:22:50 [Note] Plugin 'FEDERATED' is disabled. 180916 22:22:50 InnoDB: The InnoDB memory heap is disabled 180916 22:22:50 InnoDB: Mutexes and rw_locks use GCC atomic builtins 180916 22:22:50 InnoDB: Compressed tables use zlib 1.2.8 180916 22:22:50 InnoDB: Using Linux native AIO /usr/sbin/mysqld: Can't create/write to file '/tmp/ibr58D1n' (Errcode: 13) 180916 22:22:50  InnoDB: Error: unable to create temporary file; errno: 13 180916 22:22:50 [ERROR] Plugin 'InnoDB' init function returned error. 180916 22:22:50 [ERROR] Plugin 'InnoDB' registration as a STORAGE ENGINE failed. 180916 22:22:50 [ERROR] Unknown/unsupported storage engine: InnoDB 180916 22:22:50 [ERROR] Aborting  180916 22:22:50 [Note] /usr/sbin/mysqld: Shutdown complete   I have searched for this problem, but nothing worked for me. Please help.

Question  I am installing a LEMP stack on a fresh minimal install of Ubuntu 14.04 LTS.  When I tried to install MySql   sudo apt-get install mysql-server   it returned an error with the following explanation:  mysql-server depends on mysql-server-5.5; however: Package mysql-server-5.5 is not configured yet.   How do I solve this problem?  What I have read  This question is very similar to , however, that question was (incorrectly, I believe) marked as a duplicate of . None of the answers to these two questions solved my problem.   I have also seen . This question was closed for being unreproducible. However, I can reproduce my problem every time I try to install mysql server on a fresh minimal installation of Ubuntu 14.04 (the key word being minimal).   Purpose of this question  I finally solved my problem, but I could not add an answer to any of the questions I linked to above, so I am creating a new question here so that I can answer it myself.


I want to compute $$l = \lim_{n\to\infty} \frac{1}{n^2} \left(\frac{2}{1} + \frac{9}{4}  +\ ... \ +\frac{(n+1)^n}{n^{n-1}}\right)$$ My first thought was to use Riemann's sums, that is $\lim \frac{1}{n} \sum_{k=1}^n f(k/n) = \int_0^1 f(x)\ dx$. In order to apply this identity, I did this $$l = \lim_{n\to\infty} \frac{1}{n^2} \sum_{k=1}^n \frac{(k+1)^k}{k^{k-1}}  = \frac{1}{n^2}  \sum_{k=1}^n k\frac{(k+1)^k}{k^{k}}  = \frac{1}{n}  \sum_{k=1}^n \frac{k}{n}\left( 1 + \frac{1}{k}\right)^k  $$ But from this, I don't know how to follow. Any help is welcome. Also I want to say that maybe this idea doesn't work to compute the limit. In that case, I will appreciate any hint to calculate $l$. Thanks in advance.

$$\lim_{n\to\infty}\frac{1}{n^2}\left(\frac{2}{1}+\frac{9}{2}+\frac{64}{9}+\cdots+\frac{(n+1)^{n}}{n^{n-1}}\right)$$    My try:  The limit can be written as follows:  $$\lim_{n\to\infty}\left(\frac{1}{n^2}\cdot\sum_{k=1}^{n}\frac{(k+1)^{k}}{k^{k-1}}\right)$$  Evaluate the following series:  $\sum_{k=1}^{\infty}\frac{(k+1)^{k}}{k^{k-1}}$  $\frac{(k+1)^{k}}{k^{k-1}}=k\cdot\frac{(k+1)^{k}}{k^{k}}=k\cdot\left(1+\frac{k+1}{k}-1\right)^k=k\cdot\left(1+\frac{1}{k}\right)^k$  Then:  $\lim_{k\to\infty}\frac{(k+1)^{k}}{k^{k-1}}=\lim_{k\to\infty}k\cdot\left(1+\frac{1}{k}\right)^k=e\cdot\infty\neq0 \Longrightarrow \sum_{k=1}^{\infty}\frac{(k+1)^{k}}{k^{k-1}}$ diverges.  Therefore:  $$\lim_{n\to\infty}\frac{1}{n^2}\left(\frac{2}{1}+\frac{9}{2}+\frac{64}{9}+\cdots+\frac{(n+1)^{n}}{n^{n-1}}\right)=0\cdot\infty$$  What to do next?


I have an Xbox One and I have the new version of Minecraft.  I tried playing on the servers but it keeps on saying that it's outdated and it couldn't connect to it. I can only connect to Lifeboat I want to play the other three but it won't let me and I don't understand why. Everything is updated I checked.   What else can I do about it?

Similar to  on the bugs in Minecraft, I would like a complete list of what error codes exist in Minecraft and how they occur, as well as how they can be resolved.


Let M be a Noetherian module over commutative ring R.   Show that R/Ann(M)  is a Noetherian ring.   I know M is Noetherian module over R then M is also Noetherian over the commutative ring R/Ann(M)  . From this result can I say R/Ann(M) is Noetherian ring?

Let $M$ be an $R$-module and $\text{Ann}(M)=\{r \in R: rm =0 , \forall m \in M\}.$ Suppose $M$ is Noetherian. Could anyone advise me on how to prove $R/\text{Ann}(M)$ is also Noetherian?   Hints will suffice. Thank you.


Show that if $G$ is a finite group of order $n$, and $H$ is a subgroup of order $\frac{n}{2}$, then $H$ is a normal subgroup of $G$.    Please help me on this. I only know that $|gH| = |H|$. How can go on beyond that to attempt the problem?

Why is a subgroup with the index of 2 normal to the group?  I believe it has something to do with it being half and having nowhere to go.


In rocket league, there are a ton of Hats (not as much as TF2, but I digress)  Does these hats change the hitbox of the car? Like if I have a big sombrero on, could the ball react differently when hit with the roof of the car that if I have the police light, or no hat at all?  EDIT: I don't know if I am unclear with what I'm asking, but it feels so. Anybody get what I'm asking?

I was just wondering if I put on a topper if it changes my hit box at all? Or if different toppers have more of a benefit over others?


Find the interval of convergence including endpoints of $$\sum_{n=0}^{\infty}  \frac{n(x+3)^n}{2^n(n^2+1)}.$$ I can find the interval of convergence but I don't know how to test endpoints $x=-5$ and $x=-1$. I don't know whether the series convergences at $x$ = $-5$ and $x$=$-1$ and need help. I don't think the series converges at $x= -5$ and  $x= -1$.   No this is not a duplicate question because the starting index of the series is different.

Find the interval of convergence including endpoints of $$\sum_{n=1}^{\infty}  \frac{n(x+3)^n}{2^n(n^2+1)}.$$ I can find the interval of convergence but I don't know how to test endpoints $x=-5$ and $x=-1$. I don't know whether the series convergences at $x$ = $-5$ and $x$=$-1$ and need help. I don't think the series converges at $x= -5$ and  $x= -1$.


I'm just about to embark on my first brew with my dad.  He mentioned that he may include half a tea spoon of sugar into each of the bottles to prevent it becoming flat.  What are other suggestions to avoid adding processed sugar to a bottle whilst still maintaining that liveliness?  ------- Edit  I have found this:   Sorry for the duplicate post.

I'm doing my second brew after great success with the well documented .   This time is the exact opposite, random recipe and random grains. I went to a brew shop and had the guy make me a 1 gallon Irish Stout kit for St. Paddy's day. I found a  and made it a little less than 2 weeks ago. It's time to bottle but it doesn't say anything about adding priming sugars. Is it standard that these always need to be added? Or do the chocolate roasted malts have the sugars already. Also how will I know when it's ready after bottling?


This  font size looks smaller than others:        Tested in Chrome for Android. Possibly an Android issue.

An issue similar to that described in  and likely to be related.  The comments for a question may vary in size:         Chrome for Android on Nexus 7 running 4.2.2 Jelly Bean. This also occurs on Firefox for Android:


I planning to print a large map(6400x15360) and I want to split that image to multiple images(1123x794). I found that -crop 1123x794 do that but How I can add offset so it will be easier for me to glue the pages after the print?

Say I have a large 800x5000 image; how would I split that into 5 separate images with dimensions 800x1000 using the command line?


Let's say I am a corporation which sells some product. Before selling product I need some documents signed by my customers.  If I create some PDF and send these PDFs to my customers to signing, do I need a licence to create these PDFs ?

I hope this is the correct place where I could ask this question. My mother is an accountant with a degree in economics. She works as a freelancer and she needs some licenses for her job.  The biggest problem is adobe acrobat standard, which costs 400€, quite a lot. I want understand if she must buy it to create pdf files or she can use some free (even for commercial use) programs that she has because of her job (the chamber of commerce provide some advantages to accountants).  She is actually using PDFCreator, which as I can read is free for business usage (open source also!!):   Thanks for any suggestion


Let $f_1(s,\tau)=\delta(e^{(\tau+s)} \sinh \tau )$.  This should be equal to $0$ everywhere unless $\tau=0$, but I think there should be some constant multiplying the delta, i.e. it should be equivalent to $f_2(s,\tau)=c(\tau,s)\delta(\tau)$ where $c(\tau,s)$ is a constant.  How can I manipulate $f_1$ to resemble $f_2$?  Thanks.

I'm trying to show that  $$\delta\big(f(x)\big) = \sum_{i}\frac{\delta(x-a_{i})}{\left|{\frac{df}{dx}(a_{i})}\right|}$$  Where $a_{i}$ are the roots of the function $f(x)$. I've tried to proceed by using a dummy function $g(x)$ and carrying out:  $$\int_{-\infty}^{\infty}dx\,\delta\big(f(x)\big)g(x)$$  Then making the coordinate substitution $u$ = $f(x)$ and integrating over $u$. This seems to be on the right track, but I'm unsure where the absolute value comes in in the denominator, and also why it becomes a sum.  $$\int_{-\infty}^{\infty}\frac{du}{\frac{df}{dx}}\delta(u)g\big(f^{-1}(u)\big) = \frac{g\big(f^{-1}(0)\big)}{\frac{df}{dx}\big(f^{-1}(0)\big)}$$  Can any one shed some light? Wikipedia just states the formula and doesn't actually show where it comes from.


I would think that it would be simple to have a car drive from A to B, but apparently I haven't been able to figure it out. My goal is to have a car begin at a certain position and angle, calculate the best path to another position with another angle, and then travel there.  Please keep in mind that this car has a minimum turning radius, so it can't simply change angles by spinning. Also, I would like to see what I can do with the car only traveling in a single direction, ie. no reversing.  I have read over many grid-based algorithms, but I don't see how I can translate those to what I need, which is most likely a series of arcs and straight lines.  The closest thing I have have found is Dubins Interval, which seems closest to what I need, though I believe it is old and has probably long since been replaced. I have sketched out paths using this method, but have had trouble translating it to programmatic form (C++). I believe the rough idea is to line up the minimum steering circles of the start and goal, start turning from the start until you are on the line, head towards the goal, and then either simply go onto the goal circle and curve it, or project an additional circle on the same line and use it to end up on the goal circle in the opposite direction.  If anyone knows of any examples, code preferred, of simple car driving path examples, I would appreciate it.

