Suppose that $G$ is a group of matrices that is a submanifold of $M_n(\mathbb{R}) \cong \mathbb{R}^{n^2}$, with group law the usual multiplication of matrices. Let $X$ and $Y$ be two left invariant vector fields. Show that $$ [X, Y ]_{I_n} = X_{I_n}Y_{I_n} − Y_{I_n}X_{I_n}$$ where, on the right hand side of the equation, the product is just the usual multiplication of matrices.  I know that the tangent space at $I_n$ can be identified with the left invariant vector fields. But without any description of $G$ how does one show this above identity? I know $[X,Y]_{I_n}(f)=X_{I_n}Yf-Y_{I_n}Xf$ where $f$ is a smooth real valued function on $G$, but I don't see any way to connect the two above facts. How does one prove this? Thank you.

Consider the Lie group $GL(n, \mathbb{R})$. Since $GL(n, \mathbb{R})$ is an open subset of the space $M_{n,n}(\mathbb{R})$ of $n \times n$ matrices, we can identify the tangent space (Lie algebra) $T_{e}GL(n, \mathbb{R})$ with $M_{n,n}(\mathbb{R})$, where $e$ is the identity matrix. I'm trying to understand the following:  For all $x, y \in M_{n,n}(\mathbb{R}) = T_{Id}GL(n, \mathbb{R})$ we have $[x, y] = xy -yx$ where $[\cdot, \cdot]$ is the Lie algebra bracket.  According to the question , this seems to be the case for matrix Lie groups in general.  So far, I've worked out the following: Let $x \in M_{n,n}(\mathbb{R}) = T_{Id}GL(n, \mathbb{R})$ and let $X \in \Gamma^{inv}(TG)$ be the left invariant vector field corresponding to $x$, i.e. with $X(e) = x$. By openness, we can choose $\epsilon > 0$ such that the curve $(-\epsilon, \epsilon) \ni t \mapsto e + tx$ through the identity is contained in $GL(n, \mathbb{R})$. For $g \in GL(n, \mathbb{R})$ let $L_g$ be the left multiplication by $g$ in $GL(n, \mathbb{R})$. Using left invariance of $X$ calculate: $$X(g) = ((L_g)_{*}X)(g) = D_eL_g(X(e)) = D_eL_g(x) = \frac{d}{dt}|_{t=0}g(e+tx) = gx$$ Now, the above implies for $f \in C^{\infty}(GL(n, \mathbb{R}))$ and $g \in GL(n, \mathbb{R})$: $$X(g)(f) = (D_gf)(gx)$$ where we identify the tangent vector $X(g)$ with the corresponding derivation at $g$.  Now how do I calculate $[x,y] \stackrel{def.}{=} [X, Y](e) \stackrel{\text{WHY?}}{=}xy-yx$ from this?


I am struggling to find out the Value of Ie and Ib here.  Ic I have taken to be Vcc/10k. If this is correct I could use Ic/alpha = Ie . I would like to know if this is the case but seems to easy to be the case?  Usually we would have Re to stabilise the heating effect and Ie would just be   Vb-0.7/Re.   I would appreciate the help.  The reason I am doing this is to try and find the Range of values for Vout based on different gain Values of beta.

I am struggling to understand two things about this circuit.  1) when input and output terminals are open circuit, why is this assumed to be in active mode?  2)What range can the quiescent output voltage of the amplifier be in?  Now I know that active mode you need EBJ to be forward bias and CBJ to be reverse bias but how would this apply in this scenario?  I understand what quiescent voltage is but I am struggling to apply his here with the input and output terminals. I would appreciate any help.  Many thanks.


I have the following code:  String queryText = userInput.toLowerCase() + '%'; return [SELECT Id, Name FROM Account WHERE Name LIKE : queryText];   And the user entered the text "G" and get results such as "George", "Google", "Game", etc etc. That works fine.  My issue is, if the user input is "%" and lets say I have an account named "%xyz", I won't get it as a result.  How can I escape the user's input here?  Thanks!

If i run below query it returns all records of that object:  Select ID, name from Contact where Name like '%%%'   This should return only those records which have % in the name. For example if i run below query it will return only those records which have test in the name.  Select ID, name from Contact where Name like '%test%'   Any idea, What is going on here?


I have a Wacom Intuos 2 and a 2009 MacBook running OS X Sierra (not High Sierra). Is there any way I can possibly get the tablet to work with my computer?

I have Wacom Graphire 3 a.k.a CT-630. This model is old Wacom tablet. So, it has no driver for 10.11.  Can I use this tablet on my Mac? Any solution?


Let $R$ be a commutative ring and $A=\{1,a,a^2,\dots\}$ for some $a\in R$. Prove that $A^{-1}R$ is isomorphic to $R[T]/(aT-1)$.    I guess I'm meant to find a surjective homomorphism between $A^{-1}R$ and $R[T]$ and then use first isomorphism theorem. What homomorphism should I use?

I am having trouble with the following problem.      Let $R$ be an integral domain, and let $a \in R$ be a non-zero element. Let $D = \{1, a, a^2, ...\}$. I need to show that $R_D \cong R[x]/(ax-1)$.    I just want a hint.  Basically, I've been looking for a surjective homomorphism from $R[x]$ to $R_D$, but everything I've tried has failed. I think the fact that $f(a)$ is a unit, where $f$ is our mapping, is relevant, but I'm not sure. Thanks


System requirements for Ubuntu 20.04 LTS has a minimum space on hard drive requirement of 25 GB. So is it ok if i only give a 15gb partition to install it or will it show error?

For a given hardware configuration, how do I find out if Ubuntu will run on it? What considerations should I take into account when choosing an Ubuntu version and  such as:    with a lighter desktop than the usual Gnome and Unity  with the even lighter LXDE desktop   Obviously Ubuntu does not run on some processor architectures. So how do I go about choosing the right version and derivate. How can I find out the minmal system requirements?


I was following a tutorial online for python and it had me do this:  akclark@enceladus:~$ pip install virtualenv    But I got the following:  Command 'pip' not found, but can be installed with:  sudo apt install python-pip   Easy enough, right? So I try it..  akclark@enceladus:~$ sudo apt install python-pip    But I get an error...  Reading package lists... Done Building dependency tree Reading state information... Done E: Unable to locate package python-pip   What am I doing wrong?  EDIT: Per Comments I have tried sudo apt update  EDIT2: I tried apt-cache madison python-pip and got   N: Unable to locate package python-pip   EDIT3: grep '^deb ' /etc/apt/sources.list showed  deb http://archive.ubuntu.com/ubuntu bionic main  deb http://archive.ubuntu.com/ubuntu bionic-security main deb http://archive.ubuntu.com/ubuntu bionic-updates main

When I try to install any package through the command line, I get an error.   $ sudo apt-get install <package> Reading package lists... Done Building dependency tree        Reading state information... Done E: Unable to locate package <package>   Can anyone help me on this?


I have a simple script that runs fine under an app ID (just touches a new file), which I am trying to get to call via my personal ID. Note the target file location is in an area that my personal ID does not have write access to (but the owner of the script does) and I have set the SUID bit on the script, yet when i invoke it as my own ID (myID myGrp) , it gives permission denied on the touch.  The script's settings are correct as such:  -rwsrwxr-x appID appGrp 1.sh   (just contains touch /myDir/1)  This is the very purpose of the suid bit, yet it does not do what it's supposed to. Note the target dir has perms as follows:  drwxrwxr-x appID appGrp myDir   i do not want to turn that w ON for the dir. Defeats the purpose. Nor do I want to turn on the sticky bit on the dir.    As well i checked my mounts and ensured that the file system that dir resides on (in this case /app) has no NOSUID set, so it's clean also. was not mounted with nosuid.  How can i fix this?

I want to ensure that my program can only be run by user xyz using root privilege. To do this, I set the setuid bit with:  chmod u+s program1.sh ls -l program1.sh rwsr-x--- 1 root house 1299 May 15 23:54 program1.sh   Also, I added user xyz to the house group so that only xyz and root can run program1.sh.  In program1.sh there is  id -u   so that it can show me the effective ID.  Running program1.sh as root, it shows root. But running with the xyz account, it shows xyz. It seems that it didn't run with root privilege. I don't know what's wrong here.


$$\int_0^{n\pi} f(\cos^2 x )\, dx = n \int_0^\pi f(\cos^2 x )\, dx$$   I am studying the chapter on Riemann integral so wondering if this equality requires the concept of Riemann integration to prove or there are other methods?

If $f$ is continuous on $[0,1]$, how can I show that $$\int_0^{n\pi}f(\cos^2(x))\,dx=n\int_0^{\pi}f(\cos^2(x))\,dx?$$  I know how to show that both integrals exist.  I believe that $n$ is a multiple of $\frac12$.  I thought that the identity $\cos^2(x)=\frac{\cos(2x)+1}{2}$ would be useful, but maybe not.  I think I should use some change of variable.


I am wondering why     ls -1 |  while read file; do       echo $file; tail -n 100 $file > >(sleep 1 && cat > $file) done     is faster than   ls -1 |  while read file; do      echo $file; tail -n 100 $file | (sleep 1 && cat > $file) done      ?    If there are 100 files in a directory then:    the second command takes almost 100 seconds to process  the first command is processed almost immediately.

I tend to use pipelines in my bash scripts over process substitution in most situations, especially in cases of using multiple sets of commands as it seems more readable to do ... | ... | ... over ... < <(... < <(...)).  I'm wondering though why using process substitution is much faster in some situations than using a pipeline.  To test this, I timed two scripts using 10000 iterations of the same attached commands with one using a pipeline and another using process substitution.  Scripts:  pipeline.bash:  for i in {1..10000}; do     echo foo bar |     while read; do         echo $REPLY >/dev/null     done done   proc-sub.bash  for i in {1..10000}; do     while read; do         echo $REPLY >/dev/null     done < <(echo foo bar) done   Results:  ~$ time ./pipeline.bash  real    0m17.678s user    0m14.666s sys     0m14.807s  ~$ time ./proc-sub.bash  real    0m8.479s user    0m4.649s sys     0m6.358s   I know that pipelines create a sub process whereas process substitution creates a named pipe or some file in /dev/fd, but am unclear about how those differences impact performance.


My nephew's Canadian visa and Passport expires on the 29th of August 2020. He has a new valid passport.  Is his visa still valid on his old passport, so he can enter in Canada on April 22 2020 and leave on May 21 2020?

I recently renewed my passport. I also have an expired passport which has my Canada visa (visitor's) valid for another three years. I have already used my Canadian visa which is multiple entry. I am planning to visit Canada this summer.  Since my valid Canadian visa is in my old/expired passport, do I need to renew/transfer my Canada visa or can I simply travel with valid visa in old passport?


Can we apply different colors for the above two Lightning tabs ?? My requirement is to apply Red color for "Item One" and Green for "Item Two". Please help me how to do.   <lightning:tabset> <lightning:tab label="Item One">     Sample Content One  </lightning:tab> <lightning:tab label="Item Two">     Sample Content Two </lightning:tab>

How can I set background color for selected tab in lightning:tabset  <lightning:tabset>     <lightning:tab label="Item One">         Sample Content One     </lightning:tab>     <lightning:tab label="Item Two">         Sample Content Two     </lightning:tab> </lightning:tabset>   Thanks in advance.


