I want to clear my computer from everything but i have no clue how I will do this with Ubuntu Plz help me before i will throw my computer throgh the window. With other words i don't want to have anything from Ubuntu left in my computer.

I have absolutely no experience with Linux, and I desperately need to get my computer back up and running again with Windows.  How do I remove Ubuntu and reinstall Windows?    Editor's note: many of the answers are about removing Ubuntu from dual-boot but keeping Windows (which is a bit complicated), while other answers are about removing Ubuntu from single-boot (which is easy: basically just format the disk while installing Windows). The question as written is ambiguous between dual-boot or single-boot.


I have a windows 7 host OS.  HW Virtualization is enabled in the BIOS. On Oracle VM VirtualBox added a Ubuntu 12.04 Guest OS.  Configured it as 64 bit.  Note:  The System->Acceleration is enabled and "Enable VT-x/AMD-V" is enabled.  Also the other Nested Paging one. Booted 64 bit Ubuntu 12.04 guest OS.  The booting went fine. Now, for some multiple system installation purposes, I need Oracle VM VirtualBox in the Ubuntu 12.04 Guest OS.  Installed the virtualbox and the addons. Now in the Guest OS virtualbox System->Acceleration is not enabled.  Can anyone suggest how we could get the Acceleration enabled on the Oracle VM VirtualBox running on guest OS (ubuntu 12.04).  Please note Oracle VM VirtualBox is running on a guest ubuntu OS.

I would like to do some lib testing on my OS. So I need several environment to run KVM. And I found my guest machine was not able to run KVM.  I was using virtualbox 4.2.


I know that both can give attacker remote access to computer. Is RAT easier to detect than rootkit? Where are they typically get installed? Can one make more damage than another? Which one is easier to remove?

What should I do if my Windows computer seems to be infected with a virus or malware?  What are the symptoms of an infection? What should I do after noticing an infection? What can I do to get rid of it? how to prevent from infection by malware?   This question comes up frequently, and the suggested solutions are usually the same. This community wiki is an attempt to serve as the definitive, most comprehensive answer possible. Feel free to add your contributions via edits.


I have a Mac iBook G4, which is not booting at all and it requires 'OS X Recovery CD', which i do not have. So I wanted to install Ubuntu on, which I already use on another system.   A step by step guide, for burning the .iso image, or a bootable USB version guide for Ubuntu 13.10 for my iBook is highly appreciated.

I already know how to do it on Mac OS X (plenty of instructions online).  But is it possible to do it on Ubuntu? If yes, how?


I am a high school student who is trying to learn abstract algebra. I know that there are many threads on this already but, I have been through them and am stuck. I have been trying to get a good grasp on abstract algebra for close to two years now. Here are some of the sources I have been through:  I started with Rotman Advanced Modern algebra but, ended up having to switch after getting to the section about Galois theory because bunches of details were left out. I tried filing them in but, I ended up confusing myself more.  I went to Knapp's Basic algebra which had many topics about algebra that I wanted to learn about but, ended up having to switch after reading the section about tensor products when details ended up being left out and I was not able to fill them in.  I tried Dummit and Foote which was a really good resource. I ended up getting stuck at the part on rings when I tried to fill in some details which I could not fill in.  I went around a third of the way through Aluffi which was another great resource. However, as with the others, there were details I had to fill in and I ended up only confusing myself trying to fill them in.  I found Sharifi's notes on Abstract algebra to be very comprehensive and detail-oriented in the beginning but just like with the others, there were details to fill in that I could not fill in.  I looked through many of the sources suggested in other threads such as Saunders Maclane, Hernstein, etc. but, I couldn't find a source that was as comprehensive as Dummit Foote or Rotman.   My favorite source of these is the one by Rotman and I am looking for a resource that covers similar topics (I was using the 2nd edition of Rotman for a while. If the third edition is more detail-oriented, please let me know). Does anyone know of an abstract algebra source that is both comprehensive and fills in the details?

Last semester I picked up an algebra course at my university, which unfortunately was scheduled during my exams of my major (I'm a computer science major). So I had to self study the material, however, the self written syllabus was not self study friendly (good syllabus overall though).  The course was split up into 3 parts, group theory, ring theory and field theory. As a computer science major we only had to study the first 2.  Now that I passed the exam for this course I want to study the field theory part ( which covers Galois theory, etc).  So, now I want to ask whether any of you know any good books on abstract algebra, which lift off at basic ring theory and continue to more advanced ring theory and to finite fields, Galois theory, ...  Please keep in mind that I am not a math major, and that I would like books which are suited for self study (thus a lot of examples and intuition).  Thanks in advance!


When I zoom in or out in QGIS, my scale will only halve or double respectively. This is the case whether I manually type the scale into the window at the bottom of the screen or select one of the set scale options. The scale automatically jumps to the nearest scale that is an exponent of base 2,256 (the smallest scale allowable for some reason), where the exponent is a multiple of 2. For example, if my scale is 144,447 and I type in or select 250,000, it automatically jumps to 288,895. This is occurring prior to adding any layers. I probably just have to uninstall/reinstall but though I would check here first.

I'm having a problem with the mouse wheel zoom setting on my macbook trackpad. The zoom occurs far too quickly for any level of precision. I noted this comment in the dev log:   2004-08-14 [gsherman] 0.4.0devel9 Added mouse wheel zoom. Moving wheel forward zooms in by a factor of 2.  How can I change the settings so that zooming occurs by a factor of 1 or .5?   I'm using QGIS 2.6 Brighton.


I discovered tmux is installed on my system. In order to find out if it was preinstalled with fedora I ran the command dnf info tmux which prints out:  Installed Packages Name         : tmux Version      : 2.7 Release      : 1.fc28 Arch         : x86_64 Size         : 765 k Source       : tmux-2.7-1.fc28.src.rpm Repo         : @System From repo    : updates Summary      : A terminal multiplexer URL          : https://tmux.github.io/ License      : ISC and BSD Description  : tmux is a "terminal multiplexer."  It enables a number of terminals (or              : windows) to be accessed and controlled                     from a single terminal.  tmux is              : intended to be a simple, modern, BSD-licensed alternative to programs such              : as GNU Screen.   Based on the above output it seems that @ means "at" so Repo: @System means "at system" (i.e. the package is not in a repository instead the package is installed at the system) or in other words (package tmux is) installed at the system.  However tracking down the transaction when tmux was installed with dnf history list tmux (which showed something like transaction ID 55), and dnf history list 55 the following line is part of the resulting output:  Install    tmux-2.7-1.fc28.x86_64               @updates   Based on the above findings which of the following understanding of @ in package management is correct?   The line above makes it clear that tmux was installed from the updates repository but assuming that @ means "at" shouldn't that mean installed at the updates repository? In other words, why does @ in the output of dnf info <packagename> mean "at" e.g. @System means "at System", but in the output of dnf history list 55, @ seems to mean "from"? Alternatively does @ mean "install the package tmux-2.7-1.fc28.x86_64 at the repository @updates", or in other words, "install the package tmux-2.7-1.fc28.x86_64 that is at the repository updates"? Which makes sense given that the line below from the same output should read as: upgraded subversion at the repository fedora/27.   Upgraded   subversion-1.9.7-1.fc27.x86_64       @fedora/27   Edit: My question is not a duplicate. Where as the other question is asking what @ means, this question is different in that I researched/investigated the meaning of @ in the package manager after which I posted a question to confirm which of my understanding of the results of the research/investigation is correct. Besides the answers to the  question are low quality. For example the first answer makes the following statement:     All "Installed Packages" are preceded by @ sign, while "Available Packages" are not. So I believe @ signs show the packages are installed.   This is not correct because for example with that flawed answer   Install    tmux-2.7-1.fc28.x86_64         @updates   would mean that tmux is already installed which it is not. So that rules out @ meaning that a package is already installed  and the second answer states:     DNF uses @ to denote the repo an installed package was installed from. As you noted   That's wrong because then @System would mean that the package was installed from your system.  My understanding of @ in the main question shows why this quote from the second answer to the other question is wrong.

When I want to list installed packages, I do it usually in one of two ways.  The old fashioned way is using rpm -qa | grep <whatever I look for>, and that's that.  But recently I wanted a more comprehensive display of my packages, and henceforth, I used dnf list --installed <whatever I look for>.  However when looking at the result there are a couple things I don't understand.  Consider this example:  # dnf list --installed zsh                   Last metadata expiration check: 0:13:25 ago on Mon Jul 11 05:48:04 2016. Installed Packages zsh.x86_64            5.2-5.fc24            @@commandline   (spaces in actual printout are wider)  So the resulting entries, are: «package» «version» «repo».  In my example that's:   package: zsh.x86_64 version: 5.2-5.fc24 repo: @@commandline   So far the resulting table is understandable, but I'm confused what the two '@@' mean in front of the repo name.  Also, "commandline" suggests the package was installed from command line (downloading the RPM, and then doing dnf install whatever.rpm in the command line, etc.). However I'm pretty sure I've installed zsh via dnf install zsh.  But that's not all.  I've several packages on my system installed from the repo @System, @fedora (however there's also fedora without the @) and things like @@commandline.  So what does that @ or @@ exactly mean in front of the repo name?  And how come I've got so many prominent packages installed from @@commandline although I'm more than sure I've installed them from the repos?


All the logcat events that I see are very recent. Is there any way to see older events from around 24 hours ago?

Is it possible to access old log files,lets say 3 months old, to see the usage on the android device, by usage i mean, any app installed or unistalled, time spent online, via wifi or cellular, time offline, times switched on and switched off,apps used and any other usage data.  Is this possible through the ADB on windows? I want to be able to connect the tablet to my PC and access all the logs for the last 3 months, currently am just getting the current date only, i cannot even get logs for yesterday. The command am using is adb logcat > currentdevicelog.txt  Any help would be highly appreciated, the version of android on the device is Nougat-7.0


It would be nice to be able to answer  by refering to the  and seeing that reviews have occurred (and what the outcome has been).

Accessing the full review history is a privilege for 10 k users but, statistics for individual reviews can be viewed by everybody ( ).  These review summaries can be somewhat useful for different aspects, such as understanding what happened to a review item that you initiated, e.g., if your close vote remained the only one on a question, you can only guess by the elapsed time whether nobody else has reviewed it or whether the review is finished with everybody disagreeing. Or you can see who performed a disputed review decision and discuss it.  My question now is: Is there any way to acess these review summaries or obtain the review ID – which would allow to find these summaries – for a particular review task?  I am aware that the above information, in particular the reviewer identity, can be abused and it may therefore be undesirable that everybody can find this information. But then, at least on small sites, it’s quite possible to obtain the review ID from guessing. Also, I can access the review summary for every review that I participated in or even skipped from my review history and the review summary for every successful edit from the edit history.