For example, say I have a car and a car has a specific minimum turning radius and I want to drive that car from point a to point b, but the car isn't facing point b.   How do I compute a path to point b?  Being able to specify the orientation at the point b would also be good (say you want to drive to your driveway and then pull in to your garage -- it doesn't do much good if you got to your driveway by driving over your lawn and are facing sideways :)  A pointer to documentation (or even just a name) would be perfectly fine -- I'm having trouble finding anything at all.  In my attempts, they work in simple cases, but fail miserably in situations such as when point b is closer to a than the minimum turning radius.   For example, how would you determine a path similar to this (the bold path):      edit: In my actual problem, there are some simple pathing constraints, but I already have an A* algorithm in place that works, but it allows things to make instantaneous heading changes, so it looks silly seeing a car suddenly make a 90˚ turn on a dime when they get to a turn point.


I was studying Ordinary Differential Equations, and my book was trying to explain the maximal interval of solution of a differential equation. If we consider this differential equation $$ \frac{dx}{dt} = x^2 \\ \text{with initial condition}~x(0)= a,~~~a \gt 0 $$ Then, the solution to this equation is $$ x(t) = \frac{1}{ a^{-1} - t}$$ Now, if $t$ starts to increase from $0$ the denominator will decrease and consequently $x(t)$ will increase, when $t =a^{-1}$ the denominator is $0$ and $x(t) = + \infty$. As we let $t$ to decrease from $0$, our denominator will increase and finally when $t = -\infty$, $x(t) = 0$. So, the solution of the differential equation is defined on the interval $(-\infty, a^{-1})$. But the problem comes when the book makes this statement  but there is no way to define the solution that extends further into the future beyond $t=a^{-1}$.  Why the function is not defined for $t \gt a^{-1}$? There is a discontinuity at $t=a^{-1}$ but beyond that the function is nice, why the solution is not defined after $t = a^{-1}$? If compare $x(t)$ with some other simple functions like, for example, $f(x) = \frac{1}{2-x}$, $f(x)$ is well defined after $x = 2$, and here we have its graph: . Why the book says that beyond $t=a^{-1}$ the solution is not defined?

Assume the IVP $$ x'=x^2, \quad x(0)=1 $$ By separating the variables and using the initial condition $$ x(t)=(1-t)^{-1} $$ Then, my book states that since $x_0=1>0$ then the solution can only be extended to the left with maximum existence interval $\, I=(-\infty,1)$.   My question is, since the solution $x(t)$ we found is defined for every $t\neq1$, why isn't the maximum interval of its existence $I^*=(-\infty,1)\cup(1,+\infty)$? Why does it depend on the sign of $x_0$?


This happens only in EEVEE cycles works fine. I reinstalled Blender 2.8 and 2.9 but problem still appearing.

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


I am confused about simple harmonic motion. I understand that it follows a sine wave but is it possible to explain why it does?

I am a Math Grad student with a little bit of interest in physics. Recently I looked into the Wikipedia page for .  Guess, I am too bad at physics to understand it. Considering me as a layman  how would one explain:   What a Simple Harmonic motion is? And why does this motion have such an equation $$x(t)= A \cos(\omega{t} + \varphi)$$   associated with it? Can anyone give examples of where S.H.M. is tangible in Nature?


I'd like to delete a chat.   The chat has more then 15 rows and therefore wont be deleted automatically.   Would it be possible to request a delete?  Edit:  Like you probably didn't notice in my above text is that I've read the post you are referring to which mine is a duplicate of.  I'm wondering how I can contact a moderator or similar to delete a chat?

I created a test room on chat, but I can't see how to delete it.


Occasionally I would like to run a program made for Mac on Ubuntu (example: ). What software can I use to run a single Mac program, like I'm able to do with ?  I like the convenience of  - sometimes you need specific settings or specific Wine version to run your Windows program, and PlayOnLinux makes it easy to provide this on per-program basis. Then you can make a desktop icon that looks and works as a native application.  Is there anything similar I can use for Mac programs in Ubuntu?

Just wondering, are there any projects like WINE, but for Mac software? That is, can we use a program that acts like a compatibility layer to run Mac apps?


I was going through the text "Discrete Mathematics and its Application" by Kenneth Rosen (5th Edition) where I am across the definition of equivalence relation and felt that it is one sided.     Definition: A relation on a set A is called an equivalence relation if it is reflexive, symmetric, and transitive.   Now let us analyze the situation of what equivalence is meant to us intuitively.  Let there be a binary relation $R$ defined on a set $A$. Now we suppose that $R$ be reflexive, symmetric and transitive.  So we have for $a,b,c \in A$    $a R a$ (by the reflexive property of R) if $a R b$ then $b R a$  (by the symmetric property of R) if $a R b$ and $b R c$ then $aRc$ (by the transitive property of R)   Intuitively we can satisfy ourselves with the fact that the above are the necessary conditions for $R$ to be equivalent. So "if $R$ is reflexive, symmetric and transitive, then $R$ is an equivalence relation"  Now working our intuition for equivalence relation $\sim$ we note the following.  Let $\sim$ be an equivalence relation on a set A, then for $a,b,c \in A$ we have,   $a \sim a$ (by the intuitive knowledge of what $\sim$ means) if $a\sim b$ then $b \sim a$ (by the intuitive knowledge of what $\sim$ means) if $a\sim b$ and $b \sim c$ then $a\sim c$ (by the intuitive knowledge of what $\sim$ means)   Now we see that (1) implies $\sim$ is reflexive, (2) implies that $\sim$ is symmetric and (3) implies that $\sim$ is transitive.  So we have "if $\sim$ is an equivalent relation then $\sim$ is reflexive, symmetric and transitive"  From the two intuitive implications we can conclude that A relation on a set A is called an equivalence relation if and only if it is reflexive, symmetric, and transitive. and not what the book says. This definition makes quite sense unlike the book definition which says that if $R$ fails to be either reflexive or symmetric or transitive then $R$ may or may not be an equivalence relation, which after all gives a weird feeling.  Correct me if my logic is wrong.

In some books the word "if" is used in definitions and it is not clear if they actually mean "iff" (i.e "if and only if"). I'd like to know if in mathematical literature in general "if" in definitions means "iff".  For example I am reading "Essential topology" and the following definition is written:     In a topological space $T$, a collection $B$ of open subsets of $T$ is said   to form a basis for the topology on $T$ if every open subset of $T$ can be written as a union of sets in $B$.   Should I assume the converse in such a case? Should I assume that given a basis $B$ for a topological space, every open set can be written as a union of sets in $B$?  This is just an example, I am not asking specifically about this sentence.


I searched around a bit for this question, but I could only find people wondering what happened to their reputation on Meta, rather than why.  Recently I've been posting a few helpful questions on ELU Meta and I have received a number of upvotes. I was confused as to where the reputation from them was going until I read that Meta votes don't "count". Why is this the case? Isn't contributing to a site designed to discuss and improve another site a helpful activity that should be rewarded?

On per-site metas, users are given a rank based on meta participation, and this ranking is seen on the default tab of the users page on each per-site meta. How is this participation numerically calculated to give a ranking? Is it by votes? Something else? Are community wiki posts included in this?


I keep getting this error when I try to push: The "path" argument must be of type string. Received type undefined.

I'm getting an error similar to  and I've checked to see if I could resolve it in the same way, but it appears to be a different issue.  Whenever I try to push, deploy or convert to metadata, I'm getting the error      TypeError [ERR_INVALID_ARG_TYPE]: The "path" argument must be of type string. Received type undefined   This error also shows up in the Problems tab in VS Code, but clicking on it gives me another error (Unable to open "": File is a directory.)    This issue was reported on the  by others over the last 8-9 months, but there's no clear resolution. I've added more detail (json error output) there.  The only "path" argument I can find is in the sfdx-project.json, and it's clearly a string:  {   "packageDirectories": [{ "path": "force-app", "default": true }],   "namespace": "",   "sfdcLoginUrl": "https://login.salesforce.com",   "sourceApiVersion": "46.0" }   I'm completely stuck with no clear way to debug this. Would appreciate any ideas...


I'm having a hard time getting over the following question, which appears in Schimmerling's "A Course on Set Theory."   (Problem) Given that $\kappa$ and $\lambda$ are infinite cardinals with $\kappa\le\lambda$, show that   $$|\{X\subseteq\lambda:|X|=\kappa\}|=\lambda^\kappa.$$  Denoting the set on the left hand side of the equation by $S$, it's not difficult to see that $S\subseteq\lambda^\kappa$. Indeed, $S$ is the set of all bijective mappings from $\kappa$ to some subset of $\lambda$ -- in other words, injections from $\kappa$ to $\lambda$. But $\lambda^\kappa$ also contains non-injective mappings from $\kappa$ to $\lambda$, and so it appears absurd that the cardinality of $S$, that is the least ordinal that could be bijected to $S$, could be its superset $\lambda^\kappa$.   Regardless, I'm trying to find a nice injection from $\lambda^\kappa$ to $S$ so that I could apply Cantor-Schroeder-Bernstein. But I haven't been able to find one so far.   Could someone explain the problem with my intuition, or provide some hints as to thinking about the question? Thanks!

Initially assume ZFC.  Let $\binom{\kappa}{\lambda}$ denotes $\left|[\kappa]^{\lambda}\right|$ where $[\kappa]^{\lambda}$ is the collection of all subsets of $\kappa$ with cardinality $\lambda$. That is, the number of subsets of $\kappa$ of size $\lambda$.  Let $\kappa$ be any infinite cardinal number. Then it is easy to see that   $\binom{\kappa}0=1$ $\binom{\kappa}n=\kappa$ for all positive natural number $n$.  $\binom{\aleph_0}{\aleph_0}=\beth_1$ $\binom{\kappa}{\lambda}\le \kappa^\lambda$ when $1\le \lambda \le \kappa$   3 is due to $\beth_1=\sum_{\lambda=0}^{\aleph_0}\binom{\aleph_0}{\lambda}$ and others besides $\binom{\aleph_0}{\aleph_0}$ sums $\aleph_0$(since countable infinite countable infinites sums to countable infinite)  $\left({}^{\kappa}_{\lambda}\right)\le \kappa^\lambda$ is due to an injection can be made from $[\kappa]^{\lambda}$ into $\kappa^{\lambda}$(maps $\{a_i|i<\lambda\}$ to $\langle a_i\rangle_{i<\lambda}$ where $a_j<a_k$ iff $j<k$)  I hypothesize that   $$\binom{\kappa}{\lambda}=\begin{cases} \kappa^\lambda,&\lambda \le \kappa \\ 0,& \lambda>\kappa  \end{cases}$$  It holds when $\kappa=\aleph_0$, but hard to induct for larger cardinals without assuming GCH. So I need some helps.


