The laptop that I have acquired only came with a 16GB SSD. I installed XFCE onto it and now the SSD is almost completely full. I have an external hard drive with 1TB of memory, and I was wondering if I could move applications over to it instead of having them take up space on my SSD. I would also like to be able to access them, having the SSD inserted into the USB 3.0 slot.

When I install a software using apt-get it installs to default locations i.e to /usr/bin, /usr/lib, /usr/share and etc. For example when I install "Meld Diff Viewer" using  sudo apt-get install meld   and use whereis command to find its location, I get the following output  adnan@adnan-laptop:~$ whereis meld meld: /usr/bin/meld /usr/lib/meld /usr/share/meld /usr/share/man/man1/meld.1.gz   Is there any way to change the install location. Lets say if I want to install it in /usr/local/ can I do it using apt-get or aptitude? I know I can compile it from source and specify prefix option to configure script or make install but it would be better (and really easier) if I could do it using apt-get as I would be able to use uninstall, upgrade and other stuff that apt-get offers


I have played on some settings and now it´s not working anymore. So I uninstalled it with sudo apt-get purge kdenlive kdenlive-data to make sure nothing is left from it. Next I reinstalled it and it's in the same settings witch are making this program unusable. I also tried a few other ways like remove it by the Software Center ore sudo apt-get remove kdenlive  If enyone cold help me that would be verry nice : )  Anthony

I would like to backup my  configuration.   Which files do I need to backup?


I know what chgrp and chown do. My question is since chown does the same thing as chgrp (and even more), what is the point of chgrp?

So there's chown which lets you change the owner and group of files and/or directories. But there's also chgrp which only changes the group. Why was chgrp created? Isn't it redundant?


I read this trilogy around 1990 and would love to re-read it.  From what I remember, the young boy was working in a castle and had a "knack".  This was the ability to feel the ground as the area leading to the castle he was working in would flood, and he would "feel" where the land was and get whatever he had in his wagon safely back to or possibly from the castle. I believe that on his mother's deathbed, his mother told him that the "knack" was actually a magic power this boy had from a word of power his mother gave him.  In this trilogy, the fewer people who knew the word, the more power the holder of this word had.  Also, there were a few "super" mages, who if I remember correctly, knew 4 words of power.  This knowledge would destroy all, but a special few.  Pretty much all I remember about this.  I don't believe it was David Duncan.  Any help would be appreciated!  Thanks.

I read a book of this series probably around 2000. I think the series was quite new then but not sure.  The main thing I remember about it is that magic is based on words of power. If you knew one word you got some extra ability, knowing two words gave you yet some other ability, and if you knew three words you became a very powerful wizard. Only one person at a time could know each word, and telling someone your word meant you died.  The main protagonist somehow gets hold of one word and then for some reason strives to learn more.  EDIT: I think that I accidentally picked up the second book of the series and never read the first one. From what I remember, the protagonist learned one word of power and got some kind of supernatural ability (cannot remember what though). He then ends up in some kind of challenge where he has to cooperate with another person who knows another word that gives super-strength.  Not very coherent memories, but I hope someone knows what series it is. It has been bugging me for years. (Not even sure if the series is good at all, but still would like to know the name.)  EDIT2:  I remember the world as being medieval-ish. I do not think there were dragons, but there may have been other humanoid races (I have a very weak recollection that there may have been an orc or similar in the story, but this could be completely wrong). The protagonist was male.


I am using \usepackage[utf8]{inputenc} so I am able write umlaute inside the tex file, but I can't search for a word that contains umlaute inside the compiled pdf.  Is this a "bug" inside LaTeX or do I have to change something in my tex file? If I copy a word that contains a umlaut like wähle this: "W ̈ ahle" appears in my clipbox.

One frequent aspect of pdflatex output that could be improved is to what extent one can select text output from the generated pdf-file and copy-and-paste it. This is essentially an issue of having the right output encoding. There are at least two important aspects to this:   In the ideal case, Unicode would be the output encoding. Ligature glyphs (such as ﬁ) are ideally de-ligated in the output (here: "fi").   It seems that output encodings are specified through the fontenc package. What is the range of possible output encodings, and most importantly: Is there a way to specify a Unicode output encoding and one that deals with ligatures in the intended way?  (Note: It is important to distinguish output from input encodings. How to use different input encodings in LaTeX has been documented widely. My understanding is that this is best handled by the inputenx package, as it supersedes the inputenc package.)    Quick guide to the solutions: The information in the answers and answer threads is a bit distributed, so here the short summary: one approach is to use \input glyphtounicode together with \pdfgentounicode=1; the other approach is to use cmap/mmap.  Addendum: Sometimes one will need to load the package accsupp and enclose one's macro definition in \BeginAccSupp{method=hex,unicode,ActualText=<codepoint>}[...]\EndAccSupp{} to generate a specific code point. See the caveat about non-BMP code points  and the fix (starting from accsupp version v0.4, 2012/11/18) , which provides the new unichar package option.


How do I find out how much disk space a program such as Skype occupies?  My SSD is getting full, and I want to see what can be deleted.

Every few days I get notices on my MacBook that it's running or run out of hard drive space. Curiously, restarting the computer will enable me to recover gigabytes of space (this past time, it was able to recover about 2.2GB). However, I can't identify anything in my personal activity that consumed that space.  It's possible that it's a rogue iTunes podcast or a huge software update that my Mac is automatically downloading - would either of these reclaim the space upon a restart?  One possibility that I can think of is that FileVault has some sort of disk leak, allocating but not freeing files. Does this make sense? Is there a tool that I can run to determine where this space is going? Assuming it is FileVault, should I try to disable it? What's the best way to turn of FileVault on a nearly full computer?


Let $f$ be a continuous real valued function on $[0,1]$ and $\int_0^1f(x)x^ndx = 0$ for $n = 0,1,2...$ Prove that $f$ is identically zero on $[0,1]$  This question was a part of a Topology exercise, but I cannot understand what relation it has to Topology. It seems like a real analysis question, where I integrate by parts (?) and show $f=0$ is required for the question to hold. But how to solve this from a topological perspective?   Unless I am understanding the "Prove that $f$ is identically zero on $[0,1]$" part wrong (?)

Suppose $f$ is continuous on $[0,1]$ and   $$ \int\limits_0^1 f(x) x^n d x = 0 $$   for all $n=0,1,2,...$. Then, $f(x) = 0$  I was trying to use by parts  $$ 0 = f(x) \frac{x^{n+1}}{n+1} \bigg|_0^1 - \int\limits_0^1 \frac{x^{n+1}}{n+1} f(x) dx $$  Thus,  $$ \frac{f(1)}{n+1} = \int\limits_0^1 \frac{ x^{n+1} f(x) dx }{n+1} \implies f(1) = \int\limits_0^1 x^{n+1} f(x) dx $$  but here I am stuck. Maybe my idea is not the best one? How would you approach this problem?


I have an iPhone 5 and just updated to iOS 9 (all german).   What I really do not like is the content of the newsfeed that is presented to me on the search screen. How can I change what content is presented to me (no more news from spiegel.de or focus.de please!) or if that is not possible, how can I completely disable news on that search screen but keep all the rest of the proactive search features on that search screen?   It appears in the US locale, the  but this app (and the switch for it) does not exist in iOS 9 that detects a german locale.

How can I turn off news headlines from Spotlight Search in iOS 9?


I want to know how to return the output of the dir command into an array. I'm using the command like this: dir /s /b *.txt how would I put each result (file name) into an array/list. Thanks

How can I setup an array variable in a DOS batch script?  I would like to load it with a list of file names to process.  I really would like to keep this as simple as possible.  Thank you.


For how many days Govt of India keep travelers under observation in airport in India who have transit in Singapore and travelling from Australia to India via Singapore ?

Due to the outbreak of nCoV-19 (Novel Coronavirus) many Countries have imposed several entry restrictions. But these are quite confusing for a lot of people. Some countries allow transit through parts of China (like Shanghai) but some restrict transit even through Hong Kong/Macau. Philippines restricted passengers coming from Taiwan too, but I think that that was later changed.  Where can one find a list of such restrictions for all the countries, ideally a source that is updated frequently


My file is encoded in UTF-8, all characters work fine it except "é"   I have tried several solutions but I always get this character � instead (and only for few words) :   Here is an example of the few option I have tried :   $auteur= utf8_decode("Aurélie ABBĀSĀBĀD");   $commAuteur = mb_convert_encoding($auteur, "HTML-ENTITIES", 'UTF-8');   I added utf8_decode to be sure I'm going from ISO-8859-1 to utf-8, then I tried also this :   $commAuteur  = iconv('UTF-8', 'ISO-8859-1//TRANSLIT//IGNORE', $auteur);   I eventually also tried this :    $commAuteur = htmlentities($auteur);   None of all these options worked correctly, and I don't understand how some é are displayed normally and others have this issue, im out of solutions any suggestions ?

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.


I am using cryptocode package to make a protocol of 4 players.  \fbox{ \procedure{name}{%  \textbf{Alice}  \< \textbf{Verisign}  \< \textbf{Eve}  \< \textbf{Bob} \\ \sendmessageright{top=\text{hello}} \<\\ \<\sendmessageright{top=\text{hello}} \<\\ \<\<\sendmessageright{top=\text{hello}} \<\\  }  }   My issues is the following:  1) how to create long arrow from Alice to Eve for example. (and arrow back) 2) how to keep the diagram size within the page size

I am using cryptocode package to make a protocol of 4 players.  \fbox{ \procedure{name}{%  \textbf{Alice}  \< \textbf{Verisign}  \< \textbf{Eve}  \< \textbf{Bob} \\ \sendmessageright{top=\text{hello}} \<\\ \<\sendmessageright{top=\text{hello}} \<\\ \<\<\sendmessageright{top=\text{hello}} \<\\  }  }   I think it is very complex package with no clear documentation. I am writing to ask from experts if it is better to stick to cryptocode or to use TikZ for such diagrams.  And if any one can help me with this example using TikZ i would appreciate it :-)  thanks


Form fillings through survey or feedback form and even email responses is now getting boring and appears to be a waste of time for many users to click on or even answer. I even revert to "you must fill this form to view this page" so that users can give us feedback about our app or site.  What do you think is the best strategy to present feedback contribution forms to users?