I would like to know if there is a software for Windows which allows me to copy a huge file from a remote desktop network to my local PC, and if this copy gets interrupted, I would like to resume the copy process. I have tried Teracopy but its Resume feature does not work when network connection gets interrupted.  This is the scenario:   I connect to a remote computer using Remote desktop, sharing a local drive, so the remote computer can see my shared drive (such as U:) On the remote computer I want to copy the remote file to the shared drive (U:). Local computer has Windows 8, remote computer has Windows 2003 There is no internet connection available in remote computer   The problem:    connection is really slow from remote computer and when there is a disconnection, I cannot resume the copy process   is there a software which offers a resume feature to avoid copying the whole file again from scratch?

I need to download a 10 GB VM file from a network drive. The problem is I periodically need to access a VPN connection which disconnects the network drive.   I am not able to resume the download after I disconnect from the VPN and re-access the network drive. I've tried 4 times.  I need the file as soon as possible for work. Will I need to wait until I finish working today to start the download and let it run over night?  I'm using Windows 7.


I had Ubuntu 16.04 or whatever running on my system (off a RAID disk pair). I tried to upgrade to 18.04 over it. Eventually I had the upgrade say that it is broken, can't finish, possibly left in an unstable state. I tried to 'repair' the problem, but -- stupidly -- uninstalled ubuntu-desktop (or whatever) & then rebooted.  Now 18.04 tries to boot, says that it is starting Light Desktop (or whatever) & the text cursor is blinking in the upper left corner on an empty screen & nothing happens. Obviously the desktop sw is broken, but I don't know what to do. I have no install CD for 18.04 (& my setup is RAID, so I would need the server install CD, I think), & when I boot into recovery mode then the package manager can't find some ubuntu server to fix the broken display package (I guess).  I would greatly appreciate some handholding. Right now I'm running 14.04 off another drive & I don't even see the other system because it is on those RAID pair of disks & this install has no support for those disks (this install happened in another machine).  Please, please help!

I am trying to boot Ubuntu on my computer.  When I boot Ubuntu, it boots to a black screen.  How can I fix this? Table of Contents:


I have a file (a document or text file to be precise) that I would like to be copied for every new user I create in the future. Is this possible? For example If I were to create a new user "test", my file should automatically be copied to the user "test" without me doing anything.   Also is it possible to change the default location of the file to be copied? I don't want it to be copied to the home directory?

On Ubuntu 10.4 I have edited the /etc/bash.bashrc file to set some variables like the command history size (HISTSIZE=5000), however if I create a new users Ubuntu by default gives them a .bashrc file in their home directory with this set as HISTSIZE=1000 which is overriding mine. How can I change the default .bashrc file that is created?


The following screenshot shows the Maitland-Niles pass to Pepe during the 4-1 Arsenal win over Rapid Wein in the Europa League.  Arsenal are in blue. Maitland-Niles is furthest to the the left in blue and is closest to the goal line. He has passed the ball to Pepe second in from the left in blue. To confirm, Pepe never connected to the ball at any point.

The offside rule on the pitch is often unclear and called suddenly. How do I know if a player is offside?


Twice recently I've noticed that my vim settings have changed to defaults.  Investigation shows that all files have been deleted from my /root/ directory.  (Yes I currently log in as root, that's a different conversation...)  Can anyone suggest why this would be happening?  The first time I assumed I'd accidentally repeated a recent command from my bash history as I had done an rm -f in a different folder shortly before hand, but on this occasion I've not rm'd anything for days and after a yum update (which included a new kernel) and a reboot the files have gone again...?  Folders don't get deleted from /root/, just files.  Any ideas?  Many thanks.

I've got 4 specific files that seem to keep disappearing from a user's home directory. As far as we know, there are no cronjobs or other automated tasks that would be removing them.  I've setup auditd on them but the logs aren't really showing anything of interest.  I can see our backup utility accessing them every night until the point they aren't there anymore, but nothing else.  Is there anything that would be causing those files to be removed that would get around auditd?  The files in question are these:  /home/username/.bashrc /home/username/.bash_profile   as well as a couple of files in that user's .ssh directory.  Copies of these files placed into a subfolder called "keepers" get deleted at the same time as well.  Changing the permissions on them to 000 and having them owned by root hasn't helped.   I've currently got inotifywait setup to log create,delete,move on that subfolder, so hopefully that will turn up something, although it doesn't log much aside from when it happened, not what caused it.


Currently, I have menu button for toggle purpose. User can switch between original web view, or striped down mobile view.    Currently, we are in original web view    On action bar, I'm showing a phone icon, which is used to tell user, "By clicking on me, you are going to switch to mobile view"    Currently, we are in mobile view    On action bar, I'm showing a web browser icon, which is used to tell user, "By clicking on me, you are going to switch to original web view"    I was wondering, for a toggle button, should the icon telling   What will be the next state if user clicks on me?   A phone icon indicates if user clicks on me, view will switch to mobile view. A web browser icon indicates if user clicks on me, view will switch to original web view.  OR, should the icon used to indicate what is current state?   A phone icon indicates current state is mobile view. A web browser icon indicates current state is original web view.

I have a quick question about buttons that toggle between two states. (Think Play/Pause, or Shuffle/Regular Play.) As the title says, should the toggle show it's current state or the state to which it will transition?  I think people are used to the Play/Pause convention. But the Shuffle/Regular play might be more confusing if you show the transition state instead of current. For example, the built-in music player on the Xbox 360 does it this way: when it's in shuffle mode, it shows the icon for direct play and vice versa and it always confuses me (am I in shuffle mode or straight play).  I see it this way: Play/Pause is more like action as in begin playing or pause playing. Yes behind the scenes it is a state transition but to the user, there is an action. Whereas Shuffle/Straight Play is an option and it's best to show the current state (and possibly have only one icon and change button to show that the option is enabled/disabled). Thoughts?


I sometimes end up requesting the man page for a "basic" command like set or pushd that is built-in into the bash/zsh shell.  So I type:  man set   …and I end up here:  BASH_BUILTINS(1)            General Commands Manual           BASH_BUILTINS(1)  NAME        bash,  :,  .,  [, alias, bg, bind, break, builtin, caller, cd, command,        compgen, complete, compopt,  continue,  declare,  dirs,  disown,  echo,        enable,  eval,  exec, exit, export, false, fc, fg, getopts, hash, help,        history, jobs, kill, let, local, logout, mapfile, popd, printf,  pushd,        pwd,  read, readonly, return, set, shift, shopt, source, suspend, test,        times, trap, true, type, typeset, ulimit, umask, unalias, unset, wait -        bash built-in commands, see bash(1)  BASH BUILTIN COMMANDS        Unless otherwise noted, each builtin command documented in this section        as accepting options preceded by - accepts -- to signify the end of the        options.   The  :, true, false, and test builtins do not accept options        and do not treat -- specially.  The exit, logout, return,  break,  con‐        tinue,  let,  and shift builtins accept and process arguments beginning        with - without requiring --.  Other builtins that accept arguments  but        are  not  specified  as accepting options interpret arguments beginning        with - as invalid options and require -- to  prevent  this  interpreta‐        tion.        : [arguments]               No  effect;  the command does nothing beyond expanding arguments  Manual page set(1) line 1 (press h for help or q to quit)   …in a thing apparently called "General Commands Manual".  Now the problem is: This man page is without any value to me. I mean, it's very nice, well-written and detailed… actually, very detailed.  I know, I can search in man pages with / thanks to the default pager less), but that does not really help here, as such a common word/string as set appears often in the command. And yes, I've tried awkward things as putting spaces around, no, this does not help:   So this is not productive, as I would have been faster searching for this problem online then, than using the man page. With "proper" man pages that do not have hundreds of commands/man pages combined, it would actually have been faster.  What I actually just want is that when I type man set this page opens, but it automatically scrolls to the command I've actually requested (i.e. set in this example).  That said alternative solutions to the problem (like splitting that huge man page, if such a thing is possible?!) are also appreciated.  I would prefer solutions for this problem for bash or zsh (or other shells, if it is such a specific problem.). However, I would obviously prefer a solution that works everywhere.

Is there anywhere you can download a manpage for every builtin commands?  I know you can just use help or man bash and search to find info about it, but I want them separated, so I can just do man read and get the read manpage.


I installed Kubuntu 19.04 in 175 GB drive by mistake. Can i partition that drive now and allocate kubuntu in a smaller space?

Previously, I have installed Windows 7 on my 320 GB laptop with three partitions 173, 84 and 63 GB each. The 63 GB partition was where the Windows was installed. The rest were for file containers.  Now I changed my OS to Ubuntu 12.04 LTS. I installed Ubuntu by replacing the entire Windows 7 on the 63 GB partition. The rest of the partitions remain as an NTFS Windows partition and I can still access them both (the 173 and 84 GB partitions).  Now I want to change the two partitions of Windows into an Ubuntu format partitions plus most importantly, I want to extend the 63 GB partition to more than a 100 GB because at the moment I am running out of disk space. Whenever I try to install any application, especially using wine, it always complains for a shortage of disk space.  How do I do the extending activity before I entirely format my laptop again and lose all the important files on my partitions?


file.txt is tab separated:  RollNo  Names    Class  Subject  Position 101     Anna     V      Maths    Average 102     Bob      V      Maths    Good 103     Charles  VI     Science  Good 104     Darwin   VI     Science  Improve 105     Eva      VII    English  Improve   I want to sort the lines so that they appear in the order Good, Average, Improve:  RollNo  Names    Class  Subject  Position 102     Bob      V      Maths    Good 103     Charles  VI     Science  Good 101     Anna     V      Maths    Average 104     Darwin   VI     Science  Improve 105     Eva      VII    English  Improve

I know there are tons of sorting questions on here, but I'm unable to resolve my use case.  I am trying to sort a list in R (on Ubuntu 16.04) and am at my wits end! I've been trying to mess with the LC_ALL=C and collate settings and can get results to sort differently, but I'm unable to get the result I need. This is what I need:  2014_Actual / 2014_Target / 2014_Percent / 2015_Actual / 2015_Target / 2015_Percent  The trick I use in windows is to delete the underscore, so: 2014_Actual / 2014_Target / 2014Percent / 2015_Actual / 2015_Target / 2015Percent, which is acceptable to my users. But obviously this doesn't work in Linux since it ignores the underscore.  Does anybody have any ideas on how I could get the above mentioned sort order at the LC_ALL level?  Thanks in advance.  EDIT: Adding clarity: the problem is that when I sort the above in Linux, it ignores the underscore and gives: 2014_Actual / 2014Percent / 2014_Target /  2015_Actual / 2015Percent / 2015_Target


In the following snippet, pointer addresses and values are referenced as the type size_t. However as the title says, the last subtraction does not make sense to me. It acts like, as if it subtracts the number multiplied with 8 instead of the actual value as seen in the int array.  #include <stdio.h> #include <stdint.h>  int main() {     int i[6] = {2, 0, 1, 0, 20, 24};      void *ptr = &i[2];      printf("%zu\n", ((size_t*)ptr));     printf("%zu\n", *((size_t*)ptr));     printf("%zu\n", ((size_t*)ptr) - *((size_t*)ptr)); }

Does anyone have any good articles or explanations (blogs, examples) for pointer arithmetic?  Figure the audience is a bunch of Java programmers learning C and C++.


