How is math mode processed in TeX? Is typing \n (in editor) in math mode equivalent to one space? I am asking, because I struggled to find a bug in source code (between a lot of matrices :-) ), and the reason was following:  \documentclass{article}                       \begin{document}        $1     2$                       \end{document}            compiles,  \documentclass{article}   \begin{document}        $1                        2$     \end{document}            but this does not. (missing $ error)  I know that I can add % between to maintain source code style, but the question is about why above error happens.
I'm just starting to learn LaTeX. I tried typing \begin{equation*}  (math goes here)  \end{equation*}  and I got a whole bunch of errors. It seems LaTeX interpreted the empty line as the equation: when it saw nothing there, I guess it just ended math mode? It then said my other commands needed $'s so I assume that's what happened. When I typed \begin{equation*} (math goes here) \end{equation*}  everything was fine. So I'm confused. If LaTeX sees an empty line in an environment, does it just interpret this as me changing my mind, and deciding not to use the declared environment?
How do I get the path and name of the file that is currently executing? I have scripts calling other script files but I need to get the filepath of the file that is currently running within the process.   For example, let's say I have three files. Using :   script_1.py calls script_2.py.  In turn, script_2.py calls script_3.py.    How can I get the file name and path of script_3.py, from code within script_3.py, without having to pass that information as arguments from script_2.py?  (Executing os.getcwd() returns the original starting script's filepath not the current file's.) Compute the moment generating function of $Y = X_1X_2 + X_1X_3 + X_2X_3$ I often have to sort a dictionary, consisting of keys &amp; values, by value. For example, I have a hash of words and respective frequencies, that I want to order by frequency.  There is a SortedList which is good for a single value (say frequency), that I want to map it back to the word.   orders by key, not value. Some resort to a , but is there a cleaner way? What does static/dynamic BVH do? In the render properties panel, under the performance rollout there is a setting for static vs. dynamic BVH.  I am simply wondering what this setting does.  From the :     The raytracing acceleration structure used is a bounding volume hierarchy... This code includes spatial splits to make it more competitive with kd-trees.   Unfortunately, though I know quite a bit about cycles, this is totally Greek to me.  I couldn't really find much else useful on the web other than it may have some impact on animations only.  Can anybody explain this better (maybe starting with BVH in general)? Cannot mount USB stick - errors out with "$MFTMirr does not match $MFT" dpkg-divert: error: rename involves overwriting `/usr/lib/xorg/protocol.txt' with different file `/usr/lib/xorg/protocol-precise.txt', not allowed I just installed Ubuntu (12.04.4) and I upgraded to 13.10  I have no idea how to fix this :/  $ sudo apt-get install -f  Reading package lists... Done Building dependency tree        Reading state information... Done The following packages will be REMOVED:   xserver-common-lts-saucy 0 upgraded, 0 newly installed, 1 to remove and 2 not upgraded. 1 not fully installed or removed. After this operation, 1,718 kB disk space will be freed. Do you want to continue [Y/n]? y (Reading database ... 175174 files and directories currently installed.) Removing xserver-common-lts-saucy ... Removing 'diversion of /usr/lib/xorg/protocol.txt to /usr/lib/xorg/protocol-precise.txt by xserver-common-lts-saucy' dpkg-divert: error: rename involves overwriting `/usr/lib/xorg/protocol.txt' with   different file `/usr/lib/xorg/protocol-precise.txt', not allowed dpkg: error processing xserver-common-lts-saucy (--remove):  subprocess installed post-removal script returned error exit status 2 Errors were encountered while processing:  xserver-common-lts-saucy E: Sub-process /usr/bin/dpkg returned an error code (1) What are some good ways to showcase someone's portfolio work online? How to pick a specific Pantone color in Photoshop? What about finding a Pantone that is close to a specific CMYK color? How would I select a specific Pantone color in Photoshop, e.g. PMS 5625?  Also, how do you pick a Pantone colour that is similar to a specific CMYK color, e.g. C61, M41, Y58, K16 green?    In this case Pantone 5615C looks closest to the CMYK color. Defend against flag spam in chat We have incidents where we get 10+ flags from the same room in rapid succession. This happens on multiple occasions and we have reason to believe it's a single user doing this.  I don't think it's of value to allow a single user to flag more then n messages in a small time period.  If we could have some anti-flag spam measures put in place, then that would be great. A more succinct expression for "The day before yesterday" Is there a more succinct expression for "the day before yesterday"?   In German for example, gestern = 'yesterday.' The prefix vor roughly means before, so logically, vorgestern means 'the day before yesterday.'   Similarly, morgen = 'tomorrow', the prefix über roughly means over, so again, übermorgen means 'the day after tomorrow.'  (In Mandarin Chinese also you have respectively 前天 &amp; 後天.)  Presumably, there are also similarly logical ways to say "the page after the next" or "the paragraph before the last", etc.   Are there no similarly succinct, and graceful, expressions in English? Truth Tables for Digital Circuits Install ffmpeg in Ubuntu 12.04 LTS Background :  I used ffmpeg to merge two videos side by side. First I install ffmpeg by following command as it suggest by Ubuntu itself.  sudo apt-get install libav-tools   or   sudo apt-get install ffmpeg   But then I realize it is not the correct version since it doesn't support for -filter_complex and few other functions.   After a few hours researcher I found  and I succeed with video conversion as well. As per that article, it is suggesting we need to build it our own.        Question :  What is easiest way to install that ffmpeg version (which is support for -filter_complex ) without following all those steps ? `/usr/bin/cd` is not working in mac terminal Here is a picture of two of them:    I searched for these connectors in  and  for an hour, but couldn't find anything similar. Can you please name these connectors for me and/or give a link to their subcategory in one of these part seller websites? I remember I saw a apt mirror somewhere containing older distributions but I cannot find it anymore. Does anybody know where to find it? Preferred languages: C/C++, Java, and Ruby.  I am looking for some helpful books/tutorials on how to write your own compiler simply for educational purposes. I am most familiar with C/C++, Java, and Ruby, so I prefer resources that involve one of those three, but any good resource is acceptable. I would like to solve the beginner's standard exercise which claims that a point of $\mathrm{Spec} \ R$ is closed iff it is a maximal ideal.  The reverse implication is easy. The direct one seems much subtler. If $P = V(I)$ then, since there exist a maximal ideal $M$ containing $P$, it would follow that $\{P, M\} \subseteq V(I) = P$, whence $P=M$. In order to show the existence of $M$ I applied Zorn's lemma to the set of ideals containing $P$.  The question is the following: is there any other proof of the above implication that does not (indirectly) use the axiom of choice? My concern is that I may be using a cannon to shoot a fly. Also, it would be the first time that I see closedness of points to require the axiom of choice. If the axiom is indeed needed in general, are there "nice" classes of rings for which we could get away without it? How to remove my passport from a blacklist in Indian Immigration? How do I change the screen resolution using Ubuntu command line? My mom and I are having a dispute on much more easy versus much easier. For example, consider the sentence:     It's [much more easy]/[much easier] to do action X than action Y.   I say that much easier is correct and that much more easy is grammatically incorrect, while she says that both are okay. I understand that both are acceptable colloquially, but which is grammatically correct here? If you could explain why, that would be even better!