After 13.04 installation, computer only boots to windows
How can I repair grub? (How to get Ubuntu back after installing Windows?)
Getting "Authentication is required" when trying to access the Play Store Over the past week, whenever I try  to open the Play Store/Market app on my phone, the app thinks for a while and then displays this error message:     Authentication is required. You need to sign into your Google Account.   But I am indeed signed into my Google account, as seen in other Google applications running on the phone, and as seen if I open the menu in the Market app and click the "Accounts" button.  I suspect this might be related to the fact that over the past few months I've had two different Google accounts synced to this device, and I have recently removed one of them from the phone. No other Google application has had any problems with removing one account.  Does anyone know how I can solve this issue? I can still install applications by using the market website (now "Google Play"), but this is still a big inconvenience. I also think I stopped getting updates. How to compute moments of log normal distribution? The computed moments of log normal distribution can be found . How to compute them? Compute $\frac{1}{e}\sum\limits_{n=0}^{\infty}\frac{n^{k}}{n!}$ for $k=0, 1, 2 ... $ Using some matlab (I know it's cheating) I found that: $$k=0 =&gt; Result=1$$ $$k=1 =&gt; Result=1$$ $$k=2 =&gt; Result=2$$ $$k=3 =&gt; Result=5$$ $$k=4 =&gt; Result=15$$ $$k=5 =&gt; Result=52$$ $$k=6 =&gt; Result=203$$  This sequence is puzzling... Can a 3rd party charger damage my macbook pro? How to apply custom headers/footers on pages with new chapters? I'm writing my final report in LaTeX for my bachelor's degree. I'm aiming at having a document similar to the .doc template used normally.   I want to have my customs headers and footers applied on pages when I'm starting a new chapter.  I'm using documentclass report with fancyhdr and lastpage packages.  My headers are defined like this:  \lhead{\myTitle} \rhead{\today} \cfoot{\thepage\ of \pageref{LastPage}}   My chapters are created using standard \chapter{title} macro.  On pages with new chapters, the only headers/footers I see is the standard page number at the bottom.  What should I do?  EDIT: I've finally gone with Peter Breitfeld's solution. I'Ve gone a step further and created my own chapter command:  \newcommand{\myChapter}[1]{     \chapter{#1}     \thispagestyle{fancy} }   Thanks for the help! What is a disputed flag? In my flagging summary under the statistics, there is 1 flag listed as "disputed".  This is the first time I've ever seen a disputed flag in my summary, so I'm just curious, what is a disputed flag? How would you even dispute a flag? Is this the same as voting a flag as invalid? I was wondering what the proper LaTeX code would be to display something like this:    You don't have to include the mathematical symbols, what is important is the structure. How does the /proc//exe symlink differ from ordinary symlinks? If I start a process and then delete the binary of it, I can still recover it from /proc/&lt;pid&gt;/exe:  $ cp `which sleep` . $ ./sleep 10m &amp; [1] 13728 $ rm sleep $ readlink /proc/13728/exe                            /tmp/sleep (deleted) $ cp /proc/13728/exe ./sleep-copy $ diff sleep-copy `which sleep` &amp;&amp; echo not different not different $ stat /proc/13728/exe    File: ‘/proc/13728/exe’ -&gt; ‘/tmp/sleep (deleted)’   Size: 0           Blocks: 0          IO Block: 1024   symbolic link   On the other hand, if I make a symbolic link myself, delete the target and attempt to copy:  cp: cannot stat ‘sleep’: No such file or directory   /proc is an interface to the kernel. So does this symbolic link actually point to the copy loaded in memory, but with a more useful name? How does the exe link work, exactly? What's the maximum value for an int in PHP? Ignoring the special libraries that allow you to work with very big numbers, what's the largest int value you can store in PHP? How should "do my homework" questions be closed? (Missing "demonstrate minimal understanding") Just recently,  question was posted. Here's the body of the question:     Write a function called highlight() that prompts the user for a string. Your code should ensure that the string is all lower case. Next, prompt the user for a smaller 'substring' of one or more characters. Then replace every occurrence of the substring in the first string with an upper case. Finally, report to the user how many changes were made (i.e., how many occurrences of the substring there were).      What would a script for this be?   This is basically a "do my homework for me" style question. In the past, I would have voted to close this question for lacking minimal understanding and moved on. However, it looks like this close reason was removed, and I'm having difficulty figuring out which alternative to use (if at all).  Here were some of the close reasons I was considering, and ultimately decided against since they didn't seem to precisely match:   Duplicate of    I sort of doubt there exists a precise duplicate of this question -- the question is a fairly specific request for some code. I could maybe link to a duplicate question that answers a part of the original (for example, checking if the string is lowercase), but it wouldn't answer every aspect of the problem. Problem that can't be reproduced/typographical error    This sort of matches, since it asks the user to produce a SSCCEE, but doesn't really match since there isn't even a problem to begin with (and closing a question because I couldn't "reproduce" a non-existent problem feels a bit silly to me) Unclear what you're asking    It's pretty obvious what the user is asking -- I could produce a 5 line script in about 20 seconds that precisely matches his spec. Too broad    The text for "Too broad" states that "There are either too many possible answers, or good answers would be too long for this format". This doesn't apply to this question -- once again, the answer I could give would be fairly short and would closely resemble solutions other people would give.   