I know this is a bit subjective, but I've been thinking and it seems obvious when to upvote or downvote an answer. But what about the question? I mean, some questions are purely self serving and don't really add anything to the community. On the other hand some questions help others, make you think, etc.   I am wondering if there is a generic standard for upvoting questions?

I have seen a few  here on Meta Stack Exchange that cover parts of this, but they are often too local, and none of them seem to cover all the relevant scenarios.  I will break it up into multiple parts in order to make this more specific:     When should I vote on a question:   What are the qualifications for a question to be deserving of being up-voted? When shouldn't I vote up on a question? What are the things that would cause a question to need to be down-voted?   How should I go about down-voting the question (do I wait a little while to give the OP a chance to change it, or do I down-vote it immediately)?  When shouldn't I vote down on a question?  When should I vote on an answer:   What are the qualifications for an answer to be deserving of being up-voted? When shouldn't I vote up on an answer? What are the thing that would cause an answer to need to be down-voted?   How should I go about down-voting the answer (do I wait a little while to give the OP a chance to change it, or do I down-vote it immediately)?  When shouldn't I vote down on an answer?  When should I vote on a comment:   While votes on comments do not affect reputation points, it might be useful to new users to know when to up-vote them.    It seems that a full, comprehensive list of these would be invaluable to new users looking to figure out how the voting system works, but this list seems to be missing from the meta site.


so here you can see that i triagulate the mesh but it doesnt change anything at all, and the other pic i keeped the ngons (that i dont wont in my mesh by the way so i need the mesh in those parts triagulated) and neither solves anyting, so how can i get a good shading of the normals, i am using a normal editor called Y.A.V.N.E to make a good shading to my models but sometimes when topology isnt good, or in carved object through booleans this issue happens in most of mesh objects.last pic is a new model that i am developing

What would be the best method for making regularly spaced holes in a cylindrical mesh? Similar to the vent holes you'd see on gun barrels like these:       Without creating any n-gons, having good topology, and not excessively increasing the tri/polycount overall (this is for models that would potentially be used in a game). It would be good to know how to do this in a way that would work where the holes overlap on the x axis of the cylinder if you see what I mean, like the MG34 barrel, and where they don't, like the SMG barrel.


I have a lenovo T530 laptop. It currently has 2 SSDs: one in the easily accessible CD/DVD/HD bay, and one somewhere else inside the case which has the operating system installed.  "My computer" reports that the Operating system SSD is 108GB capacity, while the other SSD is 111 GB capacity. Both of the harddrives are filling up and it's a struggle and a juggling act to keep a little free space available.  I had a geeze at the prices of SSDs these days and was delighted to discover that they have come down in price dramatically since I last was shopping around. I would like to upgrade the operating system SSD so that it has between roughly 0.5TB and 1TB space.  Now, my question is: How can I move my operating system to the new harddrive? Is there some software that can mirror the entire contents of my current Operating system harddrive over to the new one? or do I have to completely start from scratch, reinstall windows etc? If the latter, I can't afford to pay for a new windows 10 license, so how would I go about transferring my existing license over to the new install?  I'm not opposed to just starting with a fresh install, but as mentioned, I can't afford a new windows 10 license. So how would I go about transferring my existing license over to the new hard drive?  edit: I should note that my laptop originally came with windows 7 installed, and I upgraded to windows 10 for free back in 2016.  edit: this isn't a duplicate. The linked question has absolutely nothing to do with this question  edit: as mentioned, I am open to a fresh install, but my worry is that i will be barred from activating the operating system and won't be able to transfer my license. I read on another question that these days windows will autoactivate after installation if it recognises your motherboard. Can someone confirm this or provide more information?

I've been using Windows 10 for a couple of month now (joined the Insider Preview).  Now my hard drive started ticking so I've bought a new SSD and I want to move the windows installation to the new hard drive, which has been connected to the computer (unpartitioned). I don't mind and I even prefer reinstalling it over again.   Since I have the free version of Windows 10 pro, can I still reinstall it anew? Does the windows 10 installation offer disk management and partition like the older Windows installations used to? How should I reinstall Winodws 10 x64 the easiest but still remain on free mode?


I have some questions about programming paradigms, design choices, and why I should want to use X when I could also do it using Y.  Here are some examples:   Why should I use Async instead of spawning a new thread to do the job? Should I use for a relational database, an in-memory database, or a specific built-in data structure to process a set of objects X times? Why should I use a thread pool instead of using a for loop to spawn X number of threads?   These kinds of questions are only possible to answer by referring to concepts, internal workings, using pseudo code, or telling personal experiences (I used to use A for a number of years, but it failed in case B).  I feel that they are not suitable for Stack Overflow, because it looks more a place to find solutions to practical problems. I also think that these kinds of questions would be instantly downvoted and marked as too broad or opinion based.  These are more on the academic side of software engineering and development, so I guess  would be a better place to ask them, but I wasn't sure.  I didn't want to add chaos to either communities and make unnecessary work for moderators by asking unrelated questions, and that's why I'm asking here. Could you please help me figure it out?

Stuff like polls, recommendations based on subjective constraints, puzzles, webcomics etc. do not belong on the serious main SE sites, where professionals should be considered at work and having just a few spare minutes ("code's compiling") to answer questions, so they should not be distracted by such things. However, I'd also like to have a home for these things still using the SE engine. For the reason I mentioned before, this needs to be a separate place though. Let's call it four.[sitename-here].com.


I'm was phrasing a file and found a error with the file name while saving to mysql database.  Original file name looks something like Thor - Thor：The Dark World but after phrasing and saving the name to mysql through PHP, the string turns to Marvels Thorï¼šthe Dark World.  It displays the same even when I ECHO the PHP variable that holds the string so this has nothing to do with mysql.  where am I doing wrong? Any suggestions?  $di = new RecursiveDirectoryIterator('/var/www/example/data/'); foreach (new RecursiveIteratorIterator($di) as $filename => $file) {           echo $file->getFilename(); //displays Marvels Thorï¼šthe Dark World          $data[] = array('file'=>array('name'=>$file->getFilename(),'path'=>$filename));    }

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'm a psychology student at the VU Amsterdam. For my statistic courses this software called IBM SPSS statistics is required andabsolutly neccesary. I bought it of the official website and downloaded the .zip file. I've tried to open it with archivemanager and it was extracting something but in the end it always said:   Invalid url: '/home/mumen420/.cache/.fr-Q2kVc7/IBM' given, exiting   I've tried to use the unzip command and that always responds with   mumen420@Laptop-chan:~$ unzip IBM SPSS Statistics 24 Linux.zip unzip:  cannot find or open IBM, IBM.zip or IBM.ZIP

I want to enter the following folder in the terminal:  Milano, Torino (Jan)-Compressed   How should I write the command cd to enter this directory?  Spaces and several other special characters like \, *, ), ( and ? cause problems when I try to use them in the command line or scripts, e.g.:    $ cd space dir bash: cd: space: No such file or directory  $ cat space file cat: space: No such file or directory cat: file: No such file or directory  $ cat ( bash: syntax error near unexpected token `newline'  $ echo content >\ > ^C  $ ls ? (  )  *  ?  \   How do I enter file or directory names that contain special characters in the terminal in general?


Is it possible to consider $S^n$ as a $0$-simplex and a singular map of an $n$-simplex so that the $n$-simplex forms the surface of $S^n$ minus a point, and the point is the singular map of the $0$-simplex? Can a (singular map of an) $n$-simplex have zero boundary for $n>1$? I am trying to understand the homology groups of $\mathbb{R}^n$ with finitely many points removed. I imagine I could use the Mayer-Vietoris exact sequence and homotopy invariance, but I want to try to find the groups directly from the definition to confirm that I am right. So, I have started by showing that $X=\mathbb{R}^n\backslash\{x_1,\ldots,x_m\}$ is homotopy equivalent (deformation retracts) to the wedge sum of $m$ copies of $S^{n-1}$ meeting at a common point, as in the diagram for $n=3,m=4$.


I have an old photo of my brother which is 29KB and resolution is 461 × 491.  I need to print it in a regular image size.  Is there a way to increase its size/resolution? either by iphone app or desktop software (but not Photoshop)  Thanks!

I have taken a picture whose resolution is less. I can resize the image easily (i.e I can scale to higher resolution) but the image quality goes for a toss, which is true because the image might not have enough pixels to scale properly.   Is resizing a means of increasing the resolution of the image ? Is it possible to increase the pixel density of the image and then resize, so that quality of the image is not affected much?   I mainly use GIMP and Picasa.


During the last years I always thought that in Java, Reflection is widely used during Unit testing. Since some of the variables/methods which have to be checked are private, it is somehow necessary to read the values of them. I always thought that the Reflection API is also used for this purpose.  Last week i had to test some packages and therefore write some JUnit tests. As always i used Reflection to access private fields and methods. But my supervisor who checked the code wasn't really happy with that and told me that the Reflection API wasn't meant to use for such "hacking". Instead he suggested to modifiy the visibility in the production code.  Is it really bad practice to use Reflection? I can't really believe that-  Edit: I should have mentioned that i was required that all tests are in a separate package called test (so using protected visibilty e.g. wasn't a possible solution too)

How do I unit test (using xUnit) a class that has internal private methods, fields or nested classes? Or a function that is made private by having  (static in C/C++) or is in a private () namespace?  It seems bad to change the access modifier for a method or function just to be able to run a test.