What can I do to get customers to contact me and give feedback on my application?  I sell a downloadable Windows desktop application, I also have a web application that is under development (so I'm primarily interested in solutions that are applicable to a desktop application but also want to know about web application solutions).  I want feedback from my users about my application, currently I get a tiny amount of feedback (and all feedback seems to come from the same small group of customers), what can I do to get more people to send me feedback?  What I already did:   I have a contact form on the web site, a link to that form is in the top navigation bar on every page on the site. I have my e-mail address in the footer on the bottom of every page on the site. I have a "Send Feedback" entry on the application's main menu that goes to the contact form. I have a "Tell us what you think" button in the app's about box, my e-mail address is also on the about box. I regularly post on my blog trying to encourage feedback (example: I'm finalizing the feature list for next version - if you have suggestions now would be a good time to send them to me) I also have an uninstall survey when you uninstall the app


I just tried to configure eth0 interface on my Ubuntu Server 14.04 Lts.  I want to set up static ip, therefore I put the following lines in /etc/network/interfaces:  ## To configure a dynamic IP address auto eth0 iface eth0 inet dhcp  ## Or configure a static IP auto eth0 iface eth0 inet static   address 192.168.1.111   gateway 192.168.1.1   netmask 255.255.255.0   network 192.168.1.0   broadcast 192.168.1.255   I can perfectly ping my router with this configuration. I also can connect to the server from my laptop via ssh. But internet is not working:  ping google.de ping: unknown host google.de   What could be wrong here?

I am using Ubuntu 12.04.  My /etc/network/interfaces file consists of:    # The loopback network interface   auto lo   iface lo inet loopback     # The primary network interface   auto eth0  iface eth0 inet static   address 192.168.1.58   gateway 192.168.1.1 network 192.168.1.0   broadcast 192.168.1.255 dns-nameservers 66.212.63.228 66.212.48.10     I ran the command: /etc/init.d/networking restart  Which responded with:   *Running /etc/init.d/networking restart is deprecated because it may not enable again some interfaces   *Reconfiguring network interfaces...   RTNETLINK answers: File exists   Failed to bring up eth0   [ OK ]     Next I ran ping google.com and received:    ping: unknown host google.com   I am not sure if my interfaces refreshed. How do I properly configure my network with my static DNS addresses?


Can someone spot the really quick fix to my problem? I'm trying to plot two distributions on the same figure using the Seaborn package. I'd like for one line to be red and the other blue. The way I have my for-loop set up now only produces blue lines. X and Y are 1-d arrays with data that I am plotting.  fig, ax = plt.subplots(1)  colors = ['r','b']  for a in [x, y]:     for i in range(2):         sns.distplot(a, bins=range(1, 25, 1), ax=ax,         kde=True, hist=False, color=colors[i])

How do I access the index in a for loop like the following?  ints = [8, 23, 45, 12, 78] for i in ints:     print('item #{} = {}'.format(???, i))   I want to get this output:  item #1 = 8 item #2 = 23 item #3 = 45 item #4 = 12 item #5 = 78   When I loop through it using a for loop, how do I access the loop index, from 1 to 5 in this case?


Let's suppose we have a long script: Foo.pyx If I execute it two times, they are going to run simultaneously.  How can I terminate the first one if I execute it two times?  Edit: terminating the later ones can also work, I just want only one instance to run at any time.

Is there a Pythonic way to have only one instance of a program running?   The only reasonable solution I've come up with is trying to run it as a server on some port, then second program trying to bind to same port - fails. But it's not really a great idea, maybe there's something more lightweight than this?    (Take into consideration that program is expected to fail sometimes, i.e. segfault - so things like "lock file" won't work)


I have already downloaded veil-evasion but i can't install it  $ apt-get install veil-evasion E: Could not open lock file /var/lib/dpkg/lock - open (13: Permission Denied) E: Unable to lock the administration directory (/var/lib/dpkg), are you root? $ sudo -i # cd Veil-Evasion -bash: cd: Veil-Evasion/: no such file or directory # apt-get install Veil-Evasion Reading package lists... Done Building dependency tree Reading state information... Done E: Unable to locate package Veil-Evasion

I get this error whenever I try to install programs using the terminal:  home@ubuntu:~$ apt-get install myunity E: Could not open lock file /var/lib/dpkg/lock - open (13: Permission denied) E: Unable to lock the administration directory (/var/lib/dpkg/), are you root?   Also I'm unable to install updates using the terminal.


I have a bash script that takes some arguments and uses some of them to loop over some action while some others (those of the form 'a=b') are passed to that action. Essentially, it looks like  args= numbers= for arg in "$@"; do     if [[ "$arg" == *=* ]]; then         args="$args $arg"     else         numbers="$numbers $arg"     fi done for number in $numbers; do     some_action $number $args done   So, for example, if I call it as script 1 2 3 a=b c=d, it runs  some_action 1 a=b c=d some_action 2 a=b c=d some_action 3 a=b c=d   The problem is with whitespaces. Sometimes I need to pass arguments like resume='5 8'. Once they are stored in $args, the distinction between spaces and arguments is lost, a call to script 1 2 resume='5 8' results in  some_action 1 resume=5 8 some_action 2 resume=5 8   so 8 is a separate argument. I tried to create the args string with newlines, using IFS='\n', but this somehow resulted in superfluous calls to some_action. Does anyone have an idea how to fix this?

Or, an introductory guide to robust filename handling and other string passing in shell scripts.  I wrote a shell script which works well most of the time. But it chokes on some inputs (e.g. on some file names).  I encountered a problem such as the following:   I have a file name containing a space hello world, and it was treated as two separate files hello and world. I have an input line with two consecutive spaces and they shrank to one in the input. Leading and trailing whitespace disappears from input lines. Sometimes, when the input contains one of the characters \[*?, they are replaced by some text which is is actually the name of files. There is an apostrophe ' (or a double quote ") in the input and things got weird after that point. There is a backslash in the input (or: I am using Cygwin and some of my file names have Windows-style \ separators).   What is going on and how do I fix it?


In Star Wars - Episode V:  The Empire Strikes Back, when Han is being urged not to go looking for Luke on Hoth, we hear this exchange:  RANDOM JERK REBEL GUY:  Your Tauntaun will freeze before you reach the first marker! HAN SOLO:  Then I'll see you in hell!  This clearly implies that people in the galaxy far, far away are familiar with the concept of hell.  Is there any evidence that they also have some concept of heaven?  I'm especially interested in the movies, but any source would do (although I would prefer a canonical source, Legends would be acceptable if nothing else is available).

In The Empire Strikes Back as Han Solo leaves to look for Luke Skywalker a rebel worker says     Your tauntaun will freeze before you reach the first marker.   Han replies     Then I'll see you in hell!   Is there a concept of heaven and hell in the Star Wars mythology? If not, to what is he referring?


Let $a = \sqrt{2+i}$ and $K$ is the splitting field of minimal polynomial of $a$ over $\mathbb{Q}$. Prove that $Gal(K/\mathbb{Q})$ is $D_4$.   I find the minimal polynomial of $a$ is $p(x)=x^4-4x^2+5$ and its   roots are $\sqrt{2+i},-\sqrt{2+i},\sqrt{2-i},-\sqrt{2-i}$. Let $b=\sqrt{2-i}$. So the splitting field of $p$ is $K=\mathbb{Q}(a,b)$. Also by rational root theorem, $p$ is irreducible over $\mathbb{Q}$. Thus $[\mathbb{Q}(a):\mathbb{Q}]=4$. Also $b\not\in\mathbb{Q}(a)$, and minimal polynomial of $b$ over $\mathbb{Q}(a)$ is $x^2-2+i$. Thus $[\mathbb{Q}(a,b):\mathbb{Q}]=[\mathbb{Q}(a,b):\mathbb{Q}(a)]\cdot[\mathbb{Q}(a):\mathbb{Q}]=2\cdot 4=8.$ Now since $K$ is the splitting field over $\mathbb{Q}$ of a separable polynomial, $K/\mathbb{Q}$ is Galois. Hence $|Gal(K/\mathbb{Q})|=8$. Hence the 8 automorphisms are $$a\to \begin{cases}a\\-a\\b\\-b\end{cases}\quad\text{and}\quad b \to \begin{cases}b\\-b\end{cases}.$$ From this how to conclude $Gal(K/\mathbb{Q})$ is isomorphic to $D_4$?  Thanks

I am trying to explicitly compute the Galois group of $x^4-2$ over $\mathbb{Q}$. I found that the resolvent polynomial is reducible and the order of the Galois group is $8$ using the splitting field $K=\mathbb{Q}(2^{1/4}, i)$. Hence I need to find 8 automorphisms. Thus do I just map elements of the same order to each other that fix the base field $\mathbb{Q}$ $2^{1/4}$ to $i2^{1/4}$


By default, after publishing codes, the post shows a html like this,
              some codes here
   I have plenty posts with codes and don't want to edit them one by one. How do I add a custom class attribute globally for all posts? to make it look like this
              some codes here
   Thanks in advance.

I'm trying to add a class to list blocks (core/list) in Gutenberg. Unfortunately, it looks like because some blocks like lists and paragraphs don't have the standard default class name of wp-block-{name} they can't be renamed using the  filter.  To get around that, I've used the blocks.getSaveContent.extraProps filter, which seems to enable me to add a class to ALL the blocks that don't already have classes. Code below is how I got that working. It's adding added-class-name to blocks likes lists and paragraphs and so on.   function addBlockClassName( className ) {   return Object.assign( className, { class: 'added-class-name' } ); }  wp.hooks.addFilter(   'blocks.getSaveContent.extraProps',   'gdt-guten-plugin/add-block-class-name',   addBlockClassName );   And I'm enqueuing it like so:  function gdt_blocks_class_rename() {   wp_enqueue_script(       'gdt-plugin-blacklist-blocks',       get_stylesheet_directory_uri() . '/dist/guten-addons.js',       array( 'wp-blocks' )   ); } add_action( 'enqueue_block_editor_assets', 'gdt_blocks_class_rename' );   However, what I want to be able to do is add a class to ONLY list blocks? Can that be done at all?


In Star Wars we hear certain members of the humanoids have a British accent. But since there's no planet England, where did it come from?  I have seen a young clone with a British accent in season 2 episode 20 of Star Wars: Clone Wars. His accent doesn't make sense because they were all raised together at the same place, so it doesn't make sense for them to pick up a different accent than the rest.

In the first 30 minutes of Star Wars IV, Leia has a pseudo-British accent.  As the movie progresses she loses her accent and gets a more American-tough girl accent.  Is there a reason behind this?


Currently building a new mountain bike. I'm fairly bike savvy and have built quite a few bikes over the years, but mainly road bikes.   I have installed/fitted a new Shimano slx group set and the hydraulic brake housing is very long. Lots of excess brake line around the handlebars, and when looking at other bikes in the shop they don't seem to have that problem. I'm fairly sure you can't shorten the housing, and not sure I want to have a crack at that if that is the case, so I wanted to see how other people get around this problem?

I bought and installed a set of pre-bled hydraulic brakes onto my bike to replace the mechanical discs that came with it. My future plan is to buy a new bike, transfer the brakes to my wife's bike and replace the old discs onto my bike and sell it.  In the meantime I have a very long rear line, about 30cm extra, that I'm struggling to manage. I've looped it and cable tied it on both sides of the loop, once back on itself and again to the front brake line. Unfortunately this solution slips a lot so I'm looking for a better one. At this stage performance of the brakes seems ok with this method.  Does anyone know of a better solution or is getting them shortened by my LBS the way to go?


