I saw a program on Windows that helped the user learn keyboard shortcuts in various applications by reminding there is a shortcut every time he used a mouse to particular task.   Is there some similar software available for Mac OS X?
OS X lets me type special characters directly on the keyboard by holding the Option. For example: — is an em dash, “ and ” are curvy quotes, etc.  Is there a good cheat sheet listing all these keys somewhere? I tend to find myself holding option and running my hands up and down the keyboard looking for a specific character.
Includepdf causes an error message from pgfplots externalization I have a file test.pdf which I include in a document containing also an externalized pgfplots picture.  When I compile the following code, I get the error message Sorry, the system call pdflatex ... did NOT result in a usable file.  In order to make my code work, I first need to remove the includepdf statement, compile (to create the externalized figures) and then compile again with the includepdf statement.  I suppose that it is a bug, or is there any possibility to solve it ?  Of course, the file test.pdf is totally independent from the externalized pictures from pgfplots.  \documentclass{scrbook}   \usepackage{pgfplots}  \pgfplotsset{compat=1.8}  \usepgfplotslibrary[external]  \tikzexternalize[shell escape=-enable-write18]  \usepackage{pdfpages}   \begin{document} \includepdf{report_test-figure44}   \begin{tikzpicture}  \begin{axis}[  xlabel=Cost, ylabel=Error]  \addplot[color=red,mark=x] coordinates {  (2,-2.8559703) (3,-3.5301677) }; \end{axis}  \end{tikzpicture}   \end{document} Order a MySQL table by two columns How do I sort a MySQL table by two columns? What I want are articles sorted by highest ratings first, then most recent date.  As an example, this would be a sample output (left # is the rating, then the article title, then the article date)  +================+=============================+==============+ | article_rating | article                     | article_time | +================+=============================+==============+ | 50             | This article rocks          | Feb 4, 2009  | +----------------+-----------------------------+--------------+ | 35             | This article is pretty good | Feb 1, 2009  | +----------------+-----------------------------+--------------+ | 5              | This Article isn't so hot   | Jan 25, 2009 | +================+=============================+==============+  The relevant SQL I'm using is: ORDER BY article_rating, article_time DESC  I can sort by one or the other, but not both. $f(x)=x/1$ is not injective? In chapter 3 of Atiyah and Macdonalds Intro to Comm Algebra there is the statement  "We also have a ring homomorphism $f:A\rightarrow S^{-1}A$ defined by $f(x)=x/1$. This is not in general injective." (Note: $A$ denotes an integral domain and $S$ a multiplicatively closed subset of $A$.)  How could this possibly not be injective? If $f(x)=f(y)$ then $x/1=y/1$ so $1x=1y$ hence $x=y$. What am I missing here? Suppose we have a magnetic field directed into the computer screen. Assume that there is no gravitational field. Now suppose we have a stationary positively charged particle in the magnetic field. The magnetic force is given by $$\mathbf{F}=q\mathbf{v}\times\mathbf{B}$$  Since $\mathbf{v}=0, \mathbf{F}=0$.  Now pick a reference frame moving to the left with constant velocity. In this frame, the particle is moving to the right with constant velocity. So, the magnetic force is directed upwards.  From what I've learnt in physics, forces are independent of choice of reference frames as long as the frames are inertial. But in the 2 inertial reference frames I have chosen, I get 2 different magnetic forces. How do we reconcile this? Which other nations are there in Attack on Titan world aside Eldia and Marley? In the Attack on Titan wikia they often mention other nations aside Eldia and Marley which supposedly have more advanced technology than this 2 nations. Which other known nations are there in Attack on Titan world aside Eldia and Marley and why are they more advanced than Marley when only Eldia is supposed to be isolated from the world? This post has been locked; locked posts can't be voted on I am having a strange problem in ArcGIS Toolbox.  I am trying to use the  tool from ArcToolbox. When I open the tool, there is no possibility to input Simplification Tolerance. Please see the attached image.  I can run the tool as a batch and from the Python window without any problem.  I am using ArcGIS 10(Editor) with Service Pack 5 on Windows 7 64Bit (English) and Windows Server 2008 64Bit (German). On both machines, I have the same problem. Any ideas?    