If you get the Android 4.2.* version phone, you will notice that there is no Developer mode any more.  How can you switch to Development mode?

I wanted to access the developer options to enable adb access on Android 4.2 but cannot find it.  How can I enable that?  Once I've activated the menu, how can I hide it again?


This is similar to . But my question is specifically about plain old <script> tags in my HTML body like so  <script type="text/javascript" src="/path/to/my/script.js"></script>   I have a custom window.onerror function that I wrote to deal with general script errors. And indeed, if such a script has a syntax error or some other runtime error occurs while evaluating the script itself, that is handled correctly by my onerror function.  But if the script fails to load at all, because of an interrupted connection or even a 404 or other server error, window.onerror is not called. How can I detect this kind of failure programmatically in Javascript?  To clarify: I realize I could just put an onerror attribute in every single script tag. I'm asking if there's a better way, something comparable to my global window.onerror or some way of making that function be called.

I'm dynamically adding <script> tags to a page's <head>, and I'd like to be able to tell whether the loading failed in some way -- a 404, a script error in the loaded script, whatever.  In Firefox, this works:  var script_tag = document.createElement('script'); script_tag.setAttribute('type', 'text/javascript'); script_tag.setAttribute('src', 'http://fail.org/nonexistant.js'); script_tag.onerror = function() { alert("Loading failed!"); } document.getElementsByTagName('head')[0].appendChild(script_tag);   However, this doesn't work in IE or Safari.  Does anyone know of a way to make this work in browsers other than Firefox?  (I don't think a solution that requires placing special code within the .js files is a good one. It's inelegant and inflexible.)


I use the command history | grep <key_word> to look for all the commands in the history with that specific key_word. That's great but sometimes not enough: I would love to see the N commands before and the M commands after each result.  For example with history | grep build, I want to see the N=10 commands before and the M=5 commands after each result. Targeting the following ideal output:     1209  git status  1210  git add .  1211  git commit -m 'bla bla bla'  1212  git push http://xxx.xxx.xx.x:xxxxx/  1213  git tag   1214  source tools/settings.sh   1215  cd demos/xxxxxxx/  1216  xxxxxxx   1217  cd demos/wait_zcu102/  1218  ls  1219  cd build.sw/      <------------------------------------- <key_word> is here  1220  ls  1221  atom .  1222  source tools/settings.sh   1223  cd demos/xxxxxxxxx/  1224  xxxxx    Is there a way to do this?

I would like to grep for a string, but also show the preceding five lines and the following five lines as well as the matched line. How would I be able to do this?


I have ply format mesh in edit mode in blender. When I select some vertices , I need the x y z coordinates to be printed as output. Is it possible?

I want to read the vertex x and y coordinates with a script or a function.  How can I do that?  The   appears to have no position I could use.  I'd take any alternative approach that could give me x and y coordinates.


I have an excel file including the following table. How should I create something similar to it? Is it better to use the table code in latex or make a figure from it and import it to latex (I did this but the quality of picture was so bad).  If I have to create a table, how should I automatically import those values to latex, because the values are too much to be written without any automatic routine.

Manually hacking tables in LaTeX is one of the less funny things when preparing a document. Naturally, there are quite a few tools that promise to simplify this. In fact, I have somewhat lost track of all the tools available, and I'd like to gather your valuable experience into one big post. Some of the tools are mentioned in , but I feel there's much more around.  I'd suggest that somebody starts an overview with an alphabetic list (so that I can accept this answer and it stays on top), and that everyone replies with a "community wiki" entry, one reply per tool, and inserts the tool into the list.  Personally, I use Excel2LaTeX, but I'm unhappy with having to fire up Windows in order to generate the LaTeX code. I'm thinking of a rewrite as a standalone Python tool using the xlrd library, but I'm not too inclined to reinvent the wheel.


Check my proof, please.  Divide into subsets $A \times C$ and $B \times D$ so that , all pairs with the same element belong to the same subset. Each such subset $|A \times C|$ bijective $C$, $|C|=|D|$ and $D$ equipotent to each subset $B \times D$. This implies , that $|A \times C| = |B \times D|$.

Suppose that $A, B, C$, and $D$ are sets with the cardinalities related as  $|A|=|C|$ and $|B|=|D|$. Prove that the cardinality of $A\times B$ is equal to the cardinality of $D\times C$.  I know that I must prove the bijection of the function $f: A \times B \to C \times D$, but I am not sure how to say this? Can anyone help me?


I have a container  with every measurement defined in 'mm' for printing purposes. However, I want to show its preview inside a 600px wide block with perfect fit. What would be the best way to scale it down?

I'm working on a kind of unique app which needs to generate images at specific resolutions according to the device they are displayed on. So the output is different on a regular Windows browser (96ppi), iPhone (163ppi), Android G1 (180ppi), and other devices. I'm wondering if there's a way to detect this automatically.  My initial research seems to say no. The only suggestion I've seen is to make an element whose width is specified as "1in" in CSS, then check its offsetWidth (see also ). Makes sense, but iPhone is lying to me with that technique, saying it's 96ppi.  Another approach might be to get the dimensions of the display in inches and then divide by the width in pixels, but I'm not sure how to do that either.


I'm wondering how to use those "(noun-y) -ing clauses" when they are at the end of the sentence.  Most grammar references I've found on the internet only talk about their use as adverbials at the beginning of a sentence. For example:     1) Wanting more money, he accepted the offer.   But I've seen many times people put them at the end of sentences:     2) He issued an attack on her at the company, describing her as an amateurish programmer.      3) She ran all the way to the playground, her friends following.   In these last two examples above, the -ing clauses don't look like adverbials to me. They can be paraphrased as separate sentences. I feel like, because they are related, instead of writing two separate sentences, the writer combines them together.  Grammatically, what are those types of -ing clauses called? And when is it appropriate to use them?

if the sentence you are analysing contains a modal verb, then it is positioned in ‘I’,any other verbs then being located in VP.      (English Syntax and Argumentation - Bas Aarts)   At first, I think the The bold clause should be "...is located..." but then I realize it might be in the form of a non-finite clause (ing clause with a subject) but I'm not sure. If it isn't, how you describe this usage? Is this common in English?


I wrote the following code:   grid = [[0,0,0,0,0],[0,0,0,0,0]]  grid2 = [[1,1,1,1,1],[1,1,1,1,1]]  grid2 = grid  grid2[0][0] = 5  print(grid2) print(grid)   And this is the output:  [[5, 0, 0, 0, 0], [0, 0, 0, 0, 0]] [[5, 0, 0, 0, 0], [0, 0, 0, 0, 0]]   Why does the variable grid also get 5 in its output? These are two separate variables and I'm only changing one? Is there anyway to not have them synced?

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


I am currently a postdoc. My PhD research has been using Finite element method for additive manufacturing simulations. I come from materials engineering background and I don't have any formal education on continuum mechanics or finite element method. I had taken some advanced courses on mechanics. But, they did not cover anything related to finite element analysis or continuum mechanics. My self study on these topics are neither structured or formalized. I read books, online videos, tried some coding and concentrated on portions applicable for my research. I have forgotten most of the theory part. As a result, I know how to model my problem statement, publish papers and develop new problem statements. But I know nothing many topics that is covered in an actual finite element course. Also, I did not do many example problems or coded my own programs (just 1d or 2d case). Now, if I get an opportunity to teach students on the theoretical aspects of the finite element, how can I be confident that I can do a good job? I have very limited teaching experience and I have taught only materials engineering courses. Please advise.

I have the opportunity to teach an undergraduate class in statistics.  However, I've never taken statistics and the material and concepts are a little foreign to me.  I'm concerned, as a graduate student, that it may take up a lot of my personal time just to learn the material, much less teach it.  I really don't want to turn the opportunity down because I know its a good learning experience, but I don't want to become overwhelmed by it.  What are some effective strategies to teach a class that you've never taken before without overloading yourself?


This is hard to search and probably easy to solve, but I keep finding articles about intersecting circles, and that is not what I'm after. I don't know what to tag this under, so if you know how to classify this better, please do.     I'd like to know how the red circle's radius is related to the radii of the larger circles, and why.

Sorry if this is a foolish question, but I'm having difficulty understanding how to solve for $r_3$ in the following diagram...    According to WolframAlpha's page on tangent circles, the radius of $c_3$ can be calculated using the following formula $r_3=\frac{r_1 \times r_2}{(\sqrt{r_1}+\sqrt{r_2})^2}$, which can be simplified to $\frac{1}{\sqrt{r_3}}=\frac{1}{\sqrt{r_1}} + \frac{1}{\sqrt{r_2}}$.  To be completely honest, I'm having a hard time understanding understanding how this formula works (as I'm a very visual person). What exactly is happening here?


Some of the more common symptoms of COVID-19 are fever and cough. There has been  of SARS-Cov-2 in feces. Do we have any further knowledge of the prevalence of GI symptoms among those with COVID-19?

Would symptoms differ from eating virus contaminated food versus breathing in virus? Would symptoms be a good indicator where the virus is located? The COVID-19 causes respiratory symptoms and I guess that is because people are breathing in virus droplets in their lungs. But if you would swallow COVID-19 contaminated food and avoid breathing in the virus would that cause other symptoms like stomach pain or diarrhea?