My Sanctuary Hills settlement in Fallout 4 has 14 settlers and I'm struggling to tell what resources each of them are assigned to - or if they're assigned to any resource at all.  Currently the only way I know to see assigned resources is by hovering over a settler in workshop mode their assigned resources will highlight in green.  This works okay if they are standing near their resource - but as my settlement has grown in physical size/ complexity/ population it's become harder and harder to use this method.  Is there another way to see which settlers are assigned to which resources?

Is it possible to see a list of the settlers in a given settlement and the jobs they are assigned to? It would make it easier to pick a settler for a new job.


A symmetric matrix in $\mathbb{M}_n(\mathbb{R})$ is said to be non-negative definite if $x^TAx≥0$ for all (column) vectors $x \in \mathbb{R}^n$. Which of the following statements are true? a. If a real symmetric $n×n$ matrix is non-negative definite, then all of its eigenvalues are non-negative. b. If a real symmetric $n×n$ matrix has all its eigenvalues non-negative, then it is non-negative definite. c. If $A\in\mathbb{M}_n(\mathbb{R})$, then $AA^T$ is non-negative definite.    I know that all of the above options are correct but I did not have proof of any one of them.can anybody tell me about the proof of them.

1.a symmetric matrix in $\mathbb{M}_n(\mathbb{R})$ is said to be non-negative definite if $x^Tax≥0$ for all (column) vectors $x\in \mathbb{R}^n$. Which of the following statements are true? (a) If a real symmetric $n\times n$ matrix is non-negative definite, then all of its eigenvalues are non-negative. (b) If a real symmetric $n\times n$ matrix has  all of its eigenvalues are non-negative , then it is non-negative definite. (c) If $ A\in \mathbb{M}_n(\mathbb{R})$, then $AA^T$ is non-negetive definite. 2. only one of the following matrices is non-negetive definite. Find it. (a) $\begin{pmatrix} 5 & -3 \\ -3 & 5 \end{pmatrix}$. (b) $\begin{pmatrix} 1 & -3 \\ -3 & 5 \end{pmatrix}$. (c) $\begin{pmatrix} 1 & 3 \\ 3 & 5 \end{pmatrix}$.      3.let $B$ be the real symmetric non-negative definite $2×2$ matrix such that $B^2=A$ where $A$ where is the non-negetive definite matrix in question $2$.write down the characteristic polynomial of $B$.      My thoughts..  For1.  (a) & (b) are true but not sure about (c). For 2. (a) is the correct option since it has all positive eigen values.they are $2,8$. For 3. Eigen values of $B$ will be $\sqrt{2}$ and $\sqrt{8}$. So the answer is $x^2-3√2x+4=0$.      Can anybody help me to verify the solutions of the above problems.


I want to develop a functionality for creating no more than one record per day. If more than one record is created should show error. How should I do this?

Any idea how to write a Validation Rule, that prevents the user from creating more than one record a day.  I have one Object called (Stundenkonto__c) it shows a Month in Timetracking. I have a Object called (Zeiteintrag__c) it is the Master Detail of (Stundenkonto__c) So the User should only be able to create only one (Zeiteintrag__c) Record a day.


Can you help me for my algebra homework? Let n be square free positive integer. Prove that Zn has no nonzero nilpotent element.

Suppose $n = p_1^{a_1} ... p_r^{a_r}$ where $p_i$'s are prime integers and $a_i$'s are positive integer.  (a) Show that the set of nilpotent elements in $\mathbb{Z}_n$ is $(p_1 p_2 ... p_{r-1} p_r)$, the ideal generated by the element $p_1p_2 ... p_{r-1} p_r$.  (b) Find a necessary and sufficient condition on $n$ such that $\mathbb{Z}_n$ does not have any non-zero nilpotent elements.  My attempt:  (a)Let x be a nilpotent element in $\mathbb{Z}_n$. Then $x^k = n$ for some $k > 0$.Note that $x \neq 1$. Since $Z_n$ is a UFD, $x =  p_1^{b_1} ... p_r^{b_r}$, where $b_i > 0$ and so $x^k = p_1^{k b_1} ... p_r^{k b_r} = p_1^{k b_1 - 1} ... p_r^{k b_r - 1}(p_1 ... p_r) \in (p_1 ... p_r)$. Hence the set of nilpotent elements is a subset of $(p_1 ... p_r)$. On the other hand, for all $x \in (p_1 ... p_r)$, $x = z_1 \cdot p_1 ... p_r \cdot z_2$ for some $z_1 = p_1^{c_1} ... p_r^{c_r}, z_2 = p_1^{d_1} ... p_r^{d_r} \in \mathbb{Z}_n$, so $x = p_1^{c_1 + d_1 +1} ... p_r^{c_r + d_r+1}$. Let k be an natural number such that $k(c_i+d_i+1) >a_i$ for all i. Then we have $x^k = p_1^{k(c_1 + d_1 +1)} ... p_r^{k(c_r + d_r+1)} = p_1^{a_1} ... p_r^{a_r}(p_1^{k(c_1 + d_1 +1)-a_1} ... p_r^{k(c_r + d_r+1)-a_r}) = 0 \in\mathbb{Z}_n$. Hence the $(p_1 ...p_r) \subseteq$ the set of nilpotent elements in $\mathbb{Z}_n$. Therefore $(p_1 ...p_r) =$ the set of nilpotent elements in $\mathbb{Z}_n$  (b) $a_i = 1$ for all $i$. If $a_i = 1$ for all i, then it is obvious then $\mathbb{Z}_n$ does not have any non-zero nilpotent elements. Now I just need to show that if $\mathbb{Z}_n$ does not have any non-zero nilpotent elements, then $a_i = 1$ for all $i$. Proof by contradiction: Suppose there exists some $a_i$ > 1. Then $p_1...p_r < n$ is non-zero a nilpotent element.


Putting an equation \label{} within a list \item, where the item is to be revealed selectively as an overlay, seems to result in LaTeX hiding the reference from itself. Here's a minimum working example:  \documentclass{beamer} \begin{document} \begin{frame}[fragile] \fontsize{6pt}{7.2}\selectfont Outside of the \texttt{list} environment (with overlays), there is no   problem resolving equation number references, e.g. \texttt{\textbackslash ref\{eq:eq1\}} resolves to eq \ref{eq:eq1}: \begin{equation}     x=1 \label{eq:eq1} \end{equation} However within a simple list, where an \texttt{\textbackslash item} appears within an overlay: equation reference labels are not accessible (even within the overlay itself). See below: \begin{list}{}{} \only<1>{\item Item 1: Not very interesting.} \only<2>{\item Item 2: \begin{equation}     x=2 \label{eq:eq2} \end{equation} The reference \texttt{\textbackslash ref\{eq:eq2\}} appears unresolved as eq \ref{eq:eq2}, although eq \ref{eq:eq1} (outside the list) is still resolved OK.} \end{list} \end{frame} \end{document}   Pasting the above code and running pdflatex on it, I get the output as attached:   Rerunning latex numerous times fails to resolve the missing reference: the log file contains:  LaTeX Warning: There were undefined references.   )pdfTeX warning (dest): name{eq:eq2} has been referenced but does not exist, replaced by a fixed one   Can anymore give me a pointer has to how to reveal these references?

For space reasons I want to break up the contents of an itemize list into separate slides, which I have been doing without much problem using \only.  However, the following minimal document complains that the label eq:formula is not defined:  \documentclass{beamer} \begin{document} \begin{frame}{Title}  \begin{itemize}  \only<1>{   \item Item 1.  }             % Comment   \only<2>{     % these lines   \item Item 2, with equation   \begin{equation}    \label{eq:formula}    xyz   \end{equation}    \item Item 3, with reference \eqref{eq:formula}.  }  \end{itemize} \end{frame} \end{document}   As you can see, it is clearly defined.  The problem goes away if you comment out the marked lines (thus, printing everything on one slide).  I see using \tracingmacros that there is a serious redefinition of \label in beamer, and as such it appears that this is a bug with detecting what slide the label is printed on.  Is that right, and what is the solution?


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?

I've associated .xul with Notepad++ so if I double-click on a .xul file, it will open in Notepad++. But Notepad++ doesn't know that XUL is just a particular type of XML, so I then have to manually click on "Language > XML" to get XML syntax highlighting. Is there a way that I can tell it: "every time you open a file with the extension .xul, automatically switch to the XML language"?


I want to write the following:  18 ± 1 nm  (that's a plus/minus sign)  I'm using the siunitx package but in their manual I can't see anything about adding errors to the numbers of units. I've tried \SI{18 \pm 1}{\nano\metre} but that outputs "18(1) nm" which isn't the format I want.

Using the siunitx package, if I specify an error with the \pm symbol then it automatically converts it to a form using parenthesis. I would like it to not do this and keep the \pm symbol, but still space the elements of the quantity and symbol in a good way.  e.g. \SI{10 \pm 2}{\kelvin} would produce 10(1) K  I would like it to produce: 10\pm1 K or something similar with spacing taken care of.


I am facing trouble with a statement made after eq 5.2.4 in sakurai modern qm and the statement is $P_1(E-H_0-\lambda P_1VP_1)$ is singular in $P_1$ subspace. How one can we show the validity of the statement.

I am facing trouble with a statement made after eq 5.2.4 in sakurai modern qm and the statement is $P_1(E-H_0-\lambda P_1VP_1)$ is singular in $P_1$ subspace. How one can we show the validity of the statement?  This question is similar to problem asked previously in this forum but haven't answered appropriately. So I am asking again here. The link for the  qn is


Three (possibly distinct) examples:   A date which never exists/existed, like February 31 A date which was 'skipped' because of calendar changes.  When Russia transitioned from the Julian to the Gregorian calendar it 'skipped' October 26, 1917, among other days. A date/time which was 'skipped' due to a daylight savings change, like 02:01 on 03/27/2011 in the USA   These all appear to be properly formatted, but don't exist, at least in some parts of the planet that recognize the standard US date/time lexicon.   discusses the phrase to show to application users when they choose an invalid date, but invalid date would include 01/blah/-2 and other entries that don't conform to an accepted date format.    I've been using the term irrational date, but I'm not a mathematician and don't know if it is appropriate to compare these situations to irrational numbers.

I wanted to use this, but I don't know if it's actually valid in English:     The specified date is invalid.It points to a non-existing day.   I'm not a native speaker, and I just want to say that the input points to a date that does not exist, like 30th February.


The TikZ Manual, section 59.5 and     explain how to declare new shapes for TikZ nodes with \pgfdeclareshape{myshape} ... to later use them with  \node[shape=myshape] (name) {text};   But is it also possible to create a new shape to place on a path, which would then be used like this?  \draw (0,0) myshape (5, 7);   How can one declare a new path command?

