I am trying to install Nvidia drivers on Red Hat  Why am I getting the following error:  rpm -i NVIDIA_kernel-1.0-2880.rh62.i386.rpm  error: Failed dependencies:     kernel = 2.2.14-5.0 is needed by NVIDIA_kernel-1.0-2880.rh62.i386 [root@INEICP-EPM-W134 Downloads]# uname -a Linux INEICP-EPM-W134 2.6.32-220.el6.x86_64 #1 SMP Wed Nov 9 08:03:13 EST 2011 x86_64 x86_64 x86_64 GNU/Linux   I have kernel 2.6. WHy is it crying about kernel 2.2 ?

I wanted to install Nvidia drivers.   Can you tell me why the following is not working :  [root@INEICP-EPM-W134 Downloads]# rpm -Uvh XFree86-4.3.0-35.EL.src.rpm  warning: XFree86-4.3.0-35.EL.src.rpm: Header V3 DSA/SHA1 Signature, key ID db42a60e: NOKEY    1:XFree86                ########################################### [100%]  [root@INEICP-EPM-W134 Downloads]# rpm -i NVIDIA_GLX-1.0-2880.i386.rpm  error: Failed dependencies:     XFree86 >= 4.0.1 is needed by NVIDIA_GLX-1.0-2880.i386     NVIDIA_kernel is needed by NVIDIA_GLX-1.0-2880.i386     ld-linux.so.2 is needed by NVIDIA_GLX-1.0-2880.i386     libc.so.6 is needed by NVIDIA_GLX-1.0-2880.i386     libdl.so.2 is needed by NVIDIA_GLX-1.0-2880.i386     libm.so.6 is needed by NVIDIA_GLX-1.0-2880.i386     libX11.so.6 is needed by NVIDIA_GLX-1.0-2880.i386     libXext.so.6 is needed by NVIDIA_GLX-1.0-2880.i386     libdl.so.2(GLIBC_2.0) is needed by NVIDIA_GLX-1.0-2880.i386     libdl.so.2(GLIBC_2.1) is needed by NVIDIA_GLX-1.0-2880.i386   Why am I getting XFree86 >= 4.0.1 is needed by NVIDIA_GLX-1.0-2880.i386 even after I have installed Xfree ? Is my installation of Xfree not correct ?  I get :  root@INEICP-EPM-W134 Downloads]# X -version  X.Org X Server 1.10.4 Release Date: 2011-08-19 X Protocol Version 11, Revision 0 Build Operating System: x86-004 2.6.18-274.3.1.el5  Current Operating System: Linux INEICP-EPM-W134 2.6.32-220.el6.x86_64 #1 SMP Wed Nov 9 08:03:13 EST 2011 x86_64 Kernel command line: ro root=UUID=d3a4df51-ed55-4e48-a17d-4235cecd9a9d nomodeset rd_NO_LUKS  KEYBOARDTYPE=pc KEYTABLE=us LANG=en_US.UTF-8 rd_NO_MD quiet SYSFONT=latarcyrheb-sun16 rhgb crashkernel=128M rd_NO_LVM rd_NO_DM Build Date: 20 October 2011  12:03:36PM Build ID: xorg-x11-server 1.10.4-6.el6  Current version of pixman: 0.18.4     Before reporting problems, check https://www.redhat.com/apps/support/     to make sure that you have the latest version.   when I do X -version


I want to download GTA V, but I don't have enough disk space and the only game I have left to uninstall is Payday 2.  However, I have been playing it frequently, even going on 17 hour marathons to 100%  it, and thus, I am reluctant to uninstall it from my system in case I need to redo everything.  I know the DLCs stay, but I'm talking about the vanilla stuff (Masks, guns, cash, levels, infamy, etcetera).

Which games (except Torchlight) store the current state of the game to the Steam cloud?   What is the Steam Cloud?  Steam is Valve's online game purchasing and digital delivery service/platform. Steam Cloud is a fairly new addition to the Steam platform that saves the state for various games to Steam's servers in the "cloud". Depending on the game it can save things like your savegames, character setup, keyboard mappings, options, etc so that any PC that you go to will download all those settings for you and keep them in sync as soon as you log into Steam.


I am using the following phrase in an abstract I'm writing:     in situ formation of planets   I wanted to ask if a hyphen is needed in this phrase, and if so where?   says that "in situ" should not be hyphenated because the two words are not two separate adjectives, but rather "in situ" is a single adjective, borrowed from Latin.  I wanted to confirm that this analysis carries over to this particular usage of "in situ".

The term in(-)situ visualization denotes a visualization or graphics that is depicted in place, for instance, a  that is embedded into text.  As the dictionaries tell, the adjective or adverb in situ is written as two words. But for concatenated terms in scientific language, oftentimes, in-situ (with a hyphen) is placed in front of the main noun. Searching for the term in Google and Google Scholar, I find both alternatives about equally frequent. Also, the  lists both versions for related terms such as in(-)situ burning.  What is the correct spelling of in(-)situ visualization? Is there a specific rule that applies?


I want to exchange a Harddrive which is in a pre-failing state, (some reallocated sectors) which is used in a raid5 array with 3 disks (software raid with mdadm).  Is it possible to set a new harddrive as a hot-spare and initialize a takeover from the failing to the spare drive?   Some methods suggest to add the drive and then set a drive failure command. As I know, in this state the raid5 is degraded and a drive failure would end up in....  so is there a possibility to "copy" the data live (or rebuild the raid) from the failing drive to the spare (without take its parity function away), and as the copy or rebuild process is finished, remove the failing drive.

I have a software RAID5 array (Linux md) on 4 disks.   I would like to replace one of the disks with a new one, without putting the array in a degraded state, and if possible, online. How would that be possible?   It's important because I don't wan't to:    take the risk of stressing the other disks so one may crash during rebuild,  take the risk of being in a "no-parity state" so I don't have a safety net for some time.    I suppose doing so online is too much asking and I should just raw copy (dd) the data of the old disk to the new one offline and then replace it, but I think it is theoretically possible...   Some context: Those disks have all been spinning almost continuously for more than 5.5 years. They still work perfectly for the moment and they all pass the (long) SMART self-test. However, I have reasons to think that one of those 4 disks will not last much longer (supposed predictive failure).


It is a central tenet of relativistic mechanics that there can be no such thing as an absolute frame of reference, and as such, it appears to me that it is physically impossible to measure the total energy of the universe, as calculations of energy depend on the velocity of objects. From this, I can consider a number of possible conclusions, which I wish to pose to you:  Does the universe have a theoretical total energy, which just happens to be incalculable?  Does the universe have a theoretical total energy, which happens to be calculable? For instance, if the calculated energy in every single reference frame would be the same?  Is there something incorrect about my logic earlier?  Or, is conservation of energy on a universal scale nonsensical? If this is the case, why would this not have significant ramifications on modern theory?

In high school I was taught energy was conserved. Then I learned that nuclear reactions allow energy to be converted into mass. Then I also heard that apparently energy can spontaneously appear in quantum mechanics. So, are there any other caveats with the conservation of energy?


I've been reading some documentation about PCA and trying to use scikit-learn to implement it. But I struggle to understand what are the attributes returned by sklearn.decompositon.PCA From what I read  and the name of this attribute my first guess would be that the attribute .components_ is the matrix of principal components, meaning if we have data set X which can be decomposed using SVD as   X = USV^T  then I would expect the attribute .components_ to be equal to   XV = US.  To clarify this I took the first example of the wikipedia page of Singular Value Decomposition (), and try to implement it to see if I obtain what is expected. But I get something different. To be sure I didn't make a mistake I used scipy.linalg.svd to do the Singular Value Decomposition on my matrix X, and I obtained the result described on wikipedia:  X = np.array([[1, 0, 0, 0, 2],           [0, 0, 3, 0, 0],           [0, 0, 0, 0, 0],           [0, 2, 0, 0, 0]]) U, s, Vh = svd(X) print('U = %s'% U) print('Vh = %s'% Vh) print('s = %s'% s)   output:  U = [[ 0.  1.  0.  0.] [ 1.  0.  0.  0.] [ 0.  0.  0. -1.] [ 0.  0.  1.  0.]] Vh = [[-0.          0.          1.          0.          0.        ] [ 0.4472136   0.          0.          0.          0.89442719] [-0.          1.          0.          0.          0.        ] [ 0.          0.          0.          1.          0.        ] [-0.89442719  0.          0.          0.          0.4472136 ]] s = [ 3.          2.23606798  2.          0.        ]   But with sk-learn I obtain this:  pca = PCA(svd_solver='auto', whiten=True) pca.fit(X) print(pca.components_) print(pca.singular_values_)   and the output is  [[ -1.47295237e-01  -2.15005028e-01   9.19398392e-01  -0.00000000e+00 -2.94590475e-01] [  3.31294578e-01  -6.62589156e-01   1.10431526e-01   0.00000000e+00 6.62589156e-01] [ -2.61816759e-01  -7.17459719e-01  -3.77506920e-01   0.00000000e+00 -5.23633519e-01] [  8.94427191e-01  -2.92048264e-16  -7.93318415e-17   0.00000000e+00 -4.47213595e-01]] [  2.77516885e+00   2.12132034e+00   1.13949018e+00   1.69395499e-16]   which is not equal to SV^T (I spare you the matrix multiplication, since anyway you can see that the singular values are different from the one obtained above). I tried to see what happened if I set the parameter withened to False or the parameter svd_solver to 'full' but it doesn't change the result.  Do you see a mistake somewhere, or do you have an explanation?

Principal component analysis (PCA) is usually explained via an eigen-decomposition of the covariance matrix. However, it can also be performed via singular value decomposition (SVD) of the data matrix $\mathbf X$. How does it work? What is the connection between these two approaches? What is the relationship between SVD and PCA?  Or in other words, how to use SVD of the data matrix to perform dimensionality reduction?


I am flying from Pakistan to the US, and will be changing flights in Toronto.  I will not be leaving the airport and my ground time in Canada is less then 5 hours.  I have a visit visa for the US.  Do I need a transit visa or some kind of visa for Canada?

I know that in the US foreigners must have a US visa if they have a connection in the US, even if they fly from a different country to a different country. That is because in the US you have to go through passport control regardless of your final destination.  What is the situation in Canada? Does a person who would need a visa to enter Canada need a visa to connect through Canada without exiting the airport?


i am using vs code. after using few days it says me update available to download so i downloaded the update but what should i do next to apply these update the update size in about to 64 MB in a zip file containing different files with different extension. i am new to Ubuntu to not able to apply these update. As i download the update it show me same file which i have been  downloading previously.  the downloading link is given here :

I just downloaded VSCode-linux-x64 from . It's a 62 MB zip file. How can I install it on my Ubuntu system?


