What's the reason behind the disagreement between behavior of lists and matrices (as vectors) in R?
Why is.vector on a data-frame doesn't return TRUE?
I have already dual systems : Windows 7 and Ubuntu installed on my laptop. The Windows 7 had been installed when I bought this laptop, and I don't have a CD.  I just installed VitrualBox under Ubuntu, hoping that I could install another Windows in this virtual machine, so that I could run some applications of Windows even under Ubuntu.  But it seems that I need a CD or ISO of Windows to boot inside this virtual machine. Otherwise, there is an error: FATAL: No bootable medium found! System halted. My question is where I could find a CD or ISO?  At the moment, I am downloading ISO from this , but do not know if it will work. By the way, I am not sure if I should pick the 32-bit or 64-bit? As my CPU is 64-bit but my Ubuntu is i386.  Could anyone help? Thank you very much. Integrate $\int_0^{\pi/2} \frac{1}{1+\tan^\alpha{x}}\,\mathrm{d}x$ Evaluate the integral $$\int_0^{\pi/2} \frac{1}{1+\tan^\alpha{x}}\,\mathrm{d}x$$ Add different materials to different parts of a mesh? How to test whether a set of four points can form a parallelogram Given four points $(x_1,y_1)$,$(x_2,y_2)$,$(x_3,y_3)$,$(x_4,y_4)$. How can we efficiently test them to make sure whether they are vertices of a parallelogram?  I think evaluating and comparing the distance between two points seems to be inefficient. What do you think? Do you have any better method? Auto-run scripts security options tkz-graph: changing individual vertex type I'm using these settings for most vertices:  \GraphInit[vstyle=Classic] \tikzset{VertexStyle/.append style = {minimum size = 5pt, inner sep = 0pt}}   But I'd like to have one or two vertices of my graph be hollow with a thick outer edge. I'm very confused about what options can be used in \Vertex, which ones can go in \SetUpVertex, for which I have to use \tikzset, etc. What's the best option here? Just noticed a minor css issue on this question:    The related questions on the right hand side have some overlapping text in Chrome:        (This only applies to this very site, Meta Stack Exchange) I've played around in the past of the 2D Flash fan-made version of the popular Valve game Portal.  It has basically the exact same mechanics, but as a 2D side-view flash game.  Lately I've toyed around with creating a simplified flash version of some of my favorite franchises (such as Zelda, Mario, Splinter Cell, etc.).  Of course, nothing is "stopping" me from just using the same mechanics and just changing the name to something not copyrighted.  I have witnessed projects that have tried to directly port a 3D game into a 2D simplified version, with the exact same plot and puzzles (Ocarina of Time in 2D comes to mind), and I have seen them being shut down.  But I am not likely going to exactly duplicate any game...just borrow some of the source material and basic underlying mechanics.  For example, if I were to make a Zelda-influenced fan game, I would have items such as the Hookshot, Boomerang, and all other sorts of ones from the Gameboy Zeldas; just with a custom plot and dungeons.  With likely the same mechanics.  What are the legal issues involved in this?  I used to think it was a "Don't do this ever; it's a bad idea."  But then I've seen the Portal clone, and now I'm curious. How to include PHP files that require an absolute path? I have a directory structure like the following;     script.php      inc/include1.php   inc/include2.php      objects/object1.php   objects/object2.php      soap/soap.php   Now, I use those objects in both script.php and /soap/soap.php, I could move them, but I want the directory structure like that for a specific reason. When executing script.php the include path is inc/include.php and when executing /soap/soap.php it's ../inc, absolute paths work, /mnt/webdev/[project name]/inc/include1.php... But it's an ugly solution if I ever want to move the directory to a different location.  So is there a way to use relative paths, or a way to programmatically generate the "/mnt/webdev/[project name]/"? Why is the voltage across a capacitor and the current across an inductor continuous? Why is the voltage across a capacitor (as a function of time) continuous? Why is the current across an inductor (as a function of time) continuous? Is there any shortcut/easy way to switch this system proxy settings? Will Unity allow making custom launcher icons from .desktop files or via menu editing system? (Right now the launcher doesn't give the option to "keep in launcher" on all programs.  For some programs I use, I have to make custom launchers or .desktop files.  For instance, daily blender builds are generally just folders with an executable.  In basic Gnome or KDE, I can make a new menu entry with the menu editing system. Then, I can also add it to Docky either from the menu or by dragging a .desktop file to it. Unity launcher doesn't support drag and drop, so thats not a bug or anything, but when I open a .desktop file, it has unpredictable results. Most time it will not have "keep in launcher". Sometime it will have a pinnable item without the .desktop's icon, and if I pin the item to the launcher, it will not call upon the program again after closing it. I've also gotten it to just work with a .desktop file for celtx. How Can I add HTML And CSS Into PDF I have an HTML (not XHTML) document that renders fine in Firefox 3 and IE 7.  It uses fairly basic CSS to style it and renders fine in HTML.  