According to  the universe is expanding with 75km/1Mpc/1s (megaparsec), which comes down to $\beta=2.43\times10^{-18}/s$, a relative rate per second.  To put this in perspective: The average distance between Earth and Sun is $149\,600\,000\, km$. Multiplying this by $\beta$ and one year, I get roughly $11.5\,m$, which means every year the Sun moves away from earth by over $11\,m$ on average, just because of the expansion of the universe (amazing enough as to think I messed up the orders of magnitude, so please check). But this is not the point. I would like to understand the nature of this expansion better.  Questions    the expansion could be measured in principle with a ruler, say a piece of metal of a given length. Is that really true or does the space inside the ruler expand with the same rate such that by counting how often the ruler fits between Earth and Sun, we would see no difference? What if we measure instead with a beam of light (ignoring relative motion for the moment) and measuring how long it takes to bounce back from Sun. Will the time be longer or is space rather like a checker board on a rubber sheet and independent how large you stretch the sheet, 8 rectangles are 8 rectangles and the light moves from rectangle to rectangle, not noticing that they are all stretched out. In (2) above, what would be the right way to measure time anyway? Let a beam of light bounce between two mirrors and count? Huh, but the distance between the two mirrors expands also, while one beam of light goes to the Sun and back, the bouncing one bounces always the same number of times independent of how much space is stretched between to measurements.   3 questions in one post may be a bit too much, so a general explanation how the expansion of space relates to (a) the size of physical objects, e.g. the typical diameter of atomic particles (1) above, and to (b) speed, wave length and frequency of light would be great.

I have looked at other questions on this site (e.g. "why does space expansion affect matter") but can't find the answer I am looking for.  So here is my question: One often hears talk of space expanding when we talk about the speed of galaxies relative to ours. Why, if space is expanding, does matter not also expand? If a circle is drawn on balloon (2d plane), and the balloon expands, then the circle also expands. If matter is an object with 3 spatial dimensions, then when those 3 dimensions expand, so should the object.  If that was the case, we wouldn't see the universe as expanding at all, because we would be expanding (spatially) with it.  I have a few potential answers for this, which raise their own problems:   Fundamental particles are 'point sized' objects. They cannot expand because they do not have spatial dimension to begin with. The problem with this is that while the particles would not expand, the space between them would, leading to a point where the 3 non-gravity forces would no longer hold matter together due to distance Fundamental particles are curled up in additional dimensions a la string theory. These dimensions are not expanding. Same problems as 1, with the added problem of being a bit unsatisfying. The answer seems to be (from Marek in the previous question) that the gravitational force is so much weaker than the other forces that large (macro) objects move apart, but small (micro) objects stay together. However, this simple explanation seems to imply that expansion of space is a 'force' that can be overcome by a greater one. That doesn't sound right to me.


I'm not sure if this is the right place for this question, but here goes.  I am often inclined to treat, without knowing if this is correct, the operators of calculus, namely $d, \frac{d}{dx},\int,\int_a^b$, as if they were "constants" that you can apply the rules of multiplication to.   So for example, I would be inclined to "multiply both sides by $dx\cdot dy$" as follows: $$\frac{y^2}{dx}=\frac{x}{dy}\implies x^2dx=ydy $$  or to "apply $\int$" to both sides as follows:  $$x^2dx=ydy \implies \int x^2dx=\int ydy$$  even though I am not sure whether $\int$ is an operator by itself, or whether $\int ...dx$ together form a single operator.   So my question is, not about whether the above particular derivations are correct, but what is the topic that one should study to learn the rules of manipulation of these operators? I'd like to really understand them, not just memorize them.   (note that I've taken an introduction to real analysis, but this focused very much on general concepts such as continuity, differentiability, integrability, without touching on the implications for the rules of manipulation of these operators)

I've read many question/answer threads here on SE re: justification for the algebraic manipulation of $\mathrm{d}y/\mathrm{d}x$ in the standard formulation of calculus. I worked up my own shot at a justification using the definition of the derivative and would like to get the input of others whether it holds. It doesn't involve pushforward maps, non-standard analysis (two things I don't yet know), or any other tool than simple limit algebra/laws, the definition of the derivative, and (implicitly), the chain rule that makes the substitution possible. If it does hold as a justification as far as it goes, i.e., in one-dimension, it would seem to me, at least, to be a simple and clear justification in the form of an example that could be useful to other beginners. If goes wrong somewhere please let me know for my own understanding.   Integrate $\int \frac{x}{1+x^2}\mathrm{d}x$.  We'll do this by substitution. We want to restate the original problem in terms of $u$. That means that we want to state $x$, $1+x^2$, and $\mathrm{d}x$ in terms of $u$. Let $u=1+x^2 \rightarrow \frac{\mathrm{d}u}{\mathrm{d}x}=2x \rightarrow \mathrm{d}x=\frac{\mathrm{d}u}{2x}$. Let's justify that last step as that's where the justification (that I speak of) is required:  By definition, $\frac{\mathrm{d}u}{\mathrm{d}x}=2x$ is defined as $$ \lim_{\Delta x \to 0}\left( \frac{u(x+\Delta x)-u(x)}{\Delta x} \right)=2x $$ Recall that the limit of a quotient is equal to the quotient of the limits as long as the denominator is not equal to zero, thus the foregoing becomes $$ \frac{\lim_{\Delta x \to 0}\left( u(x+\Delta x)-u(x) \right)}{\lim_{\Delta x \to 0} \Delta x } =2x $$ Multiplying both sides by $\lim_{\Delta x \to 0}\Delta x$ and then dividing both sides by $2x$ yields $$ \frac{\lim_{\Delta x \to 0}\left( u(x+\Delta x)-u(x) \right)}{2x} =\lim_{\Delta x \to 0} \Delta x $$ which, in the limit, is equal to $$ \frac{\mathrm{d}u}{2x}=\mathrm{d}x $$ Rearranging we have $$ dx=\frac{\mathrm{d}u}{2x} $$ as desired.


What is the highest polynomial degree that has an application in real life, and what is that application? My google search yielded 3rd degree at most.

What polynomials occur in "nature"? I am interested in polynomials of degree three and higher. I am aware of  and .  Edit:  There are some formulas under  category.   I am particularly interested in full polynomials, as opposed to pure power laws. For example $y=at^2+v_0 t + y_0$ for a projectile uses a complete polynomial, while Boltzman law is just a power law.


Problem      Let $A$, $B \in M_n(\mathbb{C}),$ $C=AB-BA$. If $CA=AC$, then $C$ is   not invertible.   To prove a matrix is not invertible, I only came up with $2$ ideas, one is to find a nonzero vector $v$ such that $Cv = 0$, and the other is to prove that $\det C = 0$. However, I have no idea how to use the condition $CA=AC$, so I don't know how to deal with $\det (AB-BA)$.  Is there any other criterion for invertibility of a matrix that is helpful to solve this problem?  I would like to prove $C$ is not invertible, rather than the stronger result that $C$ is nilpotent, so basically this is not a duplicate of another question.

I saw this in a  and am putting it here for posterity.  Problem: Let $A$ and $B$ by square matrices and set $C=AB-BA$. If $AC=CA$, prove $C$ is nilpotent.


I have a laptop that was shipped with Windows 7. For some reason, the PC was always extremely slow with Windows 7, so on one day of frustration I took a spare drive and installed Ubunto into it. However, even though the performance was great, we kind of missed having Windows on that PC (full MS-Office compatibility, Amazon Prime Video in HD, among other details that only work on Windows).   When I heard about the free upgrade to Windows 10, I decided to delete the Ubuntu drive and install the Insider Preview. The laptop now runs quite smoothly, better as new. However, I am wondering how the upgrade process would be in this case:   I could install the old drive and click the icon after running all the upgrades, but I have no interest on upgrading to Win10 over the old Win7 installation, it is just too full of HP-Bloatware, I want a clean install. Is or will there be any way to get a Win10 key using the product key from Windows 7?

Is there any information about if Windows 10 Technical Preview will then be upgradable to the final release ?  I'm asking that because I would like to use it on my primary PC (I'm aware of the risks but I accept them), in place of Windows 8.1 But I'd like to avoid to reinstall all after the release of the final version.


If $f$ is an entire function on $\mathbb{C}$ such that $|\operatorname{Re}(f(z))|\leq k|z|^m$, for all $|z|$ sufficiently large, for fixed positive real $k$ and natural number $m$, then $f$ is a polynomial of degree not exceeding $m$.

Let $f$ be an entire function such that $|Re(f(z))| \leq |z|^n, \forall z$   where $n$ is a positive integer.  Could anyone advise me how to show $f$ is polynomial of degree at most $n \ ?$  Hints will suffice, thank you very much.


Apologies if this is a simple question, this is my first time here, and I am a noob at statistics. I have a series of numbers and I want to find cutoff points that clearly separate, or group, the data.  Say I have this data:    You can see it is clearly grouped into two groups, the large values, and the small values.  (Maybe 3 groups, with that first positive value being a group of its own.)  Is there any algorithm to determine these groups automatically/programmatically?

The following describes what I'm trying to accomplish, but it's possible an alternative problem statement can describe my goal:  I want to    divide the following numbers into groups where the variances of the numbers within each group are not too large, and the differences between the averages of groups are not too small  compare the distribution obtained in the end with the "perfect" ones and see how "different" it is from being perfect.     Layman's explanation of goal  , and determine the "income brackets" each population is in.  The income bracket is supposed to be self-adjusting based on the input data.  My goal is to ultimately measure or calculate the difference between the income brackets.  I assume there will be many brackets, and want to see how far "apart" each tier is.  Here is a sample of hourly income for a sample set of a population of 20, and a total income of 3587:  Population= 10                   pop=2   population=5              population =3 10, 11,13,14,14,14,14,14,15,20,  40,50  ,90,91,92,93,94      999,999,900    How can I use mathematical concepts to group, sort and analyze data that acts like income distribution over a given population?  At the end of the calculation, I want to determine tiered income distribution, where a perfect distribution would look (something) like this   (each person makes $10 more per hour than the previous; total is 3587) 89, 99, 109, 119, 129, 139, 149, 159, 169, 179, 189, 199, 209, 219, 229, 239, 249, 259, 269, 279   or this:   (evenly distributed groups of people make the same per hour)  (gaps between income groups is consistent and not "too far") (income total is 3587) 99 99 99   129 129 129   159 159 159   199 199 199  229 229 229  269 269 269    Question  How should I analyze the population groups, and measure the gap in a way that will tell me how much is needed to make it more like the last two model sets listed above?