I have got an mp3 file, let's say it is 25 minutes long. I understand that any software is capable of extracting the first 20 minutes of the file as a new MP3 file. However, I would like to find a solution that would do this "loss-lessly", i.e., keep the original MP3 blocks and just use the first 4/5 of the blocks and modify the header accordingly. This way, no quality loss is imposed by the extraction process. I'm cutting the file in a space where couple seconds of silence happen, so cutting between blocks should be possible.  (A good analogy would be to take a cut-out of a JPG file at the boundaries of the blocks simply by taking only the blocks inside the cutout. One can decode the file, cut it and encode it again, but with a quality loss.)  (As far as I know, by default, software would decode the file into a waveform, extract the demanded part and encode it again using the MP3 algorithm. This is not what I want, since the 2nd compression unnecessarily reduces the quality.)  (I prefer a linux solution, but I can access windows as well.)

I have a 400 MB MP3 file at 96 kbps, taken from a CD.  I want to split this into many files.   Is there any way to do that without affecting the quality of audio, or maybe without re-encoding the file?


I have spent months looking into a new laptop. It's primary use will be editing and developing photos in Lightroom but I will also be putting together photo and video slideshows in Premier Elements and maybe even premier pro in the near future. What I cant decide is what is more important; dedicated graphics card like the higher end Surface Book or more processing power like in the Dell Xps with Core i7 and 16GB of RAM. Can anyone give me a definitive answer. My budget is up to £1600 - I think.

How important is the following in purchasing a laptop that will be used for image editing:   processor speed amount of RAM integrated vs. dedicated graphics card HD speed (SSD; or 5400/7200/10000 rpm)


I have the below code:  Map<String, Map<Double, String>> map = new HashMap<>(); Map<Double,String> Amap = new HashMap<>(); map.put(getValuesTypes.FUT(), HERE);   Instead of creating a Map first and put it at "HERE", I'm looking for a function like I could use with a List there Arrays.asList(...) so that i can just enter at "Here" ?.asMap({1.0,"A"}, {2.0,"B"})

How would you initialise a static Map in Java?  Method one: static initialiser  Method two: instance initialiser (anonymous subclass) or some other method?  What are the pros and cons of each?  Here is an example illustrating the two methods:  import java.util.HashMap; import java.util.Map;  public class Test {     private static final Map<Integer, String> myMap = new HashMap<>();     static {         myMap.put(1, "one");         myMap.put(2, "two");     }      private static final Map<Integer, String> myMap2 = new HashMap<>(){         {             put(1, "one");             put(2, "two");         }     }; }


I have a SQL Server instance that has a linked server to an Oracle server. There is a table on the Oracle server called PersonOptions which contains the following data:  ╔══════════╦══════════╗ ║ PersonID ║ OptionID ║ ╠══════════╬══════════╣ ║        1 ║ A        ║ ║        1 ║ B        ║ ║        2 ║ C        ║ ║        3 ║ B        ║ ║        4 ║ A        ║ ║        4 ║ C        ║ ╚══════════╩══════════╝   I need to pivot that data so the results are:  ╔══════════╦═════════╦══════════╦══════════╗ ║ PersonID ║ OptionA ║ Option B ║ Option C ║ ╠══════════╬═════════╬══════════╬══════════╣ ║        1 ║       1 ║        1 ║          ║ ║        2 ║         ║          ║        1 ║ ║        3 ║         ║        1 ║          ║ ║        4 ║       1 ║          ║        1 ║ ╚══════════╩═════════╩══════════╩══════════╝   Any suggestions?


Find The minimum value of $$2^{\sin^2 \alpha} + 2^{\cos^2 \alpha}.$$   I can easily get the maximum value but minimum value is kinda tricky. Please help.

The question is what is the minimum value of $$2^{\sin^2x}+2^{\cos^2x}$$ I think if I put $x=\frac\pi4$ then I get a minimum of $2\sqrt2$. But how do I prove this?


For example: you want to start file "hello.txt" in python, you will use this code:  os.startfile("hello.txt) But the system will open "hello.txt" with default program If I want to start "hello.txt" with Sublime Text or notepad+ or any program which is not a default program. What I have to do:?:( Thanks (and sorry for my bad english)

How do you call an external command (as if I'd typed it at the Unix shell or Windows command prompt) from within a Python script?


Let $p$ be a prime number. Prove that there exists an integer $a$ such that $p\mid(a^2-a+3)$ if and only if there exists an integer $b$ such that $p\mid(b^2-b+25)$.  I'm getting a bit confused with this problem. I was trying to show first the case $(\Longrightarrow)$ by factoring $a^2-a+3= (a-1)(a-3)+3a$, which would imply that $p\vert(a-1), p\vert(a-3)$ and $p\vert3a$. Looking at the last condition $p\vert3a$ it seems that this would only be true if $p=3$? Similarly for $(\Longleftarrow)$ the term $b^2-b+25$ factors as $(b-1)(b-25)+25b$ which would imply also that $p\mid(b-1), p\mid t(b-25)$ and $p\mid 25b$. Is this going anywhere or should I consider something else?

Use the modulo version of the quadratic formula and Euler's criterion to decide if the following has a solution or not.  $2x^2+5x+8 \equiv 0\pmod{37}$  I'm not sure how I would use what was being asked of me to decide if this has a solution or not, but I have came to the conclusion that it does not, because I plugged in every possible answer $0-36$, and none of them were congruent to zero.  The way people have answered the question, isn't exactly the way I need.  I have made some progress, but I'm not exactly sure how to finish:  $2x^2+5x+8 \equiv 0\pmod{37}$  $x^2+21x+4\equiv0\pmod{37}$  $x^2+58x+841\equiv837\pmod{37}$  $(x+29)^2\equiv23\pmod{37}$  I know that if $p$ is an odd prime and $p$ doesn't divide $a$, then $x^2\equiv a\pmod{p}$ has a solution or no solution depending on whether $a^\frac{p-1}{2}\equiv 1  \space\space \text{or}\space -1\pmod{p}$.  This is where I get stuck.  Can someone help me from here?  I have a feeling this problem has no solutions, so could someone also explain to me what to do if a problem like this did have solutions.


I saw a computer for 3D modeling (Autocad, 3DsMax, Sketchup, etc) which has an NVIDIA graphics card on it.  The computer had several "NVIDIA Performance Drivers" installed on it, including one specifically for Autocad.  What are these for?  Does the graphics card not handle this well enough by default?  Does this mean each and every program could potentially require a performance driver??!!!    ...and for multiple systems with different graphics cards, potentially a separate performance driver, for each card, for each program!?!

I have a nVidia Quadro FX 1700 graphics card and there are different drivers offered at the nVidia driver page:   Quadro ODE Graphics Driver Quadro Performance Driver Quadro Partner Certified Driver   And 2 software specific drivers:   AutoCAD Performance Driver 3ds Max Performance Driver   So my question is: What is the difference between the 3 first drivers and which one is the best for gaming?  EDIT: The Driver I´m currently using is linked .


I am currently finishing my dissertation which consists of an introduction and three publications labelled A, B and C. The dissertation will be published in a book form and it is customary (in our department) to have before each included paper an empty page consisting only of "side bar" indicating the label of the paper. (This makes it easier to browse.) Part of my problem is that I don't know the proper name of this "side bar", see attached pictures for what I mean.      To my question: These side bar pages are usually added by the printing company, by hand, but is it possible to do this with LaTeX?   The papers themselves are added as pdf files via  \includepdf[pages=-]{Papers/Paper-1.pdf}   So generating such side bar pages as disjoint pdf pages with hand adjusted labels would be fine.  Edit: Apparently the "side bar" thing is called a thumb index, and the solution can be found from another question listed in the comments.

I would like to place a letter (that indicates which letter in the dictionary is shown) on the outer side of the book, set it for example in a darker box and position that letter vertically. Users of the dictionary can later easily access  a searched headword by using the letter division on the side.   Minimum example:  \documentclass[twocolumn]{book} \usepackage[top=1.5cm, bottom=1.5cm, left=2cm, right=2cm]{geometry} \usepackage{fancyhdr} \usepackage[utf8x, utf8]{inputenc} \usepackage[T1]{fontenc} \newcommand\entry[3][]{\hangpara{2em}{1}{\fontfamily{phv} selectfont{\textbf{{#2}}}}\      #3\ifx\relax#1\relax\markboth{#2}{#2}\else\markboth{#1}{#1}\fi     \par}\nopagebreak[4] \newcommand*{\dictchar}[1]{\centerline{\LARGE\textbf{#1}}\par} \pagestyle{fancy} \fancypagestyle{basicstyle}{% \fancyhf{} \renewcommand{\headrulewidth}{0.4pt} \renewcommand{\footrulewidth}{0pt} \fancyhead[LE,RO]{\textbf{\chaptitle}} \fancyhead[LO,RE]{\textbf{\thepage}}} \fancypagestyle{dictstyle}{% \fancyhf{} \fancyhead[LE,LO]{{\fontfamily{phv}\selectfont{\textbf{\rightmark}}}} \fancyhead[CO,CE]{\thepage} \fancyhead[RE,RO]{{\fontfamily{phv}\selectfont{\textbf{\leftmark}}}}} \begin{document} \pagestyle{dictstyle} \dictchar{a} \entry[headwords]{headwords}{translations} \clearpage \dictchar{b} \entry[headwords]{headwords}{translations} \end{document}   How can I place thumb indexes from \dictchar values now to the right odd and left even margin?


While in manual mode with auto focus, could not get the camera to focus for night astrophotography.  Tried different combinations of ISO, TV and AV.  I noticed that the EV was all the way to the right.  What does that tell you? Could the combination cause the camera not to focus?  Thanks

I've been doing a bit of astrophotography and the problem that I almost always have is nailing focus.  I'll manually focus on a bright star or the moon (which hopefully isn't an option!) by magnifying on live view, leave the lens on manual focus, and then rotate the camera to the target.  My problems happen two fold:   Evenly greatly magnified on the live view screen, there's very little difference between in focus and slightly out of focus of a bring point light source.  It's extremely difficult to tell in camera if its right, but painfully obvious once on the computer after the exposure. I think sometimes the focus ring gets bumped while moving the camera to the target.  So my focus ends up way off.   What are techniques or methods to help here?  I've seen some reference to some sort of diffraction mask that could help, but don't know anything about it.  My particular DSLR doesn't tether to a laptop, so computer aided focus is out for me (but it may be worth mentioning in general for a wider audience with similar issues).


I am css begginer and i have a problem with div arrengment. I want to place a div in the top part of the screen, 150px 100% width. and another div right below which will take the reminder part of the screen. If I add the second div "height: 100%" it surpass the screen size and makes me scroll and i dont want that. just that it will take the free screen area, and adjust to window size. thank you!!

I am working on a web application where I want the content to fill the height of the entire screen.  The page has a header, which contains a logo, and account information. This could be an arbitrary height. I want the content div to fill the rest of the page to the bottom.  I have a header div and a content div. At the moment I am using a table for the layout like so:  CSS and HTML    #page {     height: 100%; width: 100% }  #tdcontent {     height: 100%; }  #content {     overflow: auto; /* or overflow: hidden; */ }

...

...