$\Pi_{i=1}^{k}(2i-1)=\frac{(2k)!}{k!2^k}$   clearly the products are in the set of the natural numbers.  Step one show that P(1) is true  $2(1)-1=1$  True.  Step 2 induction assumption  $\Pi_{i=1}^{k}(2i-1)=\frac{(2k)!}{k!2^k}$  This is what we assume to be true.  Step 3  $P(k+1)$  $\Pi_{i=1}^{k+1}(2i-1)=\frac{(2k+1)!}{(k+1)!2^{k+1}}$  The right hand side can be reduced to $\frac{2}{2^k2}$  $\Pi_{i=1}^{k+1}(2i-1)=2(k+1) + \Pi_{i=1}^{k}(2i-1)$  which is the last product times the multiplication of all the previous products.  $=2k+1 + \frac{(2k)!}{k!2^k}$  $=\frac{(2k+1)(2k)!}{k!2^k}$  $=\frac{2k+1(2)}{2^k}$  I am not sure how to continue this proof.

I have this formula which seems to work for the product of the first n odd numbers (I have tested it for all numbers from $1$ to $100$):  $$\prod_{i = 1}^{n} (2i - 1) =  \frac{(2n)!}{2^{n} n!}$$  How can I prove that it holds (or find a counter-example)?


I saw many howto's for creating a hotspot in Ubuntu 14.04 (in AP mode) using system settings. They are perfect.   How do I create a hotspot using only command line however?   I tried messing around with eth0 and eth1 but I did not get anything at all.   (The same question has been asked some months ago, but it was not answered).

Although many questions have already been asked regarding WiFi hotspot, I didn't get any of the solutions working for me.  I connect to the Internet using a 3G Dongle of Huawei 3772 (Vodafone). The connection type is Mobile Broadband connection. I have to share this Internet connection with my other devices like mobile phones and laptops.  How can I create a WiFi hotspot connection for this connection.  I am using Ubuntu 12.04 LTS.  I would like to note that I have already tried some help links from Ubuntu but, they are so confusing that I could not understand them.


my team had follow the document () and (). However, we meet some issue that the API shows success but not receive the email that we choose. Please check out the link including the coding we had, we used the second API to check the status, and it shows 404.   Coding Screen shoot:  Delivery links:   Is there anyone know how to solve this issue?  Thank you.

I followed the instructions and got success response but I didn't receive email.  Then I used the id to get Email Status and got 404 error.  Here is my json :  POST :   {     "To": {         "Address": "example@gmail.com",         "SubscriberKey": "example@gmail.com.tw"     },     "Options": {         "RequestType": "ASYNC"     } }   GET : {id}  Please let me know how I can resolve the issue.


How many displays/monitors can a Mac Mini 2020 M1 support? There are 2 USB4 ports and one HDMI. Don't count DisplayLink and AirPlay displays.

How do I find out the number, type, resolution & refresh rate of additional monitors I can attach to my MacBook or MacBook Pro?  This is an attempt at a canonical QA, as per the Meta QA -   to try prevent the myriad "same but different" questions we get on every possible combination of computers, cable & monitors There are perfectly good resources out there that Ask Different should not have to duplicate the efforts of.


Below I had tried to come up with a method to find the path to figure out the shortest path but every time I run the program I get a nullpointer exception at the findshortestPath1 at the int cols = myArray[rows].length I don't know how to solve this problem.  If you have other methods I can try to solve this, tha twill be greatly appreciated.  *******UPDATE******* Okay I updated that code with your suggestions, but I was still getting problems at   minCosts[0] = myArray[row][col]   and  findShortestPath(myArray, minCosts, row, col);   Code:  import java.util.Random;   public class Triangle{   public static void createTriangle(int numRows){       int rows=numRows;      int max =9, min =2;      int[][] myArray = new int[rows][];      Random random = new Random();  for (int i = 0; i < rows; i++) {  myArray[i]= new int[i+1];   //Below is used for organizing the triangle System.out.println(""); for(int p=rows-i; p>0;p--) System.out.print(" ");  for (int j = 0; j <=i; j++) {  //below puts the spacing between each column in the triangle System.out.print(" ");    myArray[i][j] = random.nextInt(max - min + 1) + min;  System.out.print(myArray[i][j]);     System.out.print(" ("+i+", "+j+") ");  }  }  }  public static int findShortestPath1(int numRows) {        int rows= numRows;      int[][] myArray = new int[rows][];       int numNodes = sumToN(rows);      int[] minCosts = new int[numNodes];       for(int row = 0; row<rows; row++) {          int cols = new int[rows].length;       for(int col = 0; col< cols; col++) {          findShortestPath(myArray, minCosts, row, col);      }      }       int row = rows;  int cols = new int[rows].length;  int min1 = -1;   for(int col = 0; col<cols; col++) {   int cost = minCosts[indexFromRowCol(rows,col)];    if(cost < min1 || min1 ==-1) {       min1 = cost;   }   }    return Math.max(0, min1);   }      private static int findShortestPath(int[][] myArray, int[] minCosts, int        row, int col) { if (row == 0) {     minCosts[0] = myArray[row][col];     return minCosts[0]; }  int minValue = -1;  if (col - 1 >= 0) {     minValue = minCosts[indexFromRowCol(row - 1, col - 1)]; }  if (col < myArray[row - 1].length) {     int cost = minCosts[indexFromRowCol(row - 1, col)];      if (minValue == -1) {         minValue = cost;     }      minValue = Math.min(minValue, cost); }  int minCost = myArray[row][col] + minValue; minCosts[indexFromRowCol(row, col)] = minCost;  return minCost; }  private static int sumToN(int n) { if (n < 0) {     return 0; } return n * (n + 1) / 2; }  private static int indexFromRowCol(int row, int col) { return sumToN(row) + col;    }    }

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?


Xanathar's Guide to Everything has a few variant options for playing on a Grid. XGtE, Page 86:  ... Choose an intersection of squares as the point of origin of an area of effect ... ... If any part of a square is under the template, that square is included in the area of effect. ...  Diagrams 2.1 & 2.2 show this, with the Cone's origin being on the intersection. Its shadow clearly covers small sections of both squares just after the intersection. PHB, Page 205:  A line extends from its point of origin in a straight path up to its length and covers an area defined by its width.  My interpretation is that this means using templates on grids increases the average Area of Effect size notably for Cones & Lines particularly. Does that seem correct? Visual example:  Which would affect all 4 enemies labeled 1 if the caster is the one labeled 2.

Lightning bolt is listed as having a width of 5 feet.   When using a battlemap, can the line of the spell be directed between squares to affect creatures on both sides with full damage?    suggests this would be true for Pathfinder rules. Its answer suggests that even if the lightning bolt passed a tiny corner of a square - the creature would take full damage. Does this hold true in 5e?


Idk why beamer thinks changing \mathbb{1} to what it does is a good idea, but how do I get it back?

I am trying to get the digit one printed the \mathbb{} font in math mode, however the command  \mathbb{1}   outputs some rubbish. I certainly saw the character I am after in some pdf's generated from latex, hence my question: how do you get it to work?


We all know that someone with a doctorate is called a Doctor (or abbreviated as Dr.), is there a formal title for someone with a Masters degree? I've never heard someone refer to a person with a masters as "Master". I've also heard that Esquire is sometimes used as a formal title for someone with a masters, is this correct or is there another title?

Why is it customary to call people with doctoral degrees doctors but not people with masters degrees masters? They are both graduate degrees that supersede the undergraduate degree.


A function $f$ between monoids is a homomorphism if $f$ preserves operations and the identity. Then, there is some function between monoids that preserves operations but does not preserve the identity. I've tried to get it thinking about $(\mathbb N,+)$, $(\mathbb N\backslash\{0\} ,\times)$ and other elementary monoids, but without success. Could someone help me with some hint? Thank you!

I have from Exercise 1 pg 33 - "Algebra - T. W. Hungerford" following:      Question to proof: Show by example that the first conclusione may be false if $G,\, H$ are monoids that are not group.   I thinked:     Proof: let be for example two monoids $(G:=\{\emptyset\}, \bot)$ and $(H:=\{\emptyset, \{\emptyset\}\}, \top)$ with: $$\begin{array}{c|c} \bot & \emptyset \\ \hline \emptyset & \emptyset \end{array} \, \, \, \,\, \,\, \,\, \,\, \,\, \,\, \,\, \,\, \, \begin{array}{c|cc} \top & \emptyset & \{\emptyset\}\\ \hline \emptyset & \emptyset & \emptyset \\ \{\emptyset\} & \emptyset & \{\emptyset\} \end{array}$$ $G$ with $e_G:=\emptyset$ like neutral element and $H$ with $e_H:=\{\emptyset\}$ like neutral element. Let be $f$ a function from $G$ to $H$ with $\emptyset \mapsto \emptyset$ (namely $x \mapsto x$), the function is Homomorphismus in fact $$ \begin{align} {\color{Red}f}{\color{Red}(}{\color{Red}x}{ \color{Red}\bot }{\color{Red}y}{\color{Red})}=&f( \emptyset \bot \emptyset)= {\color{Green}f}{\color{Green}(}{\color{Green}\emptyset}{\color{Green})}= \emptyset \\ {\color{Red}f}{\color{Red}(}{\color{Red}x}{\color{Red})} {\color{Red}\top} {\color{Red}f}{\color{Red}(}{\color{Red}y}{\color{Red})}=&f(\emptyset) \top f(\emptyset)= \emptyset \top \emptyset= \emptyset \\ &\text{with }x,y \in G \end{align}$$ but it means that $$ \begin{align} f(e_G)&\neq e_H \\f(e_G)={\color{Green}f}{\color{Green}(}{\color{Green}\emptyset}{\color{Green})}=\emptyset &\neq \{\emptyset\}= e_H \end{align}$$ Therefore $f$ ist Semigroup-Hom but not Monoid-Hom...   Is it correct?


I am not an expert on Ubuntu, so this is probably a very basic question.  When I open a terminal and perform a ls -la in a directory, I get:  jverstrynge@devjverstrynge:/home/httpd$ ls -la total 4 drwxr-xr-x  6 root     root       91 Dec 11 14:11 . drwxr-xr-x  6 root     root       56 Dec 10 11:19 .. drwxr-xr-x  2 tfr      tfr         6 Oct 22 13:49 softgallery-future drwxr-xr-x 11 tfr      tfr      4096 Oct 22 14:06 softgallery-old drwxrwxrwx 10 www-data www-data  138 Dec 11 12:37 softgallery2 drwxr-xr-x  6 www-data www-data  149 Feb  9  2015 subscription   The softgallery2 line is displayed in green. What is the meaning? Does it mean it's a mount? How can I check this?

What do the different colours in Ubuntu's ls command mean? For example, when I type the ls command in one of my folders, I get one of the files in light green, the other (which is a folder) in blue with green highlighting.   What do those colours mean, and there is any manual about all the colours?


Let $I=\int^1_0\frac{\sin x}{\sqrt x}dx$ and $J=\int^1_0\frac{\cos x}{\sqrt x}dx$. Then which of the following is true?  $I > \frac23$ and $J > 2$ $I < \frac23$ and $J < 2$ $I < \frac23$ and $J > 2$ $I > \frac23$ and $J < 2$   I tried to do it using the small angle assumption and also by graphical method. The correct answer is Option 2.