So, what should I do here? Am I misunderstanding how the close reasons should now be used? Should I use the "other" close reason and explain that the OP should have put in more effort? Should I simply downvote, perhaps leave a comment, and move on? Or is the new policy to embrace these kinds of questions and just post an answer? I see this often in the build scripts of projects that use autotools (autoconf, automake).  When somebody wants to check the value of a shell variable, they frequently use this idiom:  if test "x$SHELL_VAR" = "xyes"; then ...   What is the advantage to this over simply checking the value like this:  if test $SHELL_VAR = "yes"; then ...   I figure there must be some reason that I see this so often, but I can't figure out what it is. Ubuntu 20.04 interface font too small after restart, even with high scaling factor So I was configuring VS code on my Notebook when suddenly I noticed that my interface font got really small on my desktop, terminal and files. I use Gnome Tweaks Tool to increase my scaling factor to 1,15 , but, even though it was active, the font stayed tiny. The solution I found was moving my scaling factor, which instantly fixed my font issue, however, every time I restart my Notebook the font gets tiny again and I have to repeat the process. I tried reseting my font configuration using this command, but had no success. gsettings reset org.gnome.desktop.interface text-scaling-factor  I also tried using the command dconf reset -f /  Finally, I tried using dconf-editor, but still had no success altering the font rendering DPI or changing the scaling factor. All of the steps I mentioned fixed my fonts temporarily, but the issue still persists when I restart my Notebook I am out of ideas and even considered getting a fresh Ubuntu install by now... My video card: NVIDIA GeForce GTX 1050 GPU Is there any gold standard for modeling irregularly spaced time series? How does one solve the matrix equation $AX+XB=C$ for $X$? It doesn't seem too difficult. I tried many times but failed.  I'm an adult student... I am now vexed about Gilbert Strang - An Introduction to Linear Algebra. I don't even understand a single word in Wikipedia: . If you have ever use some nice workable materials or lecture notes? You can generously upload and share the links of the lecture notes and assignments. Different subjects/ topics are welcome, as long as you deem they are nice and workable.   The problem origins from a system of diff equation, using undetermined coefficients (matrix) to find the particular solution. Try $y_p=X\begin{pmatrix}   e^{\alpha t} \\ e^{\beta t} \end{pmatrix}$  $\dot{y}+Ay=C\begin{pmatrix} e^{\alpha t} \\ e^{\beta t}\end{pmatrix}$   $\dot{y_p}=X\begin{pmatrix} \alpha &amp; 0 \\ 0 &amp; \beta \end{pmatrix} \begin{pmatrix}e^{\alpha t} \\ e^{\beta t}\end{pmatrix}$  substitute $\dot{y_p}$ and $y_p$ into the original differential equation..  $X\begin{pmatrix} \alpha &amp; 0 \\ 0 &amp; \beta \end{pmatrix}+AX=C$ In Adobe Photoshop I am able to select multiple layers at once with Shift+Click.  How can I do that in GIMP? I have a file with values organized in columns, and separated by commas, as in the file below:   324,01,1,113333600000,1,, 016,01,1,134954200000,1,, 770,01,1,109069200000,1,, 853,01,1,111518800000,1,,   When I use the following awk command, the delimiter is being changed from commas to spaces   Code:  awk -F, '{$4=$4/1024}{print $0}'   The output becomes:   324 01 1 110677343.75 1   016 01 1 131791210.93 1   770 01 1 106512890.62 1   853 01 1 108905078.12 1    How can I change the value of the field without changing the delimiter? What HTML tags are allowed on Stack Exchange sites? Order of some quotient ring of Gaussian integers Flattening iterator So, I understand that for a NPN transistor to work the emitter-base junction needs to be forward biased and the collector-base junction needs to be reverse biased.  I understand how current flows from the emitter to the base when forward biased, but I can't seem to wrap my head around how it flows from the emitter, through the base, and into the collector.  From what I understand about the depletion region of a PN junction diode, when forward biased, the electrons in the N-type material are repulsed by the negative charge of the supply (say a battery) and the holes in the P-type material are repulsed by the positive charge from the supply, thus narrowing the depletion region and allowing electrons to flow from the N region to the P region.  I also understand that the holes and electrons are attracted to the source charges when reverse biased, widening the depletion region and blocking any electrons from flowing.  What I don't understand is what happens to the depletion region of the collector-base junction that allows electrons to flow from the emitter to the collector even though the collector-base junction is reverse biased.  Take a simple common emitter circuit for example.  I apparently am not cool enough to post pictures yet so you'll have to use your imagination.  So pretend we have the base connected to the positive terminal on a 1v battery (Vbb).  The collector is connected to the positive terminal on a 10v battery (Vcc).  The emitter and both negative terminals are connected to ground.  Also pretend that there is some kind of current limiting.  How does current get from the emitter through to the collector?  I can see how they are at different potentials, but I don't understand how this overcomes the reverse biasing of the collector-base junction.  Can anyone tell me what actually happens at the junction to allow current flow and how changing Vbb will affect that current?