I would like to create a carc path macro (centered arc, that acts like circle, without changing the current position) in a way to be able to write :   \draw (0,0) carc(30:90:1) carc(30:90:2) carc(30:90:3);   I know how to do it with latex macro :  \def\carc(#1:#2:#3){++(#1:#3) arc(#1:#2:#3) ++(#2+180:#3)}   and then I can use :   \draw (0,0) \carc(30:90:1) \carc(30:90:2) \carc(30:90:3);   But I'm wondering, if there is a way to do this in pure TikZ ?  Is it a way to create new macros that acts like circle, rectangle, arc, ... on paths ?


i have skype installed but if i close the "main menu" it is still running in the background but i cant open it again. How can i open the window again?

I'm new to Ubuntu. I use Skype and often the main window just disappears from my desktop. The Skype instance itself is still running in the background. I know this because I can see its notifications on the bottom right side of the screen.  If I click on the Skype icon again, Ubuntu will launch a new instance instead of maximizing the running instance. Of course this will not work because Skype will not let you sign in: Another instance of Skype may be running.  How do I refocus/bring to the foreground the existing Skype instance? In Windows, you can restore running instances through the taskbar. I've tried cycling through open windows, but the running instance window is no where to be seen.


is there a possibility, while displaying an itemize, to go to an independent frame (or something like that) to show an example for example, and then go back to the itemize ?  something like... that :  \begin{frame}[first]  \begin{itemize}   \item<1> foo   \item<2> bar   % go to [second] and then go back here to see 3rd point   \item<3> baz  \end{itemize} \end{frame}  \begin{frame}[second]  % Some examples \end{frame}   (I don't care if the example second frame is not a real "frame", I'd just want to know the best way to this kind of stuff)

My MWE:  \documentclass{beamer} \usepackage[english]{babel} \usepackage{calc} \usepackage[absolute,overlay]{textpos} \usepackage{pdfsync} \mode<presentation>  \title[AAA]{AAA} %\subtitle \institute[AAA]{BBB} \author{AAA} \date{BBB}  % Define the title of each inserted pre-subsection frame \newcommand*\titleSubsec{Next Subsection} % Define the title of the "Table of Contents" frame \newcommand*\titleTOC{Outline}  \begin{document}  \section{Section 1}  \begin{frame}\frametitle{Section 1 - A}     \begin{itemize}         \item <1-> Blablabla:             \begin{itemize}               \item Blablabla                 \item Blablabla                 \item Blablabla                 \item Blablabla                 \item $\cdots\cdots\cdots$             \end{itemize}         \vspace{0.5cm}         \item <2-> Blablabla:             \begin{itemize}               \item Blablabla                 \item Blablabla                 \item Blablabla                 \item Blablabla                 \item $\cdots\cdots\cdots$             \end{itemize}     \end{itemize} \end{frame}  \begin{frame}\frametitle{Section 1 - B}     PHOTO \end{frame}  \begin{frame}\frametitle{Section 1 - A}     \begin{itemize}         \item <1-> Blablabla:             \begin{itemize}               \item Blablabla                 \item Blablabla                 \item Blablabla                 \item Blablabla                 \item $\cdots\cdots\cdots$             \end{itemize}         \vspace{0.5cm}         \item <2-> Blablabla:             \begin{itemize}               \item Blablabla                 \item Blablabla                 \item Blablabla                 \item Blablabla                 \item $\cdots\cdots\cdots$             \end{itemize}     \end{itemize} \end{frame}  \end{document}   What I basically want is to get rid of page 2 and page 4 of the pdf output file. That is, on the first slide I want to show item <1>, then I want to show a slide with just a photo, and then I want to show item <1> together with item <2> on a new slide.


I have a Series in pandas consisting of empty lists.  >>> s = pd.Series( [[]] * 20, index= range(0,20) )  I want to add tags to certain elements by index.   >>> for i in [1,3,5,7,11]: ...     s.loc[ i ].append('prime')   but this is what I keep getting:  >>> s 0     [prime, prime, prime, prime, prime] 1     [prime, prime, prime, prime, prime] 2     [prime, prime, prime, prime, prime] 3     [prime, prime, prime, prime, prime] 4     [prime, prime, prime, prime, prime] 5     [prime, prime, prime, prime, prime] 6     [prime, prime, prime, prime, prime] 7     [prime, prime, prime, prime, prime] 8     [prime, prime, prime, prime, prime] 9     [prime, prime, prime, prime, prime] 10    [prime, prime, prime, prime, prime] 11    [prime, prime, prime, prime, prime] 12    [prime, prime, prime, prime, prime] 13    [prime, prime, prime, prime, prime] 14    [prime, prime, prime, prime, prime] 15    [prime, prime, prime, prime, prime] 16    [prime, prime, prime, prime, prime] 17    [prime, prime, prime, prime, prime] 18    [prime, prime, prime, prime, prime] 19    [prime, prime, prime, prime, prime] dtype: object   Which is not what I want.    I would like it to be like this:  >>> s 0     [] 1     [prime] 2     [] 3     [prime] 4     [] 5     [prime] 6     [] 7     [prime] 8     [] 9     [] 10    [] 11    [prime] 12    [] ...   I've been banging my head against the desk for an hour on this.  Total pandas newb.   UPDATE  The following works as expected.   s = pd.Series( [[]] * 20, index= range(0,20) ) >>> for i in [1,3,5,7,11]: ...     s.loc[ i ] = s.loc[ i ] + ['prime']   I will eventually want multiple 'tags' on each index, this is a fall back for the moment.  I still would like to know why the append doesn't work.

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


I'm on Ubuntu 12.04 LTS.  I want to create a link from the WorkSpace folder on my desktop.  I did right click on that folder and choose Make Link option from the menu. And did move/paste or copy/past that link on the desktop, but...  When I perform system restart, the link is broken.  So, is it possible to create a link from a folder that is in E:\, on the desktop, without creating a helper link as known from windows "send to" functionality?

I'm using ubuntu 14.04 LTS. When I start my pc and click on any bookmark from the file manager it shows this error:   Unable to find the requested file. Please check the spelling and try again. Unhandled error message: Error when getting information for file '/media/angel/DOC/edu': No such file or directory   But when I open DOC drive and again clink on the same bookmark it works properly. Can anybody tell me why is this happening and how to solve this issue?   Edit: Output of lsblk is following: (ubuntu is installed in sda5)  NAME   MAJ:MIN RM   SIZE RO TYPE MOUNTPOINT sda      8:0    0 119.2G  0 disk  ├─sda1   8:1    0  91.3G  0 part  ├─sda2   8:2    0     1K  0 part  ├─sda5   8:5    0  24.1G  0 part / └─sda6   8:6    0   3.8G  0 part [SWAP] sdb      8:16   0 465.8G  0 disk  ├─sdb1   8:17   0  93.2G  0 part  ├─sdb2   8:18   0     1K  0 part  ├─sdb5   8:21   0  93.2G  0 part  ├─sdb6   8:22   0  89.3G  0 part  ├─sdb7   8:23   0  93.2G  0 part  ├─sdb8   8:24   0  93.2G  0 part  └─sdb9   8:25   0   3.8G  0 part  sr0     11:0    1  1024M  0 rom     After opening the disk drive the output of lsblk is bellow:   NAME   MAJ:MIN RM   SIZE RO TYPE MOUNTPOINT sda      8:0    0 119.2G  0 disk  ├─sda1   8:1    0  91.3G  0 part  ├─sda2   8:2    0     1K  0 part  ├─sda5   8:5    0  24.1G  0 part / └─sda6   8:6    0   3.8G  0 part [SWAP] sdb      8:16   0 465.8G  0 disk  ├─sdb1   8:17   0  93.2G  0 part  ├─sdb2   8:18   0     1K  0 part  ├─sdb5   8:21   0  93.2G  0 part  ├─sdb6   8:22   0  89.3G  0 part /media/angel/DOC ├─sdb7   8:23   0  93.2G  0 part  ├─sdb8   8:24   0  93.2G  0 part  └─sdb9   8:25   0   3.8G  0 part  sr0     11:0    1  1024M  0 rom   The output of sudo blkid gives the following information about sdb6:  /dev/sdb6: LABEL="DOC" UUID="04280A22280A12FA" TYPE="ntfs"


I was trying to test for multicollinearity using VIF. Here is my codes: mreg.mod = lm(price ~ bedrooms + bathrooms + sqft_living + sqft_lot +                floors + condition + grade + sqft_basement + sqft_above                + sqft_living15 + sqft_lot15 data = data) summary(mreg.mod) tidy(vif(mreg.mod))  But an error that says "there are aliased coefficients in the model" pops up. I was wondering if this has to do with my lm model?

While building a regression model in R (lm), I am frequently getting this message  "there are aliased coefficients in the model"   What exactly does it mean?  Also, due to this predict() is also giving a warning.  Though it's just a warning, I want to know how can we detect/remove aliased coefficients before building a model.  Also, what are the probable consequences of neglecting this warning?


NTFS offers the option to compress files on the fly, but as far as I know you need to enable this functionality when you format the volume.   Is there a way to enable it on an already formatted NTFS volume, apart for the obvious "move files away, re-format, re-import files". Possibly using a Linux boot?  If not, some insights on the technical why?  NOTE: In my case, the checkbox in the properties window for folders (see Techie007 answer) is greyed out, I just guess that it's because it has not been enabled at format time. There is no such checkbox on the drive's properties window  Context: I use win7, I'm using a 3GB external drive, formatted as NTFS with default options

I have a USB drive formatted with NTFS. I would like to use "compress contents to save disk space" option, although it is greyed out.    It works fine on the C: drive. Any suggestions?


My shoes are [of] the wrong color. This new wallpaper is [of] an odd pattern.  At first, one could say these are noun phrases functioning as predicate nominatives; however, the awkwardness in meaning suggests that a preposition was omitted and the subject complement is actually an adjectival prepositional phrase. Is this the case? If so, when is the omission allowed?

Skyscrapers are of various shapes.   Skyscrapers are various shapes.      Why do we use of in the sentence above?  Is there any difference in meaning between the two sentences?


I would like to write a sum in my tabularx environment. Usually I would go into the full math mode with $$\sum_i ...$$ and the "i" would be right below the sigma symbol.  However, this doesn't work inside the tabularx and if I instead use $\sum_i$ I can compile without an error, but the index for the i is on the bottom right of the sigma instead of right below.  How can I make the sum symbol with the index below the sigma inside of a tabularx?  Thanks for your help!