How to find bounds of $$I=\int_0^1\frac{\sin x}{\sqrt x}$$ and $$J=\int_0^1\frac{\cos x}{\sqrt x}$$     A) $I>2/3$ and $J>2$   B) $I<2/3$ and $J>2$   C) $I>2/3$ and $J<2$   D) $I<2/3$ and $J<2$


I would like to use align inside of itemize as an item, but without a newline. How can I do this?  MWE  \documentclass[a5paper]{scrartcl} \usepackage{amssymb, amsmath} % needed for math \usepackage[utf8]{inputenc} % this is needed for umlauts \usepackage[ngerman]{babel} % this is needed for umlauts \usepackage[T1]{fontenc}    % this is needed for correct output of umlauts in pdf \usepackage{geometry} \begin{document} \begin{itemize}     \item ba dfasdfasd sadf     \item asdfa sd $x^2$ asdfasdf     \item \begin{align*}                 x^2 + 2x -10 &= 31\\             \Leftrightarrow x^2 +2x + 21 &= 0\\             \Leftrightarrow (x+1)^2+20 &= 0           \end{align*}     \item adfasd asdfas \end{itemize} \end{document}   Results in:    It seems to me that there is also a newline after align or at least more whitespace than there should be. If it is possible, I would like to remove that, too.

How to make the first line of aligned equations sit in the same baseline as the bullet and make the equation left justified?    \documentclass{article} \usepackage{amsmath} \begin{document} \begin{itemize}     \item $3!=3\times2\times1=6$     \item $\tfrac{5!}{3!}=\tfrac{5\times4\times3!}{3!}=5\times4=20$     \item \begin{align*}                     \frac{n!}{(n-2)!}   &=\frac{n\times(n-1)\times(n-2)!}{(n-2)!}\\                                                         &=n\times(n-1)\\                                                         &=n^2-n                 \end{align*} \end{itemize} \end{document}


I am currently using Ubuntu 14.04 on my laptop. I want to upgrade to 18.04 LTS but I am not quite sure if it will work.  My CPU is dual core 1.7 GHz 4th Generation i5-4210U. I upgraded my RAM from 4 GB to 16 GB. Also I am going to install Ubuntu 18.04 on SSD.  So only sort coming with respect to recommended system requirements is CPU. It was stated to have minimum of 2 GHz Dual Core processor.  My question is will it work? Should I give it a go at least?

I have a device on which I would like to install Ubuntu. How do I find out if Ubuntu will work on it?


I know my question doesn't make sense all ready. Suppose I have points $(0,0,0,0)$ and $(1,1,0,0)$. The distance traveled is zero since $ds^2 = 0$ in this case. And light has moved from one point to another. And since these two points are distinct, it has traveled on the manifold ¿presumably? along a geodesic.    But I don't quite follow what this means. How can $ds^2$ be zero and I can move somewhere? If $ds^2$ doesn't measure spacetime distance, how can I say, for instance, the sun is 0.00001581 light years away from the earth?

Let's suppose I have a spacetime manifold $M$. Let $p$ be a point on my manifold. Now I move from $p$ to some other point $p'$. Presumably I should have moved some "distance" right? How can I speak of notions of space and time if I have no conception of distance?   But now consider light moving through spacetime. Suppose my light starts at $p = (0,0,0,0)$ and travels to $p' = (1,1,0,0)$. By the definition of the spacetime interval $ds^2 = dt^2 - dx^2 - dy^2 - dz^2$, this should mean $ds^2 = (1)^2 - (1)^2 - 0 - 0 = 0$. So $ds^2=0$.   Yet I have moved from point $p$ to $p'$. So I clearly have moved along some path along the curve, but the length of this path is zero. Shouldn't that mean $p$ and $p'$ are the same point?   Note: I think I may be suffering from an overly Euclidean mindset and my brain hasn't adapted yet enough to the non-Euclidean logic of semi-Riemannian manifolds.   My Question   Can someone resolve this contradiction?


I was surprised to see that I earned a Sci-Fi badge on CS:    I reproduced this on other sites; the drop-down always uses the icons from current site C, not those from the site E the badge was earned on.  Ideally, the icons from E should be used. If that is infeasible, please use the default circles. Using icons from C is definitely confusing.

It's so cool that the notification reminds you of the colour of badge you've earned. But I am a little puzzled by the symbols:      Is it feasible to use the symbol from the earned site? At the moment it uses the symbol from the site I happen to be on (as you can see by looking to the left of the dropdown in each case.)


As in the topic. I don't like wasting space. I run all apps that I can in full screen mode + extensions such as  , but still there's plenty of software where the window bar is visible and takes space. Windows 10. Under Linux I used and enjoyed

This was possible in XP and Windows 7 (see ) - but I haven't been able to find the settings in Windows 10.  Is this still possible?  Thanks.


I've seen similar question on stackexchange,  However, the answer does not provide whether how Google treats different port website as different website (such as subdomain) so to summarize, does Google treat below sites as different as subdomain? or identical as subdirectory? https://example.com vs. https://example.com:####

I host my website on Azure and I have recently activated a feature to make it possible for me to directly access each server instance in our web farm by a port number. For example http://example.com:10015 and http://example.com:10016.  I'm a bit nervous of duplicated content in Google and I do not want Google to detect these URLs in some way and start to index them. I recently had this problem with Azure's default cloudapp.net domains and I have now both added a 301 for this domain and also a robots.txt rewrite so I disallow bots for this domain.  I wanted to use a robots.txt rewrite rule for the different ports as well but it doesn't seems to work for some reason. I don't know if it has to do with Azure's handling, but for example the SERVER_PORT variable is returning port 80 even if I go the to port 10015.  Anyhow, I was just trying to add my site with a port specification in Google Webmaster Tools, but that didn't work. So basically my question is if I have to worry about this at all, does Google even treat different ports as different sites?


I'm a complete beginner and I have been trying to solve this problem for hours now without success. I know there are other questions like this one and I've tried to apply the answers to my problem, but just don't seem to be working. So I have a TIFF file which is a map of my country and a shapefile which contains coordinates. Both files are in the same coordinate system - MGI 1901 Slovene National Grid, but they just don't overlap in ArcMap. I tried Project and Define projection tools to try and change the coordinate system of the shapefile with my coordinates, but nothing works. If it helps - in QGIS they overlap perfectly without any kind of manipulation beforehand. Does anyone have any idea of what else I can try?

I put 4 different layers into my ArcMap document, but only one of them will show up on the map! I should be seeing the other 3 layers as well. When I do a Zoom to layer, I can see one layer, but I cannot figure out how to make the other 3 show up at once on top of each other.  Before I opened ArcMap, I used ArcCatalog where I right-clicked 3/4 of the shapefiles and  clicked Properties → Coordinate system → Import and then clicked on my Trees layer, which has the coordinate system I want the other 3 to have. But when I opened ArcMap the 4 layers did not overlap, nor could I move them above or below each other.


This is what I tried:  (.)(?=.*\1)   This removes all instances of duplicates and leaves only the last instance, ie.  telnet -> lnet  I want this result:   telnet -> teln  How do I do this? I tried looking behind, but that only accepts a fixed length as far as I know.  Need to find a REGEX for this. I know other methods to achieve this without regex

Is there a built-in that removes duplicates from list in Python, whilst preserving order? I know that I can use a set to remove duplicates, but that destroys the original order. I also know that I can roll my own like this:  def uniq(input):   output = []   for x in input:     if x not in output:       output.append(x)   return output   (Thanks to  for that .)  But I'd like to avail myself of a built-in or a more Pythonic idiom if possible.  Related question:


I have the following if statements: if can_move == True:         return "ok" else:     return "error"  if can_run     return "great" else:     return "error"  The issue I have is if the else statement is run, then the other if statement doesn't execute. I would like both of them to execute simultaneously.

The canonical way to return multiple values in languages that support it is often . Option: Using a tuple Consider this trivial example: def f(x):   y0 = x + 1   y1 = x * 3   y2 = y0 ** y3   return (y0, y1, y2)  However, this quickly gets problematic as the number of values returned increases. What if you want to return four or five values? Sure, you could keep tupling them, but it gets easy to forget which value is where. It's also rather ugly to unpack them wherever you want to receive them. Option: Using a dictionary The next logical step seems to be to introduce some sort of 'record notation'. In Python, the obvious way to do this is by means of a dict. Consider the following: def g(x):   y0 = x + 1   y1 = x * 3   y2 = y0 ** y3   return {'y0': y0, 'y1': y1 ,'y2': y2}  (Just to be clear, y0, y1, and y2 are just meant as abstract identifiers. As pointed out, in practice you'd use meaningful identifiers.) Now, we have a mechanism whereby we can project out a particular member of the returned object. For example, result['y0']  Option: Using a class However, there is another option. We could instead return a specialized structure. I've framed this in the context of Python, but I'm sure it applies to other languages as well. Indeed, if you were working in C this might very well be your only option. Here goes: class ReturnValue:   def __init__(self, y0, y1, y2):      self.y0 = y0      self.y1 = y1      self.y2 = y2  def g(x):   y0 = x + 1   y1 = x * 3   y2 = y0 ** y3   return ReturnValue(y0, y1, y2)  In Python the previous two are perhaps very similar in terms of plumbing - after all { y0, y1, y2 } just end up being entries in the internal __dict__ of the ReturnValue. There is one additional feature provided by Python though for tiny objects, the __slots__ attribute. The class could be expressed as: class ReturnValue(object):   __slots__ = ["y0", "y1", "y2"]   def __init__(self, y0, y1, y2):      self.y0 = y0      self.y1 = y1      self.y2 = y2  From the :  The __slots__ declaration takes a sequence of instance variables and reserves just enough space in each instance to hold a value for each variable. Space is saved because __dict__ is not created for each instance.  Option: Using a  (Python 3.7+) Using Python 3.7's new dataclasses, return a class with automatically added special methods, typing and other useful tools: @dataclass class Returnvalue:     y0: int     y1: float     y3: int  def total_cost(x):     y0 = x + 1     y1 = x * 3     y2 = y0 ** y3     return ReturnValue(y0, y1, y2)  Option: Using a list Another suggestion which I'd overlooked comes from Bill the Lizard: def h(x):   result = [x + 1]   result.append(x * 3)   result.append(y0 ** y3)   return result  This is my least favorite method though. I suppose I'm tainted by exposure to Haskell, but the idea of mixed-type lists has always felt uncomfortable to me. In this particular example the list is -not- mixed type, but it conceivably could be. A list used in this way really doesn't gain anything with respect to the tuple as far as I can tell. The only real difference between lists and tuples in Python is that lists are , whereas tuples are not. I personally tend to carry over the conventions from functional programming: use lists for any number of elements of the same type, and tuples for a fixed number of elements of predetermined types. Question After the lengthy preamble, comes the inevitable question. Which method (do you think) is best?


I have a mbp late 2012 retina in wich I have installed mavericks and debian in dual boot with efi support. Well this morning I've done a repair in recovery mode on my mac and then I was no more able to boot. I have a blank folder with question mark inside displayed when I try to boot. I've tryied in recovery mode to reinstall the os since i've  a recent backup on a hard drive, but it fails right after it downloaded the packages saying an error occurred. Same thing when I try to recover my backup, it fails.  I suppose the repair somehow trashed the boot partition. I have to say I have filevault enabled, I dont know if it changes anything. How can I fix it? Considering that I've tryied all of the solutions on this answer [ which btw is about lion and it's not my case

I am attempting to boot up my 2009 MacBook Pro, but when it starts it immediately shows a white screen with a 'question mark folder' — it keeps blinking until the computer shuts down (unless I keep it in the charger, then it just goes on).  I have tried to do the start up whilst holding down the option/alt button, and only the arrow comes up. I don't have the startup system disk (or any other) but the system has been updated to OS X Mountain Lion from the Mac App Store.  Before this, there had been other problems: when I deleted things they didn't go in the Trash but instead it looked like it just deleted it completely. After some time it wouldn't save or download, saying there wasn't enough space (even though I deleted items).