Newbie here.   Im trying to learn Python and work with datasets, ive kinda got thrown into the deep end at work. The language is clearly very powerful but very different to anything else ive experienced before.   I need some clarity / help / explanation on the following please.  Partial Algo code  history = data.history(context.stock_list, fields="price", bar_count=300, frequency="1d") hs = h.iloc[-20:] p = h.iloc[-1]   What is Difference Between 3 Variables Shown?  hs1 = history.iloc[:20]    hs2 = history.iloc[20:] hs3 = history.iloc[-20]   history creates a data sets of 4 asset prices, as can be seen from image under "additional info"  Ive researched and learned data iloc is a    However what I do not understand is the [:20], [20:], [-20] indexes(?) attached to iloc function in the 3 example variables shown above  Questions   hs1 = history.iloc[:20],  According to my research following  on pandas dataframe hs1 = history.iloc[:20] singles out deletes the first 20 columns within the dataframe, is this correct? hs2 = history.iloc[:20]  What is difference to above variable? hs3 = history.iloc[-20] Why a minus - and no : inside the index?   Additional Info  History variable creates dataset of 3 assets    Hope this makes sense, please comment if you need any additional info any help and advice much appreciated.

I need a good explanation (references are a plus) on Python's slice notation.   To me, this notation needs a bit of picking up.   It looks extremely powerful, but I haven't quite got my head around it.


I am using  for a project on converting analog signal to digital signal. It has a built in multiplexer which we have to use to provide an analog signal to one of the pins. However what happens is:   Sometimes it latches to a particular value say 1000000 and remains at there no matter how many times start of conversion is pressed which should set the inner counter to 0. Sometimes it gives slightly wrong output off by 100 or 1000 and when I press start of conversion, it gives correct output, so its not reliable every time. And most seriously, suppose the control for multiplexer according to datasheet are such that input pin 1 should be active, instead, it works only when the input is given to pin 5 for one particular IC and pin 3 for other.   Since the frequency of 555 clock is 33Hz I thought switch bouncing would be not a concern, hence avoided it.  I have been trying to fit it in logic since 3 days however each day some new error happens. I have replaced it twice from my college lab and now the technician doesn't want to replace it anymore . What is amiss here ?    This is the circuit design taught to us for the similar ADC0804:  Since it doesn't use capacitors I ignored decoupling capacitors.

I am using  for a project on converting analog signal to digital signal. It has an inbuilt multiplexer using which we have to provide an analog signal to one of the pin. However what happens is ;  Sometimes it latches to a particular value say 1000000 and remains at there no matter how many times Start of Conversion is pressed which should set the inner counter to 0.  Sometimes it gives slightly wrong output off by 100 or 1000 and when I press Start of conversion, it gives correct output, so its not reliable every time.  And most seriously , Suppose the control for multiplexer according to Datasheet are such that input pin 1 should be active, instead, it works only when the input is given to pin 5 for one particular IC and pin 3 for other. I have been trying to fit it in logic since 3 days however each day some new error happens. I have replaced it twice from my college lab and now the technician doesn't want to replace it anymore . What is amiss here ?


I've been working on something that uses lots of blockdata commands. It was all going well until I needed to put a enchanted book that works with anvils into the command so that I could get it out of the chest above and be able to use it to enchant something with efficiency v but I don't know how to make it work. Here is the command so far:  /blockdata ~ ~3 ~ {Items:[{id:403,StoredEnchantments:,Count:1,Slot:0}]}   When I put in the correct stuff for StoredEnchantments it doesn't appear. What I'm trying to do is make this command into a blockdata command where the enchanted book will appear in the chest instead of my inventory:  /give @p minecraft:enchanted_book 1 0 {StoredEnchantments:[{id:32,lvl:5}]}

I am making a Minecraft Mini Game adventure map, and one of the levels has a /setblock command, I am using the command in a way to spawn an item in a chest (Wooden Button) I need the wooden button to have CanPlaceOn tag so it can be placed on a log. I have tried this command: setblock 294 5 -1251 minecraft:chest 0 replace {Items:[{Count:1,Slot:0,id:minecraft:wooden_button,CanPlaceOn:[log]}]}`


In the isosceles triangle $ABC$, $M$ is the median of $HD$ and $AH$ is perpendicular to $BC$ and $HD$ is perpendicular to $AC$. Prove that $BD$ is perpendicular to $AM$.

I need a synthetic proof on this problem without the use of trigonometry.     Question: Let $ABC$ be a triangle with $AB=AC$. If $D$ is the midpoint of $BC$, $E$ the foot of perpendicular drawn from $D$ to $AC$ and $F$ the midpoint of $DE$, prove that $AF\perp BE$.    The proof is very easy using coordinate geometry.    I'm stuck at: Since point $F$ is midpoint of $DE$, it is fixed and is not a trivial information. But I can't see a way to use this information.


I've seen multiple ways on how to solve it online (and most likely the majority are wrong), but I don't know how to solve this fully so that I could get the full grade during my exam.  The question is as follows:     Prove that if $\sum a_n$ is convergent with $a_n > 0$ for all $n$,   then $\sum a^2_n$ is also convergent.   I understand that the starting point to prove this is that $\lim a_n =0$, but after that I really don't know what I'm supposed to say.

Let $(a_n)$ be a sequence of positive terms and suppose that $\sum_\limits{n=0}^{\infty} a_n$ converges. Show that $\sum_\limits{n=0}^{\infty} a_n^2$ converges.   This is in the section on the Comparison Test so that must be what I'm supposed to use.  But I don't see how.  $(a_n)^2$ might be smaller or larger than $a_n$ depending on $a_n$.  And I can't use the Comparison Test with some other series because there's no info here about how fast $\sum a_n$ converges.  Hmm.  Any hints?


Which one is correct: 'The first two quarters of current financial year' Or 'The first two quarters of the current financial year'

"The new laws are seen as an attempt to gag the press." In this sentence why the definite article 'the' is used before 'laws'(noun). I always get confused when to use 'the' and when not to. My teacher taught me, it is used when both speaker and listener are aware of what they are talking about i.e. both of them are familiar with that(noun). Can someone please clarify this? I have a feeling that I should've used 'the' before 'speaker' and 'listener' in the above sentence. Am I right?


As I understand it,  is a service that'll let you skip to the front of the line. To get it you have to go to an enrollment center and have your biometrics taken. It's my understanding that this visit to the enrollment center does not need to be scheduled.  I have a few questions about how it works.   Can I just get to the airport early and do it before my flight? Or would I be better of taking a half day of vacation and taking care of it, myself, a few weeks before the flight? Does CLEAR work at all hours? Like let's say I have a flight that departs the airport at 11pm. The airport in my hometown does have a few scant flights that depart at that time but, by and large, all the shops are closed and TSA is basically a skeleton crew at that point. If it wouldn't work then at what times would CLEAR work? Is there a website that'd list the hours for CLEAR? There are a few promo codes for CLEAR floating around the internet.  has two. idk if they're still valid (the post I linked to is over a year old) but let's say they are. Can I use them if I choose to register in-person as opposed to online? What if my trip isn't for six more months. How soon before the trip should I register? Like if I register right now - a full six months before my trip - could I still get my biometrics taken when I'm at the airport about to catch my flight or will I need to get my biometrics taken before?   Thanks!

TSA Pre-Check and Global Entry allow passengers to more or less avoid the full-body (millimeter wave) scanners and instead use metal detectors.  You also don't have to take off your shoes or take out your laptop.  This is an important benefit to many of us -- even more important than cutting the line. But TSA Pre-Check and Global Entry are only offered to US citizens, permanent residents, and . The rest of humanity is SOL.   seems to offer a solution as you only need a USA driver's license to apply, which means F1 students or H1B workers from any country, for example, are eligible.  But I'm unclear about the benefits of CLEAR. Do you  get the same pre-check benefits such as avoiding the full-body scanner if you don't have TSA Pre-Check? If you don’t, is there really that much benefit?


It would be great if I have two passwords to my account, so that if I forget one, I can still login without much trouble.  Is it possible to do this?  By "two passwords" I mean two login passwords...

I'd like to join three ideas into one interesting and sometimes useful feature. There was a question about using multiple passwords earlier this year, but it didn't receive much attention. I'd like to ask the question again after showing an interesting and new way to use the feature. The three original posts I found to be interestingly combined were:        Basically I'd like to login to my account with two passwords and depending on the password I use, I would get a different content in my home directory. In a way I would get a cryptographically hidden account into my system. So the question is, is it possible to allow multiple passwords to log on to Ubuntu/Linux for the same user?


A field embedding from K to K is an injective homomorphism. What is an example of a field embedding which is not surjective (and therefore not an automorphism)?

Can we find a field $K$ and an endomorphism $f$ of $K$, such that $f$ is not trivial and $f$ is not surjective? In other words, can we find an endomorphism of $K$ which is not an automorphism?


I'm trying to prove that  $$ \sqrt{2\sqrt{3\sqrt{4\cdots\sqrt{n}}}} < 3 $$  for any $n$ and have decided to use strong induction and instead just show that  $$ \sqrt{k\sqrt{(k + 1)\cdots\sqrt{n}}} < k + 1 $$  for any choice of $k$. Does anyone have an idea on where to proceed from here?

Problem: prove $\sqrt{2\sqrt{3\sqrt{\cdots\sqrt{n}}}}<3$ by induction. I tried some, but stopped in $\sqrt[2^n]{n+1}$. Also tried with $2\sqrt{3\cdots}<3^2$ and so on.


I am Egyptian; I have a valid US visa and I am travelling from the US to Dublin through London Heathrow. My layover is just 1:25 hours, and I need to change terminals (Terminal 3 to 2) at Heathrow, and I don't need to claim baggage.   My Irish visa is not BC/BC BIVS biometric endorsed. Do I need a UK transit visa?

Is there a website or some other way to find out if I need a transit visa for a short stop in the UK on my way somewhere else? Ideally this should give me the answer for all nationalities, and take into account any other visas I may have.


The collection of fonts available to a web developer is depressingly limited. I remember reading long ago about TrueDoc, as a way of shipping fonts alongside a website - but it seems to have languished. Has anybody used this, or something similar? Is it supported by enough browsers? Am I missing a good solution?  Note that a responsible web developer does not use fonts that are only available on Windows (and especially ones that are only available on Vista), nor do they use a technology that isn't supported by at least the majority of browsers.    Update: As several people have pointed out, there's nothing wrong with providing a list of fallback fonts for people who don't have the specific font you use. I do in fact always do this, and didn't mean to suggest that this was wrong.  While my question was badly phrased, what I meant was that a designer should not make too many assumptions about what the client will have available. You should plan for how all users will see your site, not just for people using your own preferred setup.