This question is about use of the group genitive versus joint possessives in a phrase and/or list.      Where two or more distinct persons, animals, etc., are in the genitive, the group genitive applies only when there is joint possession, responsibility, relationship, as in 'William and Mary's reign' and 'Jack, Tom, and Mary's uncle.' If two separate possessions or other relationships are concerned, each noun must clearly be shown in the genitive.   (Eric Partridge, You Have a Point There, Routledge, 1978)  In this case there is the example of a grammar question on a Jetstream (ESL) test.  There are two possible questions, A: "What are Liam's and Noel's jobs?"  versus B: "What are Liam and Noel's jobs?"   (Answer: They're singers.)  Jetstream claims that 'B' is the correct question, i.e. group genitive. Why would 'A' NOT be correct given that 'jobs' is plural and Liam and Noel each have their own respective jobs?  Is this because 'singers' here acts as a type of job and they both share the same type of job?   Or could Jetstream be wrong on this one?  Or is it an ambiguous case?    Absent the answer, one might not presume when asking the question that both Liam and Noel have the same type of job, so could it still be correct to use the joint possessive form?   The test simply had the following list without possessive forms and the student had to supply the apostrophes and s's where appropriate. The italicized answer in parenthesis was the only correction the system made and it specifically indicated that "What are Liam's and Noel's jobs?" was incorrect.       Is this your umbrella? –  No, it isn't. It's my friend's umbrella.       Are these your keys? –  No, they aren't. They're Peter's.       What are Liam's and Noel's jobs? (What are Liam and Noel's jobs?) –    They're singers.       Is your husband's name Sam? –  Yes, it is.       What are your daughters' names? –  Their names are Tracy and Lily.       Is this the teacher's computer? –  Yes, it is.       That's a nice phone! –  Yes. It's Colin's. It's the new Samsung.       When is your parents' anniversary? –  It's on November 17th.

Which option is grammatical?        There will be readings from Nikki Giovanni’s and Alice Walker’s writings.   There will be readings from Nikki Giovanni and Alice Walker's writings.      Saying it out loud the latter sounds right, but looking at it the former looks better.


Is there a disable all command setting or command or any suggestions on how to move, I am 1600 blocks away from the command but I know the coordinates.

I set a command block to /tp. It was supposed to activate only if you had 0 time left, and to activate the command block with a hopper clock to keep giving it power.   But it is not checking if you have 0 time left, so it keeps teleporting me. I can't get close enough to the command block to break it, so I'm stuck in a neverending teleport loop.  Any ideas?


I have this awk command to increment a number inside a file:  awk -F"." '{$4=$4<=99?$4+1:0;print}' OFS="." post_all/version.ini > tmp && mv tmp post_all/version.ini   This works fine from bash, but when I try to add it to my bashrc it fails...  I tried adding alias update_version=awk -F"." '{$4=$4<=99?$4+1:0;print}' OFS="." post_all/version.ini > tmp && mv tmp post_all/version.ini  and the errors I got were:  -bash: =99?+1:0: No such file or directory -bash: print} OFS="." post_all/version.ini > tmp && mv tmp post_all/version.ini: No such file or directory

So before I reformatted (to get rid of Windows), I simply used this command to open documents by putting it at the end of the ~/.bashrc file:  alias commandless= 'gnome-open ./Documents/the-linux-command-line.pdf; gnome-open ./Documents/linux.odt'   But now everytime I start the terminal, it says:  bash: alias: gnome-open ./Documents/the-linux-command-line.pdf; gnome-open ./Documents/linux.odt: not found   before even typing anything in, and when I run the command nothing happens, not even error messages.


Let's assume $r < a < b < t$ , and a function $f:[r,t] \to \mathbb{R}$ , $f $ differentiable in $(r,t)$, with $f'(a)< 0 < f'(b)$ . Prove that there exists $c$ such that $a<c<b$ and $f'(c) = 0$  (So basically, i want to something like Bolzano for $f'$, although $f'$ may not be continuous)

I'm reading a book which gives this theorem without proof:     If a and b are any two points in an interval on which ƒ is differentiable, then ƒ'   takes on every value between ƒ'(a) and ƒ'(b).   As far as I can say, the theorem means that the fact ƒ' is the derivative of another function ƒ on [a, b] implies that ƒ' is continuous on [a, b].  Is my understanding correct? Is there a name of this theorem that I can use to find a proof of it?


How do you do a negative regex query in Mongodb?   I want to find all documents, where "Name" does not contain the string "james". E.g. filter out "james" or "john james" or "john james peter" or "somethingjames"  This works, but ONLY if the string begins with "james".   db.name.find({"name":/^((?!james).)/i});   What's wrong?

I know it's possible to match a word and then reverse the matches using other tools (e.g. grep -v). However, is it possible to match lines that do not contain a specific word, e.g. hede, using a regular expression?   Input:  hoho hihi haha hede   Code:  grep "<Regex for 'doesn't contain hede'>" input   Desired output:  hoho hihi haha


How do you use prepared statements without having any parameters to bind, f.ex. an SELECT query for retrieving all columns and rows within an table?  As i understand, prepared statements are good for security and efficiency, but isnt it possible to use it ONLY for either security or efficiency?  I have tried to look up answers on this, but without any luck.  Code (outputs nothing)  $stmt = mysqli_stmt_init($link); $sql = "SELECT * FROM `table`"; mysqli_stmt_prepare($stmt, $sql); mysqli_stmt_execute($stmt); $res = mysqli_stmt_get_result($stmt); while($row = mysqli_fetch_array($res)){     foreach($row as $val){        printf($val\n);        }     }

If user input is inserted without modification into an SQL query, then the application becomes vulnerable to , like in the following example:  $unsafe_variable = $_POST['user_input'];   mysql_query("INSERT INTO `table` (`column`) VALUES ('$unsafe_variable')");   That's because the user can input something like value'); DROP TABLE table;--, and the query becomes:  INSERT INTO `table` (`column`) VALUES('value'); DROP TABLE table;--')   What can be done to prevent this from happening?


I added a div element into a variable and appended it to the document:  var faceDiv = $("<div class='dropDownJsFace dropDownJsArrowDown' />");   Now I'm attempting to reference that div within the .on() function via e.target like so  $(document).on("click", function(e){     if(e.target == faceDiv)     {         alert("done");       } });   To clarify, I want it to specifically reference that dynamically created div, as apposed to the class .dropDownJsFace.

I have a bit of code where I am looping through all the select boxes on a page and binding a .hover event to them to do a bit of twiddling with their width on mouse on/off.  This happens on page ready and works just fine.  The problem I have is that any select boxes I add via Ajax or DOM after the initial loop won't have the event bound.  I have found this plugin (), but before I add another 5k to my pages with a plugin, I want to see if anyone knows a way to do this, either with jQuery directly or by another option.


Suppose, I take an irrational number, q, and an integer n, and I want to print the truncated value of q after keeping exactly n digits after the decimal.   Example:  Input: q = 3.14159625, n = 3 Output: 3.141

How do I format a number in Java? What are the "Best Practices"? Will I need to round a number before I format it?  32.302342342342343 => 32.30 .7323 => 0.73  etc.


How to show that   $\limsup \{a_n\}=-\liminf \{-a_n\}$  I could use this property : if $a= \sup(X) $ then, $-a=\inf(-X)$?   where  $\lim\sup\{a_n\}=\lim_{n\rightarrow\infty}[\sup\{a_k\,|\,k\geq n\}]$  $\liminf\{a_n\}=\lim_{n\rightarrow\infty}[\inf\{a_k\,|\,k\geq n\}]$

How can we prove that $\liminf x_n = -\limsup (-x_n)$?  The definitions we are using are $\limsup x_n = \lim\limits_{n\to\infty} \sup\{x_k; k\ge n\}$ $\liminf x_n = \lim\limits_{n\to\infty} \inf\{x_k; k\ge n\}$


I am using Ubuntu 16..  I want to run the following command  apt-get update   It is working after executing the following  sudo -i   and exporting http_proxy.  But when I execute   sudo apt-get update   after exporting http_proxy, the command results in error. How can I run apt-get update without having to use a root shell?

I need to configure proxy. There wasn't apt.conf file in etc/apt/ so I've created it using nano.   But I don't understand what I need to write there. I've written  http_proxy = http://lgn:pwd@192.168.1.254:8080/ there and then restarted networking. But when I try to apt-get update - it doesn't work.   Actually I don't understand what port and ip I should write in apt.conf file(there was example with 192.168.1.254 ip and 8080 port so I decided to use them).


I never saw any discussion on it in meta - but it seems common knowledge that it is unacceptable to both vote to close a question and also answer it.  What about questions that should be migrated?  If a user asks a software question in SO, and I voted to migrate it to SU, is it acceptable if I also propose an answer to it, in SO?

I've noticed quite a few cases () where people not only vote to close a question, but then also answer said question. At best this is just silly, and at worst it is totally hypocritical and seems almost like rep whoring (since often the closers answers are the only ones that remain to be voted on since no new answers can be given).  If you want to close a question, it makes more sense to simply add a comment if you feel the need to say something. This also leaves the option open for the author of the question to delete it if they want to. If the author realizes they've asked a duplicate, or they want to avoid the onslaught of downvotes that can often accompany a closed question, they should be allowed to delete it. However, if any answers to the question have upvotes, the author can't delete it.  So why do people answer and close? Should we try to crack down on this sort of thing, via either new features, clearly stating it in the FAQs, or just getting the word out through commenting when we see it?  EDIT: Just to clarify, I'm asking this in relation to SO, not MetaSO.


Prove that $ \frac{1}{1*5} + \frac{1}{2*7} + \frac{1}{3*9}+... = \frac{8}{9} - \frac{2}{3}\ln(2)$  I got the answer using the hint given in the question  It mentioned to consider the integral$\int x^2 \ln(1-x^2)dx$. I evaluated the integral by integration by parts.  Then I again evaluated by applying Taylor series. I equated both expressions and took limits of integration from 0 to 1 to obtain the result.  Is there any other way to solve this question? Without the hint, I would never have thought of considering that Integration.  What I tried: $\sum_{i=1}^{\infty} \frac{1}{i(2i+3)} = \frac{1}{3} \sum_{i=1}^{\infty} \frac{1}{i}-\frac{2}{2i+3}$  But both of the above series diverge

Prove that $$\sum_{i=1}^{\infty} \frac{1}{i(2i+3)} = \frac89 -\frac23\ln2$$  I tried using integration but failed miserably. Hints please.


I have the following text..  [start] this is my line [end]   My output should be:  this is my line   Need help..  Tried a combination of :  sed -n '/start/,/end/p' $File  & sed -e "s/]/']/" -e "s/\[/['/"   $file   but it brings up the pattern too.

I'm going to submit form using cURL, where some of the contents is come from other file, selected using sed  If param1 is line matching pattern from other file using sed, below command will works fine:  curl -d param1="$(sed -n '/matchpattern/p' file.txt)" -d param2=value2 http://example.com/submit   Now, go to the problem. I want show only text between 2 matching pattern excluding the matching pattern itself.  Lets say file.txt contains:  Bla bla bla firstmatch It is a long established fact that a reader will be distracted by the readable content of a page when looking at its layout. secondmatch The point of using Lorem Ipsum is that it has a more-or-less normal distribution of letters, as opposed to using 'Content here, content here', making it look like readable English.   Currently, lots of "beetween 2 matching pattern" sed command won't remove firstmatch and secondmatch.  I want the result to become:  It is a long established fact that a reader will be distracted by the readable content of a page when looking at its layout.