Suppose an old closed question has an historical lock on it, making impossible to vote/comment/flag on any post.  What should we do if such questions have a high visibility but contains some outdated or wrong information?  indicates that such questions should be unlocked (and potentially removed), but what about cases where most of the information is still accurate and useful?  For instance:    I think this post still deserves a historical lock as the information provided is indeed useful. Only little parts of it are gradually becoming outdated and still being hit every time one queries for cocoa best practices.  What should we do when a historical-locked question provides, say 85% of useful up-to-date information and 15% of outdated one?

My understanding is that a question is historically locked because the information in it is too valuable for the question to be deleted.   But if the "valuable information" becomes obsolete, what happens then?  We cannot modify the question content, or the answers for a historically locked question, right?


I recently messsed up a migration to table-per-file for my dbs. In the end I (thought) I dropped all dbs, deleted any left over files, and then started over from scratch, importing only dbs I needed as I went.  However, today I find loads of these in my log:  InnoDB: Error: table 'db/table' InnoDB: in InnoDB data dictionary has tablespace id 384, InnoDB: but tablespace with that id or name does not exist. Have InnoDB: you deleted or moved .ibd files? InnoDB: This may also be a table created with CREATE TEMPORARY TABLE InnoDB: whose .ibd and .frm files MySQL automatically removed, but the InnoDB: table still exists in the InnoDB internal data dictionary. InnoDB: Please refer to InnoDB: http://dev.mysql.com/doc/refman/5.5/en/innodb-troubleshooting-datadict.html InnoDB: for how to resolve the issue.   Going to the URL, I find near the end.   If this occurs, try the following procedure to resolve the problem:      Create a matching .frm file in some other database directory and copy it to the database directory where the orphan table is located.      Issue DROP TABLE for the original table. That should successfully drop the table and InnoDB should print a warning to the error log that the .ibd file was missing.   What does "Create a matching .frm file" mean? Since it directly speaks of creating a "file", I would assume this is something like touch [file], but then it doesn't make any sense that I should copy it from one directory to another.  I tried it anyway and mysql complained about the table not existing, so that's not it.

So I have a test db server that was setup on a replication stream.  Over the name an optimize came through that quickly filled up the space on the slaves datadir.  Mysql dutifully was just waiting for some more space.  This datadir is a file system used ONLY as mysql's datadir so there wasn't anything else to free up.  I had a 4 gig innodb test table that wasn't part of the replication stream so I figured I'd try something to see if it'd work, and being a test environment I wasn't too worried if things went horribly wrong.  Here's the steps I took   Flushed the table I was about to move Placed a read lock on it (even though nothing was writing to it and it wasn't in the replication stream) Copied the .frm and .ibd over to a filesystem w/ some spare room Unlocked the table Truncated that table - this freed up enough space for the optimize to finish have replication start chugging along again. Stop slaving/shutdown mysql Copy the file out of tmp back to the data dir Restart mysql   Nothing shows up in the .err log, things look good. I connect and use mydb; and see the table I was messing with in show tables.  But, if I try  select * from testtable limit 10;   I get the error  ERROR 1146 (42S02): Table 'mydb.testtable' doesn't exist   From what I can tell so far I can read from all the other tables just fine and replication started back up w/o any complaints.  Is there anything I can do to recover from this point?  I can rebuild it from scratch if need be but was curious what others thought about this venture in general.  Was there anything about the series of steps I took that would have ended up w/ more flawless results?    What if this wasn't a test server I couldn't just 'do it live' and see what happens?  What would have the best way to free up space temporarily on a production slave if I had to like that?


I am a very beginning user of ShareLaTex. Generally I use only the most simple \documentclass{article} which is sufficient for my purpose. However, I consider the left-right top-bottom margins are too wide. How can I reduce them to 1" only?  Thanks for your time and help.

I just started to learn LaTeX after seeing some amazing examples of scientific articles produced using it; I was also told that, unlike some other other text programs, LaTeX automatically produces articles respecting some publication standards. Well, after playing around with it for a while, I have to say my PDFs are anything but pretty, particularly when compared to those examples I mentioned before! My margins are really too large, my font size seem to be too small, my default paper is not A4 (and even when I set it manually to A4, the top margin then take an even more ridiculous amount of space). After reading a bit, I obviously found out how to control these elements, but the whole point for me to start learning LaTeX was not to fool around with such things. So here is (are) my question(s): am I doing something wrong? Is all this a matter of configuration? Or am I being delusional and my output PDFs actually ARE all in the expected standards? (I am using MiKTeX, and I tried three editors so far: TeXworks, LyX and WinEdt8)  Here are some examples I found on the internet of what I am talking about. The first seems to me as a simple article without any extra layout commands. Notice the size of the margins, fonts, etc. This is how my PDFs look like.   Now compare that previous PDF with this one here:  Unfortunately this one is written in two column format but I couldn't find another example online with just one column. Note how everything is balanced, how the margins are small, how the font is smaller as well, etc.  As a final note, I just would like to say that I really don't mind learning LaTex and that I am not expecting to produce amazing documents from day one; I just think that, in case my problems here are really sound, then I might have came to LaTeX with the wrong set of mind.  Thanks a lot!


My old laptop stopped reading the hard drive. In bios it said there wasnt one. I replaced it. Now it shows the disk in bios.   I dowloaded linux cinnamon onto a usb. Now. I can get the laptop to run linux from the usb. Everything works great.  I thought i properly formatted the new drive and then copied linus to it . added the boot driver. Changed the boot order back to the hdd first . but it wont boot linux from the hdd. If i take the usb out it doesn't boot any OS.   Help?

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


Can somebody help me understand why the following relation holds: If $ a,m,x \in \Bbb{N}$ and $m\geq 2$ with $x | m $ and $x | a\iff x | (a\bmod m) $

I read this in a math textbook, stated as obvious fact. I cannot wrap my head around why this works. I understood the division lemma, and also got the algorithm to work: but the proof of why the algorithm works, just said "because of the equation" that I put in the question.  Could you please elaborate on why it works?


I made a homemade pasta salad dressing. These are the ingredients:  - Mayo - Sour Cream - Fresh Lemon Juice  - Dried herbs/spices  I'm just wondering if mixing the lemon juice together with sour cream and mayo will cause it to go bad sooner than the expiration dates call for on the items separately.  Does anyone have any experience with this?  Thank you!!

How long can I keep salad dressings that I made?  Since this is probably affected by what it's made up of, let's say we're talking about different salad dressings made from a combination of the following ingredients: mayonnaise, ketchup, mustard, vinegar, sugar, garlic, oil, salt, pepper, lemon juice...  And are there any other ingredients that I should watch out for that could affect salad dressing shelf life? Any rules of thumb regarding storing salad dressings...?


How can we mathematically prove that a free electron can't absorb a photon totally?

As simple as in the title.. I would like to know also some mathematics about it!


I have an external hdd partitioned into two. One of the partitions has Linux (Ubuntu) installed on it (bootable). The thing is I have forgotten the password of it's user (single user).  How can I reset the password of user by plugging the external hdd to another Linux machine and then editing some file, using some command through terminal, changing the bash(remember doing something similar long time ago), or something else?  And I do not want to get into Grub etc. Booting through that drive is not an option (although it is but I am not willing to get into it and don't want to restart the running("another") Linux machine).

How do I log into my Linux laptop if I have forgotten both the username and password?


If Earnings means an item that adds value to any stack.  And, If Deductions means any item that subtracts value from any stack.  Then what single <word> can be an either Earning or Deduction?  As in:   You will be Earning 200 this June.  (plus 200) You will be Deducted 100 this July.  (less 100) You will be <word> +500 this August.  (plus 500) You will be <word> -400 this September.  (less 400)

I’m looking for a generic word that means “debit or credit”.  Say I have a transaction, and I don’t know whether it’s a debit on the account or a credit on the account, and I want to ask about it, is there a word I can use?   For example, if I were asking whether a book were green or blue, I would ask, “What’s its color?”  If I ask whether a transaction was a debit or a credit, can I fill in the blank, “What’s its _?”  (Background: I’m looking to name a variable while programming, and the best I can come up with is type, which is not very descriptive).


How do you choose the order p and q for a ARMA(p,q) process for modeling a time series?  Can that be told from ACF or PACF alone, just like for a AR(p) or MA(q) process?

Having a bit of difficulty identifying the appropriate ARIMA model by looking at ACF/PACFs.   I know that AR(1) models, the ACF has a geometric progression from its highest value at lag 1 and the PACF has a spike at lag 1 and then then cuts off afterwards.   Could someone possibly explain how I identify the rest? AR and MA please?!?


I'm new to QGIS and stuck.  I have a shapefile of 1 ft contours for an area.  I want to load it into mapbox so I can turn it into a layer for Gaia GPS, but the shapefile is too big for mapbox and it gives an error.  I was told I could use QGIS to cut out a smaller piece from the contour map but I can't figure out how to do that.  I can load the contour map and see all the contours, but can't figure out how to select a portion of it and save to a new shapefile.

I have a line layer and a polygon layer. Both files have the same SRS. I want in a new shape file only the lines covered by the polygons.   I tried in QGIS the Vector -> Geoprocessing -> Clip tool but I only get an empty shapefile.  How do I do this with QGIS?


Let $A_{(m\text{x}m)}$ and $B_{(m\text{x}m)}$ nonnegative definite symmetric matrices.  Prove or disprove: $AB$ is diagonalizable. It seems to be false, but I have some problems to find a counterexample.

I've already proved this with B positive definite using the fact that $B^{-\frac{1}{2}}$ does exist and AB is similar to $A^{\frac{1}{2}}BA^{\frac{1}{2}}$, but since B is positive semi-definite I don't know if that is true. I also know that $A^{\frac{1}{2}}$ and $B^{\frac{1}{2}}$ are defined.  I´m trying to see that $A^{\frac{1}{2}}BA^{\frac{1}{2}}$ is similar to $A^{\frac{1}{2}}A^{\frac{1}{2}}B$, but i'm having problems with that.  Any hint would help, thanks!


Given a distribution with PDF equal to a*N1 + (1-a)*N2, where N1 and N2 are the PDF's of normal distributions with some mean and variance, is the sum distribution also a normal distribution? The total probability is equal to 1 clearly, but is it normal?

I know that in the case of Gaussian mixture, the "intuition" is that you're drawing from a PDF which itself is just a sum of weighted Gaussian PDFs.  I don't understand the intuition behind how the sum of two iid Gaussian RVs leads to a Gaussian RV. I know the maths behind it, but I'm having a hard time visualizing how the sum of two Gaussian RVs leads to a Gaussian RV (and not a mixture).