I'm trying to figure out a decent solution (especially from the SEO side) for embedding fonts in web pages. So far I have seen , which doesn't even work on Firefox, and . The second solution is for titles only. Is there a solution available for full text? I'm tired of the standard fonts for web pages.  Thanks!


I am trying to install mongodb on my laptop with Ubuntu 16.04 LTS. When I executed this command  echo "deb [ arch=amd64,arm64 ] http://repo.mongodb.org/apt/ubuntu xenial/mongodb-org/3.4 multiverse" | sudo tee /etc/apt/sources.list.d/mongodb-org-3.4.list   this error showed up:   sudo: unable to resolve host architect   Note: I have tried with [ arch=i686,i686 ] which is my pc architecture. What's the problem?

And when I tried the following commands /etc/hostnames and /etc/hosts, it says:  bash: permission denied.


In Windows Task Manager, when displaying the Details view, there is a process conhost.exe, whose Command line is shown as \??\C:\Windows\system32\conhost.exe 0x4. What does the prefix \??\ mean? I am aware of the prefix \\?\, which allows longer paths and special characters, but I assume this is something distinct.

This is about the registry on a 64-bit Windows 7 Home Premium (my friend's computer). I was going to set the system to clear the pagefile at shutdown by setting the REG_DWORD value ClearPageFileAtShutdown in HKLM\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management to "1".  My question is however about the questions marks in the values ExistingPageFiles and PagingFiles in this registry location.  The question marks are shown in below image.    The questions I wanted to ask are:   Are the paths used in these values supposed to have questions marks in the beginning? What function do these question marks serve?


My Samsung monitor has the following Color Modes Cool 2 Cool 1 Normal Warm 1 Warm 2  With factory settings, the monitor has a minor red tint; if I switch to Cool 1, it looks normal; whites look white. Calibration Question When setting White Point in Spyder3 Elite, I have the following choices. If Cool 1 looked normal (eliminating the reddish tint), should I "dial in" that setting on this screen? If so, what does Samsung Cool 1 correspond to on Spyder's White Point scale?  UPDATE I set the monitor to Cool 1, Spyder to 7500k, ran calibration, colors look great, though based on the profile, I'm not sure why White Point shows no difference between uncalibrated and calibrated.

I've got the Xrite Eye One Display 2, and tried the advanced calibration today for the first time.  It asked what white point I wanted, and had a default of 6500K.  I didn't realize that was up for discussion!  I would have assumed the daylight temperature, around 5500K, would be desired.  What temperature do I want my whites to be? Why can't white just be white?!


I have a small table of 10 cities (in one table) that I am snapping to the nearest road (in another table) with the following select and storing the table snapped_cities:  Select b.id, ST_Closestpoint(ST_Collect(a.geom), b.geom) as geom into snapped_cities from roads a inner join cities b on ST_Dwithin(a.geom, b.geom, 1000) group by b.id;   I would however like to have road ids and not just the geom (a.id above). How do I modify the select above to get these?  I use postgresql 9.2 and postgis 2.0  thanks,


I am new to C and I want perform this task: declare and initialize a string and then reassign each string element to a new value.  Writing the code in this way:  char *str = "geeksforgeeks\0";  for (int i = 0; str[i] != '\0'; ++i) {     str[i] = 'a'; }   throws a segmentation fault.  But if I write the code in this manner:  char string[] = "geeksforgeeks\0"; char *str = string;  for (int i = 0; str[i] != '\0'; ++i) {     str[i] = 'a'; }   the program behaves correctly.  Also this code:  char str[] = "geeksforgeeks\0";  for (int i = 0; str[i] != '\0'; ++i) {     str[i] = 'a'; }   behaves correctly.  What is the difference between the two? Should't be equivalent?

The following code receives seg fault on line 2:  char *str = "string"; str[0] = 'z';  // could be also written as *str = 'z' printf("%s\n", str);   While this works perfectly well:  char str[] = "string"; str[0] = 'z'; printf("%s\n", str);   Tested with MSVC and GCC.


How to horizontally center the elements inside "scoreBox" ?  They are currently just left aligned.    .voteButtons {   display: inline-block;   text-align: center; }  .HP {   display: inline-block;   text-align: center;   width: auto !important;   margin-left: 5px !important; }  .scoreBox {   display: flex;   margin-top: 10px;   padding-top: 10px;   text-align: center;   width: auto !important; }

     <%= post.upvotes - post.downvotes%> score

I'm trying to horizontally center a <div> block element on a page and have it set to a minimum width. What is the simplest way to do this? I want the <div> element to be inline with rest of my page. I'll try to draw an example:  page text page text page text page text page text page text page text page text                -------                | div |                ------- page text page text page text page text page text page text page text page text


Is there an argument, apart from experiments, that we know this is true?   And if we only know it by experiment, how do we know the experiments are precise enough to conclude this?  Stated differently, what argument is there that prevents us from replacing c in the Lorenz transformations by $c' = c + \epsilon$

I will try to be as explanatory as possible with my question. Please also note that I have done my share of googling and I am looking for simple language preferable with some example so that I can get some insight in this subject.  My question is what is so special about $c$? Why only $c$. Its like chicken and egg puzzle for me. Does Einstein reached to $c$ observing light or does he got to light using some number which turned out equal to $c$.   Why is $c$ not relative. If something has zero rest mass like a photon why they only travel at $c$ in vacuum and not with $c+1$ or $c-1$?


I can't join my iPod to my iPad with the latest version of mcpe I was wondering if The message came up to you :logged in at at her location ?

I am having trouble getting onto a server in Minecraft PE on iOS. When I tap on the person's server it just says invalid name:    I have tried turning off and restarting the iPad, going to home screen and logging back into the server but I have had no luck and no change. Is there a reason why this is so?


I notice that on many examples one is keen to convert Age to a categorical age range. I am wondering if that is always necessary. The famous golf play decision tree example has ranges for temperatures up-front. I would have thought from other examples the golf play with actual temperatures would give near enough the same predictions. I am going to test that in the next free time slot. I am looking at a diabetes case in which the example states let us "bin" the ages. To me the age is an automatically in its own right ordinal attribute and I would have thought tat for logistic regression we would not need to bin / categorize it. Age has a limited range.

I'm wondering what the value is in taking a continuous predictor variable and breaking it up (e.g., into quintiles), before using it in a model.   It seems to me that by binning the variable we lose information.   Is this just so we can model non-linear effects?  If we kept the variable continuous and it wasn't really a straight linear relationship would we need to come up with some kind of curve to best fit the data?


Ok so this is what the output looks like in the PDF document:    But this is what the input looks like in Lyx:    As you can see, the symbols that show up while writing in the Lyx document are completely messed up, the \nabla symbol shows up like a bold N, the minus sign shows up as "lyxminus" in red letters... Like what is going on here? Am I missing a package or something?  I'm using Linux Mint 19 and Lyx 2.3.0.

I updated LyX to 2.3.0-1, and found that LyX was displaying all the "-" characters in Math Mode as "\lyxminus". No such problem occurs when entering outside of Math Mode. LyX also seems to have no problem compiling to TeX, and the PDF output looks normal.  I removed and re-installed LyX, and this issue was still there.   Does anyone have any ideas on what might be going on? I am using Linux Mint 18.2 Sonya.  Note: I previously saw this question ask about the same thing, but the author appears to have deleted their post:


I just got an inbox notification asking me to vote in the community moderator primaries. It seems a big part of the community moderator role is processing flags (see also )  My question: are moderators really the right people to process flags? Couldn't we / SO's bots identify people with large scores (>10k?) for questions with specific tags, and delegate this responsibility to them for that tag? Seems to me that they have earned the knowledge and standing for this role.

there are certain tags where the current moderators, as a group, are not, currently, "active". Active being defined as all moderators, as a group, have posted more than 30 questions or answers in the past year. Disclaimer: Obviously this doesn't disqualify the current moderators from being able to act in an appropriate manner on other tags and I'm fairly certain they would be asking and answering less now that they have to deal with all the flags. It's also not to say that the current moderators don't know more than the nominees about these tags; just that they haven't been posting much in them recently. However, there are a number of common tags where the current nominees, as a group, are active and the current moderators are not. Notably the following:  TagName        Nominees -------------- --------  database       41        performance    25        vb.net         78        image          31        json           56        visual-studio  22        android        165       asp.net-mvc-3  62        c              86        silverlight    22        xcode          22        ajax           81        asp.net-mvc    54        multithreading 28        c++            238       facebook       258      When joined against the current list of nominees this list returns everyone! Which was a little surprising but a great indication of the diversity of the nominees.  (making it look really awful) there are several nominees who are individually "active" in tags that the current moderators are not (in no particular order)                                  ,                            ,   Does any of this matter? Is it wiser to have moderators that add to the collective knowledge of the current ones? Even taking this into account there's still some noticeable "gaps" in both the current moderators and the nominees "expertise" Second disclaimer: I actually intend on casting one of my votes for someone not on this list so I'm going to partially ignore it!


I thawed steaks in the frige and added soy sauce to marinade them..they were in the frige for 2 days..I didn't use the steaks and so I refroze them.  Is it okay to thaw them and serve them?

I've often been told by people that I shouldn't refreeze meat (particularly hamburger meat) once it has been thawed.  However, this seems a little silly to me.  I can't imagine how meat that hasn't been bought fresh and local could find its way to my kitchen with out thawing and being refrozen a couple of times.  How much damage can one more thawing and refreezing really do?  Can it really be that dangerous disease wise? Or is this just one of those urban myths?


I used an  for, uh, calculating the spoke lengths that I need. The results of the calculator are as follows:  Front  Left - 276.5mm Right - 277.8mm   Rear  Left - 275mm Right - 273.4mm    The rims are WTB KOM Tough i35 27.5" with an ERD of 568mm. The hubs are Shimano XT M8110-B. Thing is, LBSs here only have limited lengths for different tire sizes. For 27.5", they only have 270mm and 275mm. Will the 275mm work for my wheels or should I just go look for the correct lengths online?

I'm building a rear wheel for the first time. I have purchased the rim and hub and am now sourcing the spokes. I put the measurements into an online spoke calculator (on wheelpro.co.uk) and it estimated 295mm and 293mm for the right and left side respectively.  Now I can find 295mm spokes but, so far, I haven't been able to find a 293. I will keep looking, but I have two questions:  1)  How precise do the spoke lengths need to be. If they are out by a millimetre is it likely to cause a significant problem?  2) If they are out by 1-2mms, is it better if they are too long or too short. So if it turns out to be impossible to get a 293mm, would a 294mm or a 292mm be a better alternative.  Many thanks in advance.  Chris


I just had nothing to do and started messing around with for loops in Java, so I wrote the following function  static int getCurrentTime() {     return (int)System.currentTimeMillis(); }   which simply gets the time for me.  Now I have my main function:  public static void main(String[] args) {     int s = 0;     int beginTime = getCurrentTime();     for (int j = 0; j < 2000000000; ++j)         for (int i = 0; i < ####; ++i)             s++;      System.out.println("done in " + (getCurrentTime() - beginTime)+                        " milliseconds!"); }   Now when I put 1 in the place of ####, I get the following output  done in 4118 milliseconds!   But when I put 3 in the place of ####, I get the following output  done in 11 milliseconds!   How is this possible? How did more iterations take less time? I'm really confused about what's happening here.