     The entire height of the page is filled, and no scrolling is required.  For anything inside the content div, setting top: 0; will put it right underneath the header. Sometimes the content will be a real table, with its height set to 100%. Putting header inside content will not allow this to work.  Is there a way to achieve the same effect without using the table?  Update:  Elements inside the content div will have heights set to percentages as well. So something at 100% inside the div will fill it to the bottom. As will two elements at 50%.  Update 2:  For instance, if the header takes up 20% of the screen's height, a table specified at 50% inside #content would take up 40% of the screen space. So far, wrapping the entire thing in a table is the only thing that works.


I have quite a number of files and directories with spaces in their filenames in my ext4 filesystems.   How should I safely find and rename them? I have bash and am running Ubuntu.    Is it possible to interactively rename each found file, i.e. be asked if I want to rename what to what for each file?  What convention for choosing filenames would you use to rename them?

I wrote the following script to diff the outputs of two directores with all the same files in them as such:  #!/bin/bash  for file in `find . -name "*.csv"`   do      echo "file = $file";      diff $file /some/other/path/$file;      read char; done   I know there are other ways to achieve this.  Curiously though, this script fails when the files have spaces in them.  How can I deal with this?  Example output of find:  ./zQuery - abc - Do Not Prompt for Date.csv


My environment is a little different. I updated from 14.04 to 16.04 to 18.04.  My desktop PC 18.04 has npm installed.  $ npm -version 3.5.2  # nodejs -v v8.10.0  # apt install npm   Reading package lists... Done Building dependency tree        Reading state information... Done Some packages could not be installed. This may mean that you have requested an impossible situation or if you are using the unstable distribution that some required packages have not yet been created or been moved out of Incoming. The following information may help to resolve the situation:  The following packages have unmet dependencies:  npm : Depends: node-gyp (>= 0.10.9) but it is not going to be installed E: Unable to correct problems, you have held broken packages.

I noticed over at the  website that node is currently at v 0.12.0.  Can someone let me know how to install the latest version of node together with npm (terminal commands please)?


As for me - Gravatar does not work at all. I can't change my last gravatar to a new one, I always get 'Whoops! Something went wrong!'. I even can't file a bug, I can either read FAQ or 'ask community for help'. It seems that Gravatar developers are very reluctant to do any technical support.  Therefore, I think Gravatar doesn't deserve to be the only viable alternative in SO Careers as it is now.

, we should have the same functionality in careers. It still only allows gravatar pictures.  There's an [old pre-native picture question][2] asking basically the same, but seeing that it has an accepted answer I created a new one.


Recently that I connect my Windows phone mobile to my Xubuntu laptop I see mtp://[usb:002,003]/Storage/ alongside the other drives.It shows my phone media files! That actually I can not find it in terminal!   So can I access to its file system information at all? and also I want to know is there any way that I could access other data on my phone like documents or messages or ... ?

I am running Linux Mint 17.1 64-bit (based on Ubuntu 14.04). Ever since upgrading from Linux Mint 14/Ubuntu 12.10, the Python script I use to sync music to my Walkman has stopped working.  Previously, when I mounted my Walkman, it would automatically show up as the path /run/user/1000/gvfs/WALKMAN/Storage Media and would work like any other file system: I could copy tracks to it, delete tracks from it, etc, all through Python. However, I can't remember if I had to make any changes to get this to happen.  Since upgrading to Linux Mint 17 (and now 17.1), when I mount the Walkman, it shows up as the path /run/user/1000/gvfs/mtp:host=%5Busb%3A002%2C007%5D/Storage Media. Furthermore, when I try to run the same file operations, they now fail. I have discovered that this happens not just through Python, but on the command line as well. For example:  david@MILTON:~$ cp '/data/Music/10SecsWhiteNoise.mp3' '/run/user/1000/gvfs/mtp:host=%5Busb%3A002%2C006%5D/Storage Media/MUSIC' cp: cannot create regular file ‘/run/user/1000/gvfs/mtp:host=%5Busb%3A002%2C006%5D/Storage Media/MUSIC/10SecsWhiteNoise.mp3’: Operation not supported   I have done some research on this problem, but the most common explanation seems to be that it was formerly solved by this PPA: https://launchpad.net/~langdalepl/+archive/ubuntu/gvfs-mtp  But now, Ubuntu versions since 13.10 contain all these changes so it should no longer be necessary. So why am I still having these errors? I am still able to do file operations on my Walkman through a graphical file manager (Caja, on Linux Mint), just not via the command line.


My post was inspired by this one ()  Although random forest models do not overfit$^{1,2}$, it can be good to know how many trees are needed for a stable solution.  My question is about the best way to calculate OOB to know when additional trees no longer provide benefit (i.e. the OOB error is stable). As I understand it we have $B$ trees fit to $B$ many bagged datasets of size $N$, trying $\sqrt{p}$ predictors at each split. After fitting all of the trees we predict the class for every observation using only the trees for which it was withheld and then comparing it to the known class. This gives a misclassification rate for each tree and each observation (these become the predicted probabilities).  In R you can plot the sequential cumulative average of the OOB errors:    You can also do this in Python but requires a little more work since the trees are created sequentially$^{3,4}$.  It seems to me that when the number of trees in small (e.g. 1) there should be high variance in the OOB error. In other words if I fit 100 random forest models with 5 trees the average OOB error will have greater variance than if I fit 100 random forest models with 50 trees. Of course since we can fit the trees in parallel it is easy to grow many trees at once for a single model.  Does it make sense to calculate some sort of boosted OOB where the OOB score for $n$ trees is the average of $b$ samples of trees? For example take 10 samples of 5 trees out of the 500 trees and calculate the average OOB score from that. Then when the variance at number of trees $n$ is small stop growing trees (perhaps calculate something similar to the Gelman-Rubin statistic for MCMC convergence).  Since trees should be grown randomly rather than sequentially I'm not sure how much value there is to this, especially since I think the OOB error converges fairly quickly in most cases. However with larger datasets this may save some computational time when the number of trees needed is unknown.   Breiman states random forest models do not overfit:  but Mark R. Segal (April 14 2004. "Machine Learning Benchmarks and Random Forest Regression." Center for Bioinformatics & Molecular Biostatistics) says it can for noisy datasets ()

Software implementations of random forest classifiers have a number of parameters to allow users to fine-tune the algorithm's behavior, including the number of trees $T$ in the forest. Is this a parameter that needs to be tuned, in the same way as $m$, the number of features to try at each split (what Leo Breiman calls mtry)?


If I kill a legendary in ORAS that I find in a mirage spot will it respawn?

I've heard that legendary Pokemon such as Kyogre/Groudon respawn after you defeat the Elite Four (if you didn't catch them). The only information that I can find seems to relate to the original version of the game.  Can players faint legendary Pokemon in order to progress the story and come back later to capture them? And are there any exceptions?  The reasoning for this is some players, myself included, wish to finish the game in order to unlock post-game features before investing time/effort soft resetting for ideal natures in legendary Pokemon.  Please avoid spoilers where possible.


I need a program that can make me multiple accouts stored in different files. This is what I've done so far but for some reason ("test" + userName + ".txt", "a"); does not work. Thank you for your time!    int main() {  char choice[10]; printf("create accout (1)"); printf("\nlogin to accout (2)\n"); scanf("%s", &choice); getchar();  if (strcmp(choice, "1") == 0) {     char userName[1000];      FILE *myFile;     myFile = fopen("test" + userName + ".txt", "a");     if (myFile == NULL)      {         printf("file does not exist");     }      else      {         printf("Enter your username: ");         gets(userName);         fprintf(myFile, "%s", userName);         fclose(myFile);     } }

I'm working in C, and I have to concatenate a few things.  Right now I have this:  message = strcat("TEXT ", var);  message2 = strcat(strcat("TEXT ", foo), strcat(" TEXT ", bar));   Now if you have experience in C I'm sure you realize that this gives you a segmentation fault when you try to run it. So how do I work around that?


I'm currently working on a voting analysis paper, most of the theory is about, "math", i'm talking about linear algebra, programming, big data, and that specific knowledge area, however the paper is all oriented into  a specific problem regarding politics as it's entirely related to voting analysis and stablishing political networks based on it, so to which kind of journal would be better to send it in order to get published, one of applied math, or one of political science. i've check and it meets requirements of both journals.  Which are the advantages of publishing on one instead of the other?

Most science research is published in subject-specific journals, of which there are many. However, there are a relatively small number of interdisciplinary journals, some of which are the most highly cited of all journals (Nature, Science); others have impact factors comparable to subject-specific journals (e.g., PLOS ONE, J. R. Soc. Interface, etc.).  If we discount arguments around open science and similar business model arguments (which could favor journals like PLOS ONE), and assume that the purpose of publishing is simply to get your research read (and cited) by the largest "relevant audience", when should one publish in an interdisciplinary journal versus a subject-specific journal (assuming they have comparable impact factors)? (Are there any papers out there that compare the fate of publications [or their authors!] in the two different types of journal?)  Thanks in advance.


I have a very simple bash script to compute the sum of numbers appear at each line of a file (I know there are better ways for doing this but I actually need this sum as an auxiliary information and the script is supposed to something more later on). The script is as follows:  TOTAL=0; cat $DATAFILE | while read LINE;  do       COUNT=`echo $LINE| awk '{print $2;}'`;       TOTAL=$((TOTAL+COUNT)); done echo "Total = $TOTAL";   However, I always get the output "Total = 0". Surprisingly enough if I move the last line inside the while loop, I get the correct result. For example if the input file contains  A 5 B 3 C 6   I get the output   Total = 5 Total = 8 Total = 14   But the current version always outputs 0. It seems the value assigned to the variable TOTAL is somehow lost.  Can anyone help me out with the issue?  Thanks in advance

Please explain to me why the very last echo statement is blank? I expect that XCODE is incremented in the while loop to a value of 1:  #!/bin/bash OUTPUT="name1 ip ip status" # normally output of another command with multi line output  if [ -z "$OUTPUT" ] then         echo "Status WARN: No messages from SMcli"         exit $STATE_WARNING else         echo "$OUTPUT"|while read NAME IP1 IP2 STATUS         do                 if [ "$STATUS" != "Optimal" ]                 then                         echo "CRIT: $NAME - $STATUS"                         echo $((++XCODE))                 else                         echo "OK: $NAME - $STATUS"                 fi         done fi  echo $XCODE   I've tried using the following statement instead of the ++XCODE method  XCODE=`expr $XCODE + 1`   and it too won't print outside of the while statement. I think I'm missing something about variable scope here, but the ol' man page isn't showing it to me.


Given That A and B are two PSD () real matrices and the following holds $$ A \leq B  $$ (meaning that $$ B-A $$ is also PSD)   can I bound the eigenvalues of A using the eigenvalues of B?  Thanks

If $B\succeq A$, show that $\lambda_n(B)\ge\lambda_n(A)$, where $\lambda_n$ is the $n$th largest eigenvalue.  It is Theorem 6 in  but the proof is only given as "by characterization." Do they mean the min/max characterization of eigenvalues, $$\lambda_k=\min\max\frac{x^TAx}{x^Tx}$$ and if so, how is that applied?  Thanks.