I've struggled with exactly what to search to find the answer to this question so I thought I would ask it instead.  I am building a small CMS script with PHP and want to prettify my urls. I have no issue with sending root level requests to my index.php as variables; for example example.com/index.php?p=about-us to example.com/about-us. However, without removing this facility I want to redirect a request like example.com/blog/a-post to example.com/blog.php?b=a-post. How can I achieve this without it getting consumed by the original index rewrite?  I apologise if the terminology I have used to describe my problem is not quite right, it's been some time since I have done any coding and I feel rusty as hell!  --Edit--  The code I currently have is below:  RewriteEngine On  RewriteCond %{THE_REQUEST} \s/+index\.php\?([^\s&]+) [NC] RewriteRule ^ %1? [R=301,L]  RewriteCond %{REQUEST_FILENAME} !-f RewriteCond %{REQUEST_FILENAME} !-d RewriteRule ^([^/]+)/?$ index.php?p=$1 [L,QSA]   I wish the user to be able to access the url  url.com/blog/a-post   But I want this to actually access  url.com/blog.php?b=a-post

This is a  about Apache's mod_rewrite.   Changing a request URL or redirecting users to a different URL than the one they originally requested is done using mod_rewrite. This includes such things as:   Changing HTTP to HTTPS (or the other way around) Changing a request to a page which no longer exist to a new replacement. Modifying a URL format (such as ?id=3433 to /id/3433 ) Presenting a different page based on the browser, based on the referrer, based on anything possible under the moon and sun. Anything you want to mess around with URL   Everything You Ever Wanted to Know about Mod_Rewrite Rules but Were Afraid to Ask!  How can I become an expert at writing mod_rewrite rules?   What is the fundamental format and structure of mod_rewrite rules? What form/flavor of regular expressions do I need to have a solid grasp of? What are the most common mistakes/pitfalls when writing rewrite rules? What is a good method for testing and verifying mod_rewrite rules? Are there SEO or performance implications of mod_rewrite rules I should be aware of? Are there common situations where mod_rewrite might seem like the right tool for the job but isn't? What are some common examples?   A place to test your rules  The  web site is a great place to play around with your rules and test them. It even shows the debug output so you can see what matched and what did not.


From some API I'm receiving latlng coordinates in a stranger format: x: 9319106.045445956, y: 7020308.253131529, I don't know what it is, but my map module works only with WGS84 coordinates: lat: 53.2011871329117, lng: 83.71485471725465  What is original coords system and how to convert these coordinates to WGS84?

I have a Shapefile but its coordinate system is Unknown, and there is no *.prj file.   How can I identify it now?


I am given a txt file (war and peace..), and i need to create a text file sorted alphabetically of all the words that appear 10 or more times (without the quantity).  The twist in this question, is that every punctuation is considered as a beginning of a new word, meaning you're is considered two words, you re.  I flipped all punctuation into new lines, and all spaces to new lines. And i used trim -c so now i have all words and their count, don't know how to show only those that appear 10 or more times.  Any help regarding a way to find all words that appear 10 or more times would be really appreciated!

I had a command which would work through a text file, count all the occurrences of the words and print it out like this:  user@box $˜ magic-command-i-forgot | with grep | and awk | sort ./textfile.txt 66: the 54: and 32: I 16: unix 12: bash 5:  internet 3:  sh 1: GNU/Linux   So it does not search line-by-line, but word by word, and it does it for all the words, not just for 1 word. I'd found it somewhere on the internets a long time ago, but I cannot find or remember it..


I've just had two comments on  deleted. One was the standard possible duplicate comment, which gets deleted when the post gets marked as a duplicate.  The other was another comment indicating a potential alternate duplicate; . It was something along the lines of:     A better duplicate might be  but it was closed as a duplicate of the first question   I've done some science. It appears as though the word "duplicate" is not enough; I wrote "duplicate test comment" on  but it didn't get deleted (I did it manually).  However, on  I wrote "possible duplicate test comment [test](some question)", this comment was deleted.  At a guess, all comments that have the word duplicate in them and a link to another question are deleted once the question is closed as a duplicate. This might be solely comments that are owned by someone who voted but I'm unable to test.  This shouldn't happen. Comments pointing out separate linkages can be incredibly useful and make the web1 a better place.  1. Pun intended; please tell me someone noticed ;-)?

A user just posted his question a second time here on meta after the first was closed as a duplicate. I wrote a comment on the second post, explaining that the answer to his question is in the linked duplicate and that he shouldn't circumvent the closure process by asking a second identical question.  When the second post was closed as a duplicate my comment was automatically deleted. As far as I understand this is a heuristic that removes obsolete comments, which it considers every comment that contains a link to one of the duplicates.  This heuristic is too aggressive and removes comments that go beyond "Duplicate here: link". I suggest that it should be changed to only remove the default duplicate comment, and not any comment that was edited by the owner nor any free-form comment that happens to include a link to the duplicate.  This also triggers for any comment that contains the word "duplicate" and link to any question, not only the question being chosen as duplicate, which makes this much worse.


I'm returning my laptop and I'm just going to go through the Windows installation via USB, delete the partitions through there, and reinstall windows. It's an HDD, in case that matters.  That's enough for ensuring that no one can somehow regain access to the data that was deleted, right?

To stupid people, like me, you would have thought overwriting each bit on a disk would render the data completely unrecoverable.  Why do disk wiping tools have the option for multiple passes, i.e. 3 or 5, even 7 and different methods?  Surely the first pass does the job?  My question - Is it just down to pure paranoia or should I be using multiple passes when wiping disks... and why?


How do i display the whole error message?  I know its HTML response and not JSON..   how do i see the rest of the <br >  to see what the error messsage is?  01-04 15:59:00.710: E/JSON Parser(13508): Error parsing data org.json.JSONException: Value <br of type java.lang.String cannot be converted to JSONObject 01-04 15:59:00.720: E/AndroidRuntime(13508): FATAL EXCEPTION: AsyncTask #3 01-04 15:59:00.720: E/AndroidRuntime(13508): Process: com.example.coa, PID: 13508 01-04 15:59:00.720: E/AndroidRuntime(13508): java.lang.RuntimeException: An error occurred while executing doInBackground() 01-04 15:59:00.720: E/AndroidRuntime(13508):    at android.os.AsyncTask$3.done(AsyncTask.java:309) 01-04 15:59:00.720: E/AndroidRuntime(13508):    at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:354) 01-04 15:59:00.720: E/AndroidRuntime(13508):    at java.util.concurrent.FutureTask.setException(FutureTask.java:223) 01-04 15:59:00.720: E/AndroidRuntime(13508):    at java.util.concurrent.FutureTask.run(FutureTask.java:242) 01-04 15:59:00.720: E/AndroidRuntime(13508):    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1113) 01-04 15:59:00.720: E/AndroidRuntime(13508):    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:588) 01-04 15:59:00.720: E/AndroidRuntime(13508):    at java.lang.Thread.run(Thread.java:818) 01-04 15:59:00.720: E/AndroidRuntime(13508): Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String org.json.JSONObject.toString()' on a null object reference 01-04 15:59:00.720: E/AndroidRuntime(13508):    at com.example.coa.OfflineSV$SyncScans.doInBackground(OfflineSV.java:419) 01-04 15:59:00.720: E/AndroidRuntime(13508):    at com.example.coa.OfflineSV$SyncScans.doInBackground(OfflineSV.java:1) 01-04 15:59:00.720: E/AndroidRuntime(13508):    at android.os.AsyncTask$2.call(AsyncTask.java:295) 01-04 15:59:00.720: E/AndroidRuntime(13508):    at java.util.concurrent.FutureTask.run(FutureTask.java:237) 01-04 15:59:00.720: E/AndroidRuntime(13508):    ... 3 more

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 had a running windows 10 17xx, which I installed from the ISO downloaded from MS, more than a year ago. Windows 10 tried to update to Windows 20H2 (October 2020), but after rebooting, it got stuck on the windows logo, for more than a day. I thought that it was a updating problem, because the older Windows 10 installed without problems, so I downloaded the 20H2 ISO from microsoft, formatted the partitions with a linux live CD, and installed Windows 20H2, but the installer, again hangs for more than a day on the windows icon immediately after booting. I believe that maybe my old hardware is not compatible with 20H2 (despite MS saying nothing about incompatibility. I have an Asus P6T motherboard, with an i7 920, which is like 10 years old (but performs similar to a new CPU). Maybe it doesn't supports some new instruction, like AVX or the non UEFI BIOS is incompatible with 20H2. So, I need to install an older version of Windows 10, and the last one was Win 10 1909, but MS does not offer to download it. It only lets to download 20H2. There is any way I can get the 1909 ISO (or the 18xx) from Microsoft? I need the most updated working version, because Win 10 tries to update right to 20H2, so I will be forced to block the updates. I need to run some software which does not installs on older than 18xx. If I cannot get an 18xx or newer W10, I will be forced to go back to W7, where my W7 versions work.

I need to repair my Windows 10 installation. Where can I get a clean ISO (with install.wim, no Install.ESD, so that I can run DISM against the WIM) of the specific Windows 10 build required for this?  In my case, I need the Anniversary update (Build 14393), Creators Update (Build 15063) or Fall Creators Update (Build 16299.15).


I am trying to make a simple one command but it keeps saying "data tag parsing failed".  What is wrong with my command?  /summon falling_block ~ ~1 ~ { Block:wool,Time:1,Passengers: { [id:falling_block,Time:1,Block:command_block,Data:1,TileEntityData: { auto:1,Command:/scoreboard objectives add tp trigger } ,Passengers: { [ id:falling_block,Time:1,Block;command_block,Data:1,TileEntityData: { auto:1,Command:/scoreboard objectives setdisplay sidebar tp } ,Passengers: { [ id:falling_block,Time:1,Block:command_block,Data:1,TileEntityData: { Command:/scoreboard players set @a tp 0 } ] } ] } ] } }     I tried using notepad++, and I already re-wrote it 5 times.

I am trying to lock some boxes in a map of mine, and I used this command:   /blockdata 10 4 9 {Lock:Elyiana's Mage Key}   At first it worked, but then when I logged back on the next day it gave me this error message:    Data tag parsing failed: Expected '}' but ''' at: {Lock:Elyiana'<--[HERE]     I don't know why it doesn't like the apostrophe in the key's name. I would change it, but it already worked and locked some other items. My version is 1.12, does anyone have an answer to my problem?


In relation to , where the accepted answer said, "If the question is poor and the user is being very lazy, and/or abusive, or even unnecessarily abrupt, I will downvote based on that....  If the post is really bad, and/or the OP gets negative towards other users in comments, then it can rain down the fires of hell."  That piqued my curiosity -- I haven't seen anything that bad yet.  How would I do a site search or a google search to find questions with very negative numbers?

I want to search for new downvoted questions to improve or flag them.   I tried in the searchbar: votes:-1 is:question   but votes:XX only works with positive numbers. I can't query for downvoted questions. Is there a work-around to this? If there's not, should this feature be added?


shows how to use a user-defined icon when using the thebibliography environment. How can I redefine the icons if I use \printbibliography from biblatex?  Edit:  In the answer I linked to, each bibliography item is set manually, and so you can add   \setbeamertemplate{bibliography item}{\includegraphics[width=1.5em]{ctanlion}} \bibitem{A} CTAN lion drawing by Duane Bibby.   in front of each seperate entry if you wanted to. With \printbibliography the whole bibliography is typeset. So if I were to say  \setbeamertemplate{bibliography item}{\includegraphics[width=1.5em]{ctanlion}} \printbibliography   it would appear in front of the bibliography as a whole, not even in front of the first entry.

I want to list my references in a beamer presentation using thebibliography environment, with the nice little    book icon (\beamertemplatebookbibitems) and  article icon (\beamertemplatearticlebibitems)   in front of each source.  Is there an icon for websites too? something like \beamertemplatewebsitebibitems? If not, is there a way to implement this easily ?