How do you write (and run) a correct micro-benchmark in Java?  I'm looking for some code samples and comments illustrating various things to think about.  Example: Should the benchmark measure time/iteration or iterations/time, and why?  Related:


I would like to know what the correct way to indicate a singular/plural pair is when the singular ends in -y and the plural in -ies.  With book you can use book(s) to indicate in writing how to form the plural from the singular, but with party, would you use party(ies) or party(s) or something else?  Is there a reference where rules are provided for this?   deals with this ‘optional (s)’, but does not mention how to add the (s) if a change in the base word also has to occur.

Sentences constructed with a word written in the singular and parenthetically in the plural are straightforward when that word does not end in -y, e.g.:     List all applicable employee(s).   How does one handle words ending in -y? Is this correct:     I will attend the party(ies).


Ryanair luggage policy has recently changed. Before I could take two bags, so if I bought something at the airport I would just put it in my luggage. Since I am now only carrying a small backpack I would like to know if they allow stuff bought at the airport as a second bag.  I've seen it before (some time ago) stated in some shops that this would be allowed. I am not sure if that applies to all airports/shops though and if the recent policy change didn't change that aspect as well.  Does ryanair allow an extra bag if bought at the airport shops?  Note: By extra bag I don't mean travel luggage/trolley bought at the airport but just a plastic bag with bottles, tshirst, etc or something equivalent. Not necessarily bought at the duty free.

I  that Ryanair now allows carrying a bag of airport purchases ("duty free") in addition to one carry-on bag, but only in certain airports.  In which airports?


Given a positive integer $k$, I'd like to be able to compute the set of positive integers $m$ such that $m$ is prime to precisely $k$ positive integers less than $m$. In other words, I'd like to compute the set $\phi^{-1}(k)$, where $\phi$ is Euler's totient function.   We could compute this by brute force using one of the lower bounds for $\phi$ to find an $N$ so that $n \geq N$ implies $\phi(n) > k$ and then we could test all $m < N$ to see if $\phi(m)=k$, but is there are smarter way to compute $\phi^{-1}(k)$?

Let $\phi(n) $ is the numbers of number that are relatively prime to n.   Then, how could we solve the equation $\phi(n) = k, k > 0?$   For example:    $\phi(n) = 8 $  I can use computer program to check all numbers that are relatively prime to $n$, but I think there must be an easier way to approach this problem.    Base on this formula: $$\prod_{i=0}^{k} p_{i}a^{a_i} $$ The only thing I can see is n must not have a prime factor > 9, otherwise $\phi(n) > 8 $. I really don't know where to start :( ? A hint would be greatly appreciated.


The site listing for Stack Overflow looks odd in my site list, perhaps because of the weird main-meta relationship that Stack Overflow and Meta Stack Overflow have.  Assuming the indentation is just there supposed to indicate the relationship (which admittedly is a bit unclear), could the reputation at least be displayed in this case since it's different than on the corresponding linked site?

EDIT Dec 4 -  We're doing it live! Please post bugs or concerns as questions tagged [top-bar]  We have rolled out our 95% completed top bar for feedback.  Note:   We are still adding a few final features, so if you have a request for a feature that is not there you might hold off on that for a day or two Yes, the bar is black1. Also give that a day or two to sink in.   I also want to specifically address the meta/main/chat links.  I'm very aware that many of you like having the links at the top of the page and that this new version is different.  The thought process behind moving these links is that the "site switcher" should be an automatic place to go when you are on a site and want to go to another one. If you haven't already developed the muscle memory for these links, getting between them required a bit of a cognitive load: You must first decide that you want to switch sites and then you have to decide which area to go to to switch.  Also, we find that less familiar users aren't entirely clear what a standalone link that says "main" or "meta" actually does... Not to mention that it hurts my UX sensibilities that we are dynamically changing links in an element that should be fixed.  It is true that we have added a click in the process, but we have also removed a lot of clicks for other common actions that are much more frequent than switching between main and meta.  All I ask is that you give it a few days and see if the new "switch sites at the top left" paradigm grows on you.  What do you think?  1.  points out that technically it's not quite black.


Tell if the point A(x,y) lies inside the triangle formed by the points P(a,b) , Q(c,d) , R(e,f) .  I can solve this by finding the sum of the areas of the triangles - APQ , AQR , ARP and comparing this with the area of the triangle PQR. But it takes a good amount of time (which is not good for M.C.Q based exams). Is there any cleaver way to solve this?

Is there an algorithm available to determine if a point P lies inside a triangle ABC defined as three points A, B, and C? (The three line segments of the triangle can be determined as well as the centroid if they are needed.)  Grid space is defined as Screen Space, that is, 2D Cartesian with the Y-Axis flipped so "up" is negative y and the origin is the upper left corner.


On Stack Overflow:    On Area 51:    Why is there no edit communities button in Area 51?  That should be added.

I can edit "YOUR COMMUNITIES" in the upper left drop-down menu from any of my communities: (e.g. )    But in  portal there's no "edit" link:    Why is that and how can I edit the list in  portal?


I need to prove that if $A$ is a square invertible matrix then $AA^\top$ ($A$ multiply $A$ transpose) is positive definite.  I tried to prove that all the eigenvalues are positive. I know that $AA^\top$ is symmetric, and its determinant is positive, and trace is positive.   Therefore: product of eigenvalues is positive , and sum of eigenvalues is positive.  In addition $0$ is not an eigenvalue. That's what I know so far but I still cannot conclude that every eigenvalue for itself is positive. What have I missed? Thanks!

Say if $A$ is an $n \times  n$ matrix, why is it that if $A^{T}A$ is positive definite, the matrix $A$ is then invertible? All I know is $A^{T}A$ gives a symmetric matrix but what does $A^{T}A$ is positive definite tell or imply or hint about the matrix $A$ itself that leads to the fact that it will be invertible?


I want to ask, is it possible to change camera focus in Blender? For example, I want the camera to focus to an object. So the other objects behind the focused object have a blur effect. How to do that? Thanks for the reply :D

I'm creating some studio-shot style images of products. I'm trying to get the foreground elements in focus while having the background blur slightly.  I've done a lot of real world studio photography and I know that depth of focus and depth of field are two different parameters (though frequently confused). Put simply, depth of field references the precise centre of the plane of focus as parallel to the image plane, while depth of focus reference the sum of the distance on either side of this plane that remains in focus.  But 2.6x only seems to offer control of the depth of field, so that only that exact plane is in focus, and everything either side gradually defocusses. Or am I missing something?  The point is, I want to know if there is a way to control the z-depth of the area in focus, not just it's distance from the camera.


For my science homework, a question came up asking how many species can have the same scientific name. I'm pretty sure that each species has a different scientific name, but just to be sure...

Since binomials are required to be unique only within a kingdom, two species can share the same binomial name if they are in different kingdoms. I know of one instance of this, Orestias elegans: this name denotes  (kingdom Animalia) as well as  (kingdom Plantae).  Are there other instances where one binomial name validly refers to two (or more!) species?


We recently started seeing SQLVDI and MSSQLSERVER errors poping up on a number of our machines.  Shortly after event 3197 (I/O is frozen on database x), we start seeing SQLVDI 1 errors (signal abort) and MSSQLSERVER 3041 errors, failure to complete the command BACKUP DATABASE. We run our backups once daily, and looking at our DB backups, they restore fine and are not corrupt.  But batches of these errors are happening throughout the day, with no logs of our maintenance plans attempting to run at those times.  Even stranger, we are seeing these errors occouring on machines that do not have SQL Server 2012 installed.  Any ideas as to what might be causing these errors? or if they can be passed off as nuisance errors?

We have an instance of SQL Server 2008 installed on a customer server. The customer's IT department is in charge of the various backups of the machine.  The SQL Server log shows there is a full backup every day at 7 PM but we can't find evidence of any plan scheduled in SQL Server.  The technicians we contacted couldn't tell us if there was some sort of automatic backup, all they told is that the entire machine is being backup up.  Using a script I found in  I found out that the physical device name is a GUID and that this means that this is an external backup process:  USE [msdb] GO  SELECT      [bs].[database_name],      [bs].[backup_start_date],      [bs].[backup_finish_date],      [bs].Server_name,     [bs].user_name AS [BackupCreator] ,     [bmf].physical_device_name FROM msdb..backupset bs   INNER JOIN msdb..backupmediafamily bmf ON [bs].[media_set_id] = [bmf].[media_set_id]  ORDER BY [bs].[backup_start_date] DESC   This is a row from the above query:     db_name 2015-09-16 19:01:23.000   2015-09-16 19:01:28.000SERVER_NAME  NT AUTHORITY\SYSTEM{424F084A-F35D-4A66-8FC7-072268A89A77} 5   Moreover the backup start and finish date spans only for 5 seconds, so I guess it's clear it's not a job of sql server.  This is a line from the log:     2015-09-03 19:02:30.71 Backup   Database backed up.   Database: db_name, creation date(time): 2012/10/12(20:52:11), pages dumped: 3290021,   first LSN: 276028:152755:172, last LSN: 276028:152827:1, number of dump devices: 1,   device information:   (FILE=1, TYPE=VIRTUAL_DEVICE: {'{95380B0A-D50B-408F-B95F-1AB8975BA7F8}5'}).   This is an informational message only. No user action is required.   So, since they can't help us what can I do to track down the process responsible of the backups? We need this because we want to coordinate the backup in an ordered manner, and do the transaction log backups too in order to keep the log at a reasonable size (now we do shrink the log every week, and this is not the good way to go).


I am new to complex numbers and wondered, what is $i^{(1/2)}$ and how do I actually create a complex number, so that $i$ has a different power than $1$ in tuple form, like $(a, b) = a + b*i^2$? Is it just $(a, bi)$?

If $i=\sqrt{-1}$, is $\large\sqrt{i}$ imaginary?     Is it used or considered often in mathematics? How is it notated?


