I have a file with 40,000 rows   head flower_all      0.992957746478873 0.00704225352112677     0.646410833917366 0.353589166082634     0.992957746478873 0.00704225352112677     0.992957746478873 0.00704225352112677     0.992957746478873 0.00704225352112677     0.992957746478873 0.00704225352112677     0.992957746478873 0.00704225352112677     0.992957746478873 0.00704225352112677     0.5 0.5   I want to keep only 3 significant digits. My desired output:  0.992 0.007 0.646 0.353 0.992 0.007 0.992 0.007 0.992 0.007 0.992 0.007 0.992 0.007 0.992 0.007 0.5 0.5   How can I do it?
I want to print the floating point number with exactly two significant digits in bash (maybe using a common tool like awk, bc, dc, perl etc.).  Examples:   76543 should be printed as 76000 0.0076543 should be printed as 0.0076   In both cases the significant digits are 7 and 6. I have read some answers for similar problems like:      but the answers focus on limiting the number of decimal places (eg. bc command with scale=2 or printf command with %.2f) instead of significant digits.  Is there an easy way to format the number with exactly 2 significant digits or do I have to write my own function?
Can I add extension methods to an existing static class? I'm a fan of extension methods in C#, but haven't had any success adding an extension method to a static class, such as Console.  For example, if I want to add an extension to Console, called 'WriteBlueLine', so that I can go:  Console.WriteBlueLine("This text is blue");   I tried this by adding a local, public static method, with Console as a 'this' parameter... but no dice!      public static class Helpers {     public static void WriteBlueLine(this Console c, string text)     {         Console.ForegroundColor = ConsoleColor.Blue;         Console.WriteLine(text);         Console.ResetColor();     } }   This didn't add a 'WriteBlueLine' method to Console... am I doing it wrong? Or asking for the impossible? MySQL 5.5.16 allows anonymous connections Apparently, I can connect to MySQL (at least from my localhost) without having to provide any username or password. I can even put anything as username, as long as the password is empty. I have access to the information_schema and test databases. I can create tables. If I run SELECT USER() it returns the proper value randomstring@localhost, where the random string is whatever I used for username when I connected.  The mysql.user table contains root@localhost, root@127.0.0.1, @localhost and pma@localhost. I manually set encrypted passwords to all the records (UPDATE user SET password=...) and only root has any privileges, the other two records have "N" for all privileges. That record with the empty username looks suspicious, but I don't think it has anything to do with this and I think it was there from the beginning.  To make matters worse, if I add a user with a password, I can only connect using empty string as password (just like if I put anything as username). If I try to connect using the username I created and password I supplied when creating it (CREATE USER .. IDENTIFIED BY ..) it doesn't work.  Does anyone know what is wrong and how I can fix this?  Note: I am using MySQL 5.5.16 for Windows, provided by the XAMPP package. In the book Principles of Physics by Resnick Halliday: The decrease in Potential energy of a parallel plate capacitor due to a dielectric is because the slab would start to oscillate and the energy would transfer back and forth between the kinetic energy of the moving slab and potential energy stored in the electric field. First of, can somebody provide me the math of the SHM and could somebody explain why it would become the potential of the capacitor i.e. the electric field and not the potential of the slab? As the slab is doing SHM, shouldn't the slab(and not the capacitor) have potential energy at one point of time and kinetic at another like a spring? If the SHM is because of the electric field due to the conducting plates in capacitors, won't they always be in one direction (Plus, it's magnitude is not even a function of distance!)? Could someone be kind enough to provide the math and the reason for Potential and Kinetic Energy transfer question? A lot of textbooks and exam boards claim that light incident at exactly the critical angle is transmitted along the media boundary (i.e. at right-angles to the normal), but this seems to violate the principle of reversibility in classical physics.  How would a photon or ray travelling in the reverse direction "know" when to enter the higher refracting medium?  It can't know, so I conclude that such light is simply reflected?  