I will be working on my 3G connection for a few days (meaning I'll be in the middle of nowhere). I don't want Windows to update and don't want any of my apps and services to connect to internet. I will be using only Chrome. I'm just trying to block all outgoing traffic with Windows Firewall and adding an Allow rule for Chrome but I suppose Block overrides Allow. So is there a way to achieve this?

Possible Duplicate:          I sometimes work outside and are using a 3G usb connection with quite a limited data allowance.  I want some fast and easy way to temporary block all incoming and outgoing traffic in windows firewall except for chrome to be sure that Dropbox or something else is not using up my data.  I've tried to set Windows Firewall Properties to "Block" which gives "Outgoing/Incoming connections that do not match a rule are blocked".  Problem: There are many allow-rules like Dropbox that would "override" the block. And I don't want to disable all rules and then enable them, since there are some that I want disabled even when I get to the office...  Any suggestions?  Thanks!


Free Shows:  free -m               total        used        free      shared  buff/cache   available Mem:          32130       22377        9553          48         200        9368 Swap:          8191         465        7726   But ps aux shows in the RSS Column(I didn't include 0's).  It only adds up to 6325.  Does free know something PS doesn't?  0.0859375 MB        /sbin/iscsid 0.550781 MB     /usr/sbin/watchdog-mux 0.617188 MB     (sd-pam) 0.667969 MB     sleep 0.777344 MB     sort 0.910156 MB     awk 1.52734 MB      /usr/bin/lxcfs 1.5625 MB       /sbin/agetty 1.67188 MB      /sbin/lvmetad 1.87891 MB      /usr/sbin/pvefw-logger 2.39062 MB      /bin/bash 2.48828 MB      /usr/sbin/rsyslogd 2.55469 MB      /usr/sbin/cron 2.57031 MB      /usr/bin/rrdcached 2.76562 MB      /lib/systemd/systemd-udevd 2.875 MB        /usr/lib/x86_64-linux-gnu/lxc/lxc-monitord 2.98047 MB      /sbin/rpcbind 3.16016 MB      pvedaemon 3.21094 MB      /usr/lib/postfix/sbin/master 3.23047 MB      pveproxy 3.28516 MB      ps 3.32422 MB      /usr/bin/dbus-daemon 3.53125 MB      /lib/systemd/systemd-timesyncd 3.58203 MB      /usr/sbin/smartd 3.85547 MB      /usr/sbin/rpc.mountd 4.32422 MB      /lib/systemd/systemd-logind 4.82422 MB      /sbin/iscsid 5.33203 MB      /usr/sbin/sshd 5.59375 MB      qmgr 5.60547 MB      /lib/systemd/systemd 5.9375 MB       /lib/systemd/systemd-journald 6.41406 MB      pickup 6.6875 MB       /sbin/init 6.70703 MB      sshd: 9.11328 MB      pve-ha-crm 13.3555 MB      pve-ha-lrm 16.6328 MB      -bash 17.0898 MB      /sbin/dmeventd 23.6094 MB      pve-firewall 28.7695 MB      task 32.1758 MB      pvestatd 35.6953 MB      pvedaemon 36.2188 MB      pvedaemon 37.9297 MB      pvedaemon 41.3477 MB      pveproxy 42.7656 MB      pveproxy 46.2617 MB      pveproxy 56.0391 MB      /usr/bin/pmxcfs 66.5078 MB      spiceproxy 71.3086 MB      spiceproxy 83.8711 MB      /usr/bin/perl 5586.38 MB      /usr/bin/kvm   EDIT:  I should note, not sure if it matters but the is Proxmox(A debian distro). You can see the largest memory user is a VM.  Also this usage spiked after a large rsync over NFS.  Could that have anything to do with it?

I'm a bit confused on some of the results I am seeing from ps and free.  On my server, this is the result of free -m  [root@server ~]# free -m              total       used       free     shared    buffers     cached Mem:          2048       2033         14          0         73       1398 -/+ buffers/cache:        561       1486 Swap:         2047         11       2036   My understanding of how Linux manages memory, is that it will store disk usage in RAM, so that each subsequent access is quicker. I believe this is indicated by the "cached" columns. Additionally, various buffers are stored in RAM, indicated in the "buffers" column.  So if I understand correctly, the "actual" usage is supposed to be the "used" value of "-/+ buffers/cache", or 561 in this case.  So assuming all of that is correct, the part that throws me is the results of ps aux.  My understanding of the ps results, is that the 6th column (RSS), represents the size in kilobytes the process uses for memory.  So when I run this command:  [root@server ~]# ps aux | awk '{sum+=$6} END {print sum / 1024}' 1475.52   Shouldn't the result be the "used" column of "-/+ buffers/cache" from free -m?  So, how can I properly determine the memory usage of a process in Linux? Apparently my logic is flawed.


Suppose we have a series of functions $$\sum_{x=0}^\infty  h(\theta, x)$$  The question is: is it correct that $$\partial _\theta \sum_{x=0}^\infty  h(\theta, x)=\sum_{x=0}^\infty  \partial _\theta h(\theta, x)$$  I would assume that the following arguments are correct: Take first the sequence not to $\infty$ but to $n$ $$\partial _\theta \sum_{x=0}^n h(\theta, x)=\sum_{x=0}^n \partial _\theta h(\theta, x)$$  We already know that this holds. Now simply take the limit as $n\to \infty$. We see then that the desired result is correct, so long as for each $x\in \mathbb N$, $\partial _\theta h(\theta, x)$ exists, and if the sequence $\sum_{x=0}^n \partial _\theta h(\theta, x)$ converges.    However, my textbook says that we need additional assumptions. We need $\partial _\theta h(\theta, x)$ to be continuous, and we need the series $\sum_{x=0}^n \partial _\theta h(\theta, x)$ to "converge uniformly".   Why do we need these additional assumptions and what is wrong with my (sketchy) proof?

Can the order of a differentiation and summation be interchanged, and if so, what is the basis of the justification for this? E.g. is $\frac{\mathrm{d}}{\mathrm{d}x}\sum_{n=1}^{\infty}f_n(x)$ equal to $\sum_{n=1}^{\infty}\frac{\mathrm{d}}{\mathrm{d}x}f_n(x)$ and how can it be proven? My intuition for this is that it should be the case, since in the limit, the summation becomes an integral and this can be interchanged with the differentiation operator, but I don't know how to justify this? Would it suffice to say that $\frac{\mathrm{d}}{\mathrm{d}x}f_1(x)+\frac{\mathrm{d}}{\mathrm{d}x}f_2(x) = \frac{\mathrm{d}}{\mathrm{d}x}(f_1(x)+f_2(x)$ because it is a linear operator and then somehow extend this to an infinite sum? Thanks in advance!


I'm trying to understand why rockets have multistages releasing their fuel tanks. Say a rocket $R$ has two fuel tanks $A$ and $B$, which respectively have masses $m_a$ and $m_b$, and the mass of the fuel in the respective tanks is $m_{fa}$ and $m_{fb}$. Let $M$ be the total initial mass, and suppose the rocket starts from rest. We use the equation $v-v_0=v_{ex}\ln(m_0/m)$, where $v_{ex}$ is the (constant) speed of the expent fuel.  First suppose the rocket spends its fuel all at once. Then  $$v_f=v_{ex}\ln\left(\frac{M}{M-(m_{fa}+m_{fb})}\right).$$  Now suppose the rocket first spends its fuel in tank $A$: $v_1=v_{ex}\ln(\frac{M}{M-m_{fa}}).$ Now the rocket detaches tank $A$, so the mass is now $M-(m_{fa}+m_a).$ Consequently, after spending the fuel in tank $B$, we have  \begin{align} v_f&=v_1+v_{ex}\ln\left(\frac{M-(m_{fa}+m_a)}{M-(m_{fa}+m_a+m_{fb})}\right)\\&=v_{ex}\left[\ln\left(\frac{M}{M-m_{fa}}\right)+\ln\left(\frac{M-(m_{fa}+m_a)}{M-(m_{fa}+m_a+m_{fb})}\right)\right].\end{align}  Now I'm not seeing how to show $v_f$ is greater in the second case, so I'm thinking I made some mistake in the argument. Can anyone clear things up?

What is the advantage for rockets to ?   Wouldn't a single stage with the same amount of fuel weigh less?  Note I would like a quantitative answer, if possible :-)


I want to show   $$\log(2) = \sum_{k = 1}^{\infty} \frac{1}{k \cdot 2^{k}}.$$  So, I start with the geometric series:  $$\frac{1}{1 - x} = \sum_{n = 0}^{\infty} x^{n} $$  Then take the integral to get   $$\log(1 - x) = -\sum_{n = 1}^{\infty} \frac{x^{n}}{n}.$$  Then plug in $x = -1$ to get   $$\log(2) = -\sum_{n = 1}^{\infty} \frac{(-1)^{n}}{n} = \sum_{n = 1}^{\infty} \frac{(-1)^{n + 1}}{n},$$  but this isn't equal to the original equality. Why not? How can I do the problem?

Problem:  Show that $$\ln2 = \sum_\limits{n=1}^\infty\frac1{n2^n}.$$  My progress:  The problem before this one had me find the Taylor series for $\ln(1-x)$ which was $$-\sum\limits_{n=1}^\infty \frac{x^n}n$$  so I figured I'd use $x=-1$ and plug that into the Taylor series. However, there was a side note stating that the Taylor series I found is only valid for $x\in(-1, 1)$. And in any case, my calculation isn't going anywhere, since I end up with the series $1-\frac12+\frac13-\frac14\cdots$  Question 1: How can I use this to solve the problem stated initially, and in the title?  Question 2: I can see why $x$ is restricted to be less than 1, to prevent taking the log of zero or a negative. Why is it not valid for x greater than 1?


I have problem with Japanese Characters. I want to store Japanese Characters into a SQL Server database. When I try to display in Terminal it's good but when I try in HTML page Japanese characters are replace with question marks. I don't understand why it's work in console and not in web browser.  I try to change collation for the database, change charset to html page, without any effect  How can I fix that?  Thanks

I'm setting up a new server and want to support UTF-8 fully in my web application. I have tried this in the past on existing servers and always seem to end up having to fall back to ISO-8859-1.  Where exactly do I need to set the encoding/charsets? I'm aware that I need to configure Apache, MySQL, and PHP to do this — is there some standard checklist I can follow, or perhaps troubleshoot where the mismatches occur?  This is for a new Linux server, running MySQL 5, PHP, 5 and Apache 2.


Here what I am getting:   Windows loads fine only if I switch to UEFI via Boot options (F12). I get the GRUB menu only in legacy mode. In GRUB 2.02 beta2-9ubuntui1.3 menu the only selection for Windows I get is:  Windows Recovery Environment(loader) (on /dev/sda1)   When I select it, I get only a blinking underscore/cursor and it freezes there.   Unlike what I saw in a similar issue(), I can dual boot, but it requires me to switch back and forth from legacy and UEFI, which is inconvenient.