I don't know if this is considered common knowledge, but personally I have found that for a typical week-long trip, the price of the hotel is greater than the price of the flight.  My trip planning, however, relies on choosing travel dates based on optimal flights, and then the traveler begins shopping for hotel rooms.  I would like to plan my holiday the other way around: shop a very particular hotel I would like to return to, and choose a week-long trip there based on the lowest hotel demand, or cheapest price. BUT: I have been unable to find anything like this.  Does such a website exist? (Search for a hotel, with no dates specified, and browse cheap/expensive times to visit that hotel)

I am looking for a site or service that allows me to search a hotel (or hotels, or a specific beach/location) for the cheapest date.   Most sites want you to tell them when you plan to visit.  I WANT the site to tell me when to visit based off of the best price


Using the fact that $1+2+\cdots+n=\frac{n(n+1)}{2}$, we can deduce that sum of first $n$ positive odd integers is $n^2$. However, is there a way of finding the sum of $1+3+5+\cdots+(2n-1)$ visually?

Since I'm not that good at (as I like to call it) 'die-hard-mathematics', I've always liked concepts like the  or the , which are easy to understand and explain but are mathematically beautiful at the same time.  Do you know of any other concepts like these?


Duplicate of:    For some time I've been having this discussion with a co-worker on how should you store attributes within a PHP class.  So which one do you think it should be used. Something like this:   Class test{     public $attr1;     public $attr2;     ..............      public function __construct(){         $this->attr1 = val;           $this->attr1 = val;         ...................        } }   Versus:  Class test{     public $data;      public function __construct(){         $this->data['attr1'] = val;         $this->data['attr2'] = val;         ..........................            } }   This is important when you have objects with many attributes that have to be stored and retrieved within often.  Also important when dealing with objects with many attributes, do you use getters and setters for each attribute or rather one method to set all and one method to get all ?

I currently have my PHP class variables set up like this:  class someThing {      private $cat;     private $dog;     private $mouse;     private $hamster;     private $zebra;     private $lion;      //getters, setters and other methods }   But I've also seen people using a single array to store all the variables:  class someThing {      private $data = array();      //getters, setters and other methods }   Which do you use, and why? What are the advantages and disadvantages of each?


It is a well-known fact that the sequence of functions $\{(1+\frac{x}{n})^n\}_{n\in\mathbb{N}}$ converges pointwise to $e^x$ on $\mathbb{R}$. How to prove that this defines a uniform convergence on compact sets?  My attempt is analogous to the proof of Dini's theorem:  Let $r\in\mathbb{R}$ and let $\varepsilon\in\mathbb{R}$ be positive. For all $n\in\mathbb{N}$ we define $$ I_n=\left\{x\in [-r,r]\mid \left|e^x-\left(1+\frac{x}{n}\right)^n\right|<\varepsilon \right\}, $$ then, by continuity of the functions involved, $\{I_n\}_{n\in\mathbb{N}}$ is a sequence of open sets. Such sequence is ascending (why?) and, by the pointwise convergence stated above, it covers $[-r,r]$.  By compactness, there exists $N\in\mathbb{N}$ such that $\bigcup_{n=0}^N I_n=[-r,r]$ and the conclusion easily follows.  Anyway, this method seems quite artificious. Also, hot to prove that $\{I_n\}_{n\in\mathbb{N}}$ is ascending? Unfortunately, $e^x-\left(1+\frac{x}{n}\right)^n$ leads to difficult computations. Is there a more direct proof, for instance, to find that $N$?

The question is     Do the polynomials $p_n(x)=(1+z/n)^n$ converge compactly (or uniformly on compact subsets) to $e^z$ on $\mathbb{C}$?   I thought about expanding $$p_n(z)=\sum_{k=0}^n a_k^{(n)}z^k$$ where $$a_k^{(n)}=\binom{n}{k}\frac{1}{n^k}=\frac{1}{k!}\prod_{j=0}^{k-1}\left(1-\frac{j}{n}\right)$$ and trying to show that $\frac{1}{k!}-a_k^{(n)}$ decreases sufficiently fast on any closed ball. That is, I tried to show $$\lim_{n\rightarrow\infty}\max_{z\in\overline{B_0(A)}}\left|\sum_{k=0}^n\frac{z^k}{k!}-p_n(z)\right|=0$$ for any fixed $A>0$, but I had difficulty with this approach.  Any help is appreciated.


To install programs in Ubuntu I usually do sudo apt-get install <program_name> -y.  There are some particular programs I install that ask me non-password configuration questions.  For example, after doing sudo apt-get install postfix -y I was asked for particular Postfix set of configurations, although the default was just fine to me.  How can one make sure an install that asks non password question won't ask it nothing? Surly, the only reason is to automate a few, particular installation processes.  Note: The solution I seek is per program, not global.

If I run:  sudo apt-get --yes install postfix    or  sudo bash -c 'yes | apt-get --yes install postfix'   an interactive prompt appears to configure postfix. I need to automate the installation of postfix (I can modify the configuration files after the install).  Is there some magic that lets me install postfix (and other package) without human intervention?


I can't find what's wrong with this.  Proof:  Every person supports the same team.  We can observe that in a set with only one person, all people within it support the same team. Now suppose that the statement is true for every set with cardinality $≤ n$. Then if there are $n + 1$ persons in a set, we take one of them and, by the hypothesis, all $n$ persons support the same team. Now put this person back to the initial set and remove a different one. Again, all the $n$ persons left support the same team. Therefore all $n + 1$ persons support the same team, and for every $k$ in $\mathbb N$, those $k$ people support the same team.

I'm bugged by the following that's summarized on p. 109 of .     False theorem: All horses are the same color.      Proof by induction:      $\fbox{$P(n)$ is the statement: In every set of horses of size $n$, all $n$ horses are the same color.}$   $\fbox{Base Case or $P(1)$:}$ One horse is the same color as itself. This is true by inspection.   $\fbox{Induction Step:}$ Assume $P(k)$ for some $k \geq 1$.   $\fbox{Proof of $P(k + 1) :$}$   Since $\{H_1, H_2, ... , H_n\}$ is a set of $n$ horses, the induction hypothesis applies to this set. Thus, all the horses in this set are the same color.   Since $\{H_2, H_3, ... , H_{n+1}\}$ is also a set of $n$ horses, the induction step likewise holds for this set. Thus, all the horses in this set are the same color too.         Therefore, all $n +1$ horses in $\{H_1, H_2, H_3, ... , H_n , H_{n+1}\}$ are the same color. QED.   The issue the instructor was trying to point out is clearly valid. For the case $n = 1$, there is only ${H_1}$. So this case says nothing about possible overlapping elements of each set of $(n + 1)$, for instance $H_2$ in the above proof.    But it was proposed in the class discussion that this was the only problem. Had you been able to prove $P(2)$ true, then a proof of the above format would have been fine.    My interpretation is that yes, you could prove all horses are the same color, if you can prove that any set of two horses will be the same color. But this format would not work.  Why not? The problem I see is that the above proof is for the existence of at least one particular pair of sets of horses of sizes $n$ and $n + 1$, such that in each set, all horses are the same color.  Particularly when the set of size $n$ is a subset of the set of size $n + 1$.  In order to prove the induction step, don't you need to prove that sets of sizes $n$ and $n + 1$, do not necessarily contain the same, overlapping elements?  You could prove that any horse can be added to a set of 2 horses.  Take the last two, and they must be the same color, and so on.  Wwhatever color the first two happen to be, all other horses must thus be the same color.    Am I misinterpreting the example, or am I making a logical error? Thanks in advance.


I know that on certain models of MacBook you can only install Windows from the SuperDrive—is there a way to circumvent this limitation? My computer is a MacBook Pro 13" from 2010, it doesn't have a disc drive and I want it to boot from a USB with Windows.

I have an iMac (bought in 2011) and I recently upgraded it with Yosemite. I am trying to install Windows 7 on it via Bootcamp.  However, its optical drive does not work, so I chose the USB key solution using the trick of modifying the file info.plist of Bootcamp (type 'usb bootcamp youtube' in google to see a video of this trick).  So I follow the process religiously and end up with the classic and famous boring screen 'No bootable device -- insert boot disk and press any key'.  So I tried to use Unetbootin (  ) to make my USB Key bootable, and tried to boot on it through the screen that appears when you maintain the Option key (Alt button) while starting the mac. Result: I never managed to have my Unetbootin-formatted USB key appear on this screen :(  I read some stuff about reFit (  ) and GParted, but I just don't know how to use them...  If someone managed to install Windows 7 on his/her iMac with Yosemite using a USB Key, please help me understand why I can't see the USB as a boot option.


I show bar chart image with this code. print(df['a'][1:].astype(int).plot.bar())  The image is very small I try to resize image by using matplotlib like this code. plt.figure(figsize=(4,3)) plt.plot(df['a'][1:].astype(int).sum())  when I run I show empty image without bar chart. How to fix it?

How do you change the size of figure drawn with Matplotlib?


Some questions contain long code listings, and it is often required to copy, download, or view the code in full, and maybe past/download it to a local file for compiler experiments.  Is there a better way for getting the code than doing tedious region select, scroll, and copy ?  Does it make sense to suggest some download link, or maybe copy link similar to the box appearing when pressing share for question or answer?; and how to make such a suggestion ?

I might just be lazy, but do you ever find it tiresome to select all the source code from a large post on Stack Overflow to copy it?  I would like a feature, possibly a Firefox extension, but preferably a JavaScript script, for automatically copying source examples to the clipboard. It's no big deal for a small snippet, but a 1000+ line posting is cumbersome to copy.  Do you guys have a better way of copying large source posts? I'm using Firefox 3.5.5 on Windows 7.


I'm working with threads in Java 8 and I'm using the next code:  Runnable runnable = () -> {             LOGGER.info(....);            someCode           };                Thread thread = new Thread(runnable);           thread.start();  My doubt is how can I stop or interrupt the thread or it will be stopped with itself? Any ideas?

How do you kill a java.lang.Thread in Java?


In general how would one show that two groups are isomorphic?   I know that to show that they aren't you would try to show that some abstract property is not satisfied, such as they have different orders etc.  I can't see a straightforward way of showing that they are isomorphic though.

In general, it is not too hard to find isomorphisms between two groups when their order is relatively low. However, as their orders grow, it becomes increasingly irritating to write down their entire Cayley tables and such. Is there a set of tricks that is generally useful when trying to prove that two groups are actually isomorphic? After all, it usually seems easier to prove that they aren't, as you just need to point out one property that doesn't correspond...  Example: in Armstrong's Groups and Symmetry, it is asked to show that the dihedral group of order 8 and the subgroup of S4 generated by (1234) and (24) are isomorphic. It is easy to send D4's "single-rotation" element r to S4's (1234) and D4's "flipping" element s to S4's (24), as they are all part of the generating set and their orders coincide, but what is the way to go from here? Also, how far should one go in showing the isomorphism - might pointing out the correspondence in generating elements even be enough?