I am using AWS to run Ubuntu server 14.04 and by mistake I issued this command  sudo chmod -R 777 /usr/   Since issuing this command, I can't switch from ubuntu to root. When I issue this command  sudo su   It shows me error   sudo: /usr/bin/sudo must be owned by uid 0 and have the setuid bit set   I don't have a backup of my server.

I needed to edit a .config file (which I know for a fact is not creating these problems, just to clear that up) and it wouldn't let me save it, so I took ownership of /etc and all contents with the command chown -hR username /etc and that let me edit the .config file but now whenever I try to install any packages or use any sudo commands, it doesn't work  (I've checked for errors in the sudo file in sudoers.d and there was nothing wrong with that).   So how do I return it to the previous owner?


I can't think of the word that describes a word snob and use of the word pretty much proves you are one.  Anybody?

What's a big-vocabulary word for someone with a big vocabulary?  I'd like to say I'm looking for a "_____".


I want to prepend a text contained in the file disclaimer.txt to all the .m files in a folder.  I tried the following:  text=$(cat ./disclaimer.txt)  for f in ./*.m do    sed -i '1i $text' $f done   but it just prepends an empty line.

I hate to clutter my source code files with licensing/attribution comments but some times it is a requirement. So having dozens of source code files (organized in a tree of subdirectories) written I need to add the same multiline comment to the beginning of each of them.  I suspect this is a very easy task to do with standard GNU/Linux command line tools though I am hardly proficient in making any serious use of them, so I beg your pardon and ask for your help.  What I need is to replace every theTargetFile.txt in ./*.txt (including in subdirectories recursively) with something like cat theCommonComment.txt theTargetFile.txt.   I would also prefer to exclude files fitting a particular more specific mask like consider all *.txt but leave *.DontTouch.txt intact.  I think the hardest part of what I actually need is a fancy find-based spell that would run through subdirectories, include *.txt files and exclude *.DontTouch.txt files.


Is there a way to open a *.lyr file in QGIS without using ArcGIS for Desktop?   I have no access to ArcGIS, so the solution explained in  is not an option.  I have a *.lyr file with a lot of information and it is not possible to reproduce it all by myself.

I am putting together a GIS server using GeoServer and need some help with importing my layer styles from ArcGIS 10 to  format.    I have one layer in ArcMap properly symbolized and labeled, how can I get this layers symbolization and labeling into a SLD file?


I use Ubuntu in a machine I own and in a machine I only have standard user permissions ( not admin). Is there any way to format a usb to ext4 and make it work (file ownership problems) if I cannot run sudo commands on the second machine? Ideally the solution would work on any other Ubuntu/Linux with whatever kind of account.

Using Ubuntu 11.10, how do I format an external or USB drive? I don't find an option to 'format' when I right click. In the new version, the drives don't come up on the desktop, but instead come on the Launcher.


Question When one/more users suggest another post answers your question (and there is a banner at the top of the page asking if question title answers your question? Yes/No), what physically happens to your question/on the site if you select Yes? (For example: is it immediately deleted, is it marked as duplicate, can people still provide answers, etc?)  Context  In my case, the suggested post partly answers / relates to my question (about 50%) - so I am more happy for my question to be linked to the suggested answer, if that's the outcome(?) (assuming my question isn't then deleted/hidden on the site) However, as the post question only partly covers my question (and in addition, several users have provided very helpful and detailed answers to my question), I definitely would not want my question (their contributions) to be deleted, if that's the outcome(?)   Related questions Please note (and for users who wish to read/learn more), there are several answers on the related topic of 'duplicate questions':   Summary: This is a feature request based on a issue caused by a much older version of SE. It is useful for context, but does not answer the above question specifically. Note (and de-dupe defence): The lead answer is 6 years old and the "new/updated" UI it shows is out-of-date.  Summary: This is a discussion about making duplicates more clear. Note (and de-dupe defence): Similar to the above, the lead answer references an old version of SE and the website has since changed. There is one answer that recommends [Change the text on the first button from "That solved my problem!" to "Yes, my question is a duplicate."] but is low-scoring (5 vs. 150+ on lead) and is also from 6+ years ago - so unclear if this is what happens or not.  I believe this question is warranted and my intention is to clarify how SE works (in the context of "Does this answer your question?"), and help remove any doubt/confusion for users. (The alternative being for users to continue to read about how SE used to work half a decade ago).

I keep seeing custom flags in the queue from question askers who are incredibly irritated because there is a big, prominent box at the top of their question. It's just a list of other questions which may have the answer they desire, and is only even displayed to them because the question is not closed yet.  This question may already have an answer here: [list]  But to an ordinary user, it is not at all clear that the box is only shown to them, or that it will go away on its own if their question never actually gets closed. Could the text for this notice be altered to make it more clear that:  They are just suggestions for the person to view. Potentially if they agree with one, they should vote to close their own question as a duplicate of it.  Their question is not closed yet. If they disagree with the duplicates suggested, they should clarify their question and explain why it's not a duplicate.   I was thinking of an altered wording such as:  You might be able to find an answer to your question here: [list] If those answers do not fully address your question, please [edit your question] to clarify your exact problem.  I went with a more direct wording for the bolded title. Since the notice is only displayed to the asker, it makes more sense to talk directly to them in the message rather than making it feel like it's supposed to be addressing the entire audience of the site. Emphasize that only that person is seeing it by talking to them. It would also be helpful to append a "More info" link at the end of the message that links them to some further documentation about duplicates, and explains how the notice works - particularly that it will go away eventually or change to a proper duplicate notice if the question does get closed.


I have read that rationals are dense in the reals, but I've been curious if the terminating decimals are as well. Since, in applied math, all effectively "real" numbers are approximated with terminating decimals, I would expect the terminating decimals to have this property, and if not I'm curious why. Here I'm defining the terminating decimals like this: $$D = \{\frac{m}{10^n} \in \mathbb{Q} : m \in \mathbb{Z} \wedge n \in \mathbb{N}_0\}$$.

The set $S$ of real numbers of the form $m/10^n$, $m,n$ integers and $n$ greater than or equal to $0$, is a dense subset of $\mathbb R$ or not??   I know dense means closure of $S$ in $\mathbb R$ is $\mathbb R$ then it will be dense. How to prove or disprove I have no idea.


Ok so I'm learning terminal.  I'm trying to cd to folder: /network/NAS/Z-1/1 Video/1 Video  After running df, the NAS volume (Windows 10 volumed on my home network btw) is mounted in "/Volumes/Z-1/" (Not sure why my "Z" folder was renamed to "Z-1"?)  Anyways, so I can change my directory to the "Z" folder (or "Z-1") on the NAS drive, but I can't change my directory to the "1 Video" folder inside the "Z" folder.  I've tried using:  cd /volumes/z-1/1 video  I've also tried using an underscore inbetween 1 and video.  Here's an image for reference:

I have a directory called "Reader 0.5" in my Desktop on Mac Os X. When to access the directory in terminal, I am using below code:  cd /Users/niho/Desktop/Reader 0.5   but it throws:  No such file or directory  error.  How can I cd into that directory?  Thanks.


I'm trying to perform a simple buffer on GeoJSON file using Python script. I am able to do it on a shapefile using Python script and on GeoJSON using QGIS fix distance buffer tool but I can't figure out how to do it on GeoJSON using Python script. I read many posts on it but none of them include working solely on GeoJSON. I also know that it is possible to convert GeoJSON to .shp but I need to work only with GeoJSON files.  My code that works for .shp file:  from osgeo import ogr  ds = ogr.Open(r'C:\vector files\tryyy.shp', 1) in_lyr = ds.GetLayer() out_lyr = ds.CreateLayer('new_buff44',in_lyr.GetSpatialRef(),ogr.wkbPolygon) out_lyr.CreateFields(in_lyr.schema) out_defn = out_lyr.GetLayerDefn() out_feat = ogr.Feature(out_defn) bufferDist = -0.00015075  for in_feat in in_lyr:      geom = in_feat.geometry()     out_feat.SetGeometry(geom)     for in_feat in in_lyr:          geom = in_feat.geometry().Buffer(bufferDist)         out_feat.SetGeometry(geom)         for i in range(in_feat.GetFieldCount()):             value = in_feat.GetField(i)             out_feat.SetField(i, value)         out_lyr.CreateFeature(out_feat)  del ds print "finish"   When I change the file from shp to geojson in the org.Open line I get:      NoneType' object has no attribute 'CreateFields'   I thought that if I read vector file as OGR datasource object then it doesn't matter which format is the original vector file.   Can someone help me understand what I should change so that the code will work on GeoJSON files?


I would like to see which files are in my jar File. I've found out that I need to use java -jar  on my CentOS VM. But how do I add the parameters tf.  At the end I have something like: java -jar "MyJarFile.jar" -tf.  When I do it like that the parameters are getting ignored..

What would be the easiest way to view classes, methods, properties, etc. inside a jar file? I'm looking for something equivalent to the very useful  Lutz Roeder .NET Reflector  - for Java


I had the following sentence in mind: "The conflict escalated quite rapidly, as I imagined/predicted would be the case". To my ears, the sentence sounds good, and a moderate amount of people have already used the phrases  and  before. However, I'm still concerned and not fully convinced about its grammaticality. Here are a few possible alternatives that should be "more grammatical" in my opinion:  As I imagined/predicted the case to be [...] As I imagined/predicted that the case would be [...] As I imagined/predicted what the case would be like [...] As what I imagined/predicted the case would be like [...] As what I imagined/predicted that the case would be like [...] As what I imagined/predicted the case to be like [...]  Unfortunately, none of these alternatives returns significant hits in Google search, as I imagined would be the case (pun totally intended). Is the phrase  "as I imagined would be the case" grammatically correct and why?  Answering to comments: Yes. That said, it's hard to explain why without having an argument to counter. Why do you think it's not grammatical? You imagine or predict something. So, according to this logic, the phrase should be answering the question I imagined/predicted what? I imagined/predicted what the case would be like. So now that I think of it, the most grammatical version of the phrase IMO should be "as I imagined/predicted what the case would be like, [...]", although it sounds quite convoluted to be honest. The phrase "as I imagined would be the case" omits what, like and inverts the relative order between the case and would be. Are all those changes grammatical?  What about the adverb as? As describes an event by comparing it to something else. So a phrase that begins with as should be answering the question: as what? As what I imagined/predicted that the case would be like. That's the version that makes the most grammatical sense to me. But, of course, nobody uses it :-)

My senior English teacher was a tad bit confused where the subject for was is in this sentence:     As was traditional for unmarried women, Jane lived at home her entire life.