I followed this  to install Ubuntu as dual-boot with Windows 8.1 pre-installed as(UEFI),but I am not able to dual-boot and tried    I first burned an Ubuntu ISO on a blank DVD-R to create the LiveCD. Even with secure boot disabled, when I tried restarting my computer, it never booted to the installation screen, and it just skipped to Windows.  After a lot of skimming, I thought I had to put my computer in Legacy Mode in order to get give my CD/ROM drive priority. I installed Ubuntu and used my existing EFI partition. Ubuntu works, but Windows doesn't, probably because my laptop is stuck in Legacy Mode. I tried switching back to UEFI using boot-repair on the Linux Terminal, and going into Advanced Properties -> Grub Location -> Ticking the checkbox for EFI, but it says I need to be in an EFI session, and now I'm just really lost and confused at what I've all done. I can see my Windows8.1 OS on a partition but I want to dual-boot Windows 8.1 along with Ubuntu?   Did I just brick my computer?


Basically somehow a portal is opened or discovered and they see humans which are dressed like the Gay Nineties in the USA or England (one character says, "It looks like Jolly Bicycle Tours...") but when a soldier from our side gets through, the creatures instantly attack and devour him, IIRC, shedding their clothing and revealing that they are somewhat differently built than humans.  The "father" creature seems to understand what has happened and fetches a book that might contain, say, a formula for traveling to our dimension and of course we are worried about this.  That's all I remember except the story is at least 40 years old but probably older.

I am trying to identify the author and title of a short story with the following plot.  A scientist narrates a story where s/he is called in to help the army investigate an unexplained phenomena.  The army has cordoned off an area where a prairie home has appeared. It is surrounded by a dome that allows things to enter but not to leave. Briefing the scientist, the Army explains that it appears that it is a family of five with mother, father, son, daughter, and grandfather. They look completely normal and live an idyllic life of the 40s or 50s.  They continue to send probes in to investigate the dome and its proprieties. Not sure if this a time anomaly or another dimension.  An Army lieutenant, so enamored by their life runs through the barrier to join the family. The Family faces split into an unnaturally wide smile full of sharp teeth runs towards him and tears him to pieces & eats him. The grandfather then looks up acts as if he can see the forces gathered outside the barrier. He then retrieves a book and it looks as if he reads it out loud and the house and barrier disappear. The narrator worries that the aliens will return.


Consider the following MWE: \documentclass{article}  \usepackage{blindtext}  \newlength\myheight \newlength\mypadding \setlength{\myheight}{2em} \setlength{\mypadding}{5em}  \begin{document} \blindtext\\ \vspace{10em} \vspace{-\mypadding}\\ This is a sentence that has been vertically shifted.\\ \vspace{\mypadding}\\ \blindtext\\ \end{document}  If we, instead of writing \setlength{\mypadding}{5em}, have \setlength{\mypadding}{3em plus \myheight}, we should get the same result (as 3 + 2 = 5).  However, as you see if you run this code and compare the outputs, these do not produce the same result.  Why is this?

In the following code, I need to use +/- where I have used it, and plus/minus where I have used it.  \documentclass{amsart} \usepackage{lipsum} \usepackage{calc} \parindent=0 pt \parskip=12 pt plus 0 pt minus 0 pt \def\headsep{25pt} \newcommand{\LAYOUT}[5]{%   \setlength{\hoffset}{0pt}   \setlength{\voffset}{0pt}   \setlength{\topmargin}{#1 - 1in - \voffset - \headheight - \headsep}    \setlength{\oddsidemargin}{#2 - 1in - \hoffset}   \setlength{\evensidemargin}{\oddsidemargin}   \setlength{\textheight}{#3}   \setlength{\textwidth}{#4}   \setlength{\marginparwidth}{#5} } \newcommand{\FULLPAGE}{\LAYOUT{1in}{1in}{9in}{6.5in}{0.75in}}  \FULLPAGE \begin{document} \lipsum[1-10] \end{document}   If I replace the plus and minus in line 5 with + and - I get an enigmatic  "missing begin{document}" error.    If I replace the minus's in lines 10-11 with "-" I get an equally enigmatic error:  "Missing number, treated as zero. Illegal unit of measure (pt inserted)."   Can somebody please explain when one can use +/- and when one can use plus/minus?  Presumably there's a good reason why latex's error messages are so completely mystifying, and why inconsistencies like these keep appearing? It's really hard to explain to my coauthors, who regularly complain that latex is the most infuriating program ever devised by mankind.  Thanks very much for any advice!   Leo


I have read a lot of documentation on disabling root user login via ssh for security reasons. I have set in /etc/ssh/sshd_config  PermitRootLogin no   If I disable root login then boot need to assume user name and password also.  If I set   PermitRootLogin without-password   Then it is secure to do this. If I use my sshkey is it secure? Please explain.

I just installed Ubuntu 14.04 on my server and I was setting up all my config files when I came across this in my sshd_config file:  # Authentication: LoginGraceTime 120 PermitRootLogin without-password StrictModes yes   This made me very worried. I thought that it was possible that someone could be logging into my server as root without a password.  I tried connecting to my server as root via:  johns-mbp:~ john$ ssh root@192.168.1.48 The authenticity of host '192.168.1.48 (192.168.1.48)' can't be established. RSA key fingerprint is 40:7e:28:f1:a8:36:28:da:eb:6f:d2:d0:3f:4b:4b:fe. Are you sure you want to continue connecting (yes/no)? yes Warning: Permanently added '192.168.1.48' (RSA) to the list of known hosts. root@192.168.1.48's password:     I entered a blank password and it didn't let me in, which was a relief. So my question is: what does without password mean and why is this a default in Ubuntu 14.04?


I know that the time between two events distributes exponentially with parmeter lambda, but, how will the time distributes between n events for example? I would guess there should be a simple connection like pdf of exp(lambda/n) but I cant get something mathematicly (my intuistion may be wrong and there is not such connection)

Let $X_1$ and $X_2$ be independent and identically distributed exponential random variables with rate $\lambda$. Let $S_2 = X_1 + X_2$.  Q: Show that $S_2$ has PDF $f_{S_2}(x) = \lambda^2 x \text{e}^{-\lambda x},\, x\ge 0$.  Note that if events occurred according to a Poisson Process (PP) with rate $\lambda$, $S_2$ would represent the time of the 2nd event.   Alternate approaches are appreciated. The approaches provided are commonly used when learning queueing theory & stochastic processes.     Recall the Exponential distribution is a special case of the Gamma distribution (with shape parameter $1$). I've learned there is a more general version of this  that can be applied.


I have a question about how the Schengen duration of stay is calculated.   My duration of stay is 17 days. Unfortunately, I will arrive at the airport at 9:00 pm on July 26th, and my departure flight is at 12:00 pm on August 12th which is around 18 days.   My question is:   Can I stay inside the terminal for 3 hours? so when I pass the border control, it is on July 27th? Similarly, Can I arrive at the airport 12 hours before my departure flight? so it is on August 11th?   Thanks,

I have searched the web a lot and could not find an answer that fits my situation. Here are two links that are quite contradictory:       My situation:  I've visited Portugal in December 2012 for 29 days on a Schengen visa valid from December 1st, 2012 to February 1st, 2013 for research purposes (I am a Ph.D. student). I want to visit Sweden from February 10th, 2013 to May 10th, 2013 (89 days). I have applied for a Schengen visa again (for research). How will the 90/180 rule work in my situation?


Will I be able to take it without having to throw it away? Do they measure on ounces or milliliters? its a 5oz bottle (not all the way full -used-) and it has 15ml and the requirements are 3.4oz and 100ml.

Is the restriction on the amount of liquid in the container, or the size of the container itself?  The  says:     Liquids, gels, aerosols, creams and pastes must be 3.4 ounces (100ml) or less per container   It sounds like it's on the amount of liquid, rather than the container itself.   I ask because I have a nice 4oz Nalgene travel container. What if I filled it half way up? That way, it's clearly less than 3oz, probably closer to 2oz.


I am running docker swarm across two Debian 8 nodes, each with 1GB ram.  I wanted to see how much memory was available to my application process (which will be a Solr server) so I did:  docker-compose run solr bash   In other words, instead of the solr server process I am just running a bash shell, inside a container otherwise identical to the one which will run my server.  If I run top this is what I see:  top - 16:23:57 up  6:09,  0 users,  load average: 0.00, 0.01, 0.05 Tasks:   2 total,   1 running,   1 sleeping,   0 stopped,   0 zombie %Cpu(s):  0.0 us,  0.0 sy,  0.0 ni, 99.3 id,  0.0 wa,  0.0 hi,  0.3 si,  0.3 st KiB Mem:   1024468 total,   634016 used,   390452 free,    93124 buffers KiB Swap:        0 total,        0 used,        0 free.   375932 cached Mem    PID USER      PR  NI    VIRT    RES    SHR S %CPU %MEM     TIME+ COMMAND    11 solr      20   0   23640   2704   2320 R  0.3  0.3   0:00.01 top     1 solr      20   0   21940   3540   3044 S  0.0  0.3   0:00.12 bash   Apparently out of 1GB allocated to the container I am using 634MB, even though the only two processes running in the container are top and bash.  How much should I expect normally to be consumed by the OS?  I assume some of this is consumed by the Docker daemon and swarm too, outside the container on the host node.  hmm, I've just read this  ...should I interpret top to mean that, of the 634MB 'used', 375MB of that is just disk cache and is available to my app process?  So I really have 766MB free -  is that right?  The point of all this is so I can start my Solr server process with a realistic memory limit, to make best use of the 1GB node without getting shut down due to out-of-memory error.  UPDATE  Ok this has been marked as duplicate, so it is the 'linux ate my ram' thing. From that page the answer is not to use top but rather:  $ dc run solr bash solr@59cb7fafca0e:/opt/solr-4.10.4$ free -m              total       used       free     shared    buffers     cached Mem:          1000        628        371          8         94        372 -/+ buffers/cache:        161        838 Swap:            0          0          0   ...and from this the 'true' free memory figure is 838MB (which seems to derive from free + buffers + cached)

This is a  about how Unix operating systems report memory usage.   Similar Questions:                    I have production server that is running Debian 6.0.6 Squeeze  #uname -a  Linux debsrv 2.6.32-5-xen-amd64 #1 SMP Sun Sep 23 13:49:30 UTC 2012 x86_64 GNU/Linux   Every day cron executes backup script as root:  #crontab -e  0 5 * * * /root/sites_backup.sh > /dev/null 2>&1   #nano /root/sites_backup.sh  #!/bin/bash str=`date +%Y-%m-%d-%H-%M-%S` tar pzcf /home/backups/sites/mysite-$str.tar.gz /var/sites/mysite/public_html/www mysqldump -u mysite -pmypass mysite | gzip -9 > /home/backups/sites/mysite-$str.sql.gz cd /home/backups/sites/ sha512sum mysite-$str* > /home/backups/sites/mysite-$str.tar.gz.DIGESTS cd ~   Everything works perfectly, but I notice that Munin's memory graph shows increase of cache and buffers after backup.  Then I just download backup files and delete them. After deletion Munin's memory graph returns cache and buffers to the state that was before backup.  Here's Munin graph:  Externally hosted image was a dead link.


Is it possible to type a question paper using MiKTeX version 2.9?  How to install the exam package once I have already installed basic packages like article, thesis.

I recently installed MiKTeX with the texmaker editor and cannot figure out how to update the packages. When I attempt to use the subfigure package with the following preamble  \documentclass[a4paper,12pt]{article} \usepackage[english]{babel} \usepackage{graphicx} \usepackage{subfigure}   I then get a prompt to install a new package, which I then set to the online directory at ctan. I then get the following error:   ! LaTeX Error: File `subfig.sty' not found.Type X to quit or <RETURN> to proceed,or enter new name. (Default extension: sty)Enter file name:! Emergency stop.<read >   How do I properly install packages to miktex? I'm absolutely confused. Thanks in advance for any help.