I was wondering if I could use the new Google Maps. I have latest stable Chrome and Ubuntu 13.04. I am currently told that I must use lite mode. Under Chrome in Windows 8 on the same machine it works perfectly.

chrome://gpu/     And      google-chrome --version  Google Chrome 27.0.1453.93           How To Enable WebGL In Chrome On Ubuntu ?


I need help installing my printer.  I put the 'tar-gz' file in a new folder and opened it, clicked on 'tar.gz', and the files were 'install.sh', the different '.ppds,' and 'rastertokpsl.'  The instructions say 'Run' when the 'install.sh' file opens, but I don't know how to do this.  I clicked install.sh and it says says the following:  #!/bin/bash if [ ! -d /usr/share/cups/model ]; then  sudo mkdir /usr/share/cups/model fi if [ ! -d /usr/share/cups/model/Kyocera ]; then sudo mkdir /usr/share/cups/model/Kyocera fi sudo cp Kyocera_FS-1041GDI.ppd /usr/share/cups/model/Kyocera/Kyocera_FS-1041GDI.ppd sudo cp Kyocera_FS-1220MFPGDI.ppd /usr/share/cups/model/Kyocera/Kyocera_FS-1220MFPGDI.ppd sudo cp Kyocera_FS-1320MFPGDI.ppd /usr/share/cups/model/Kyocera/Kyocera_FS-1320MFPGDI.ppd sudo cp Kyocera_FS-1325MFPGDI.ppd /usr/share/cups/model/Kyocera/Kyocera_FS-1325MFPGDI.ppd sudo cp Kyocera_FS-1061DNGDI.ppd /usr/share/cups/model/Kyocera/Kyocera_FS-1061DNGDI.ppd  sudo cp rastertokpsl /usr/lib/cups/filter/rastertokpsl if [ -f /usr/lib/cups/filter/rastertokpsl ] && [ -f /usr/share/cups/model/Kyocera/Kyocera_FS-1041GDI.ppd ] && [ -f /usr/share/cups/model/Kyocera/Kyocera_FS-1061DNGDI.ppd ] && [ -f /usr/share/cups/model/Kyocera/Kyocera_FS-1220MFPGDI.ppd ] && [ -f /usr/share/cups/model/Kyocera/Kyocera_FS-1320MFPGDI.ppd ] && [ -f /usr/share/cups/model/Kyocera/Kyocera_FS-1325MFPGDI.ppd ]; then echo "Installation completed" else echo "Installation failed" fi

Whenever I open a .sh file, it opens it in gedit instead of the terminal. I can't find any option similar to Right Click → Open With → Other Application... → Terminal.  How do I open this file in the terminal?


This is astounding that this happens and I don't have an explanation. A simple console application as created by visual studio:  #include <stdlib.h> #include <crtdbg.h>  #include "stdafx.h" #include "ConsoleApplication.h"  int _tmain(int argc, TCHAR* argv[], TCHAR* envp[]) {     double a;     a = 3.4;      return 0; // <=======  Debug break point set here }   The value of a is 3.3999999999999999 instead of 3.4. To most programmers this isn't an issue, but why can't the number 3.4 be stored exactly as a double? Thinking about the binary it doesn't make sense.

double r = 11.631; double theta = 21.4;   In the debugger, these are shown as 11.631000000000000 and 21.399999618530273.  How can I avoid this?


In our daily lives, we generally use $10$ digits to define the numbers, i.e., $0$ to $9$. Based on these ten digits, we define all the natural, rational, and irrational numbers, etc. This representation is known as the decimal representation. I know that one could also define the number system in other ways. For example:  Unary: 1 11 111 1111 ... Binary: 0 1 10 11 100 ... Hexadecimal: 0 1 2 3 4 5 6 7 8 9 A B C D E F ...  Similarly, I can define my own number system, for example say: $\alpha \,$ $\beta\,$ $\gamma\,$ $9\,$ $\alpha \alpha \,$ $\beta^{2} \alpha\,$... But I am wondering, why do we use the decimal system to learn mathematics or say in our everyday lives. I know that a computer uses a binary number system since the most basic unit of storage is $0$ or $1$. However, I want to know, why humans use the decimal number system. Is there any logical advantage of using decimal representation over say Unary, Binary, or anything other? Thanks.

After learning about the binary number system (only 2 symbols, i.e. 0 and 1), I just thought why did we adopt the decimal number system (10 symbols) after all?  I mean if you go to see, it's rather inefficient when compared to the octal (8 symbols) and the hexadecimal (16 symbols)?


Let $R$ be a commutative, unital ring and let $I$ be an ideal of $R$. Prove that if $I$ is prime then $R/I$ is an integral domain.   This makes sense, but I'm not sure how to prove it using only the axioms. I know an ideal of $R$ is prime iff $\forall a,b\in R,$ if $ab\in I,$ then $a\in I$ or $b\in I.$ Also, integral domains are commutative, unital, and have no zero divisors. As well, $R/ I$ is the set $\{[a] : a\in R\},$ where $\forall a,b, a\sim b$ iff $a-b \in I.$      How do I show that commutativity preserved by the quotient ring? Also, how do I show that $R/ I$ is still unital?      Is commutativity preserved because $\forall a, b\in R/I, [a][b]=[ab]=[ba]=[b][a]$?      How do I show that if $a,b\in R$ such that $ab=0,$ then $a=0$ or $b=0$?

Here is the theorem and proof in my textbook.     Thm.  Let $P$ be an ideal of a commutative ring $R$ with identity $1$.  Then $P$ is a prime ideal of $R$ if and only if $R/P$ is an integral domain.   Proof.   Suppose that $P$ is a prime ideal of a commutative ring $R$ with $1$.  Then $P$≠$R$ implies $1+P≠0+P$. Hence $R/P$ is a commutative ring $R$ with identity.  Assume that $(a+P)(b+P)=0+P$.  Then $ab+P=0+P$ and $ab∈P$.  By the definition of a prime ideal P we get $a∈P$ or $b∈P$.  That is, $a+P=0+P$ or $b+P=0+P$.  Thus $R/P$ is an integral domain.   Conversely, if $R/P$ is an integral domain, then $1+P≠0+P$ and $R/P$ is a commutative ring $R$ which has no zero divisors.  Hence $P≠R$.  Assume $ab∈P$.  Then $ab+P=0+P$ and $(a+P)(b+P)=0+P$.  Since $R/P$ is an integral domain, we get $a+P=0+P$ or $b+P=0+P$.  So $a∈P$ or $b∈P$.  Thus $P$ is a prime ideal.    I am having problems understanding proof with "Conversely, if $R/P$ is an integral domain, then $1+P≠0+P$.".  I know that $R/P$ has an identity. (cause it is ID)  But, why doesn't "$P$" have an identity?  Isn't there a case $P=R$?  Please help me understanding. I think $P≠R$ should be with condition of Thm..  Thank you in advance.


I am currently reading through Rudin's Principles of Mathematical Analysis and I am learning about fields and their properties. Note that this is the initial chapter - I am just starting off.  I was wondering which field property enables us to multiply on both sides of an equation and still preserve equality.  There is a very clear proposition stated in the book that gives me this for inequalities: $$ \text{If} \ \ x > 0 \ \ \text{and} \ \ y < z \ \ \text{then} \ \ xy<xz. $$  However, the only proposition that seems useful for this in the case of equalities, is stated as an implication and not an equivalence: $$ \text{If} \ x\not= 0 \ \ \text{and} \ \ xy=xz \ \ \text{then} \ \ y=z. $$  Any help would be much appreciated.

It seems that given a statement $a = b$, that $a + c = b + c$ is assumed also to be true.  Why isn't this an axiom of arithmetic, like the commutative law or associative law?  Or is it a consequence of some other axiom of arithmetic?  Thanks!  Edit: I understand the intuitive meaning of equality. Answers that stated that $a = b$ means they are the same number or object make sense but what I'm asking is if there is an explicit law of replacement that allows us to make this intuitive truth a valid mathematical deduction. For example is there an axiom of Peano's Axioms or some other axiomatic system that allows for adding or multiplying both sides of an equation by the same number?   In all the texts I've come across I've never seen an axiom that states if $a = b$ then $a + c = b + c$. I have however seen if $a < b$ then $a + c < b + c$. In my view $<$ and $=$ are similar so the absence of a definition for equality is strange.


I am independently studying calculus using MIT's publicly available materials on OCW.  One of the Final Exam practice question is the following:  Suppose the series $\sum_{n=1}^{\infty}a_n$ converges absolutely.  Prove $\sum_{n=1}^{\infty}(e^{a_n} - 1)$ converges absolutely.  Since the rest of the practice problems have been more or less trivial, I suspect that I am missing something obvious, but I am not sure what.    A hint -- the lighter the better, please! -- would be most welcome...

It's a question from a test that I had, and I don't know how to prove this, so I am forwarding this to you.    $\sum \limits_{n=0}^{\infty }\:b_n$ is absolutely convergent series . How to prove that the series $\sum \limits_{n=0}^{\infty }\:(e^{b_n}\:-\:1)$ is also absolutely convergent?  We cannot assume here that $b_n\:\ge 0$ for every $n$.


I’m looking for routes served by a Boeing 747 out of Seattle. I know Lufthansa has a Seattle to Frankfurt but haven’t been able to find any other ones. Trying to fly on the Queen of the Skies before they all get decommissioned like United and Delta have done. Thanks in advance!

I'd really like to fly with an Airbus A380. But how do I find and compare the price of flights that are carried out by specific kind of plane? I don't want to fly just anywhere; I plan to go from Vienna, Austria to Indonesia this summer, possibly with a stop-over in Hong Kong, Singapore or Bangkok.  I checked if any there are any regular commercial flights with A380s to/from my home town. There aren't, so the way to go is probably to first fly to a major hub somewhere in the Middle East or South East Asia (which I'd have to do anyway since there don't seem to be many direct flights from Vienna to SEA).   So far, I simply searched for flights like you'd usually do and then checked which planes they use; this is very, very tedious, especially when one is very flexible in dates.    How do I find cheap flights that are carried out by a specific type of plane?


I suppose this is an unusual use case. But I've run into it a few times now.  Is it possible to force all inherited classes to have public static variables that are defined in the child class?  Aka:  APacket.ID   = 0; // Abstract parent class, has static ID variable (0) PacketPos.ID = 1; // Inherits from APacket, has static ID variable (1) PacketVel.ID = 2; // Inherits from APacket, has static ID variable (2)   I want all my network packet classes to have unique and public static ID and Length variables.  Is something like this possible?