My Ubuntu 18.04 installation sometimes randomly freezes. I saw in one question that maybe this is a Gnome problem, and the solution proposed was to downgrade from bionic-proposed to main. What does that mean, and how can I do that?

I have an Ubuntu GNOME 16.04 with GNOME 3.18 64-bit VM, and in that VM I needed to test something in the xenial-proposed channel so I activated it in the software-properties-gtk, ran sudo apt-get update && sudo apt-get dist-upgrade and installed all the upgrades from the xenial-proposed channel as I couldn't find a way to get it just to upgrade the package I needed.  Now however I wish to downgrade all the packaged upgraded to their xenial-proposed versions to their version in the stable/normal channels, but how can this be achieved? Can I use ppa-purge to do this? And if so, how?  If I just disable the xenial-proposed channel via the same means that I enabled it will the packaged installed and upgraded to their xenial-proposed versions start to receive updates again from the stable/normal channels once the version numbers there are higher than the installed or will I receive no updates at all then until I enable the xenial-proposed channel again?


How do I find using the Squeeze theorem  $$\lim_{n\to \infty}\sum_{k=1}^n \frac{1}{\sqrt{n^2+k}} \;,$$  using the fact that  $$ \lim_{n\to \infty}\frac{n}{\sqrt{n^2+n}}=1.$$  Thank you very much for your help,   C.G

Direct way leads to nowhere.  $$\lim_{n\rightarrow \infty} \sum^{n}_{i=1} \frac{1}{\sqrt {n^2 +i} } = \lim_{n\rightarrow \infty} \sum^{n}_{i=1} \frac{1}{n \sqrt {1 +\frac{i}{n^2}} } = $$  $$ = \lim_{n\rightarrow \infty} \frac{1}{n} \cdot \lim_{n\rightarrow \infty} \sum^{n}_{i=1} \frac{1}{\sqrt {1 +\frac{i}{n^2}} } = 0 \cdot \sum^{n}_{i=1} 1 = 0 \cdot n $$  So, I tried to apply squeeze theorem:  $$\lim_{n\rightarrow \infty} \sum^{n}_{i=1} \frac{1}{\sqrt {n^2 +i} } \leq \lim_{n\rightarrow \infty} \sum^{n}_{i=1} \frac{1}{n}  = 1$$  Could you help me to figure out the lower bound?


Given a vector $\begin{bmatrix}a\\b\\c\end{bmatrix}$ what is a simple solution to find any vector perpendicular to it?

Given a vector $n \in \mathbb R^3$, how can I find (any) perpendicular normal $x$, such that $n^T\cdot x=0$ for all possible values of $n$ (i.e. with no edge cases)


I have a line in my code:  force=sizeGoalForceKappa*tanh((origRadius-v->radius)/origRadius)*(oldDist+minSpacing-v->radius)/minSpacing;   The code is at revision 881. Is there a way to see history of only this line, while ignoring other changes? Showing log for a single file ignores other files. Can I get a log for a single line, or something similar? I would like to see how definition of "force" has evolved over time, and when "force" was introduced. SVN Blame only gives me the revision in which a line was last changed.

Is it possible to see the history of changes to a particular line of code in a Subversion repository?  I'd like, for instance, to be able to see when a particular statement was added or when that statement was changed, even if its line number is not the same any more.


I would appreciate if somebody could help me with the following problem:   Q: How many solutions are  there to the equation  $$ a+b+c+d = 30 ,(a\leq b\leq c\leq d) $$ where $a,b,c,d\in \{1,2,\cdots,30\}$

What is the total number of solutions of an equation of the form $x_1 + x_2 + \cdots + x_r = m$ such that $1 \le x_1 < x_2 < \cdots < x_r < N$ where $N$ is some natural number and $x_1, x_2, \cdots, x_r, m$ are integers?  Also, what would be the solution in the relaxed case where $x_1, x_2, x_3, \dots, x_r$ could be equal?


To remove the last node of the list, I just traversed till the last node and assigned it to null. But I still see the last node value. I am wondering why node = null does not have any effect.  void deleteLastNode(Node node){     while(node.next != null)     {         node = node.next;     }     node = null; }

I always thought Java uses pass-by-reference. However, I've seen a couple of blog posts (for example, ) that claim that it isn't (the blog post says that Java uses pass-by-value). I don't think I understand the distinction they're making. What is the explanation?


So, I made a searching system test (This code searches items out of the "diakok" named database) and there is a problem with it. When I type in my name (Géró Kristóf) it says there are no names in the database like this, but when I write it as Gero Kristof, it finds that right (but it doesn't write out the name, because of these special letters), while there are é and ó instead of e and o in the database. I tried changing the encoding types also in the database and the code, but nothing works right. (With names which don't have special characters, it works just fine)  <?php   $keresesi_tipus = 'felhasznalonev';   $keresesi_kifejezes = trim($_POST['keresesi_kifejezes']); header("Content-type: text/html; charset=utf-8");   if (!$keresesi_kifejezes) {     echo "Nem adott meg keresni való nevet. (1-es hibakód)";     exit;   }    if (!get_magic_quotes_gpc()) {     $keresesi_tipus = addslashes($keresesi_tipus);   }   @ $adatbazis = new mysqli('localhost', 'root', '', 'diakok');   if (mysqli_connect_errno()) {     echo "Hiba! Nem sikerült csatlakozni az adatbázishoz. (2-es hibakód)";     exit;   }    $lekerdezes = "SELECT * FROM diakok WHERE ".$keresesi_tipus                 ." LIKE '%".$keresesi_kifejezes."%'";   $talalat = $adatbazis->query($lekerdezes);   $talalatok_szama = $talalat->num_rows;    echo "
A keresésnek megfelelő diákok száma: ".$talalatok_szama."
";    for ($i = 0; $i < $talalatok_szama; $i++) {     $sor = $talalat->fetch_assoc();     echo "
".($i+1).". Teljes neve: ";     echo htmlspecialchars(stripslashes($sor['teljes_nev']));     echo "
 Felhasználóneve: ";     echo stripslashes($sor['felhasznalonev']);     echo "
 Kategóriája: ";     echo stripslashes($sor['kategoria']);     echo "
";     echo "
";   }   $talalat->free();   $adatbazis->close(); ?>   Here is a pic about the database:

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.


Zorn's lemma states that, if X is a partially ordered set such that every chain in X has an upper bound, then X contains a maximal element.  I think that $(Z^+,\le)$ satisfies the conditions of Zorn's lemma. The order is partial and every totally ordered subset has an upper bound in $Z^+$. Yet, since $Z^+$ is infinite, it has no maximal element.  Where is the fault in my reasoning?

Zorn's Lemma states that if every chain $C$ in a partially ordered set $X$ has an upper bound then there is at least one maximal element in $X$.  Let $n\in \mathbb{N}$, $C_n \subset \mathbb{N}$ be the set containing the natural numbers $\{1,\dots,n\}$. Then if $k\le n$, $C_k\subset C_n$, so $C_n$ is a chain. Also, $C_n$ has an upper bound, such as $n+1$. But what is the maximal element of $\mathbb{N}$?  There's something I don't get in Zorn's Lemma statement.


Let $f$ be an entire function s.t. $\forall z \in \mathbb{C}, f(z)\text{ is real}\iff z\text{ is real}$. Prove that $\exists a,b \in \mathbb{R}$ s.t. $a\neq 0$ and $\forall z \in \mathbb{C}, f(z)=az+b$.  I think I have a proof for this using some advanced theorems, but I want to find one that can be done by elementary means (by a student in undergraduate complex analysis).

Let $f$ be a holomorphic function defined on $\Bbb C$ such that $f^{-1}(\Bbb R)=\Bbb R$. Prove that there exists $a,b \in \Bbb R, \; a \neq 0 \;$ such that $f(z)=az+b \;$ for every $z \in \Bbb C$.  I was given a hint: define the function $g(z)=\frac{f(z)-f(0)}{z}$. such $g$ is also holomorphic in $\Bbb C$ since the only singularity is in $0$, and it is a removable singularity since we can define $g(0)=f'(0)$. Next I thought about proving $g$ is bounded, and thus constant (using Liouville's theorem), but pretty much out of ideas. How can I finish the proof/solve in another way?


Although Quora and Stack Overflow work in different domains, both inherently share one common thing, they are Q & A sites.  One feature that Quora has, which I believe is not on Stack Overflow (or I was not able to find it) is Ask To Answer, inviting someone to answer a question.  I am not talking about bounties, but a general request to someone to answer a question, that just might have gone ignored by people (as it happened to me of late). A person might not be willing to offer a bounty, in which case, their question remains unanswered.

When I browse through other questions to find my answer, sometimes I'll find answers similar to what I'm looking for, and though they don't exactly answer my question, the author might be able to do so. Could we have a feature on SO that will let me request that another user answer my question, in case I find someone who could potentially answer my question?


I'm fairly new to LaTeX and having trouble with citations when using texmaker.   I have used Mendeley to produce what i believe is the .bib file containing all relevant references. (File produced = library & Filetype = BibTex Database, when double clicked "library" is opening in TEXworks). The bibtex file (library) seems to be in the correct format i.e.  @report{refname, abstract = {}, author = {}, doi = {}, file = {}, issn = {}, journal = {}, keywords = {}, month = , number = {}, pages = {}, pmid = {}, title = {{}}, url = {}, volume = {}, year = {} }   Within Texmaker i have the generic Latex source saved as testdoc.tex  \documentclass[a4paper,12pt]{report} \begin{document} Blahblah \cite{refname} \bibliographystyle{plain} \bibliography{library} \end{document}   however within the PDF my citations do not appear to work and have the warning message   LaTeX Warning: Citation `refname' on page X undefined on input line XX. No file testdoc.bbl.