I'm now after a way of converting it to PDF.  I have tried:   : it had huge problems with tables.  I factored out my large nested tables and it helped (before it was just consuming up to 128M of memory then dying--thats my limit on memory in php.ini) but it makes a complete mess of tables and doesn't seem to get images.  The tables were just basic stuff with some border styles to add some lines at various points; : I actually had better luck with this.  It rendered some of the images (all the images are Google Chart URLs) and the table formatting was much better but it seemed to have some complexity problem I haven't figured out yet and kept dying with unknown node_type() errors.  Not sure where to go from here; and : this seems to work fine on basic HTML but has almost no support for CSS whatsoever so you have to do everything in HTML (I didn't realize it was still 2001 in Htmldoc-land...) so it's useless to me.   I tried a Windows app called Html2Pdf Pilot that actually did a pretty decent job but I need something that at a minimum runs on Linux and ideally runs on-demand via PHP on the Webserver.  What am I missing, or how can I resolve this issue? I have an intuitive scenario. Consider we have a spaceship just below the event horizon of a BH, which is merging with another black hole.  Finally, the singularities merge and we have a single black hole again.  But, in the transient stage, it is unclear to me if a timelike world-line would exist to leave the system.  I suspect, the metric is probably far too complex for an analytical solution, but in the worst case, it could be maybe solved numerically.  As far I know, black hole merges are examined mainly in an inspiral scenario. I suspect, maybe the escape is possible only if they have a hyperbolic-like orbit (i.e. there is no inspiral, but they simply collide).  Is it possible? What is the difference between the "jessie" and "jessie-updates" distributions in /etc/apt/sources.list? The  gives this example file:  deb http://httpredir.debian.org/debian jessie main deb-src http://httpredir.debian.org/debian jessie main  deb http://httpredir.debian.org/debian jessie-updates main deb-src http://httpredir.debian.org/debian jessie-updates main  deb http://security.debian.org/ jessie/updates main deb-src http://security.debian.org/ jessie/updates main   What is the difference between the jessie and jessie-updates distribution entries? If a Matrix Has Only Zero as an Eigen-Value Then It Is Nilpotent Unable to catch JsonMappingException Generic htaccess redirect www to non-www I would like to redirect www.example.com to example.com. The following htaccess code makes this happen:  RewriteCond %{HTTP_HOST} ^www\.example\.com [NC] RewriteRule ^(.*)$ http://example.com/$1 [L,R=301]   But, is there a way to do this in a generic fashion without hardcoding the domain name? Tikz and ctable incompatibility, gives error when printing When I print a report I get an error:     An error exists on this page. Acrobat may not display the page   correctly. Please contact the person who created the PDF document to correct the problem   After a lot of debugging, I've found that this MWE reproduces the problem. I've tried it on three different computers with the same error.   \documentclass{standalone}           \usepackage{tikz} \usepackage{ctable} \begin{document} \begin{tikzpicture} \filldraw[opacity=.5] (0,0) rectangle (1,1); \end{tikzpicture} \end{document}   When loading the ctable package, the image is changed (the opacity disappears), so it seems the error comes from some incompatibility between ctable and opacity in tikz. The error only appears when trying to print though, acrobat before attempting to print. (Printing either to a pdf file or to a real printer)  I have the following versions of tikz and ctable:      tikz.sty    2013/12/13 v3.0.0   ctable.sty    2014/04/25 v1.29   How can I fix this?    EDIT: I found the warning Transparency disabled: incompatible with tikz package from ctable so I guess this incompatibility can explain the error in the first MWE.  However, I continued digging and found that the spy library seem to be incompatible with ctable as well.   Here's an MWE that generates the same error when printing (either to a pdf file or to a real printer):   \documentclass{standalone}           \usepackage{tikz} \usetikzlibrary{spy} \usepackage{ctable} \begin{document} \begin{tikzpicture}[spy using outlines={size=2cm,connect spies}] \begin{scope} \spy on (-3,.25) in node at (2,0); \end{scope} \end{tikzpicture} \end{document}   There seem to be a serious problem with using tikz + ctable, can it be fixed? Confusing article status for journals of American Mathematical Society: "reviewing" AND "being handled by an editor" The web page of my article in the AMS editorial system for some three months says &quot;Article status: Reviewing&quot; and in the next line &quot;Your paper is being handled by an editor&quot;. I find this confusing as the &quot;reviewing&quot; status appears to suggest that the article is with the referee(s) rather than with the editor but this in turn seems to contradict the line &quot;Your paper is being handled by an editor&quot;.  Could someone with enough experience with AMS journals please explain how should one interpret the combination of &quot;Article status: Reviewing&quot; and the line &quot;Your paper is being handled by an editor&quot; at the article page? More broadly, which are the possible article statuses in the AMS editorial system?  Many thanks in advance.