I was given a solution to include "Chapter" before my section entries in the ToC, however the number of the section does not get transferred to the ToC! For instance, in the MWE below, the sections are called "Chapter 1 \break Section One" and "Chapter One \break Section Two", however in the ToC, the sections are listed as "Chapter Section One" and "Chapter Section Two", and thus omitting the section numbers. I'd like to include these section numbers in the ToC.  Thanks!  \documentclass[12pt]{article} \usepackage[utf8]{inputenc} \usepackage[english]{babel} \usepackage[showframe]{geometry} \usepackage{titlesec} \usepackage{titletoc}  \addto\captionsenglish{ \renewcommand*\contentsname{\centerline{TABLE OF CONTENTS}}}  \titleformat{\section}[display]% {\null\vskip1em\sffamily\bfseries\filcenter}{Chapter \thesection}{0em}{}[] \titleformat{name = \section, numberless}[block]% {\null\vskip1em\sffamily\bfseries\filcenter}{}{0em}{} \titlespacing*{\section}{0em}{1em}{1em}  \titlecontents{section} [7em] % ie, width of contentslabel + 0.5em {\medskip} {\contentslabel[\MakeUppercase\chaptername~]{6.5em}}%\thecontentslabel {\hspace*{-6.5em}} {\titlerule*[0.5pc]{.}\contentspage}  \begin{document}  \tableofcontents \newpage  \section*{An Unnumbered Section} \addcontentsline{toc}{section}{An Unnumbered Section} \section{Section One} \subsection{A first subsection} \section{Section Two} Content  \end{document}

Basically, here's my MWE, and I need to include "Chapter" before every section title in the ToC (without changing anything else).      \documentclass[12pt]{article} \usepackage[utf8]{inputenc}  \usepackage[english]{babel} \usepackage[titles]{tocloft} \usepackage{titlesec} \usepackage{titletoc}  \addto\captionsenglish{ \renewcommand*\contentsname{\centerline{TABLE OF CONTENTS}}}  %\renewcommand{\thesection}{CHAPTER} %\renewcommand{\cftsecpresnum}{Chapter \thesection} \titleformat{\section}[display]% {\null\vskip1em\sffamily\bfseries\filcenter}{Chapter \thesection}{0em}{}[] \titlespacing*{\section}{0em}{1em}{1em}  \titlecontents{section} [1.5em] % ie, 1.5em (chapter) + 2.3em {} {\contentslabel{1em}} {\hspace*{-1.5em}} {\titlerule*[0.5pc]{.}\contentspage}  \begin{document} \newpage \tableofcontents \newpage  \section{Section One} \section{Section Two} Content \end{document}   The commented out code is what I've already tried. The first one just changes the number to "CHAPTER" and doesn't move the text in the ToC (so it just overlays on top of the name of the section), and if I include "\thesection" after "CHAPTER" it creates an infinite loop definition error. The second one causes no differences, and the code still compiles.  Thanks!


I'm really new to python or programming in general.   I am trying to make a function that draws input from the user and check if it is an integer.   However, after checking that the input is an integer, I am unable to use the variable outside of the loop, with an error message shown below:  python3.7 new.py  How much is your balance in your account? >123 Traceback (most recent call last): File "new.py", line 14, in <module> print(f"Thank you, your account balance is {b}.") NameError: name 'b' is not defined    def inputintegertest():     while True:         try:             a = int(input(">"))             b = "${:.2f}".format(a)             break         except ValueError:             print("Please enter a number.")  print("How much is your balance in your account?")  inputintegertest()  print(f"Thank you, your account balance is {b}.")

What exactly are the Python scoping rules?  If I have some code:  code1 class Foo:    code2    def spam.....       code3       for code4..:        code5        x()   Where is x found?  Some possible choices include the list below:   In the enclosing source file In the class namespace In the function definition In the for loop index variable Inside the for loop   Also there is the context during execution, when the function spam is passed somewhere else. And maybe  pass a bit differently?  There must be a simple reference or algorithm somewhere.  It's a confusing world for intermediate Python programmers.


Given a square matrix $A,D\in \Bbb{R}^{n \times n}$ a. $\det(\bigl(\begin{smallmatrix} A & 0 \\ 0 & I \end{smallmatrix} \bigr)\bigr)$ = det(A) (Already done) b. The determinant of a triangular matrix equals to the product of its diagonal entries. (Already done) c. Any real square matrix $A$ may be decomposed as $A = QR$ where $Q$ is an orthogonal matrix (its columns are orthogonal unit vectors meaning $Q^TQ = QQ^T = I$) and $R$ is an upper triangular matrix. If $A$ is invertible, then the factorization is unique. This is called $QR$ decomposition. Prove that  det $(\bigl( \begin{smallmatrix} A & B \\ 0 & D \end{smallmatrix} \bigr)) = \det(A)\cdot \det(D)$ Hint: First prove that $(\bigl( \begin{smallmatrix} A & 0 \\ 0 & D \end{smallmatrix} \bigr)) = \det(A) \cdot \det(D)$ using the fact that $\det(AB) = \det(A)\cdot \det(B)$ (for every two matrices $A$, $B$) and part a and then use the $QR-$decomposition.

I'm trying to prove the following: Let $A$ be a  $k\times k$ matrix, let $D$ have size $n\times n$, and $C$ have size $n\times k$. Then,  $$\det\left(\begin{array}{cc} A&0\\ C&D \end{array}\right) = \det(A)\det(D).$$  Can I just say that $AD - 0C = AD$, and I'm done?


I'm really sorry if this has been answered before, but here is my problem I have this:   array (size=256)       0 =>             array (size=2)<br>                 0 => string 'name_a'                 1 => string '2175'       1 =>             array (size=2)                 0 => string 'name_d'                 1 => string '1'       2 =><             array (size=2)                 0 => string 'name_c'                 1 => string '715'       3 =>             array (size=2)                 0 => string 'name_b'                 1 => string '5'   And I want to be able to sort it by the number from most to least or/and name and if I add more info for each name such as time value. Its a huge array(over 400 I think) and I need to display it one by one, from top to bottom. If anyone have any ideas, I'd love to hear them!

I have CSV data loaded into a multidimensional array. In this way each "row" is a record and each "column" contains the same type of data.  I am using the function below to load my CSV file.  function f_parse_csv($file, $longest, $delimiter) {   $mdarray = array();   $file    = fopen($file, "r");   while ($line = fgetcsv($file, $longest, $delimiter))   {     array_push($mdarray, $line);   }   fclose($file);   return $mdarray; }   I need to be able to specify a column to sort so that it rearranges the rows.  One of the columns contains date information in the format of Y-m-d H:i:s and I would like to be able to sort with the most recent date being the first row.


Sorry for any mistakes, I'm Italian  Hello everyone, I'm writing a novel, in which the Earth is devastated by enormous geological cataclysms (something like the end of the world), and to implement my cataclysm, I thought of a primordial black hole with a mass similar to that of the Earth. At first I thought to stabilize the black hole inside the Earth, but it would have destroyed the planet, and I do not want to destroy it; or so thought to pass away from one side to the Earth from the black hole, causing very powerful shock waves, which first pierce the mantle, causing the eruption of every volcano on earth, and then the crust collide, greatly destabilizing the tectonic plates , causing massive earthquakes on a global scale, and triggering the formation of giant tsunami impacting against every continent. such a scenario is likely, or not.  ps: I hope that the question is connection to physics.

If a small black hole (say about .1 mm radius or 1% of Earth's mass) came flying along at the speed of a comet or higher and impacted the earth, what would happen? Would it pass through the earth (and atmosphere) with minimal damage? Would it leave a crater (entry or exit?) Would it create a big enough shock wave to significantly damage the earth? Would it be captured and wander around inside the earth?  I read a book a few years ago with this as the primary part of the plot, and I have wondered about the physics ever since.


If I take a picture of a flat surface perpendicular to the direction of the lens (i.e. the surface is facing directly at the camera), and I focus on the center, are the points off center in perfect focus, since they are further from the lens than the center point?  Alternatively, do camera lenses have a way to account for this?  If in fact the points off center are slightly out of focus, couldn't this have a significant effect on achieving focus across the entire surface, especially if the camera were close to the object?  Thanks to anyone who can shed some light on this.

This is something I just realised I don't entirely know the answer to, so I'm going to ask it here as I think it's interesting.  In most non-scientific writing on depth of field, diagrams generally show camera and subjects as being perfectly parallel, e.g.    However, is this a more accurate representation of the focal plane?    Are there ways to optically alter the shape of the focal plane?  Note: Obviously these diagrams are two dimensional, but I'm assuming in the second diagram the shape would be spherical with the sensor at the center.


How to prove the following claims ?  Let $b_n=b_{n-1}+\operatorname{lcm}(\lfloor \sqrt{3} \cdot n \rfloor , b_{n-1})$ with $b_1=3$ and $n>1$ . Let $a_n=b_{n+1}/b_n-1$ .   Every term of this sequence $a_i$ is either prime or $1$ . Every odd prime of the form $\left\lfloor \sqrt{3}\cdot n \right\rfloor$ greater than $3$ is a term of this sequence. At the first appearance of each prime of the form $\left\lfloor \sqrt{3}\cdot n \right\rfloor$ greater than $5$, it is the next prime of the given form after the largest prime that has already appeared.   A few first terms of this sequence can be found at  .  Implementation of this generator in PARI/GP can be found .

How to prove or disprove following statement :     There are infinitely many primes of the form : $\lfloor \sqrt {3} \cdot n \rfloor $    Note: This is a problem I made myself.  There is a theorem that states :  $\lfloor nx \rfloor = \begin{cases}  n\lfloor x \rfloor, & \text{if } 0 \leq \{x\} < \frac{1}{n} \\  n\lfloor x \rfloor +1, & \text{if } \frac{1}{n} \leq \{x\} < \frac{2}{n} \\  n\lfloor x \rfloor +2, & \text{if } \frac{2}{n} \leq \{x\} < \frac{3}{n} \\  \vdots \\  n\lfloor x \rfloor +n-1, & \text{if } \frac{n-1}{n} \leq \{x\} < 1 \\ \end{cases}$  where $\{x\}$ is a non-integer part of $x$ .  Hence :  $\lfloor \sqrt{3}\cdot n \rfloor = \begin{cases}  n, & \text{if } 0 \leq \sqrt{3}-1 < \frac{1}{n} \\  n +1, & \text{if } \frac{1}{n} \leq \sqrt{3}-1 < \frac{2}{n} \\  n +2, & \text{if } \frac{2}{n} \leq \sqrt{3}-1 < \frac{3}{n} \\  \vdots \\  2n-1, & \text{if } \frac{n-1}{n} \leq \sqrt{3}-1 < 1 \\ \end{cases}$  How can I proceed from here ?


If I try to use sudo kate to edit a system file, I get the message:  Executing Kate as root is not possible.  So how can I edit a system file? I put up this question so that I could answer it myself.  As far as I can tell, none of the suggestions involving gksudo have any advantage over the solution I proposed: just edit the file as a non-root user, save it when you're done, and provide the root password at that time.

I'm using Kubuntu 18.04 and I want to run the kate editor with root privileges  sudo kate produces the message running kate as root is not possible. I think that's utterly silly.  How can I bypass it? Answer: just edit the file, even if it's a system file, using plain oldkate.  You don't need root privileges to edit it; you only need root privileges to save it.  When you save a system file, you'll be asked for the root password.  Supply it and the save takes place.  Easy!!


