How do people like Madame Pomfrey learn magical healing?
Does higher education exist in Harry Potter?
How to calculate Area Under the Curve (AUC), or the c-statistic, by hand I read somewhere that according to relativity, it is possible - involving black holes and other stuff - to jump into the past. Is it possible for anything to go back in time either continuously or by jumping? Computer wont boot to windows I recently installed a Linux operating  system (backtrack 5 r3) I couldn't connect to the internet with it so I removed the partition manually. After that, whenever I turn on my computer it goes to a command line that says "error no File-system found" "Grub Rescue/"  I have tried f12 and booted into all the options. I also put Ubuntu 12.04 on my flash drive and tried installing it on the computer, the installation failed saying "No Available Space"  My hard-drive is 500g with about 250 left. I put the hard drive in another computer (as a secondary just to see the files. It had 2 partitions a main and one with 1 gig. I formatted it with no difference.  My Problem: I can't boot into Windows Why didn't Doc remember Marty's outfit? In Back to the Future 3, Doc (from 1955) sends Marty back in time wearing a cowboy outfit.  But then, Doc (from 1885) doesn't remember that it was him who offered this outfit to Marty.   Does this mean there are two different Docs (from differing timelines) or is it the same Doc but he somehow forgot the outfit. What's the starting wealth for higher levels? Do fixtures trigger model callbacks? A and B disjoint, A compact, and B closed implies there is positive distance between both sets Manual/automatic line breaks and text alignment in TikZ nodes How can I insert a line break in a TikZ node? Simply putting \\ where I want the break doesn't work (see MWE).  Is there a way to make lines break automatically at some specified width?  And can I control the alignment of the text (left, right, centered, justified)?  \documentclass{article} \usepackage{tikz} \begin{document} \begin{tikzpicture} \node {First line\\second line}; \end{tikzpicture} \end{document} In QGIS, I want to make polygons from a set of intersecting lines. Looking at the screenshot here, I want chop the purple line (it's a closed line, not a polygon) where it crosses the green and blue lines. The result hopefully would be a polygon where I have hatched in red. I have quite a few to do.    I have tried the QGIS tool previously called Polygonizer (see ), but now called Polygonize. This is a tool that, given a layer containing a set of crossing lines arranged essentially like a # symbol, should create a polygon from the enclosed space in the middle.  (In QGIS 2.01, Polygonize is in the top menu bar: go to Processing -> Commander, then type "Polygonize" on the command line, select "Processing algorithm: Polygonize" from the list that appears, and press Enter.)   At the momemt Polygonize doesn't work properly. Is there another way to do what I want to do?   For example, wouldn't it be great if the QGIS 'Split Feature' command was able to work like MapInfo's 'Polyline Split', where you select the polygons to split, then select an already-drawn polyline to split by, and voila. But Split Feature seems not to work that way.    UPDATE: Detail of problems with running Polygonize.  I have 64-bit QGIS 2.01 installed to Windows 7 from the installer package, QGIS-OSGeo4W-2.0.1-3-Setup-x86_64.exe.  The routine processed an output from my shapefile, but did not create a polygon from the region enclosed by intersections between the blue, green and purple lines. (Note: in the actual input file, all these lines are on the same layer; the screenshot just colours them differently for illustrative purposes). What I got instead was a simple conversion of the purple outline to a polygon, as though the program completely ignored the blue and green lines.  When I node-edited the closed purple line, to open it so that I had a set of open crossing lines like in the # symbol, and then ran Polygonize again, nothing happened. No crash, but no visible polygon in the output file.    When I used Nick Hopton's own  data, I got a crash; see screenshot: counting number of specific string in each row I have a SNP table looks like this  A N N N N N N N N N N N N C N N N C N N N N N N N N N N N N N N N N N N N C N N N C N N N N N N N N N N N N N N N N N N C C N N N N N N N N N N C C N N N C C N N N N N N N N N N N N N N N N N   I want to count total number of N in each row? any idea how to do that How to save picture to iPhone photo library? Why is boiling water loud, then quiet? Water in my electric kettle makes the most noise sixty to ninety seconds before the water comes to a full boil. I have been fooled many times by the noisy kettle, only to discover that the water was not yet hot enough for tea. The kettle is only at a full boil after the noise has subsided.    I have noticed the same phenomenon with many other kettles, including conventional kettles on kitchen ranges; it is not a peculiarity of this electric kettle.  Why does the boiling become quieter as the water reaches full boil? When you boot from live CD, or doing the first boot after installing Ubuntu, splash screen looks awesome. But as soon as you enable nvidia-current driver, installed with apt-get, splash screen goes all crazy.  With crazy I mean that resolution is very low, font(I assume) is very weird and it all looks like it's been broken.  This happened with 10.04 and now again with 10.10.  How do I fix splash screen after enabling nvidia drivers? SQL Server: Examples of PIVOTing String data Trying to find some simple SQL Server PIVOT examples.  Most of the examples that I have found involve counting or summing up numbers.  I just want to pivot some string data.  For example, I have a query returning the following.  Action1 VIEW   Action1 EDIT   Action2 VIEW   Action3 VIEW   Action3 EDIT     I would like to use PIVOT (if even possible) to make the results like so:  Action1 VIEW EDIT   Action2 VIEW NULL   Action3 VIEW EDIT     Is this even possible with the PIVOT functionality? How to install squid-deb-proxy-client via preseed/early_command Using Lucid, installing from the Lucid mini.iso.  Both AMD64.  In the following I've tried as \, all of apt-get, apt-install, anna-install, dpkg:  d-i preseed/early_command string &lt;cmd+opt&gt; squid-deb-proxy-client   I've also tried:   d-i preseed/early_command string /usr/bin/wget \     -O squid-deb-proxy-client_0.3.1_all.deb \     http://ubuntu.media.mit.edu/ubuntu//pool/universe/s/squid-deb-proxy/squid-deb-proxy-client_0.3.1_all.deb &amp;&amp; dpkg -i squid-deb-proxy-client_0.3.1_all.deb   Is this possible, and if nor what is the earliest point one can get a installation to use the squid-deb-proxy server? Sometimes you see a video of a fan or a propeller spinning very fast, and the apparent rotation is distorted. The fan can appear to be moving in the opposite direction of rotation, or even stationary. This optical illusion is known as the wagon-wheel effect. If I understand correctly, this occurs because the camera framerate is slower than the frequency at which the fan makes one rev, so stroboscopic effects should be expected.   Does the wagon-wheel effect occur only in videos, or can we observe it just with the eye? How to make sure that Qt5.4.2 is installed properly I installed qt5.4 from  in Ubuntu 14.04, but when I run:   qmake -v   I always get the old version Qt5.2.1, although I think it is installed here Qt version 5.4.2 in /opt/qt54/lib. Can anyone tell me how to make sure that Qt5.4.2 is installed properly?   Thanks Ubuntu 18.04 - Dell XPS13 9370 no longer suspends on lid close the (surely simplistic) model of a bipolar junction transistor one is taught in foundational physics course appears to be symmetric. - So, what is the difference between the collector and the emitter of a real BJT? If the transistor were symmetric one would not make this distinction...  Also:   Do BJTs have a 0.6V voltage drop like diodes? Are BJTs conductive in both directions, i.e. E-C and C-E?   Many thanks. Blender 2.80 AV Sync missing? I just installed Blender 2.8 and for the life of me I can not find AV Sync anywhere and video editing has become impossible. Is there some new setting I am unaware of?