I am developing a set of classes that implement a common interface. A consumer of my library shall expect each of these classes to implement a certain set of static functions. Is there anyway that I can decorate these class so that the compiler will catch the case where one of the functions is not implemented.  I know it will eventually be caught when building the consuming code. And I also know how to get around this problem using a kind of factory class.  Just curious to know if there is any syntax/attributes out there for requiring static functions on a class.  Ed Removed the word 'interface' to avoid confusion.


I'm not sure if I'm on the right forum for this. I've been a TeX user for awhile now, and I like to play around with different fonts. I was wondering what font they are using in the link below, and if this document was not typed in LaTeX (I'm not completely sure that it is), please refer me to another Exchange and I will delete this question.

Is it possible to identify the font used in a specific document/picture?  Answers to this question should identify:   Possible methods to do this (perhaps one answer per method) and adequately describe how to use it (as opposed to merely stating it); Ways of finding the identified fonts, if possible (free or not); and Any prerequisites associated with the method used, if required (for example, "In order to use method X, your document has to be in format Y").   This question is meant as an FAQ, based on an . Its aim is to facilitate the community with the general procedures involved in font identification. Similar cases are solved on a per-usage basis on 's  tag.


I'm attempting to install Gentoo through VirtualBox. Well, technically I've already installed it, but I still need a WM. While trying to emerge Xorg , I ran out of space, and so I resized the /dev/sda3 (main) partition by deleting it and creating a new one, but unfortunately, the /dev/root partition(?) doesn't resize with it, and I can't modify it with fdisk (can't open/detect it). I've read it's a symlink, so I guess it's not technically a partition? I don't know. I'm using Systemd rather than OpenRC if that matters (probably doesn't but I felt like I should mention it). With df -h I'm getting Filesystem    Size  Used  Avail  Use%  Mounted on /dev/root     3.7G  3.5       0  100%  /  (Can't post whole thing since I don't have mouse support installed)

For resizing LVM2 partition, one needs to perform the following 2 commands:  # lvextend -L+1G /dev/myvg/homevol # resize2fs /dev/myvg/homevol   However, when I perform lvextend, I see that the changes are already applied to the partition (as shown in Gnome Disks).  So why do I still need to do resize2fs?


I have inherited a shell script (#!/usr/bin/sh and I am not allowed to change the shell; i.e I can't, for instance, use a bash solution)).  It references a file in a relative path e.g DIR=$PWD/../SOME_DIR.  When I echo $DIR the output is something like /home/user/scripts/../SOME_DIR.  How can I get the absolute path name (no ..) into a variable (to be used in a  later echo)? I.e /home/user/SOME_DIR  It has been a few decades since my last shell script, and Google is not my friend today

I have a script which finds files in the directory specified by user.    #!/bin/bash  # make sure about the correct input if [ -z $1 ] then     echo "Usage: ./script_name.sh    path/to/directory" else     DIR=$1     if [ $DIR = '.' ]     then          echo "Find files in the directory $PWD"     else           echo "Find files in the directory $DIR"     fi      find $DIR -type f -exec basename {} \;  fi   if I input    $ ./script_name.sh .   script gives me correct substitution ./ to $PWD and shows (for example)    $ Find files in the directory /root/scripts     But I can't make a decision how to substitute ../ to the name of the directory  immediately above in the hierarchy.  If I input    $ ./script_name.sh ..     script gives me the output    $ Find files in the directory ..     Does anybody know how to substitute ../ to the actual name of the directory?


If you look at Vader's armor from inside, the eye holes were red-tinted.  Does that mean Vader always sees everything around him in red? Is there a specific reason why his armor was designed such way which can give him disadvantage?

Are there any sources that talk about  about Darth Vader's visual acuity?  His life-supporting armour is quite advanced but does it provide any useful augmentation to his visual abilities?


In phase 10, can I pick up a card from the discard pile and then relay that card back down in the discard pile?

While playing Phase Ten, is it legal to pick up the top card of the discard pile and then immediately discard that exact card?


I am trying assignment of an Institute in which I am not a student and I am unable to think about this problem.      Problem If there exist integers $a$ and $b$ such that $(a, b) = 1$ and $1+ \frac{1}{2} + \ldots + \frac{1}{p-1} = \frac{a}{b}$ then prove that $p^2 | a$ , assuming that $p\geq 3$.    Can someone please help how to approach this problem.

According to the theorem, if  $$1+\frac{1}{2}+\frac{1}{3}+\frac{1}{4}+\frac{1}{5}+\cdots+\frac{1}{p-1} =\frac{r}{q}$$  then we have to prove that $r\equiv0 \pmod{p^2}$.  (Given $p>3$, otherwise $1+\dfrac{1}{2}=\dfrac{3}{2}$, $3 \not\equiv  0 \pmod 9$.)  I guess there's a $(\bmod p)$ solution for this, but I don't really get how to start it.


One example of a non-Hausdorff topological space in which all compact subsets are closed is the co-countable topology on an uncountable set, as demonstrated .   It was claimed (as a now-deleted answer to the above question) that the compact complement topology on $\mathbb{R}$ was another example, but this was proven incorrect .   Can someone provide an additional example of a non-Hausdorff space in whihc all compact subsets are closed?

Is it possible to have a topological space having all compact subsets closed, but the space itselt is not Hausdorff?  I couldn't find any counterexample. I tried $\mathbb R$ with cofinite, point inclusion and point exclusion topologies, but these didn't work.  Any suggestion in this context will be helpful for me.


How can I get from CDG airport to Hotel du Cadran, 10 Rue du Champ de Mars, 75007 Paris, France, with minimum number of transfers?  I do have luggage to carry.  I prefer to travel by train, if possible.

Paris has 3 airports (Orly, Roissy, Beauvais), what are the options to go to or to come from there?  (There is also Vatry (XCR) but there is very few flights and i see the shuttle system is currently off.)


I have two virtual machine running on a virtual box.   VM 1 and  VM 2  The network is in the NAT mode (default).  Both the machines have the same IP address.So I assume that they are in two different networks.  My requirement is that I should be able to communicate from  VM 1 to VM 2 using IP. i.e  I would like to ping from VM 1 to VM 2 and back.  For this I would prefer if they were a part of the same network.Is there some routing functionality implemented in Virtual Box?  How do I created and internal network with two VM's that can talk to each other using IP.

I have one physical machine, on it there are 2 virtual machines. One of the VM is the application machine, another is the db machine. All are running Windows XP.  I am using Sun Virtual Box for virtualization purpose.   One thing I notice is that on both virtual machines, the IP address is exactly the same.   The problem with this is that I can't connect to the db machine, using MySQL Administrator from my application machine, because I will have to specify the IP of server host, which, in this case, is exactly the same for both db machine and application machine!  I also try to use Hamachi address ( because the Hamachi address is different for different VM), but I always get a "cannot connect" problem, even though I can, from one VM, ping the Hamachi address of another VM.  Any idea how to solve this?  Edit: Dave has a . Here is  on how to configure Sun Virtual Box 2.2 bridged connection.


Hi I have been in a relationship with a single mum for a far while now and I have began to notice a lot of things that happen that make me think about what to do as I am clueless, I am also a single parent.   When her child is screaming at the top of her lungs and causing a scene for no reason... There is no punishment "she's only a child" is what I am told.  When her child trashes the house with rubbish and I ask her to pick it up " you can't expect her to clean up she's just a kid"  She runs out of the house and hides for some time and destroys a gift made by my child for me for farthers day and "you can't punish her she's only 5" is what I am told...  I have no idea on what to do please help... I am at my end here...

The kid will soon grow up to the age when she'll need to be disciplined.  My husband and I are NOT on the same page regarding disciplining the child.   I think if the kid cries because one parent has refused to give into her demands and decided to time out her, the other parent should not intervene and console the child since that'll give the child a message that mama is bad and daddy is nice rather than letting her understand the problem.   My husband thinks if daddy doesn't intervene to console the child when she cries (w.r.t above mentioned situation), the child will think that both parents are on each other's side and no one loves her.  I don't know whose opinion is correct. I also don't know how to deal with child if both the parents are not on the same page.


Which of the following sentences is/are grammatically correct? Of the correct ones: what is the difference in meaning? Are there other (more correct or more precise) ways to express the same meaning?   Being 19 weeks outside the womb my baby has learned to grab things. Having been 19 weeks outside the womb my baby has learned to grab things. Having been being 19 weeks outside the womb my baby has learned to grab things.     The answers to  don't help me because:     The sentences in the linked question do not include a period of time and mentioning periods of time changes the tense usage. The sentences in the linked question imply causal relationship whereas my sentences imply temporal relationship.

Being a teacher, she likes children.    AND    Having been a teacher, she likes children.   What is the difference between these two?


I'm looking for the name of a book series I read when I was younger (maybe early 2000s?) that follows a family of very long-lived wizards/magicians who live in a tower in some sort of secret grove and watch human society evolve from a distance. There are multiple books, possibly each one following a different wizard/generation of wizards. I think one of the main characters is a woman who dresses in blue. I think the opinions of the common people towards magic change throughout the series, but definitely at some points they're feared/hated/persecuted and have to hide their identities when they go out into the world. One of the early novels might follow a human man/boy who meets a talking cat (possibly one of the wizards in disguise) which helps him unlock his magic powers. I think there's a scene where he's defending a castle and uses a spell to multiply his breath into a gale that blows away attackers. There's a scene about the trees in the forest around the wizards' grove. They dive into the tree's minds and see their slow-paced long-term view of the world. The wizards might worship, or even be servants of, some sort of god that lives in the grove with them. Near the end of the series they have a confrontation with an evil uncle who lives in a cave or something.

I remember reading a book series around 2008 - 2009 — probably as an ebook but maybe a hard copy — which for the life of me I cannot recall. My google-fu skills have failed me too. So here are the details I remember   The name of series started with B... something like Bar@@@@ Set in fantasy time with medieval setting. There was a ancient wizard, who was sort of immortal, or maybe just very very old, disguised as a common man at the start Hero was a young boy, introduced as an orphan, working in some rich noble's kitchen or kitchen farm Magic was used ages ago, but common folk have mostly forgotten about it There are several kingdoms, one in snow, one is an island, one is open grassland, and then there is a huge, big bad evil kingdom in north Wizard helps forge / renew alliance between all kingdoms slowly, having to work through some politics Wizard keeps training the boy in various arts as the series progresses There is eventually a war, but the good kingdoms sort of manage to defeat the evil king (he may have been crazy / megalomaniac) After war, wizard and boy go to the location where evil god (something with T... Tarturs or something) is sleeping, but whose evil keeps seeping into the world The boy, now trained and grown up, fights the god and eventually wins There may have been a middle aged woman, fiery in temper, also a witch, probably daughter of ancient wizard, and mother of hero   I also remember not really liking the books then, sort of having too many deus ex machina, but for some reason have them stuck in my mind recently. Any help would be deeply appreciated!


so I needed to chown a folder and I accidently wrote      chown -R admin:admin /   And that chmowned all files for ~5sec then came up an error that it can not chown something and I stopped.  After I noticed I can not login in VestaCP, I changed password for VestaCP, but still could not log in.  So I checked the pass with somekind of Vestatool + standard login and it worked, so I understood this issue is because of the chmod - VestaCP cant' probably create a session file or something. Where should I look to set correct permissions? I checked most folders abd can not find any fault with them, comparing to my other server. Everything else seems working, also did a restart - booted up and running.