I'm very familiar with how symbols display differently in inline mode (with $ ... $) vs. how display math shows them (with \[ ... \] or $$ ... $$).  Two examples would be with limits  $\lim_{n\rightarrow \infty}f(x)$   vs.  \[ \lim_{n\rightarrow \infty}f(x) \]   and with sums  $\sum_{n=1}^{x} n^2$   vs.  \[ \sum_{n=1}^{x} n^2 \]   My Question is:     How do you display these things in inline mode (with all the nice inline formatting) as if they were in display mode ?   The inverse -- how to display things in display mode as if they were in inline mode -- is also of interest.


A recent question had a comment which intrigued me, so I went to Wolfram Alpha and put in $\cos(36°)$ and it was half the golden ratio?  Why is $\cos(36^\circ) = \frac{\phi}{2}$? Is there a nice geometric proof? I have never heard this before and it's quite fascinating. Is it a coincidence?  Is there something special about the angle $\frac{\pi}{5}$?

Good morning! I'm having trouble with this problem... It's just taking me forever and I'm worn out and I'm lost on how to use a double angle identity for $72=2⋅36$  The problem reads as follows  An exact value for $\cos36°$ can be found using the following procedure. Begin by considering $\sin108°$. Note that $108=72+36$ and use the sine sum identity. Also note that $72=2⋅36$ and use double angle identities. If there are any common factors in each term, factor them out and cancel them if they are not equal to zero. You should eventually obtain a quadratic equation containing $\cos36°$. Use the quadratic formula to obtain the exact value for $\cos36°$. (Note that the quadratic formula should give two solutions. One can be disregarded - why?  Thank you in advance to anyone who can help.


I am creating a table which has create_date and modify_date field in mysql, but I am struggling in decide which data type is the best choice for these 2 fields. Should i use date time for both fields, or should i use date time for create_date and time stamp for modify_date ?

Would you recommend using a  or a  field, and why (using MySQL)?   I'm working with PHP on the server side.


can anyone, please, tell me why this code does not work?  var newbie  = [];  for ( var c of "greetings"){   var newbie += c; };   I am trying to put characters of "greetings" to an array newbie.

How do I append an object (such as a string or number) to an array in JavaScript?


I am trying to upgrade my PC from Ubuntu 16.04 to 18.04. However, when I try to do this through both the update centre and terminal, I get the following message before the installation is automatically aborted: -  A problem occurred during the update. This is usually some sort of  network problem, please check your network connection and retry.  W:Failed to fetch  http://archive.ubuntu.com/ubuntu/dists/vivid/universe/source/Sources  404 Not Found [IP: 91.189.88.149 80]  , W:Failed to fetch  http://archive.ubuntu.com/ubuntu/dists/vivid/restricted/source/Sources  404 Not Found [IP: 91.189.88.149 80]  , W:Failed to fetch  http://archive.ubuntu.com/ubuntu/dists/vivid/multiverse/source/Sources  404 Not Found [IP: 91.189.88.149 80]  , W:Failed to fetch  http://archive.ubuntu.com/ubuntu/dists/vivid/main/source/Sources 404  Not Found [IP: 91.189.88.149 80]  , W:Failed to fetch  http://archive.ubuntu.com/ubuntu/dists/vivid-updates/universe/source/Sources  404 Not Found [IP: 91.189.88.149 80]  , W:Failed to fetch  http://archive.ubuntu.com/ubuntu/dists/vivid-updates/restricted/source/Sources  404 Not Found [IP: 91.189.88.149 80]  , W:Failed to fetch  http://archive.ubuntu.com/ubuntu/dists/vivid-updates/multiverse/source/Sources  404 Not Found [IP: 91.189.88.149 80]  , W:Failed to fetch  http://archive.ubuntu.com/ubuntu/dists/vivid-updates/main/source/Sources  404 Not Found [IP: 91.189.88.149 80]  , E:Some index files failed to download. They have been ignored, or  old ones used instead.    Restoring original system state  Aborting Reading package lists... Done     Building dependency tree           Reading state information... Done   I would appreciate it if someone could help me fix my problem.

Recently I have installed an older version of Ubuntu on my old machine. Whenever I try to install any software, I get an error saying it couldn't be found:  $ sudo apt-get install vlc Reading package lists... Done                Building dependency tree        Reading state information... Done     E: Couldn't find package vlc


The idea of self-answers seem to be slightly against the primary purpose of this site. This site doesn't want to accumulate the kind of junk other sites tend to (I think). Also, this site wants to become an encyclopedia of non-trivial, useful information in the form of questions and answers.  But if self-answers are allowed, then the question-answers (might be) more inclined towards being trivial or not useful for a lot of people.   My question is: What kind of self-answered questions must be promoted to be more suitable for this site. What kind of topics? etc.

I might want to answer my own question because:  I arrived at a solution before there were any other correct answers or I like mine better, can I still answer my own question?  I have a folder with lists of code snippets for things I always forget or get wrong, such as regular expressions for processing XML, common WinForms control idioms, etc. Is it considered poor etiquette for Stack Overflow to ask a question I already know the answer to, and then self answer, just so it gets recorded on the website?   Related:          For more information, see "" in the .


I am trying to setup vagrant with virtual box on my ubuntu server 16.04. Atm I think that the error I get is due to I miss a GUI. 0x80004005 is the error it spits out. First I thought is was a permissons error but no, after a while I reinstalled all software packages. Still no luck.  Anyone has any suggestions what I am dong wrong?  This is my output:  vagrant up Bringing machine 'default' up with 'virtualbox' provider... ==> default: Clearing any previously set forwarded ports... ==> default: Clearing any previously set network interfaces... ==> default: Preparing network interfaces based on configuration... default: Adapter 1: nat ==> default: Forwarding ports... default: 22 (guest) => 2222 (host) (adapter 1) ==> default: Running 'pre-boot' VM customizations... ==> default: Booting VM... There was an error while executing `VBoxManage`, a CLI used by Vagrant for controlling VirtualBox. The command and stderr is shown below. Command: ["startvm", "bd4ed1d2-8ddc-4faa-b993-9ab4526e80ab", "--type", "headless"] Stderr: VBoxManage: error: The virtual machine 'admin_default_1496300210785_96841' has terminated unexpectedly during startup with exit code 1 (0x1) VBoxManage: error: Details: code NS_ERROR_FAILURE (0x80004005), component MachineWrap, interface IMachine

I tried to use my Virtual Box and this is the error I received - (I just updated to the new Ubuntu also) and I am VERY new at this Linux OS.     Kernel driver not installed (rc=-1908)      The VirtualBox Linux kernel driver (vboxdrv) is either not loaded or   there is a permission problem with /dev/vboxdrv. Please reinstall the   kernel module by executing      '/etc/init.d/vboxdrv setup'      as root. Users of Ubuntu, Fedora or Mandriva should install the DKMS   package first. This package keeps track of Linux kernel changes and   recompiles the vboxdrv kernel module if necessary.


The Planck charge and mass values seem rather unusual.  Is this an indicator that there is a lack of understanding in current theory, or is there a logical explanation for the magnitude of these two numbers?  I read in a paper by Forsythe, that Planck mass might be the geometric mean between the mass of the smallest possible particle and the mass of the universe.  Could this be correct?

Unlike most  named after "Planck" such as Planck length, Planck temperature, etc, the  seems more closed to daily life. It is about $10^{-5}$g, same order of magnitude of one eyebrow hair or a flea egg.  I am just wondering is there any interesting explanation about the relation between Planck mass and the mass of small lives such as flea.


Since a few days Windows 10 is being very inconsequent in registering single clicks. This is hugely annoying as many actions are now done twice, or a totally different action then what I had in mind.  This happens in all kinds of programs, like   Automatically click the browser back button twice Automatically open folders instead of selecting them Select all units of a kind in Starcraft 2, instead of a single unit Automatically open emails in new screen in Outlook, instead of selecting them And this list goes on..   I have set "Open new folders on double click" in Folder Options => General.  What else can I try to solve this issue?

I have a generic Logitech USB Optical Mouse (couldn't find a model number) and occasionally when I am doing a single click, it registers as a double click instead.  For example, when I click a file once, it opens it rather than selects it. What could be the source of this problem?


Ok guys so I downloaded and installed garena plus with wine but something wasn't working so now I want to uninstall it. I'm new on Linux and it's hard for me to figure out where the application is installed. Please help me

I want to remove Spotify version 0.61 because it crashes on start up. But when I hit the "remove/modify" button it deselects my selection (spotify) and chooses the program above it (Counter-strike 1.6). I have tried to remove counter strike, BUT it gives me an error with a missing file.   So I'm stuck and I have no idea how to move on please help me.  The normal way to remove wine software doesn't work as I have said. This is how-to:  Wine --> uninstall wine software --> select program --> remove/modify button.   wine's uninstall program can't open the "uninstall.ini" file (counter strike 1.6)


I have read  and I don't buy it     Because genetics influence susceptibility to migraine, it can be   shaped by evolution. Fitness-impairing disorders, including severe   headache, tend to disappear as a result of natural selection, and   their frequency decreases to near the rate of spontaneous   mutation. However, migraine has not   diminished over millions of years of evolution. Its prevalence has at   least been maintained at a high level, and has even been shown to be   increasing.   This phenomenon suggests that a central nervous system (CNS)   susceptible to severe, intermittent headache has been linked to an   important survival or reproductive advantage.   the argument in wiki is equivalent to since we know that evolution is correct - it means that headaches must benefit us somehow otherwise we wouldn't have it so let's think of some reasons - which is in my opinion is a fallacy.  I could believe that this is a bad side effect of some more efficient to survival trait like being smart, ()     Finally, migraine may be a component of imperfect central nervous   system design. Evidence has suggested a dysfunction of pain-inhibitory   pathways in migraine and discordant interaction between the ancient   brain stem design and the more evolved neocortex.   EDIT:  I have read the  and , and I agree that they do partially answer my question in regard that a mild 'badness' can get past. I would argue that my question is different in a way that I am referring to specific point The trait might have a tradeoff which essentially makes no change to the overall fitness  The way I understand it is that one gets some 'perk' that is beneficial in some situations and disadvantageous in others and they cancel each-other out. (I just don't see how without some huge benefit migraines would get past). What I am asking is what so advantageous we must have gotten - that such horrible thing like migraines got through.  Are there any studies done - that incapacitating migraines are coupled with an evolutionary trait?

If a trait would be advantageous to an organism then why hasn't it evolved yet?  Conversely, if a trait is not advantageous or mildly disadvantageous, why does it exist?  In other words why does evolution not make the organism more "perfect"?    This is a general question that would be applicable for any kind of trait. Please keep the answers precise and scientific.   Read this meta post for more information:


From the  I asked just now, I now know that the plus or minus doesn't matter for $ \boldsymbol{\nabla} V$ in math (since the opposite vector field $\vec{-F}$) must be conservative as well. $$ \textbf{F}=- \boldsymbol{\nabla} V$$ Since I think it's more appropriate to open a new question, then my question is: why does $F = -\boldsymbol{\nabla} V$ in the first place?