Is this correct? I installed Ubuntu 18.04, and I want to customize the fonts. I have already change all the setting by tweak tool. But the system default font not be changed, is anything I need to do? Number of equivalence classes of matrices under switching rows and columns I have been thinking about this problem:  Suppose we have all $R$ by $C$ matrices, where the values are integers in $[1,n]$. Two matrices are equivalent under interchanging rows and columns. For example,   1 5     0 0       would be equal to itself and to  0 0 1 5   and would be equal to  0 0  5 1   and would be equal to   5 1 0 0   How many unique such matrices are there?  Any ideas how to go about it? Any help much appreciated! The Stack Overflow search shows questions twice. See  for example.  Results include "A: Add Search Engine into MVC Music Store" and "Q: Add Search Engine into MVC Music Store".  Why is search displaying the question twice, and what does "Q" and "A" mean?  Edit:   @Stephen answer :  The search is returning both a question (Q) and an answer (A) to the question, as both posts match your search criteria.  and my another question  If the question have multiple (like 100) answer ,then the answer link(A: Question Link) shown 100 times?  Is it correct functionality ? But i saw only one answer link , not a other answer link .. why ? Downloading from the main Ubuntu archive is slow even when it's not release day, how can I get apt-get to automatically use a mirror that is close to me? Sometimes when I'm making a sauce or soup that needs to be a bit spicy, I have no troubles spicing how I want to.  But if the dinner party is a bit late, or I made the sauce in advance to really draw out all the flavors of the spices, vegetables and meat, sometimes I end up with a way too spicy/hot dish.  You can always pour a bit water and try to dilute it a bit, but that also takes away all of the good flavor. So is there some trick that I'm missing I can use, when this happens to me (other than being more careful or using the spices later)? I'm editing a book that includes about 25 papers written in LaTeX by different authors.  Since many of them use the same \label, to avoid collisions I redefined the \label command (and \ref and \pageref and \cite and \bibitem)  so that if the third paper has  \label{main_theorem} the aux file actually uses the tag "iii:main_theorem", and \ref{main_theorem} actually refers to the same tag.  I did a similar thing for \cite and \bibitem.  %*************** bib/cite hacks \let\TheReal@citex=\@citex \let\TheReal@bibitem=\@bibitem \let\TheReal@lbibitem=\@lbibitem \gdef\@lbibitem[#1]#2{\TheReal@lbibitem[{#1}]{#2\roman{chapter}}} \gdef\@bibitem#1{\TheReal@bibitem{#1\roman{chapter}}} \gdef\@citex[#1]#2{% \toks@={}\count@=0% \@for\@citec:=#2\do{% \advance\count@ 1 \ifnum\count@=1\edef\0{\the\toks@\expandafter\expandafter\noexpand\@citec\roman{chapter}}% \else\edef\0{\the\toks@,\expandafter\expandafter\noexpand\@citec\roman{chapter}} \fi% \toks@=\expandafter{\0}}% \TheReal@citex[#1]{\the\toks@}% } %************** label/ref/pageref hacks  %%%%%%%%%%%%% must be before ams pkgs \let\TheRealLabel=\label \let\TheRealRef=\ref \let\TheRealPageref=\pageref \gdef\label#1{\TheRealLabel{\roman{chapter}:#1}} \gdef\ref#1{\TheRealRef{\roman{chapter}:#1}} \gdef\pageref#1{\TheRealPageref{\roman{chapter}:#1}}   This all worked fine until I used hyperref, which seems to ignore the redefinition of \label, whether I load it before or after the above code.  Any suggestions?  It would be nice if the redefinition would work whether or not hyperref was loaded, so I don't want to just grab the defintion of \label out of the package and tweak it.  I'm also open to alternative methods.  Redefining \label and \ref just seemed the most straightforward (to me) solution.  Note that I also want to be able to refer to the inner labels from outside, as well.  For example, I might want to say "the main theorem of the third paper is  \ChapRef{iii}{main_theorem}  from within the introduction (a different chapter). How to quickly move one layer to a different group in large Photoshop files, without dragging? Update (March, 2012): This has been rolled out to all sites in the network.    Behind the scenes we've been hard at work making some changes to how we track reputation.  Here are some of the issues we're aiming to address with these changes:   Reputation Skew (your actual reputation doesn't match what's shown) Up/Down votes oddities (mostly with the daily rep cap, the magical +2) Historical Deletes (not impacting rep immediately, contributing to skew) Unaccepts (display issues in the profile) User Deletion (magically missing rep, another skew contributor)   To be clear: reputation values are not changing, every action in the system is still worth the same amount.   