I'm having some problems with my bibliography in Texmaker. My code is:  \documentclass[11pt, a4paper]{article} \usepackage{graphicx} \usepackage{amsmath} \usepackage{natbib} \usepackage[utf8]{inputenc}     \usepackage{natbib} \usepackage[usenames,dvipsnames]{xcolor} \usepackage[left=2cm,right=2cm,top=2cm,bottom=2cm]{geometry} \begin{document}  ....  \cite{Johnson} \bibliographystyle{plain} \bibliography{mybib}  \end{document}   I also created a new file (File > New) that I saved as mybib.bib:  @Article{Johnson, author = {Edgar G. Johnson and Alfred O. Nier}, title = {Angular Aberrations in Sector Shaped Electromagnetic Lenses for Focusing Beams of  Charged Particles}, journal = {Physical Review}, year = {1953}, volume = {91}, number = {1}, }  @phdthesis{Zoran, author = {Zoran Racic}, title = {\'Etude et essais du spectromÃ¨tre Ã  plasma {DYMIO} de la  mission {MARS 96}}, publisher = {UniversitÃ© Pierre et Marie Curie}, year = {1996} }   When I compile my .tex file, I only have a [?] appearing.  Could you tell me what my mistake is?


What does it mean, formally, when we say that a digit in a number is a ?

In my textbooks,  are defined as:   “Significant figures by definition are the reliable digits in a number that are known with certainty.”  “A significant figure is the one which is known to be reasonably reliable.”    Reliable means giving the same result on successive trials or reliable information can be trusted to be accurate. However, at the end of each of the two definitions it is also written that ‘the last digit of a number is generally considered uncertain in the absence of qualifying information.' For example if the mass of an object is 12.248 gm, the last digit which is ‘8’ is uncertain by plus or minus 0.001 gm. This uncertainty is unreliability in the information. So, the digit ‘8’ is uncertain, and thus according to the definition 1 it is not a significant figure. However, the rules for significant figures say that ‘non-zero digits are all significant’. Due to the last digit ‘8’, if the object was weighed with careful handling minimizing the chances of error, the figures preceding ‘8’ that are (1, 2, 2, 4) are certain and reliable. If the mass of another object is 2 gm, then it is uncertain by plus or minus 1 gm i.e. its mass could be 3 gm or could be 1 gm.  ‘2’ is therefore not certain! What is the reason that significant figures are defined to be the reliable digits in a number? In what sense they are said to be reliable?


Is there single word that describes that I learned and became proficient in using a skill but is not as strong as mastered.  I want to say, "I (blank)ed a new technique." I learned it, but I have also become quite proficient in using it. Although I am proficient, I wouldn't say I have mastered the technique.

I'm looking for the noun form of "person with intermediate skill". For example, in the context of a particular activity, "person with no skill" might be designated a novice, and "person with much skill" might be designated an expert. However I know of no such word in between these two extremes.   My only thought is amateur, which has a distinct meaning from describing level of skill, although skill level can often be inferred. I'm looking for a better solution.  EDIT: due to the attention this question has received, I'll try to offer some clarification in order to reduce repeat questions.   "Journeyman" would certainly not work. I am a software developer by profession. However the word I'm looking for should hopefully be profession-agnostic. I am trying to designate the skill level of the person that some learning material might be appropriate for. The word that I'm looking for follows the preposition "for".   For Beginners  For [word for intermediate-skilled person] For Experts  Sorry, but even after all the great answers, I'm still learning towards "amateur" even though it is technically incorrect. Also, the word should not be so esoteric that only people with English degrees know what it means. Keep the ideas coming!


I am attempting to write a script to list all the shebang lines in python files.  What I would like to do is  sudo bash -c 'for logf in $(find / -name "*.py"); do fgrep '#!/usr/bin' "$logf"; done'   This gives error bash: !/usr/bin': event not found. I understand why, although the meaning of the error is unclear.  The trouble is I can't figure out how to pass a string to bash which includes another string without command execution.  If I leave off the "#!" it works, but of course includes a number of other lines.   I have tried practically every combination of escape and string without success.

I recently learned about , but am having trouble making it work with relatively sophisticated commands. For example, I would like to ask watch to run the following command on zsh every three seconds*: for x in `command_1 | grep keyword | cut -d' ' -f1`; do command_2 "word[word=number]" $x; done  as you can see the line above includes single quotes, double quotes, among other special characters. So I tried: watch -n 3 "for x in `my_command | grep keyword | cut -d' ' -f1`; do command2 "rusage[mem=7000]" $x; done"  but then I got:  no matches found for x in !@#$# ....; done  I tried other combinations without success. Here's one of those attempts: watch -n 3 "for x in $(bjobs -w | grep pre_seg | cut -d' ' -f1); do bmod -R "rusage[mem=7000]" $x; done"  which also results in a similar error. Any ideas how to make this work?  *I would also be intersted in solutions that work on bash


If you scroll down on the Ask Question page you get a 'footer overflow' as seen below:

When I can scroll down far enough to have the hot network questions overlap the footer (because my question is short) there is no background under the text:    Could they either be given a white background: (just disable the transparency option)    Or stop at the footer:      This also happens with the help text on some sites, as per this bug report:     Ubuntu 14.04.1 (Latest LTS Version), . Same problem with  and .  Windows 10 Pro,  and .  (Images linked to screenshot of browser)  My question is different from  because my issue is the lack of background on the footer.   I think there was a site redesign?


So I'm having A VERY STRANGE scenario, I've simplified the code, but having the  SAME issues.  def write_to_bf_of_lpr(bf_source, bf_destination, lpr_index, start, length):     for x in range(length):         bf_destination[lpr_index][start + x] = bf_source[start + x]  source = ['a','b','c','d','e']  destination = [[0]*5]*3 dets2=[[0, 0, 0, 0, 0], [0, 0, 0, 0, 0], [0, 0, 0, 0, 0]]  for x in range(1):     write_to_bf_of_lpr(bf_source=source,bf_destination=dets2,lpr_index=x,start=1,length=2)  for x in range(1):     write_to_bf_of_lpr(bf_source=source,bf_destination=destination,lpr_index=x,start=1,length=2)   this code is quite simple to understand, what I wish to do is only change specific  array each time (or iteration).  Now: when I write in shorented version: destination = [[0]*5]*3 it is changing ALL the arrays within SINGLE iteration.  When I write in the LONG version (which is not preferable ) I get the CORRECT version.  You can see that dest2 is the correct, while destination is the wrong answer.   The funny thing is, that I simply COPIED the values from the short version... and there's different result...  Is it Pycharm bug, python, or am i missing something? please see screenshot of the output

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


so i'm working on my CS project in which we need to sort a list of DVD's by director. it'll compile, however when i run it i'm getting a null(in java.util.Arrays) i've called java.text.numberformat and java.util.* is that i forgot to add anything in my imports? thanks friends.   public void addDVD(String title, String director, int year, double cost, boolean bluray) {     DVD newDvd = new DVD(title, director, year, cost, bluray);     int index = Arrays.binarySearch(collection, newDvd);     if(index >= 0) {         System.out.println("DVD with title " + newDvd.getTitle() + " already exists.");     }     else {         int index1 = -index - 1;         collection = insertDVD(collection, newDvd, index1);         System.out.println("DVD with title " + newDvd.getTitle() + " added.");     }     totalCost += cost; }

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


There aren't any natural number $n$ for which the given condition is satisfied. Here is how I proved it:  For $\sqrt{n-1}+\sqrt{n+1}$ to be rational, $\sqrt{n-1}$ and $\sqrt{n+1}$ must individually be rational as the sum of two positive numbers can't be rational if at least one of them is irrational.  For $\sqrt{n-1}$ and $\sqrt{n+1}$ to be individually rational, $(n-1)$ and $(n+1)$ must be perfect squares. We can see that the two numbers differ by $2$: $(n+1)-(n-1)=2$. This is not possible as consecutive squares differ by at least $3$. $\blacksquare$  The book I am using proves the same conditions in a more involved way:  If $\sqrt{n-1}+\sqrt{n+1}$ is rational, $\frac{1}{\sqrt{n-1}+\sqrt{n+1}}$ must also be. Multiplying by $\frac{\sqrt{n-1}-\sqrt{n+1}}{\sqrt{n-1}-\sqrt{n+1}}$, we get $\frac{\sqrt{n-1}-\sqrt{n+1}}{2}$ is rational $\implies \sqrt{n-1}-\sqrt{n+1}$ is rational.  The proof then proceeds to do what I did but for both $\sqrt{n-1}-\sqrt{n+1}$ and $\sqrt{n-1}+\sqrt{n+1}$.  There is also an answer on  that proves the same in a way similar to the book prove I just mentioned.  Is the way I have proved the same incomplete or wrong?  My question is not duplicate because it is asking why my proof is wrong. The linked duplicate asks for a proof; I have provided the proof, both mine and the one found in book, with the question.

Find all natural numbers n such that ${(n+1)}^{1/2}-{(n-1)}^{1/2}$ is a rational number I think there wouldn't be any natural number as the square of a rational number is rational, which is not possible in this case. Am I correct please help me


I'm quite new to Ubuntu. I've installed synaptic using the command:   sudo apt-get install synaptic   and this is the concluding line of the output:   synaptic is already the newest version (0.84.2). 0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.   But seems the synaptic application package refuses to launch upon prompting for authentication of password.  What's the problem and how can I fix it?

I installed Ubuntu 17.10. Now I am having trouble with gksu:  $ gksu -dg synaptic No ask_pass set, using default! xauth: /tmp/libgksu-HgUjgQ/.Xauthority STARTUP_ID: gksu/synaptic/8760-0-alex-XPS-15-9530_TIME4974977 cmd[0]: /usr/bin/sudo cmd[1]: -H cmd[2]: -S cmd[3]: -p cmd[4]: GNOME_SUDO_PASS cmd[5]: -u cmd[6]: root cmd[7]: -- cmd[8]: synaptic buffer: -GNOME_SUDO_PASS- brute force GNOME_SUDO_PASS ended... Yeah, we're in... Unable to init server: Could not connect: Connection refused (synaptic:8767): Gtk-WARNING **: cannot open display: :1 xauth: /tmp/libgksu-HgUjgQ/.Xauthority xauth_env: (null) dir: /tmp/libgksu-HgUjgQ   If I don't use -g, the password dialog is disabled. So looks like a problem with creating a tty for root.  Any advice?