I just ran this a few seconds ago. I managed to do Ctrl - C as soon as I realized what I started doing.  So far the only directory it's started going through is /bin.  I'm afraid to do anything else. So far I realized I can't use su as my normal user anymore.  Luckily I still have another root terminal open. What do I do?


After upgrading to Ubuntu 17.04 from 16.10, I've lost the feature of typing in Unicode layout for Tamil language. Also there is no option to select Tamil (India) which was present in the version 16.10; instead it shows only Tamil (Sri Lanka).  I don't know how to get those things back. Currently I'm using IBus for typing in Indian Languages. But I wish it could be there in default keyboard options.

I've upgraded from Ubuntu 16.10 to 17.04 today. I'm from Bangladesh, and Bengali is my native language. There was an option to set keyboard layout to Bengali in all previous Ubuntu versions I've used. But there's no such option in 17.04, strangely. I can use Bengali by installing the package ibus-m17n,  so I thought maybe there was some problem during my upgrade. But then I checked my friend's PC which runs ubuntu 16.10 and found that ibus-m17n was not installed in 16.10 but there's option for Bengali keyboard layout. So is Bengali keyboard support really removed from 17.04, or was there a problem during my upgrade?


My Sony Vaio HDD has been formatted and I want Ubuntu on it--can it be done? And how--I can't even seem to find Linux for laptop OS downloads.

I would like to see a full how-to guide on how to install Ubuntu.


According to normal probability distribution theory which says that for $n$ independent, identically distributed, standard, normal, random variables $\xi_j$ the expected absolute maximum is  $E(\max|\xi_j|)=\sqrt{2 \ln n}$  Regarding this, why do we need to multiple the above-mentioned estimate by $\sigma$ (Standard Deviation) in order to derive the expected absolute maximum for a normal, random variable with zero mean?

Is there a nice limiting distribution of $\max( X_1,X_2,...,X_n) $ as $n$ goes to $\infty$, assuming that they are iid normal distributions with variance $\sigma^2$.   This is almost certainly a well known problem with a clever proof and nice solution, but I've been digging around and haven't found anything.


I have ubuntu 13.04 desktop installed and I've been reading about kernel 3.9s release yesterday. My issue is that I have no sound output with HDMI, something the new kernel apparently fixes. In reading, I've also come across kernels built for specific processors (I have an i5 on this laptop).  I guess my question is there a place to get this 3.9 kernel for my i5 processor for install in ubuntu?

I'm running the current stable Ubuntu version (Oneiric) but have issues with the shipped kernel. Newer kernel versions seem to have fixed it, but the kernel-ppa/ppa does not contain the most recent kernel which is why I want to install the kernel from the next stable version (Precise). Since I want to be able to unload out of tree kernel modules, the mainline kernel from  cannot be used.  I also have have Virtual Box installed which also need to work in the new kernel so the "kernel headers" have to be upgraded as well.  How am I supposed to install the kernel packages from the next stable version (Precise) without upgrading all other packages?


I want an image to be my hyperlink in Google sheets.  Here is my formula:  =HYPERLINK("google.com/de", IMAGE("http://s5.favim.com/orig/69/hi-love-quote-start-Favim.com-658946.jpg"))   The image shows up on the sheet - but it is no longer a hyperlink.

I need a cell that contains an image to also contain a hyperlink.  Following formula is the only one I found but doesn't work (error analyzing formula)  =HYPERLINK("URL", image("URL"))   Following formula I tried shows a blank cell but the link works  =hyperlink("URL"; Image("URL"))


The flagging history page displays a sidebar that shows the numbers of each type. My feature request is to allow clicking those numbers to show the actual flags that are waiting for review etc.  It would make it much easier than skimming down the page looking for the flags still in review.

Here is my flagging summary on SU:   Your flagging history   32 posts flagged as requiring moderator attention    2 are waiting for review   3 were marked valid   1 were marked invalid   (older flags were not recorded valid/invalid)    2 posts marked as spam    It is too complicated to look for invalid flags. Would it be possible to make filters on the top of the page (like on favorites for example) with:  By date, By type (off-topic, spam, dupes), By status (accepted, pending, rejected)  It would make it easier for reviewers to check their flagging and eventually know what to improve on.  Or is there another easy way to audit this?


I am trying to understand the formulas of ridge regression, lasso, and elastic net. If I got it correctly, the only difference between these 3 shrinkage methods is the penalty term,   i.e. for ridge regression $\lambda\sum_{j = 1}^{p}\beta_j^2$,  for lasso $\lambda\sum_{j = 1}^{p}|\beta_j|$,  and for elastic net $\lambda\sum_{j = 1}^{p}(\alpha\beta_j^2+(1-\alpha)|\beta_j|)$.  According to , the formula for ridge regression is   \begin{equation} \hat{\beta}^{ridge} = argmin_{\beta}\left\{\sum_{i=1}^{N}(y_i - \beta_0 - \sum_{j=1}^{p}x_{ij}\beta_j)^2 + \lambda\sum_{j=1}^{p}\beta_j^2  \right\},  \end{equation}  so we are adding the ridge penalty to a usual linear regression model.  Since I assume that the only difference between ridge regression, lasso, and elastic net is the penalty term I would expect that the formula for the lasso would be  \begin{equation} \hat{\beta}^{lasso} = argmin_{\beta}\left\{\sum_{i=1}^{N}(y_i - \beta_0 - \sum_{j=1}^{p}x_{ij}\beta_j)^2 + \lambda\sum_{j=1}^{p}|\beta_j|  \right\} \end{equation}  and  \begin{equation} \hat{\beta}^{elnet} = argmin_{\beta}\left\{\sum_{i=1}^{N}(y_i - \beta_0 - \sum_{j=1}^{p}x_{ij}\beta_j)^2 + \lambda\sum_{j=1}^{p}(\alpha\beta_j^2+(1-\alpha)|\beta_j|)  \right\} \end{equation}  for the elastic net respectively.  However, according to  the formula of the lasso is   \begin{equation} \hat{\beta}^{lasso} = argmin_{\beta}\left\{\frac{1}{2}\sum_{i=1}^{N}(y_i - \beta_0 - \sum_{j=1}^{p}x_{ij}\beta_j)^2 + \lambda\sum_{j=1}^{p}|\beta_j|  \right\} \end{equation}  with a $\frac{1}{2}$ in front of the first $\sum$. According to  there should be a $\frac{1}{N}$ in front of the first $\sum$.  Question 1: Why do I have to put a $\frac{1}{2}$ or a $\frac{1}{N}$ in front of the first $\sum$. What is the correct formula for the lasso?  Question 2: What is the correct formula for the elastic net? Do I also have to put $\frac{1}{2}$ or $\frac{1}{N}$ in front of the first $\sum$?

This question might be dumb, but I noticed that there are two different formulations of the Lasso regression. We know that the Lasso problem is to minimize the objective consisting of the square loss plus the $L$-1 penalty term, expressed as follows, $$ \min_\beta \|y - X \beta\|_2^2 + \lambda \|\beta\|_1 \; $$  But often time I saw the Lasso estimator can be written as $$ \hat{\beta}_n(\lambda) = \displaystyle\arg \min_{\beta} \{\frac {1}{2n} \|y - X \beta\|_2^2 + \lambda \|\beta\|_1 \} $$  My question is, are the equivalent? Where does the term $\frac {1}{2n}$ come in? The connections between the two formulations is not obvious to me.   [Update] I guess anther question I should ask is,  Why is there the second formulation? What's the advantage, theoretically or computationally, of formulating the problem that way?


In my program I pass the path to a file which may be still being written to by another process (independent external non-c#).  How can I check the file is fully readable and accessible before I actually send the path back to the client? FileIOPermission with Demand for reading did not work for me, so I am wondering if there is some other way of doing this without attempting to read the whole file upfront.  Thank you.

This is how I do it at the moment. I try to open the file with the FileShare set to none. So I want exclusive accesss to the file. If I can't get that then its a good bet somebody else has the file locked.  There's got to be a better and faster way. Any ideas?              try             {                 using (FileStream fs = File.Open(GetLockFilename(), FileMode.Open, FileAccess.ReadWrite, FileShare.None))                 {                     fs.Close();                 }                 // The file is not locked             }             catch (Exception)             {                 // The file is locked             }


I have a Dell Latitude 2120 small laptop with an Intel Atom (N550) CPU that has run Ubuntu 16.04 LTS for a year or so.  Recently I installed Ubuntu 18.04 LTS.  The boot process gets to the "moving dots" stage, the mouse cursor arrow eventually appears, but it is frozen and the system hangs at the dots stage.  I have tried boot-repair to no avail.  The system boots successfully from the "live USB" drive, but not on its own.  There is some web traffic that suggests that (1) Intel Atom needs a 32-bit system for Ubuntu and (2) 32-bit ISOs are no longer available from Ubuntu.  Is there a solution to this?

I've just updated to 18.10 from 18.04 and immediately hit a snag. My os doesn't boot anymore. It starts then comes to a moment when splash appears then it disappears and what I see is a message that [ok] Started Gnome Display manager. Sometimes it's something other but still no boot. Funny enough that if I hot ALT + F2 during boot it seems to restart gdm or something because I see how splash blinks and gdm loads, I can enter password and everything seems to be working. Well, my question is what could it be and how to fix it because it's quite annoying.   Specs are: AMD® Ryzen 5 1500x quad-core processor × 8 15,7 GiB GeForce GTX 1060 6GB/PCIe/SSE2


How can I search for multiple filename extensions in Windows 8?  Semicolon does not work:

I know how to , but I'd like to add a bunch of different extensions and avoid the tedious job of adding every single one. Is there a command line tool or registry key I can use to accomplish this?


I have a small sample from an unknown, possibly non-parametric population. I would like to create a new, different sample from the population based only on what I can extract from the small sample I have.  Is there a way to do it, given that my sample is small? Specifically, can I resample from that sample using bootstrapping and hope I can get closer to the "true" mean and variance of the population? (Let's assume for a moment these two parameters are enough to characterize the population.)

I have just learned about the concept of bootstrapping, and a naive question came to mind: If we can always generate numerous bootstrap samples of our data, why bother to obtain more "real" data at all?   I do think I have an explanation, please tell me if I'm correct: I think the bootstrapping process reduces variance, BUT if my original dataset is BIASED, than I'm stuck with low variance and high bias, no matter how many replicas I'm taking.


I have a compaq Presario R3000 running hardy heron 8.04 with gnome.  I want to update to the latest version, but i am having a bit of trouble.  I've tried using Update Manager but when I try to upgrade to 10.04.4 (which is the only option) it says that it is no longer supported, but i keep going, and it starts downloading stuff then prepares to upgrade, but then when i gets to "setting new software channels" it gives an error.  I don't know how to boot off a usb.

