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Ubuntu Software doesn't open in Ubuntu 20.04 If i click on Ubuntu Software, it doesn't open. I have a fresh install of Ubuntu 20.04. I tried try to upgrade all packages, but it doesn't fix this problem.  If I try to run killall software-center there is no process with this name, and software-center returns command not found. If I try to reinstall it with apt I have these results:  $ sudo apt-get --purge --reinstall install software-center Reading package lists... Done Building dependency tree        Reading state information... Done Package oracle-java8-installer is not available, but is referred to by another package. This may mean that the package is missing, has been obsoleted, or is only available from another source E: Package 'software-center' has no installation candidate Is it true that if $A$ is a nonnegative primitive matrix, then $AA^T$ is also primitive? Obviously $A^T$ is primitive but in general product of primitive matrices is not primitive.  Any hint? Single word for people who are like "a frog in the well" Is there a single word describing someone who is like a frog in a well? The frog believes the well is the entire world. How can I describe people who think that their own small environment is the entire world? How to create an annuity timeline on LaTeX I was wondering, how can I create a timeline exactly like this one:    on LaTeX?  I am a Finance student, and write all of my notes using LaTeX. These timelines, are giving me a headache. Since we use a lot of different timelines because of annuities. I want to learn how to create one basic timeline, so that I can then change anything I want. But basically, I want something like this, with the arrows and everything.  Thank you so much guys! Is wildcard search possible in Gmail? What Happened to The Latex Symbols In the Libreoffice-Texmaths Equation Editor? I recently purged Libreoffice because it was buggy.  I then reinstalled the latest version from apt and now it's missing the symbols above the equation editor.  Here is the current Texmaths equation editor:   There used to be shortcuts for latex including frac{}{} and various set theory operations, as well as the binomial distribution on the top of the window.  What happened to them and how do I get them back? I just figured that they were in some package and installed all packages useing sudo apt install libreoffice*, but this didn't help after I refreshed the program.  EDIT 0: I'm using Kubuntu 19.04  sarah@LesserArk:~$ sudo apt-cache policy libreoffice-texmaths libreoffice-writer texlive libreoffice-texmaths:   Installed: 0.43-2   Candidate: 0.43-2   Version table:  *** 0.43-2 500         500 http://us.archive.ubuntu.com/ubuntu disco/universe amd64 Packages         500 http://us.archive.ubuntu.com/ubuntu disco/universe i386 Packages         100 /var/lib/dpkg/status libreoffice-writer:   Installed: 1:6.2.2-0ubuntu2   Candidate: 1:6.2.2-0ubuntu2   Version table:  *** 1:6.2.2-0ubuntu2 500         500 http://us.archive.ubuntu.com/ubuntu disco/main amd64 Packages         100 /var/lib/dpkg/status texlive:   Installed: 2018.20190227-1   Candidate: 2018.20190227-1   Version table:  *** 2018.20190227-1 500         500 http://us.archive.ubuntu.com/ubuntu disco/universe amd64 Packages         500 http://us.archive.ubuntu.com/ubuntu disco/universe i386 Packages         100 /var/lib/dpkg/status Subcaption defaulting to capital letter labels? I seem to be having a unique problem. There are many questions asking about how to change subcaption to a label with capital letters but for me my program is defaulting to capital letters when I would prefer lowercase.  My preamble  \documentclass[12pt,reqno]{amsart} \setlength\parindent{0pt} %no auto indentation for new paragraphs \usepackage{geometry}  \geometry{a4paper}  \usepackage{natbib}  \usepackage[latin1]{inputenc} \usepackage{amsmath, amsthm, amssymb, calc, dsfont}    \usepackage{enumerate} \usepackage{subcaption, caption, graphicx} %figure packages \usepackage{authblk} %author affiliations \usepackage{setspace, lineno} %double spaced etc. options, line numbering  \usepackage{tikz} \usetikzlibrary{shapes,arrows,chains,automata,positioning}   My figure  \begin{figure}[h!]   \centering   \begin{subfigure}[]{0.48\textwidth}           \includegraphics{Figure1.pdf}           \caption{}           \label{FigPractice}    \end{subfigure}    \begin{subfigure}[]{0.48\textwidth}           \includegraphics{Figure2.pdf}           \caption{}           \label{PracticeAge}   \end{subfigure}   \caption{a caption} \end{figure}   I've also tried \renewcommand{\thesubfigure}{\alph{subfigure}} Testing a UPS by unplugging it from the wall At an Not For Profit/Charity I volunteer for occasionally we were very fortunate to be provided (donated) with a brand new 3Kva APC UPS. This is total overkill for our modest server rack (four mid-range servers and a switch!) but hey, I'll take what I can get!  Pressing the TEST button on the front indicates that yes, the UPS does work. Brilliant. But it only tests it for about 15 seconds.  My question is - will I degrade the UPS by unplugging it from the wall to see how long it will last? My plan is to unplug it, and wait until the battery meter reaches its last LED before plugging it back in, so that I know about how long I will have in the event of a power outage.  Do people do this on a regular basis? I'm guessing no (Lead Acid is very different to Li-Ion batteries)... but what kind of harm would it do if this were to happen (on purpose) every 6 months? Why does the set of all singleton sets not exist? Open chrome and launch the settings page Most efficient way to append arrays in C#? I am pulling data out of an old-school ActiveX in the form of arrays of doubles. I don't initially know the final number of samples I will actually retrieve.  What is the most efficient way to concatenate these arrays together in C# as I pull them  out of the system? Prove that $n=\dfrac{5^{125}-1}{5^{25}-1}$ is a composite number   My attempt,  Let $x=5^{25}$, so that $5^{125}-1=x^5-1=(x-1)(x^4+x^3+x^2+x+1)$  $=(x^4+9x^2+1+6x^3+6x+2x^2-5x^3-10x^2-5x)(x-1)$  $=((x^2+3x+1)^2-5x(x+1)^2)(x-1)$  I'm stuck at this point and don't know how to continue anymore. Hope someone can provide a detailed solution. Thanks a lot. I'm working with jQuery and looking to see if there is an easy way to determine if the element has a specific CSS class associated with it.  I have the id of the element, and the CSS class that I'm looking for.  I just need to be able to, in an if statement, do a comparison based on the existence of that class on the element. I am looking for a multivariable calculus book that is really physics oriented.  Anyone know of any?  EDIT: My wife is looking to brush up on multivariable at the same time she needs to brush up on the related physics. What's the difference between the list methods append() and extend()? Sometimes writing braces and omitting them produces the same result:  \tilde{\psi}  \mathrm{e}^{\mathrm{i} \pi}   vs  \tilde \psi   \mathrm e^{\mathrm i \pi}   Or (taken from Werner's comment below)   \frac{1}{2} vs \frac12   If that's the case, how bad for the quality of my code is omitting them? Of course, if one compiles a pair of formulas, there is no difference. But, since I ignore how TeX works, my point is: if one writes long codes with these habits,   doesn't TeX go somehow crazy because I'm not writing as it expects?   For instance, does it have any effect on how fast are long documents compiled? Any reason to keep them? Suppose $u$ is an element of a ring with a right inverse. I'm trying to understand why the following are equivalent.   $u$ has at least two right inverses $u$ is a left zero divisor $u$ is not a unit   If $v$ and $w$ are distinct right inverse of $u$, then $u(v-w)=0$, but $v-w\neq 0$, so $u$ is a left zero divisor. It's also clear that if $u$ is a left zero divisor, it cannot be a unit (else I could cancel $u$ from $ub=0$ to see $b=0$).  I'm having a heck of a time seeing why $u$ is not a unit implies $u$ has at least two right inverses. I tried the contrapositive, but saw no good approach. What am I missing? Why does the jquery change event not trigger when I set the value of a select using val()? Why did I apparently get +97 for joining a site? Don't worry! I got all my 100 reputation :) It just didn't appear that way...    The notification says +100, but why does it say +97 at the top?  Edit  I created an account on server fault, and this time it says +96. I assume it's because of the down votes on this question; however, I thought down votes aren't shown in the rep you gain. Gravitational waves and time