I am running on Ubuntu 17.10, and I want to install the Intel Graphics Tool (version 2.0.6). It installs fine, however running it results in the below error message:       Distribution not supported   What can I do to fix this, if anything?

My Ubuntu version is new, and Intel Graphics Installer doesn't allow me to install the Intel video drivers. It says "Distribution not supported" How can I resolve this problem?


I frequently find this expression in literature and such. I couldn´t find anything on it on the net, only more of these expressions without explanations how to handle or understand them correctly:  "I have years of experience proofreading, editing and translating. From simple CVs and cover letters to Master Theses, it is important that your work be perfect and I will make sure that your end product is error-free."  Is that actually idiomatic language? Can it be replaced by "is"?

Possible Duplicate:          Given the sentence     John brings his lunch to school,   is it correct to say     It is important that John brings his lunch to school   (using the third person singular present form of bring), or     It is important that John bring his lunch to school   (using the infinitive form of bring)?  [Edit: The answers indicate that this is actually the subjunctive form, not infinitive.]  I have been told that the infinitive form is correct, but if this is correct I would like an explanation. It doesn't seem like adding it is important should modify the tense of the rest of the sentence.


I have a load of messages with attachments. I want to keep the email but get rid of the attachments. This will free-up a load of space.

I'd like to free up some storage space and delete attachments from most/all the messages in my Gmail. I've long since downloaded and used any attachments I need or care to keep. How can I delete attachments from Gmail, but keep the messages?  I've read  and , but the first is a little old, and the second is too manual. (I have thousands of messages archived. Forwarding each one to myself would take forever.) I'm looking for a less manual/tedious solution.  How can I purge old attachments that do nothing now but take up space, and still keep the original, valuable messages?


If $ Y $ is irreducible set so is $cl(Y)$.  If $cl(Y)$ is reducible then $cl(Y)= A \cup B$ where both $A$ and $B$ is closed in $cl(Y)$. Now how do we proceed?

Start with an irreducible space $X$. Take a subset $Y$ that is irreducible. Show that the closure of $Y$ is still irreducible.   I imagine we are supposed to start with saying, assume we have a decomposition for $\bar Y = S\cup T$ and then somehow derive a contradiction to $X$ or $Y$'s irreducibility, but I am struggling.


i have been trying to make a program that checks if a national identification number is valid how ever i have run into a issue and i can't find an answer anywhere.   I am using a string to store the users input of the identification code and i need to somehow covert the string to int keeping the symbol instead of getting an ascii value.  Example: (lets say the user inputs the string persKods as 111199-11111 the 5th symbol is 9 so the year value should output as 9 instead of 54 which is its ascii value)  int day,month,year; year=this->persKods.at(4); cout << year; // it outputs 54 instead of 9 :/

I have a string of digits, e.g. "123456789", and I need to extract each one of them to use them in a calculation. I can of course access each char by index, but how do I convert it into an int?  I've looked into atoi(), but it takes a string as argument. Hence I must convert each char into a string and then call atoi on it. Is there a better way?


This is a mystery encountered at work today.  Note that this behavior seems to be specific to a binary that I do not know the contents of, but any ideas as to how this phenomenon could occur would be welcome.  It's not of much consequence whether or not this mystery is solved, but it would be gratifying to know what could cause this.  Basically, it looks like this: With either of these two commands, mystderr contains the output that mybinary printed to stderr (desired behavior): $ ./mybinary 3>&1 1>mystdout 2>&3 3>&- | cat > mystderr $ ./mybinary 3>&1 1>mystdout 2>&3 3>&- | while read line; do echo "$line"; done | grep -P ".*"; done > mystderr  With either of these two commands, mystderr contains nothing, strace shows that perl/grep get the input but do not write to stdout: $ ./mybinary 3>&1 1>mystdout 2>&3 3>&- | perl -pe '/.*/p' > mystderr $ ./mybinary 3>&1 1>mystdout 2>&3 3>&- | grep -P ".*" > mystderr  Why does cat know what to do, but grep doesn't?  Why does just feeding the lines through a bash loop cause grep to figure out what to do?

Trying to capture only the packets return time from ping output, I issued  $ ping 192.168.0.1 | grep -o '[^ =]* ms'   and it worked, displaying each packet time when it arrived. Since I also wanted to get rid of the unit of time, thought this would suffice:  $ ping 192.168.0.1 | grep -o '[^ =]* ms' | grep -o '^[^ ]*'   But, to my surprise, it hangs, showing no output. Replacing the first command with an echo of a sample line from ping output, however, works as expected (it outputs 5.07):  $ echo '64 bytes from 192.168.0.1: icmp_seq=10 ttl=64 time=5.07 ms' | grep -o '[^ =]* ms' | grep -o '^[^ ]*'   I found other means of getting only the time without the milissecond unit, but still: What is the issue with ping command? Why is passing it through one pipe is OK, but not through two?  PS: These below also fail, while their echo versions succeed, thus the problem can't be with grep  $ ping 192.168.0.1 | grep -o '[^ =]* ms' | sed 's_ ms__' $ ping 192.168.0.1 | grep -o '[^ =]* ms' | cut -f 1 -d ' ' $ ping 192.168.0.1 | cut -f 7 -d ' ' | cut -f 2 -d '='


If a question is closed or put on hold, usually nobody bothers to fix spelling mistakes in it. But if a new user does it, should the edit be approved? It does technically edit the post, although not in a way that could possibly lead to it getting reopened.  Basically the question comes down to "is that an appropriate way to gain reputation"? Do we trust users more because they can find poorly spelled questions and correct them? On the other hand, editing questions is often pointed out as a good way to get comment privileges and closed question are an obvious source for edit-worthy looking posts.

There is a question on one of the SE sites that had a pending suggested edit: trust me, the way the original question was, it was needed. Before I even thought to approve the edit, I went to close it as a duplicate (as it was), but the suggested edit was still there.  If the question is being closed anyways (as a duplicate or otherwise) do I reject or approve the suggested edit? What is the proper etiquette?


I found lie-dragging at following picture, i can not understand why L and N have property of (12)

Wikipedia's article on  includes the following excerpt:     Suppose that an observer is moving along a geodesic, and carries with herself a system of rigid straight measuring rods (a coordinate system). Each rod is a straight segment; a geodesic. Assume that each rod is parallel transported along the trajectory. The fact that these rods are physically carried along the trajectory means that they are Lie-dragged, or propagated so that the Lie derivative of each rod along the tangent vanishes.   I don't understand the last sentence, which seems to equate Lie dragging with physically dragging an object. That's certainly a nice physical interpretation for something I thought was just a mathematical tool, but I can't see how Lie dragging is even relevant here.   Why is Lie dragging needed to describe what happens when you hold a ruler? Isn't that just parallel transport of the vector pointing along the ruler? Along what vector field are we doing the Lie dragging? Isn't there only one vector around, the observer's velocity?


Upon loading my terminal (since trying to install composer globally) I'm being spammed with countless amounts of -bash: 1: command not found before I even type any commands.  I'm not quite sure what to do, but this is all that happens, I load up terminal and get;  -bash: 1: command not found -bash: 1: command not found -bash: 1: command not found -bash: 1: command not found   for an unlimited amount of times until I close the terminal.  Can anyone help me fix the issue, or reset my terminal, or anything?    Update:  Trying to run rm -i ~/.profile ~/zsh* ~/.bash* like advised in the comments I got the below:  -rm: ~/.profile: No such file or directory -rm: ~/zsh*: No such file or directory -rm: ~/.bash*: No such file or directory   I still get the command not found error.

every time I start my terminal, it always says "-bash:  .: command not found" twice.  Does anyone know how I can get rid of that?


I was working on a PGRE practice problem:      A brick of mass $m$ falls onto a masses spring with spring constant $k$ from a height $h$ above it. What is the maximum distance the spring will be compressed from its equilibrium length?   I use conservation of energy and get that  $x = \frac{mg}{k}(1+\sqrt{1+\frac{2kh}{mg}})$ with the book confirms is correct. However, in the limiting case that h goes to zero, this reduces to $x=\frac{2mg}{k}$ (which the book also notes is correct). If h is zero though, the problem is just find the equilibrium of a spring of spring contact k supporting a brick of mass m, in which case doesn't Newton's second law just give $mg - kx = 0$ implying $x = \frac{mg}{k}$?   I also tried to solve this by saying that when the brick is initially on the spring (in the case that h=0) then the system has gravitational potential energy of zero. Once the spring reaches its equilibrium, the energy will be $0.5kx^2 - mgx=0$ which also gives me $x=\frac{2mg}{k}$  I seem to recall something in my first year physics course about the average force of the spring, but I can't remember anything definitive. Can anyone explain where this factor of two comes from?

I thought this would be a particularly simple problem but it is turning out to be quite the opposite. I am sure I am doing a very simple mistake.   The problem statement is that there is a mass which is just barely kept on the spring (help by the force equal to the weight of the spring) such that the spring is uncompressed. As soon as I let the object go, it will compress the spring and come to rest at some height. The energy stored in the spring will be equal to the difference in the potential energy at the two height of the spring (compressed and uncompressed),  $$mgh_i -mgh_f= 1/2 kx^2$$ Furthermore, the compression of the spring would just be the difference in the $h_f -h_i$. This gives me two roots for compression,  $$ x=0 $$ And the second would be, $$ mg=1/2kx $$ But then by this, $kx=2mg$ and $kx$ is force by Hooks law, but then does it means that the force compressing the spring is twice the weight of the object? That sounds odd. I was expecting I would just recover Hooks law but I guess I am doing something wrong here. But I am not sure what that is.   Any help will be much appreciated.  P.S. This is not a homework problem. We are designing a project for our school.  Thanks for your time.


I have a friend who has been playing magic for a long time, and he told me that in one game he could beat a player who used a card called  with a card called  causing him to not be able to attack it long enough to recover and win. When reviewing the effects of both cards, it struck me that Progenitus has a "protection against all" effect and left me wondering if the effect of Norn's Annex could really stop a card with such an effect. I have some experience playing Magic but I don't know if it really worked my question is really a card with an effect like the one in Norn's Annex can affect Progenitus or was it just luck of misinterpretation of effects?

Example 1) Let's say I have some random creature with protection from white, and my opponent plays , a white card with the effect "Destroy all creatures." Can my creature with protection from white be destroyed by a white card that isn't actually targeting it specifically?  Example 2) I was playing a match with a friend where I had  on the field against his 3 zombies. Is he able to declare his zombies as blockers even though Elite Inquisitor has "protection" from zombies?  If he can declare them as blockers, does protection mean that no damage is dealt by the zombies to  Elite Inquisitor?