Why is the potential energy equals to the negative integral of a force? I am really confused with this negative sign. For example, why there is a negative sign in the gravitational potential energy and what does it mean?   I read that the negative sign means you do the same force but in the opposite direction.  Doesn't that mean the object shouldn't move?


I used to alt-space x to toggle a terminal window between maximize (fullscreen) and unmaximize. This was in Ubuntu 16. But in Ubuntu 18 and 20 this doesn't work anymore. Is there some settings/preferences I'm not aware of to enable this or some other keyboard shortcut?

On Ubuntu 16.04 LTS I have used simple keyboard shortcut to set property Always on Top (Nautilus window as example):   Alt+Space,    t After next Alt+Space or right mouse click I see that window was set to Always on Top.     In standard Ubuntu 18.04 LTS with GNOME Shell I can press Alt+Space:    but it does not react to t.  Seems to be a real .    How to enable such menu accelerators/mnemonics in standard Ubuntu 18.04 LTS?


I am working on an application, where i would like the user to first register and than log in to the application.   Can i make the user perform both actions from a single form i.e. as soon as he registers he may be logged in or go for separate forms for both the actions

I have notice some sites have the same form for login, register and forgotten password.  Below the form you have 3 buttons    i forgot my password register log me in   What are the pros and cons on using this approach and which version would you go for.


I'm having exactly the same issue in this question:    Has anyone found a solution please?

The hard drive on my MacBook Pro has two partitions. One with the OS and the other with data.  Yesterday, from a USB boot drive, I performed a clean installation of Mountain Lion to the OS drive. I created the USB boot installer from InstallESD.dmg that I received from purchasing the OS from the Mac App Store.  Now I can't see or mount my data partition.  I'm wondering if there's a problem with the MBR. In Disk Utility it shows up as "disk0s4", but it's greyed out.  Any ideas on how I can mount the data partition so I can get my data off it?  For diskutil list disk0 the result is:   /dev/disk0    #:                                 TYPE NAME         SIZE       IDENTIFIER    0:                GUID_partition_scheme             *500.1 GB   disk0    1:                                  EFI              209.7 MB   disk0s1    2:                            Apple_HFS MacBook OS    99.5 GB   disk0s2    3:                           Apple_Boot Recovery HD  650.0 MB   disk0s3    4: 46860E2C-2310-4F96-99F6-616D0B4CB55D              399.6 GB   disk0s4   Here's the result of diskutil info /dev/disk0s4  Device Identifier:        disk0s4 Device Node:              /dev/disk0s4 Part of Whole:            disk0 Device / Media Name:      MacBook Data  Volume Name:              Not applicable (no file system)  Mounted:                  Not applicable (no file system)  File System:              None  Partition Type:           46860E2C-2310-4F96-99F6-616D0B4CB55D OS Can Be Installed:      No Media Type:               Generic Protocol:                 SATA SMART Status:             Verified  Total Size:               399.6 GB (399629668352 Bytes) (exactly 780526696 512-Byte-Blocks) Volume Free Space:        Not applicable (no file system) Device Block Size:        512 Bytes  Read-Only Media:          No Read-Only Volume:         Not applicable (no file system) Ejectable:                No  Whole:                    No Internal:                 Yes Solid State:              No


There was a previous problem in my homework that basically demonstrated that:  10C7 = 9C6 + 8C6 + 7C6 + 6C6   And our question is:   "Use that fact to derive a summation formula involving expressions nC1."   I'm not entirely sure what this means, but I'm assuming we are to use Sigma.  This is what I came up with:  $${}_nC_r = \sum_{i=r - 1}^{n-1} {}_iC_{r-1}$$  I'm not sure if I'm even using legal notation here, so any help would be greatly appreciated.

After reading , the most popular answer use the identity $$\sum_{t=0}^n \binom{t}{k} = \binom{n+1}{k+1}.$$  What's the name of this identity? Is it the identity of the  modified.  How can we prove it? I tried by induction, but without success. Can we also prove it algebraically?  Thanks for your help.    EDIT 01 : This identity is known as the  because, on Pascal's triangle, when the addends represented in the summation and the sum itself are highlighted, a hockey-stick shape is revealed.


I recently came across this , in David Morin's weekly problem set. The solution to which I figured, as explained . But I also came across the solution explained in this . Here the author solves the problem in n dimensions too and concludes that in 2-dimensional space, the object that gives maximum field would a thin circular plate, and not the planar cross-section of the 3D object found to give maximal field before.   I tried to verify this by calculating fields for the 2 different candidates, but I found the field for a uniform circular plate on a point on the circumference diverges to infinity. Same is the case for various objects, like a uniform semicircular plate at the centre. Why does this happen? Why is it that the field does not diverge for a uniform sphere at the surface of the sphere but it does for other objects? Also, will this be practically experienced?

I found this interesting problem in :     Given a point $P$ in space, and given a piece of malleable material of constant density, how should you shape and place the material in order to create the largest possible gravitational field at $P$?   Any ideas?


I have a local git repository that is configured to connect remotely over SSH on Gitlab (let's call it git@gitlab.com:myrepo/myproject.git), after cloning repositories I like to keep only a specific folder of the project locally, I do it using the command:  git filter-branch --prune-empty --subdirectory-filter subdirectory HEAD~..   This command makes the local repository keeps track of the subdirectory folder on the remote git project (and overlook all the files that are before this folder on my project). As long as I'm using it only for pulling it's fine... The problem is if I try to push changes to that remote branch, if I try I see the following error:  $ git push -u origin master To git@gitlab.com:myrepo/myproject.git  ! [rejected]        master -> master (fetch first) error: failed to push some refs to 'git@gitlab.com:myrepo/myproject.git' hint: Updates were rejected because the remote contains work that you do hint: not have locally. This is usually caused by another repository pushing hint: to the same ref. You may want to first integrate the remote changes hint: (e.g., 'git pull ...') before pushing again. hint: See the 'Note about fast-forwards' in 'git push --help' for details.   I haven't found anything to this specific case on git push --help. Does anyone know if it's possible to push on a remote folder when I only have a subfolder of the project on my local repository?

I have my Git repository which, at the root, has two sub directories:  /finisht /static   When this was in , /finisht was checked out in one place, while /static was checked out elsewhere, like so:  svn co svn+ssh://admin@domain.com/home/admin/repos/finisht/static static   Is there a way to do this with Git?


I know that we can use CtrlLeft Click to add a file to the selection in windows explorer. It is also possible to use ShiftArrow to extend the selction to adjacent files.  How can I select files that are not adjacent though - without using the mouse?  I noticed that I can use CtrlArrow to move some kind of cursor onto a file without actually selecting it, but then how can I select the file I want selected once that cursor is on it?  Bonus Points if you also know how to jump to a filename and add this to the selection, but that would be a different question

If I've got a file (or files) selected in Windows Explorer, the only way I've found to "unselect" them is click with the mouse on some empty space.  I thought Esc would do this, but it doesn't. Also changing focus with Tab or Shift + Tab doesn't work; the file(s) are still selected even if focus goes to the address bar for instance.  Does anyone know of a keyboard shortcut to do this?


I'm trying to load several images into an array. But for some reason, I get a NullPointerExeption when trying to do the actual loading (ImageIO.read()). I can't see whats wrong, probably from fiddeling around with it too much that I got blind for the mistake. This is the loop that tries to load the images:  for (int i = 0; i <= 1; i++) {         try {             image[i] = ImageIO.read(new File(String.format("TDs/TD%d.png", i)));             bg[i] = ImageIO.read(new File(String.format("BGs/BG%d.png", i)));         } catch (IOException e) {         }     }   I currently have only two images to switch between, but I'll change that soon.   The painting happens using  g2d.drawImage(bg[1], 0, 0, null);   Both variables are initialized by  Image[] image, bg;   And last but not least proof that all images are actually there is found     Thanks for helping a stupid person.   EDIT: Thank you alot for the answers, as initiaizing the array this way works! I feel like an idiot now since I looked at all other array inits to find that they were initialized exactly the same way as you told me... Sorry for stealing your time!  PS: No need to handle IOExeptions since these are textures for a game - they don't change and you can't / shouldn't change them either. I will add a Messagebox with a message in case someone decides to mess around anyways.

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


I'm digging into Python and encounters a weird result when using is statement.  The initial statement :      is will return True if two variables point to the same object.   My test case :  #_________ # 1st case #_________ a = 256 b = 256 a is b >>> True  #________ #2nd case #________ a = 257  b = 257  a is b >>> False  #________ #3rd case #________ a = 257; b = 257; a is b  >>> True   Question :  1. Why, in the second case, a and b are not the same object while they are the same in the first one ? 2. Why they a and b are the same in 3rd statement but not in the 2nd ?  Thanks in advance for enlighten me.

Why does the following behave unexpectedly in Python?  >>> a = 256 >>> b = 256 >>> a is b True           # This is an expected result >>> a = 257 >>> b = 257 >>> a is b False          # What happened here? Why is this False? >>> 257 is 257 True           # Yet the literal numbers compare properly   I am using Python 2.5.2. Trying some different versions of Python, it appears that Python 2.3.3 shows the above behaviour between 99 and 100.  Based on the above, I can hypothesize that Python is internally implemented such that "small" integers are stored in a different way than larger integers and the is operator can tell the difference. Why the leaky abstraction? What is a better way of comparing two arbitrary objects to see whether they are the same when I don't know in advance whether they are numbers or not?


Is publishing in open access journal a good impression ? I mean publishing in such journals (where one has to pay money), will it be valuable compared to other journals ?

A colleague and I recently submitted a paper to a journal with an impressive-sounding name, the "International Journal of Artificial Intelligence and Computational Research". According to ,      IJAICR is a referred [sic] journal in the field of computer science, artificial intelligence and soft computing methods.   It was accepted two days after we submitted it. That's too fast. We were suspicious. Although the journal said that all papers are peer-reviewed, we could not see how that was done in two days. Plus, we received no comments from the reviewers. Also, the submission guidelines didn't ask for a "blind" copy (without our names or any references to who we were).   But wait, there's more.  The acceptance letter asked us to send them US$300 to publish it. We did not. We've withdrawn our submission and will submit a new version of the paper to a more reputable journal in the coming months.  How might we make a better choice of respectable journals before we submit next time?


F12 does not work correctly. When I press the button, Blender shows me the last render (maybe older) result every time. I removed and add again the camera and there is no another camera. I rebooted the computer, downgraded to 2.82 from 2.9 but I cannot view any new result when I press F12. How can I fix that? If u necessary I can upload .blend file anywhere.