Recently I have installed an older version of Ubuntu on my old machine. Whenever I try to install any software, I get an error saying it couldn't be found:  $ sudo apt-get install vlc Reading package lists... Done                Building dependency tree        Reading state information... Done     E: Couldn't find package vlc


I'm skeptical about a lot of things in physics, but I have a great interest in it and I'm studying it in college next year. However I am very skeptical about some things. I find that for physics, it helps a lot to see a real life demonstration (video) of what's being explained. I understand the whole radioactive decay thing, but I have not been able to find a single video which shows an element decaying. Why is this? Does radioactive decay actually exist or is it a theory? Surely it cant be hard to put an element with a half life a a few days/weeks in front of a camera to show it's decay. If radioactive decay is occuring in an element, then how does the element ever actually form into a significant amount if it's constantly decaying?

Ignoring the quantum zeno effect (if possible?), can we observe in real-time the transformation of one element to another? I'm talking about an amount visible to the naked eye where one could see obvious changes in colour, reflectivity, phase, surface finish etc. occurring in say, seconds or minutes.


Suppose we have independent random variables $X_1,\ldots,X_n$ with the same distribution. Let $F(\cdot)$ be the cumulative distribution of $X_i$ for all i We are interested in the cumulative distribution of (Max,Min) where $\text{Max}=\max\{X_1,\ldots,X_n\}$ and similarly for min. This is what I've worked out for far;  Let $G(x,y)$ the cumulative distribution of (Max,Min)  \begin{align} G(x,y) & = P(\text{Max}\leq x, \text{Min} \leq y) \\[8pt] & = P(\text{Max}\leq x) - P(\text{Max} \leq x, \text{Min} \gt y ) \\[8pt] & = P(X_1 \leq x,\ldots,X_N \leq x) + P(y \lt X_1 \leq x) \\[8pt] & = F^n(x) - [F(x) - F[y]]^n \end{align}  Is this correct? Thanks

Let $X_1,\ldots,X_n$ be independent random variables with common cumulative distribution function $F$. I am trying to find the joint cumulative distribution function of $$U=\min(X_1,\ldots,X_n)\quad\text{and}\quad V=\max(X_1,\ldots,X_n).$$ The result that I get is $$F_{U,V}(u,v)=F(v)^n-(F(v)-F(u))^n,$$ but this seems wrong because letting $u\to\infty$ gives the marginal CDF $$F_V(v)=F(v)^n-(F(v)-1)^n,$$ while it should be $F_V(v)=F(v)^n$. I obtained the result as follows $$\begin{align} F_{U,V}(u,v) &= P(U\leq u,V\leq v) \\ &= P(V\leq v)-P(U>u,V\leq v) \\ &= P(X_1\leq v,\ldots,X_n\leq v)-P(u<X_1\leq v,\ldots,u<X_n\leq v) \\ &= F(v)^n-(F(v)-F(u))^n. \end{align} $$ But $$F_V(v)=P(V\leq v)=P(X_1\leq v,\ldots,X_n\leq v)=P(X_1\leq v)\cdots P(X_n\leq v)=F(v)^n.$$ What is wrong with these computations?


Time to time I come across the following situation:  I notice that something is wrong on SE and needs to change. I go to Meta.SE to find out this already have been reported by someone with little yet positive feedback from community and no official response. I also have something (in my opinion) valuable to further justify that this problem needs fixing.  Now, what am I supposed to do next?  Upvote the question pointing the problem out. Most obvious thing to do, but doesn't help much with attracting attention. Comment of question pointing adding my idea on why it's so important. Not bad, but will help even less in ways of attention. Post an answer instead of comment from previous point. But I don't really have an answer?.. Post another question with my arguments only to be closed as dupe. Seemingly rather effective at attracting attention, but I know better than doing so. Post a bounty on question (after commenting and upvoting): probably good at getting attention, but whom am I offering rep to? The answer I'm expecting would be from SE itself and it feels odd to give away internet points to point out someone else's design issues. Give up my ideals and take part in Twitter Driven Development. Probably efficient, but makes me sad.

I posted a question here on Meta Stack Exchange, or on a per-site meta, regarding a bug I found in the system. I got no comments, or a few comments stating that this is a legitimate bug (and not by design). However, it's been quite a long time, and no official response was ever posted there.  Or, I had an idea for a new feature, but realized it's already requested, either by searching or posting a request myself only to have it closed as a duplicate of the existing one. It's been a while since the original request was filed, but no official response has been made.   I'm aware that staff members are , but either my post isn't about one of the indicated topic areas for which they're accepting escalation requests for that month, or I already flagged to request escalation but it was declined, so the instructions there don't apply for my post.  What can I do to draw attention to meta questions for the SE team, so they can give an official response, and possibly implement the bug fix or feature?  Note: This is different from other general questions which ask for how to get attention for unanswered questions, since the procedures on meta sites are different, and getting an official response isn't necessarily the same as getting a good answer.


Let's say that I have a base class X with only one virtual function.  I extend it to Y and override that function.  I didn't provide explicit destructor for X and Y.  What happens during the destruction in this statement.  Y y; X *x= &y; return; . . . X*x = new Y; delete x; return;   Which will cause memory leak..

I have a solid understanding of most OOP theory but the one thing that confuses me a lot is virtual destructors. I thought that the destructor always gets called no matter what and for every object in the chain. When are you meant to make them virtual and why?


I have purchased a new laptop with windows 8.1 preinstalled. I want to use ubuntu 14.0.1 on my laptop without uninstalling windows. I have created bootable usb stick for installing ubuntu. But when i open wubi.exe install inside windows option is not there. Is there something like you can't install ubuntu 14.0.1 inside windows?  If not, then how do i accomplish this task?

I'm absolutely new to Linux. I would like to know how to install Ubuntu alongside the pre-installed Windows 8+ OS.  Should I do it with Wubi, or through the Live USB/DVD?  What steps do I need to take to correctly install Ubuntu?


I have  a select query, i would like to run it 50 times in parallel(to load test) ie. 50 independent times(a separate process).  if i run like this  for (int i=0;i<=49;i++) {  //record start time before the query  //Code that runs the select query...  //record end time after the query }   I need to test the select query for 50 times, do I need to use 50 different threads or running that query in for loop 50 times, which is the correct approach?  Is there better way to check the consumption time of the query for say 50 times ? Do i need to use threads? I am not sure how to use Threads, don't have much idea of threaded programming, any sample will help.

I need to find a bottleneck and need to accurately as possible measure time.  Is the following code snippet the best way to measure the performance?  DateTime startTime = DateTime.Now;  // Some execution process  DateTime endTime = DateTime.Now; TimeSpan totalTimeTaken = endTime.Subtract(startTime);


Consider a code:  public class MyDto implements Serializable {     private String myField;     public MyDto (String myField) {         this.myField = myField;     }  }   As I see this code works (I hope), but I have no idea how java serialization/deserialization construct object before it sets fields. Any idea?  About duplication  I have not found any constructor or immutable key words in  page. So this question is a bit different. Also  describes difference between json/xml etc not some specific feature to java serialization.

I've been lately trying to learn more and generally test Java's serialization for both work and personal projects and I must say that the more I know about it, the less I like it. This may be caused by misinformation though so that's why I'm asking these two things from you all:  1: On byte level, how does serialization know how to match serialized values with some class?  One of my problems right here is that I made a small test with ArrayList containing values "one", "two", "three". After serialization the byte array took 78 bytes which seems awfully lot for such low amount of information(19+3+3+4 bytes). Granted there's bound to be some overhead but this leads to my second question:  2: Can serialization be considered a good method for persisting objects at all? Now obviously if I'd use some homemade XML format the persistence data would be something like this  <object>     <class="java.util.ArrayList">     <!-- Object array inside Arraylist is called elementData -->     <field name="elementData">         <value>One</value>         <value>Two</value>         <value>Three</value>     </field> </object>   which, like XML in general, is a bit bloated and takes 138 bytes(without whitespaces, that is). The same in JSON could be   {     "java.util.ArrayList": {         "elementData": [             "one",             "two",             "three"         ]     } }   which is 75 bytes so already slightly  smaller than Java's serialization. With these text-based formats it's of course obvious that there has to be a way to represent your basic data as text, numbers or any combination of both.  So to recap, how does serialization work on byte/bit level, when it should be used and when it shouldn't be used and what are real benefits of serialization besides that it comes standard in Java?


My ListView crush when its empty. I want to show on it EmptyView. I've found few 'solutions' but they didnt helped me.. I've tried ' List valueList = new ArrayList<>(); ' and with that setEmptyView working, but when ListView shouldn't be empty I only saw setEmptyView...  Please help me to fix it, here is my code:  Adapter:  List<User> valueList = new ArrayList<>();   Here I've got error without ArrayList:  @Override public int getCount() {     return this.valueList.size(); }   Activity:   @Override     protected void onPostExecute(Void result)     {         progressBar.setVisibility(View.GONE);         ListView.setVisibility(View.VISIBLE);         ListAdapterClass adapter = new ListAdapterClass(studentList, context);         if(adapter!=null && !adapter.isEmpty()) {              ListView.setAdapter(adapter);         } else {              MessagesListView.setEmptyView(findViewById(R.id.tv_no_result));         }      }   ERROR (without ArrayList)  java.lang.nullpointerexception: attemp to invoke interface method 'int java.util.List.size()' on a null object reference

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?


Let's say publication A has a nice overview of a topic and cites B and C sources to back up a few important points. Should I cite A, since it provided me with B and C? Or do I have a responsibility to read these citations? What if B is a 40-page, esoteric paper that I am unlikely to read. This seems like a rabbit hole, and I'm not sure how far down my due diligence should take me.

I have some questions regarding secondary citations (in an computer-science research paper that should be published in a journal). I know that they should be avoided when possible, but it is not always that easy. More specifically, my situation is this:  Article A says:     The average value of ... in ... is ... [B]. [C]’s study says that in ... the value is ...   This statement is exactly what i need for my paper. If I read [B] and [C], I see that [A] cited them correctly and if I would have found these two other articles myself, I would have written the same.  Now how to cite this in a correct way?      [B] and [C] say (cited in [A]) ...   and do a “bad” secondary quote;    [B] and [C] say ...   and neglect the investigation done by [A] and peform citation plagiarism;    [A] says ...   and neglect that the data was the achievement of [B] and [C].    [A] says based on the findings of [B] and [C] ...   and do a secondary quote again.


$stmt = $conn->prepare("INSERT INTO users (username,created) VALUES (?,?)"); $stmt->bind_param("ss", $_POST['username-reg','whatdoiputhere?']); $stmt->execute();   I want to add a "now" date/timestamp that can also be inserted simultaneously so that i can keep track of when users create accounts. is there a function that i need to write/reference to get the current date? or is there an already known function that i just need to reference? i am new to php, sorry

Which PHP function can return the current date/time?