I have reinstalled the software but the problem remains. What are integers $x$ and $n$ such as $ x^4+x^3+x^2+x+1 = n^2$? What are the integer numbers $x$ such as $x^4+x^3+x^2+x+1$ is the square of an integer?  $0$ and $-1$ are obvious answers, but how many are there? Can I control voltage of USB data pins? CSS to make HTML page footer stay at bottom of the page with a minimum height, but not overlap the page I have the following page (deadlink: http://www.workingstorage.com/Sample.htm ) that has a footer which I can't make sit at the bottom of the page. I want the footer to  stick to the window bottom when the page is short and the screen is not filled, and stay at the document end and move down as normal when there is more than a screenful of content (instead of overlapping the content).  The CSS is inherited and befuddles me. I can't seem to change it properly to put a minimum height on the content or make the footer go to the bottom. What prevents this magnetic perpetuum mobile from working? Programmatically download (seamless) NED tiles? I used to download 1/3 arcsecond elevation geotiffs from extract.cr.usgs.gov using web services.  But a few days ago, that stopped working, probably because USGS reorganized their site.  I tried emailing USGS and haven't heard back yet.    I could, of course, manually download states or degree tiles using the seamless server, but I want to do it programmatically so that users of my trip planner can get elevation data for their region without human intervention.  And SRTM isn't high enough resolution for bicycle/wheelchair trip planning.  Any ideas? What is inertia of a body? I try unsuccessfully to install the ECW support (mainly to use ECW file in QGIS 2.2). We attempt to follow and adapt the howto provided by .  My first supprise was the repository ubuntugis-unstable is unavailable for trusty and the repository  doesn't have libgdal-ecw-src package. Finally in desperation we add ubuntugis-unstable for the raring distribution in source.list.  And apply the following commands   chmod +x ERDAS-ECW_JPEG_2000_SDK-5.1.1.bin ./ERDAS-ECW_JPEG_2000_SDK-5.1.1.bin # Select option desktop read only sudo cp -r ERDAS-ECW_JPEG_2000_SDK-5.1.1 /usr/local/ sudo ln -s /usr/local/ERDAS-ECW_JPEG_2000_SDK-5.1.1/Desktop_Read-Only/lib/x86/release/libNCSEcw.so /usr/local/lib/libNCSEcw.so sudo ldconfig sudo apt-get install libgdal-ecw-src sudo gdal-ecw-build /usr/local/ERDAS-ECW_JPEG_2000_SDK-5.1.1/Desktop_Read-Only   The ECW format seems to be installed  gdalinfo --formats | grep -i ecw   ECW (rw+): ERDAS Compressed Wavelets (SDK 5.1)   JP2ECW (rw+v): ERDAS JPEG2000 (SDK 5.1)   But .... Gis crash when a ECW raster file is open with the following message :   QGIS died on signal 4Abandon (core dumped)   If anyone have an idea How to find regression coefficients $\beta$ in ridge regression? In ridge regression, the objective function to be minimized is: $$\text{RSS}+\lambda \sum\beta_j^2.$$   Can this be optimized using the Lagrange multiplier method? Or is it straight differentiation? Syntax error while defining an array as a property of a class Remove Windows entry in GRUB menu How can I check the actual size used in an NTFS directory with many hardlinks? On a Win7 NTFS volume, I'm using cwrsync which supports --link-dest correctly to create "snapshot" type backups. So I have:  z:\backups\2010-11-28\cygdrive\c\Users\... z:\backups\2010-12-02\cygdrive\c\Users\...   The content of 2010-12-02 is mostly hardlinks back to files in the 2010-11-28 directory, but there are a few new or changed files only in 2010-12-02. On linux, the 'du' utility will tell me the actual size taken by each incremental snapshot. On Windows, explorer and du under cygwin are both fooled by hardlinks and shows 2010-12-02 taking up a little more space than 2010-11-28.   Is there a Windows utility that will show the correct space acutally used? Since the  would it make sense to create a Stack Exchange site dedicated to homework help? It wouldn't have to be limited strictly to homework either, possibly including discussions of puzzles and brain teasers and possible approaches to solving them.  I have a programming background so I would be interested in helping with CS or math related homework, discussions of programming contest problems, etc. Topics don't necessarily have to be related to programming either. That's just where my interests are.  What are your thoughts? How to match * with hidden files inside a directory How to match the hidden files inside the given directories   for example   If I give the below command it's not giving the result of the hidden files,     du -b maybehere*/*   how to achieve this simple using a single command instead of using   du -b maybehere*/.* maybehere*/*   as I need to type maybehere twice.