I have a MacBook Air running Mac OS X Lion 10.7.5. I wish to upgrade it to macOS Sierra, but it requires at-least OS X Mountain Lion 10.8 which is not available anymore in the App Store.  Is there any other way to update the OS?

Sometimes it's hard to search for older versions of macOS & OS X  on the App Store.  This is an attempt to provide the canonical QA for this issue, as per the Meta QA -  I expect it to be modified over time to hopefully become a complete information resource.  How can I get any older version of a Mac OS to be able to run as a VM, or to reinstall on my Mac?


Ok so i am running windows 8 on my computer currently and trying to get Ubuntu up and running in a dual boot.  My system has UEFI secure boot (for the record its a laptop).  When i boot up my Ubuntu from a flash drive it does not recognize windows 8 is installed on my system.  Also if it is any help, Windows 8 and the drive i am try to install Ubuntu on is a solid state drive.  And before anyone asks i have trying disabling secure boot.  Any help would be greatly appreciated!

I'm absolutely new to Linux. I would like to know how to install Ubuntu alongside the pre-installed Windows 8+ OS.  Should I do it with Wubi, or through the Live USB/DVD?  What steps do I need to take to correctly install Ubuntu?


The  in question is:$$ \dot\rho  + 3H \left(ρ + P\right) = 0 \,.$$ I’m a layperson so I don’t know why this equation is sometimes called fluid equation, energy conservation equation, or continuity equation.  Does this equation prove that energy is not conserved in an expanding universe since it shows that the energy of a fluid with negative pressure will increase with the expansion; the energy of a fluid with positive pressure will decrease with the expansion?  Is it well established that this equation correctly describes the relation between pressure and energy density of fluids (with zero, positive, negative pressure) in an expanding universe? If so, it could be a definite proof that energy is not conserved in an expanding universe.

In popular science books and articles, I keep running into the claim that the total energy of the Universe is zero, "because the positive energy of matter is cancelled out by the negative energy of the gravitational field".  But I can't find anything concrete to substantiate this claim. As a first check, I did a calculation to compute the gravitational potential energy of a sphere of uniform density of radius $R$ using Newton's Laws and threw in $E=mc^2$ for energy of the sphere, and it was by no means obvious that the answer is zero!  So, my questions:   What is the basis for the claim – does one require General Relativity, or can one get it from Newtonian gravity? What conditions do you require in the model, in order for this to work? Could someone please refer me to a good paper about this?


I thought up an other math problem, and hope you all will find it interesting. Given is a rectangle ABCD. The points P on the line AB, Q on BC, R on CD and S on AD are inner points of the rectangle sides. Inner points of a line are all points of this line except the end points. Now it shall be determined for which positions of the points P, Q, R and S, the rectangle PQRS has the smallest circumference. Thanks for all good answers

I'm supposed to find a quadrangle of the smallest perimeter possible inscribed in a rectangle. The inscribed quadrangle has each of its four vertices on another side of the rectangle.   Let's call the rectangle ABCD and let the shorter side be $a$ and the larger $b$. Let's call the quadrangle $KLMN$.   So for example $K$ lies on $AB$, $L$ on $BC$, $M$ on $CD$, $N$ on $AD$.  I think that the sides of $KLMN$ would be the shortest of its diagonals intersected at the right angle, because then by the law of cosines, we have $KL^2 + LM^2= KM^2 + 2 KL \cdot LM \cdot \cos  \angle KLM$, and $\cos  \angle KLM \le 0$ if $\angle KLM \ge 90 ^{\circ}$ and $KM$ is the shortest if it is parallel = equal to the proper side of the rectangle.  Could you tell me if I'm right or correct me if I'm wrong?  Thank you.


My grub has the following versions which I want to remove.   Ubuntu, with Linux 4.1.0-rc5-next-20150529 Ubuntu, with Linux 4.1.0-rc5-next-20150529.old Ubuntu, with Linux 4.1.0-rc4-next-20150525 Ubuntu, with Linux 4.0.0-rc6-next-20150402+ Ubuntu, with Linux 4.0.0-rc6-next-20150402+.old   I tried the following methods to remove:  Using Synaptic tool and I have typed the following commands:   uname -r     dpkg --list | grep linux-image      sudo apt-get purge linux-image-x.x.x.x-xyz   sudo update-grub2   Both of the methods failed to remove the kernel versions.

Every time I install a new Linux kernel, it gets left in the grub_config, making the boot menu longer each time.    I know I can manually search through the installed packages and remove them.  Does Ubuntu provide any easier way to clean them up or keep them from showing in the boot list?


I encountered the following exercise (Exercise 3.9, page 24) in the book A Course in Galois Theory by D. J. H. Garling (Cambridge Univ. Press) :  Assume that $R$ is an infinite commutative ring with a multiplicative identity for which $R/I$ is a finite ring for every non-zero ideal $I$ in $R$. Prove that $R$ must be an integral domain.  Not even sure how to approach this! I don't have a feeling why this assertion should be true.

How can we show that if $R$ is an infinite commutative ring and $R/I$ is finite for every nonzero $I \unlhd R$, then $R$ is an integral domain?   I tried proceeding by contradiction: assume $a$,$b$ $\in R \backslash \{0\}$ and $ab=0$; then $R/(a)$ and $R/(b)$ must be finite, say $R/(a)=\{k_i + (a) : 1 \leq i \leq m\}$ and $R/(b)=\{l_j + (b) : 1 \leq j \leq n\}$. Does this mean $R$ must be finite? Or what about using the fact that $R/(a,b)$ finite?  Thanks for any help with this!


Sometimes I want to be able to quickly kill the process that has the most intensive hard disk usage. How do I do it?  With the solutions described  I would have to open another terminal to invoke a kill. Is there a way to monitor and potentially kill with the same app?

I'd like to do some general disk io monitoring on a debian linux server. What are the tools I should know about that monitor disk io so I can see if a disk's performance is maxed out or spikes at certain time throughout the day?


I'm getting System.FinalException: Record is read-only Trigger.Grossamount while I try to save record on Sales__c. trigger Grossamount1 on Sales__c ( after insert, after update) {     if (trigger.isAfter){         if( Trigger.isUpdate || Trigger.isInsert) {             List<Recurring__c> childListToUpdate = new List<Recurring__c>();                          for(Sales__c t: Trigger.new){                 if(t.Type__c == 'One Time' ){                     t.Gross_Amount__c = t.Amount__c;                 }                   else if(t.Type__c == 'Recurring' ){                     Date new1= t.Sale_Date__c;                     t.Amount_Recurring__c = t.Amount__c * t.Term__c;                     Recurring__c child = new Recurring__c();                     child.Sales__c = t.Id;                     System.debug(child.Sales__c);                     child.Name = t.Name;                     child.Amount__c= t.Amount__c;                     child.Due_Date__c = new1;                     if(t.Frequency__c == 'Quarterly'){                         for(integer i =0; i < t.Term__c; i++){                               Date new2 = new1.addMonths(4);                             new1 = new2;                                 System.debug('Hi');                             childListToUpdate.add(child);                         }                      }                     else if(t.Frequency__c== 'Weekly'){                         for(integer i =0; i < t.Term__c; i++){                                                            Date new2 = new1.addDays(7);                             new1 = new2;                                   childListToUpdate.add(child);                         }                      }                     else if(t.Frequency__c== 'Monthly'){                         for(integer i =0; i < t.Term__c; i++){                               Date new2 = new1.addMonths(1);                             new1 = new2;                                 System.debug('Hi');                             childListToUpdate.add(child);                         }                      }                     else {                         for(integer i =0; i < t.Term__c; i++){                               Date new2 = new1.addMonths(12);                             new1 = new2;                                 System.debug('Hi');                             childListToUpdate.add(child);                         }                      }                 }                 else {                     t.Amount_Service__c = t.Amount__c;                     t.Gross_Amount__c = t.Amount_Service__c;                 }                 }             insert childListToUpdate;         }     } }

I am writing a trigger to get all the Opportunity competitors into a field on Opportunity, however, getting an error while testing it.  Error: updateCompetitors: execution of AfterUpdate caused by: System.FinalException: Record is read-only: Trigger.updateCompetitors: line 24  Can you please check the below code and suggest me what's wrong with this?  trigger updateCompetitors on Opportunity(after insert, after update){    List<Opportunity> OppIds = new List<Opportunity>();     for (Opportunity opp: trigger.new){         OppIds.add(opp);     }  List<OpportunityCompetitor> oppComps = new List<OpportunityCompetitor>();  oppComps= [select id, CompetitorName, Strengths, Weaknesses from OpportunityCompetitor where OpportunityId in: Trigger.newMap.keySet()];  List<Opportunity> OppstoUpdate = new List<Opportunity>();   for (Opportunity opp: OppIds){     String allcomps = null;      if( oppComps.size()>0 ) {       for (integer i = 0; i < oppComps.size(); i++){          allcomps = allcomps + oppComps[i].CompetitorName+',';       }     }    opp.OpportunityCompetitors__c = allcomps;    OppstoUpdate.add(opp);  }    update OppstoUpdate; }


I have a Canon 70D APS-C sized sensor camera. I currently have a Sigma 10-20mm, a Canon 50mm 1.8, a Canon 75-300mm and of course the kit lens. I want to buy the Canon 24-105mm F4 L as an upgrade.   I am fully aware that on my crop sized sensor it will look more zoomed than on full frame. However I have tested my camera at the cropped 24mm on my sensor and I dont find the focal length to be an issue. My only concern is that I heard from a couple of places that using a full frame lens like the 24-105 L will reduce the megapixels or the quality in some way. I was wondering if this was true and how/why it happens.   Also I will be using this lens for video, getting the cinematic shots mainly at 70mm + at F4 to get the best bokeh I can out of the zoom. I don't want advice on alternative lenses or comments on how this lens will be too  'long' as I have got a 10-20mm wide for the wide end, and I want thislens for cinematic zoomed video look.But I just want to make sure the lens on a crop size camera will not affect the quality in a bad way.

I see a lot of questions comparing full frame (e.g EF for Canon, FX for Nikon) and crop lenses (e.g. EF-S for Canon, DX for Nikon) but I can't find the answer to what would be the differences between the photos taken with say a 50mm f/1.4 EF and EF-S lenses both used with   same APS-C sensor sized camera same ISO same f/1.4 f-stop same focal length same shutter speed   What would be the resulting differences in the photos? Which one would   be brighter than the other due the EF-S lens concentrating the light more? no that's wrong. Both put the same amount of light from the same FoV on the sensor. have greater depth-of-field? neither less problems towards the edges? generally the full frame more lens flare? generally the full frame lens unless there is, or you provide more shading anything else? not really, unless you start down the road of which one is typically of better build quality.   Edit: Added the answers from what seems to be the general consensus from the multiple answers and comments.  Results: My desire to buy a fast medium-high quality lens compatible with both full frame and crop camera's doesn't have to be hampered by the APS-C sensor size of my current camera.  This means I'm willing to part with more money to get a higher performance/quality lens as the performance/quality will be useful now and when I upgrade my camera.  Though reading reviews of some full frame lenses with short focal lengths, look out, as some are really only made to perform well on crop cameras even though they fit on a full frame camera and will give you a full frame picture, the edge quality is very bad.