Here’s what will be different:   Your reputation will be correct at all times Deletions will have a much more immediate effect on reputation, not waiting on a recalc  (but reputation sync takes up to 5 minutes on a delete/undelete action; as to not block the user's response thread, it's offloaded to a background queue) Recalcs will no longer be necessary Up/Down vote reversals will restore the correct reputation amount Up/Down vote reversals will correctly adjust to the reputation cap The reputation history in your profile will be more detailed and accurate (e.g. when a post is deleted, you'll see that in the reputation tab of your profile)   This means your reputation will go up and down more than it has previously, but it will be in sync.  To think of it more easily: imagine that a recalc will be done after every action in the system.  Probably the biggest impact many will be concerned with is that you may see your reputation drop in cases where it didn't seem like it did before  This was effectively happening before, but the results of that change were not applied immediately, but on the next rep recalc.  Post deletion is the biggest factor here, previously it didn't (immediately) account for the reputation impact...that will no longer be the case.  Reputation changes from the deletion will now be applied within the hour, and most other changes will be instant.  Now the part that will make everyone throw vegetables our way:  this will require a global recalc to get everything in sync.  We'll be rolling it out first here on meta, then the rest of the network...the enabling of the detailed rep view and global recalc on each individual site will coincide.  During the rollout you will see empty reputation tabs on profiles as we transition to the new storage behind the scenes, they'll be restored as the recalc rolls though each user.  We’ll put up a blog post on  before the network-wide rollout.  If you have any questions about this change or details I may have left out, please do so in answers below so that we can clear up as much as possible before this rolls out. Mysql: Select all data between two dates What's the recommend way of changing the font size in a particular table? Is there a better way than enclosing all values with, for example, the \tiny function. Why doesn't my flash fire from the hot shoe trigger? I have a Yongnuo YN-560 III and a pair of RF-603II (C3) triggers. I have a Canon Rebel T5i.   I put one trigger on the hot shoe.  When this trigger is in TX mode I get a blue comm light and I can fire a test flash using the large test button on the trigger. But when I press the shutter button to take a picture, there's no flash.  The trigger and flash are on Channel 1. The trigger on the hot shoe is set to TRX. TX is fine, TRX gives me no flash. The flash and camera are in M mode.  I don't have a trigger on the flash because the Mark III has a built-in trigger The problem seems to be the camera.  The trigger can talk to the flash but the camera is not sending a flash command through the trigger in the hot shoe to the flash.  Grateful for anything you could suggest. In my native language, we can say:     I have dog   Because I don't want to say a dog (one dog, how many dogs) or the dog (that dog, the listener don't care which dog).  p.s. after 3 years later, I have to say, why I ask this question, is I still cannot grasp how to use the right 'article word'. sometimes, a noun will use an article, sometimes, a noun could not(or omit) the article word before it. there aren't a formula for this. So, I have to remember all the time! I feel so frustrate Is there any difference in meaning between 'efficacy' and 'efficiency'? Image Alpha Background Renders Black when using "Import Images as Planes" I must be missing something here.  I'm doing an extremely simple Import Image as Plane using the AddOn and the imported image has an alpha background but it renders (and even previews in the material preview) as black where the alpha background should be.  When I import, I select Emission &amp; Transparent so the material setup is automatic.  I've read similar issues but people are typically missing the transparent node and connecting the Alpha channel from the image into the Mix Node factor.  But this is all here.  I must be missing something really stupid but I've wasted so much time trying to fix this thing.  Any help would be greatly appreciated.  Not sure if it matters but I'm using 2.74 RC2.  Many thanks!  I created this dummy blend file to test outside my project but problem still exists.  Here is the simple .blend file: If G is a group, prove that $(ab)^n =a^nb^n$ implies G is abelian. I need to prove the equivalence of the following two statements, if $G$ is a group:     $G$ is abelian $\Leftrightarrow$  for each $a,b$ in $G$: $(ab)^n = a^n b^n$ for each integer $n$   I have done the $\Rightarrow$ implication, but I have no idea how to approach $\Leftarrow$, any hints are very welcome. Term to describe users' initial dislike of user interface change What is the best term to describe the fact that most users have an initial dislike of any change to a UI even though it may really be net better over time?  Note: Question originally appeared