Blender is rendering an older version of my project, not the most recent one. I have made it using the Blender Render but it does not want to render in cycles either. A black and grey screen is rendered as if everything is transparent. Checked general camera, lighting and compute devises in case I messed something up but I can't find anything. All my textures and objects look normal, does anybody know what is wrong or what to check?  Ok added link:


My PC specifications:   Dell Latitude D830.  Fresh install of Ubuntu 12.04 (64bit) dual boot with windows xp pro 6 days ago.  Chip ID is Broadcom BCM4311. PCI-ID is [14e4:4312] Last week I installed Ubuntu 12.04 (32bit) on two other old Dell laptops, an Inspiron 6000 and an Inspiron 9000, with absolutely no problems.  One dual boot and the other on its own. I am totally new to this, never installed an os before and having never even seen Ubuntu before last week...so simple answers please :)   This third install went very smoothly, though I had to do it hardwired to the internet, since it couldn't find the wireless:  wireless works perfectly in Windows.  When restarting after the OS install, the screen got stuck on the Ubuntu logo splash page with the 5 dots.  I pressed the button and then rebooted. I have tried all that I could find in this forum on fixes for shutdown or resart, none of them have worked.  The screen stays stuck on the Ubuntu with the 5 dots screen and I then push the button to complete the shut down.  The last fix I tried was from this  So I've left issue for now and trying to get the wireless working, with no success on the contrary.  I've just installed the bcmwl-kernel-source package from .  The wireless connection still didn't work, so I shut down and rebooted.  Now after rebooting, there is still no wireless connectivity. The wireless switch on the computer is on. There is still no wireless choices in the menu bar. I decided to run the update manager and it doesn't work anymore.  Throws a Not all updates can be installed error with a list of reasons. When I press close, I get another error, this time Software index is broken, its impossible to install or remove any software - again with suggestions.  I then went and found on the forum how to uninstall what I had just installed through the terminal, hoping to get back to where I started from, since both the update manager and the terminal were working before the install.  The terminal gives me the following result:  sudo apt-get remove bcmwl-kernel-source.   Message reads on the Terminal:   E:  Could not get lock /var/lib/dpkg/lock - open - (11:  resources temporarily unavailable) E:  Unable to lock the administration directory (var/lib/dpkg ), is another process using it?   Nothing is running in the background.  I'm rather exasperated since every move I make is bran new, and after spending days reading in the forum and trying what seems to work for others nothing does.  Before starting to try to fix the wireless today, everything in Ubuntu works beautifully, now if I can't do updates or use the Terminal, that's not so good.

I'm having serious problems installing the Broadcom drivers for Ubuntu. It worked perfectly on my previous version, but now, it is impossible.   What are the steps to install Broadcom wireless drivers for a BCM43xx card?  I'm a user with no advance knowledge in Linux, so I would need clear explanations on how to make, compile, etc.    lspci -vnn | grep Network showed:   Broadcom Corporation BCM4322 802.11a/b/g/n Wireless LAN Controller [14e4:432b]      iwconfig showed:  lo        no wireless extensions. eth0      no wireless extensions.   NOTE: Answer below is updated every time new information is added and confirmed working.


\begin{aligned} \sigma^{\prime}(x) &=\frac{\partial}{\partial x} \frac{1}{1+e^{-x}} \\ &=\frac{e^{-x}}{\left(1+e^{-x}\right)^{2}} \\ &=\frac{1}{1+e^{-x}} \cdot \frac{e^{-x}}{1+e^{-x}} \\ &=\sigma(x)(1-\sigma(x)) \end{aligned} I do not understand what is the last step in this derivative. How can you factor out the last term? \begin{aligned} \sigma(x)(1-\sigma(x)) \end{aligned}

In my AI textbook there is this paragraph, without any explanation.     The sigmoid function is defined as follows      $$\sigma (x) = \frac{1}{1+e^{-x}}.$$      This function is easy to differentiate because      $$\frac{d\sigma (x)}{d(x)} = \sigma (x)\cdot (1-\sigma(x)).$$   It has been a long time since I've taken differential equations, so could anyone tell me how they got from the first equation to the second?


It seems some software had a bug and created a endless path of folders like:  folderA/folderB/folderC/folderA/folderB/folderC...    I cannot delete it because Windows says that the path is too long.  How can I delete them?

On one of our Windows 2003 file servers somehow someone or something managed to create infinitely recurring directory trees within some of the users' home folders, and they can't be deleted.  You wind up with something like this:  D:\Student\2012\user.name\servername\student\2012\user.name\servername\student\2012\...   And it continues infinitely as far as I've been able to tell.  Trying to delete the directory tree from the system it resides on results in "Error deleting file or folder: Cannot delete file: ". Trying to delete it from a Windows 7 system connected to the network share results in a "folder in use" error.  If you navigate down the directory tree as far as you go you eventually reach a directory that cannot be opened or deleted (if right clicked none of the standard options appear), however if you try to open the same directory from a share on another system it can be opened, however Windows Explorer becomes extremely slow.  I've tried the suggestions in  post, as well as booting the server with a Linux disc and trying to rm -rf the directory, neither worked.  It is a mystery.  Edit: I might also add that it's possible to rename the directories, just not remove them.


Please help me to solve the following limit using high-school methods(no approximations or DCT). I was thinking to use the squeeze theorem but I can't find the best boundaries to evaluate it. $$\lim_{n\to\infty}n\int_0^1 \frac{x^n}{1+x+x^n}dx$$

$$\lim_{n \to \infty }n\int_{0}^{1}\frac{x^{n}}{1+x+x^{n}}dx$$  I factorize $x^n$ then I tried with $u=1+x^{1-n}$ but I didn't get too far. Also I tried to get something from $0<x<1$. I know that if $x$ is from $(0,1)$ then $x^n$ tends to $0$ as $n \to \infty$.


Hello good people of the Ubuntu universe I'm stuck installing drivers for a Edimax EW-7622UMn I have extracted the tar-tgz file but have no idea what I need to type in to Terminal. If anyone can help? So I can just copy and paste the exact command line it would be massively appreciated.

I have downloaded tar.gz files. But I don't know how to install it. How do I install this kind of file?


Light travels with a speed of $3\times10^8{m\over s}$. My question is that was the light initially accelerating or it archived the speed in an instance? If it was accelerating then why it did not accelerate beyond that?

Photons travel at the fastest speed in our universe, the speed of light.  Do photons have acceleration?


Consider the following sentences:   John and Mary are not tall. Neither John nor Mary is tall   Is the first one acceptable (especially in formal writing), or should I always use the second?  Update: I don't think this question is a duplicate of . In particular, this question is not about which verb to use in the neither/nor sentence but about whether the other (first) sentence is acceptable. To be sure, the doubt is whether it is correct to use a compound subject (John and Mary) to talk about features that are essentially individual (John is not tall and Mary is not tall).

I was watching the film A Game of Shadows starring Robert Downey Junior and Jude Law when this line came up, "...neither you nor I is in control..." (I can’t remember the exact words that ended the phrase; if anyone can supply them, it would be much appreciated.)   It immediately struck me as being odd. When I mentioned this to my boyfriend; an English native speaker, with a PhD in something sciency, he told me it was correct. When I asked why, he couldn't explain but put forward the following sentence as an example. "Neither of us is in control..." However, I disagreed with the wording and said the sentence should have been: "Neither one of us is in control..." The genderless third person, one, is singular, and hence, so too the verb that follows. And we say, "one is" NOT "one are".      "Neither you nor I are in control over ..."    I believe the above sounds better, but it is more logical to say:     "Neither you nor I am in control..."    because the verb agrees with the subject closest to it; however, I'm not sure if I have ever read or heard this solution. So, I tried inverting the subject and auxiliary verb order and the resulting phrase was:    "Neither you nor am I in control..."    which sounds very formal, pompous, and ... odd. Am I imagining things?  The two subjects you and I are two separate individuals who are not joined together, I agree the verb should be in the singular; but why should we use "is"? We don't say, "you is" or "I is". Before anyone rushes off to claim my question is a duplicate of a previous Stackexchange one:  I want to explain why the answer to that question fails to explain why my boyfriend and the film makers consider the  sentence below correct:     Neither you nor I is in control...   As I see it, Michael and Albert are two separate individuals, it therefore stands to reason that the verb should be singular, and "is" agrees with the subject. If I rephrase the neither and nor construction, I would get:          Michael is not correct but neither is Albert   OR          Michael is not correct and Albert isn't either.      Which have the same meaning, (either being the negative equivalent of neither) the sentences are grammatical which leads me to conclude that the verb must be singular and hence         Neither Michael nor Albert is correct      However, when I rephrase the "neither you nor I" sentence following the same procedure I have to say this:        You are not in control but neither am I (‘I am’ is ungrammatical)   OR              You are not in control and I’m not either.      which leads me to surmise that the sentence below must be grammatically correct        Neither you nor I am in control"      So, why does my boyfriend insist that the sentence ought to be:     Neither you nor I is in control   Which one of us is right and why?


I have demonstrated that  only is measured based on the gravitational pull of where you live.  For example, the gravity on the surface of Mars is three times smaller than the gravity on the surface of Earth.  So my question is simple: If we take into account that weight is only measured based on gravitational pull on that , if there was no gravity how would we define mass?  That is, would mass weigh anything if no gravitational pull acted on it? Then what would be mass?

We know a mass of an object of one kilogram as an object that weighs W = mg = 9.8 N and we reference it to that, (when it should as a fundamental parameter describe weight not the opposite). But if we were to describe mass to an alien civilization on an alien planet we are exchanging knowledge with, by sending them a one kilogram object, according to their gravity they will measure it differently.  Also their star could be curving space time in such a way, or their velocity according to SR will cause them to perceive mass on our planet -if they observe from away- differently.  If we asked a crew on a space ship moving at a speed close to the speed of light wrt us, or moving in a gravitational field they don't know about, to measure the mass of our planet, they will get different results. On the same principle, we could be measuring the mass of far celestial objects like planets, differently.   I perceive space time as full of curves and irregularities. We know the about some of these and we don't about others. I mean we know about the earth's gravity, the sun's but we ignore the effect of the galaxy and the cluster, dark matter, and who knows what else. Besides we change our position all the time with relation to these external factors that bend spacetime. So our measurements to an outside neutral observer, say these aliens could change.  I've found definitions of  like "the quantity of matter in an object" but that seems like the good old: mass = volume x density, but mass is the more fundamental quantity than either of them, with which theses parameters should be described by mass not the opposite, not to mention how relative these other quantities are, considering SR and GR. Or "The resistance of an object to acceleration" but again you have to describe how fast that object is moving and what spacetime it's in according to SR and GR.  So what makes us so confident that mass is such a universal value, when we built everything on a concept referenced by our own gravity, and maybe our own reference frame?  How do we describe mass to the aliens, who don't know about our (g)?  How do we measure the mass of celestial objects say planets, by units like kilograms, and pounds, while they are not subject to the earth's gravity, (I'm well aware of the difference between weight and mass). I mean that's what they will weigh -ignoring their own gravity- if they were in our atmosphere on a huge scale? So what's the method?  Bottom line Is there a direct way to   like we do with other fundamental values like length and temperature, other than using a scale or , i.e not depending on other physical parameters to describe it?  --Forgive the length..


I've been using Ubuntu to for years now, I'm an EE and love the system. This week I was having trouble with Ubuntu so I decided to do a fresh install parallel with Win XP.  The install crashed midstream and now I can not boot at all. I believe all I need to do is repair the grub.cfg file, or maybe another file?  So, I booted from my liveCD and went into the file structure and everything seems intact, However, the grub.cfg file looks like it's a mess. I don't remember how to gain access to GRUB via permissions. I did it once before a year ago.  Any one with any ideas?

I installed Windows 7, which ate Ubuntu's boot file. When starting up the computer, it now goes straight to Windows, without giving me the option of booting Ubuntu.   How can I get Ubuntu back?


I have a text file on one of my computers that is running 12.04. I was planning to use ssh to allow for another computer to read this text file. The issue is that the system that I am working with is basically logging some information on this text file at real time. I need for the computer that is going to read this text file, to read the text file at real time as well.  I am not savvy at all with ssh, but I am familiar with ubuntu. If anyone can provide some insight as to how to do this, or if it is even possible to read this text file at real time while another system is logging info it would be greatly appreciated.   Thank you.

Via command line, I have a log file I'd like to keep track of.  What I want is to have, basically, a tail that refreshes when the log is updated making the text scroll upwards as new lines are appended to the log file.  Is there anything out there that does that without having to write some code?


I have this file in the following path:  A = I:\user\me\count.txt   I want to check whether or not the count.txt exists in another path because I want to tag them as existing in the other folder.  As an example, lets say:  path1 = I:\user\me\personal\ path2 = I:\user\me\work\

How do I check whether a file exists or not, without using the  statement?


It's very common to ask for additional information on a question.  This is perhaps most common with new users who are a little unfamiliar with the need to put all relevant information in their question to start with.  To be blunt, I'm a little tired of explaining to new users that an edit is better than a comment, particularly where we ask "please add the output of..." I note that some users have taken to explicitly asking OPs to edit their question and adding an edit link in their comment.  But still this is missed.  More recently, adding a comment to a new user's question displays a little note saying:     ... is a new contributor. Be nice, and check out our Code of Conduct.   Could there be a similarly formatted note to new contributors commenting on their own question or answer:     If you need to add more information please  your [question][answer] instead of adding a comment.

Especially on technical sites, as even sporadic users will have noticed, new users very often don't include important information into the question they're posting.  This usually leads the first user passing by to leave a comment asking for clarifications, which punctually get posted in the comments section.  Many times there's not even the need for a user to ask OP to do so, OP just does that because they forgot something or because they want to improve their question by adding more details.  In any case this leads to:   Important information posted into the comments section, where they shouldn't stay; Question not bumping up in the active questions tab, which doesn't help fixing point #1; Unless OP pings one of the users that left a comment in doing so, none of the user who commented will get to know that the requested clarifications were posted, which doesn't help fixing point #1 either.   I think it would be convenient to prompt new users with a popup similar to the popup prompting to leave an explanation upon downvote when a new user leaves a comment under the following conditions:   OP hasn't been prompted before (i.e. do this only upon OP's first attempt to comment); OP is commenting on their own question; OP didn't benefit from the association bonus.   The message could go something like this (feel free to rephrase):     Comments shouldn't be used to add important information to the question; if you're adding information useful for your question to be answered, please  your question instead.   Mock-up:    This could also be a great opportunity to teach new users how to reply to comments:     Comments shouldn't be used to add important information to the question; if you're adding information useful for your question to be answered, please  your question instead. If you're replying to a comment of another user, you can use @username, where username is the username of the user you're replying to without spaces, to notify the user of your reply.   Mock-up:


I want to create objects from different classes extending the same class. Can you explain how it will work. Examples would be nice.  Thank you.   class MainClass{     private <T extends DataPoint> void someMethod(Class<T> clazz) {       new clazz(2,3);//<-- create object of class (did not work)    }     private void anotherClass(){       someMethod(GreenDataPoint.class);       someMethod(BlueDataPoint.class);    } }  class DataPoint {    int x;    int y;    DataPoint(int x, int y) {       this.x = x;       this.y = y;    } }  class BlueDataPoint extends DataPoint {BlueDataPoint(int x, int y){super(x,y);...}}  class GreenDataPoint extends DataPoint {GreenDataPoint (int x, int y){super(x,y);...}

Is it possible to create an instance of a generic type in Java? I'm thinking based on what I've seen that the answer is no (due to type erasure), but I'd be interested if anyone can see something I'm missing:  class SomeContainer<E> {     E createContents()     {         return what???     } }   EDIT: It turns out that  could be used to resolve my issue, but it requires a lot of reflection-based code, as some of the answers below have indicated.  I'll leave this open for a little while to see if anyone comes up with anything dramatically different than Ian Robertson's .


My class extends AppCompatActivity  This is my class  public class Login extends AppCompatActivity {      @Override     protected void onCreate(Bundle savedInstanceState) {         super.onCreate(savedInstanceState);         setContentView(R.layout.activity_login);          final Button loginBtn = (Button) findViewById(R.id.login_btn);         loginBtn.setOnClickListener(new View.OnClickListener() {             public void onClick(View v) {                 // Perform action on click                 Login login = new Login();                 try {                     login.getAccessCode();                 }                 catch (IOException e){                     Log.e("LOGIN", "I got an error", e);                 }              }         });     }      public void getAccessCode() throws IOException {         RequestParams params = new RequestParams();         params.put("a", "a");          QuidoRestClient.post("/login/generateCode", params, new JsonHttpResponseHandler() {             @Override             public void onSuccess(int statusCode, Header[] headers, JSONObject response) {                 // If the response is JSONObject instead of expected JSONArray                 Log.d("LOGIN",response.toString());                 String code = "";                 try {                     code = response.getString("code");                 }                 catch (JSONException e){                  }                 Context context = getApplicationContext();                 CharSequence text = "Hello toast!";                 int duration = Toast.LENGTH_SHORT;                  Toast toast = Toast.makeText(context, text, duration);                 toast.show();             }              @Override             public void onSuccess(int statusCode, Header[] headers, JSONArray data) {                 // If the response is JSONArray instead of expected JSONObject             }         });     } }   This is the error  java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.Context android.content.Context.getApplicationContext()' on a null object reference   I've also tried   Toast toast = Toast.makeText(Login.this, text, duration);   I've solved the issue by calling my method directly instead of Login login = new Login();

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


If I wanted to cast finger of death but I'm all out of 7th level spell slots, could I cast it using an 8th or 9th level spell slot, even though it doesn't change the spell's effect?

Many spells have "At higher levels" that provides for more targets or more damage.  For example Magic Missile can be cast as a second level spell and shoot 4 missiles instead of it's 3 as a first level spell.  Can a spell without that verbiage, such as Firestorm be cast in higher level slots for the same effect as the lower level spell?


I just want to make a simple animation of an tomato hitting a surface and spills over it like that.  I already imported tomato object, made it rigid and it hits surfaces. I just don't know how to make it break open and spills over yet not leave the solid tomato.

So I have a simple bouncing ball animation, but I just wanted to something "weird" for the ending. Is there a way to change the ball's material on the fly, where after the last bounce it changes materials and physical composition from a rigid body(baked animation now) to a fluid sim?  (within 30-40 frames)


I'd like to proof that eigen values of this matrix is given by (8-16) and bellow to (8-17), my trouble is about solve p-degree polynomial.

This question aims to create an ""  of numerous questions that ask about determinants of specific matrices (I may have missed a few):              The general question of this type is  Let $A$ be a square matrix of rank$~1$, let $I$ the identity matrix of the same size, and $\lambda$ a scalar. What is the determinant of $A+\lambda I$?  A clearly very closely related question is  What is the characteristic polynomial of a matrix $A$ of rank$~1$?


I have a text file which is usually filled with multiple lines which I want to "print" with a while loop. The text inside this file contains variables - my problem is, that these variables are not interpreted unlike a similar test-string containing variables stored inside the script. Is it possible to also interpret those variables from my external file or do I have to parse them beforehands etc.? What is the difference between $LINE_INSIDE and $LINE_OUTSIDE? I tried some suggestions from other questions like ${!varialbe_name} and different constructs with quote signs but with no luck so far.      #!/bin/bash     # color.sh     BLUE='\033[1;34m'     NC='\033[0m' # No Color      LINE_INSIDE="${BLUE}Blue Text${NC}"     echo -e ${LINE_INSIDE}      while read LINE_OUTSIDE; do             echo -e ${LINE_OUTSIDE}     done < text_file   Output:    Additional Information: I (indeed) also have shell-commands in my input-text-file which should not by executed. Only the variables should be expaned.

I am reading a csv file in bash script as follows:  resource='/data/bscs/' while IFS='|'read seqid fname fpath  do     echo "FILENO:         $seqid"     echo "FILENAME:       $fname"     echo "FILE_PATH:    $fpath"                     done < "report.csv"   My csv file has following values :  3|sample1.txt|$resource/operation/  I want the $resource to expand inside $fname. Instead, I am getting this output:  FILENO:         3 FILENAME:       sample1.txt SOURCE PATH:    $resource/operation   I have tried the following:  "${fpath}"   $(echo $fpath)  How can I achieve this?


filterType = 0;              if((Name !=  " " &&  !Name .isEmpty() ) |( userName != " " && !userName.isEmpty() ) | userLock == true | (HQ !=  " " && !HQ.isEmpty() ) |  Area !=  0.0  | Route != 0.0 | ( Label != " " && !Label.isEmpty() )){                  filterType = filterType + 1;             }                if( (Phone != " " && !Phone.isEmpty() ) | (URL != " " && !URL.isEmpty()) |( City != " " && !City.isEmpty() ) |  (Date != " " && !Date.isEmpty())| (Email != " " && !Email.isEmpty()) ){                 filterType = filterType + 2;              }    If any of above string contains value then filter type should be added but java throws null pointer exception. How can I fix it?


I am trying to count the number of files in a remote directory. I have the following code:    ssh server.com<<RUNTHIS    FILE_COUNT=$(ls -AU /foo/bar/test_dir)   echo "$FILE_COUNT" > ~/file_count.txt    RUNTHIS   When I run this I get: ls: /foo/bar/test_dir No such file or directory But the directory is there. If I do ls /foo/bar/test_dir directly to the server it lists the directory. Also the following works and saves the contents to the file:    ssh server.com<<RUNTHIS    ls -AU /foo/bar/test_dir > ~/file_count.txt RUNTHIS   What is wrong in the first snippet?

cat >run_pos2bed3.sh <<EOF ls 2*/peaks.txt | while read id; do echo $id done; EOF   after input it  nano only show  ls 2*/peaks.txt | while read id; do echo  done; EOF   How can I add $id after EOF?