A question matrix multiplication commutative?
If $AB = I$ then $BA = I$
Use of "Or", inclusive or exclusive? My wife and I are playing a game where you roll dice and move so many spaces in a grid "vertically or horizontally".   In the use of English it is very common to say, this or the other when it comes to making a choice  (exclusive or). Now I know that "or" can also be inclusive, for example "she couldn't read or write", or can be clearly used as an xor "you either come or not" making the statement true for only one of the options but not both.   My issue is where it is not clear whether it is an inclusive/exclusive or, the best example being our game.   I argue that you can move in either direction (inclusive) and the normal use of this conjunction in English should be inclusive unless specified otherwise.   Is this right? operators as strings I need to evaluate a mathmatical expression that is presented to me as a string in C#.  Example noddy but gets the point across that the string as the expression.  I need the evaluate to then populate an int.  There is no Eval() in C# like in others langugaes...  String myString = "3*4";   Edit:  I am on VS2008   Tried the Microsoft.JScript. = Its deprecated method (but still complies - warning)  However the Microsoft.JScript dll that I have doens work on      public object InvokeMember(string   name, BindingFlags invokeAttr, Binder   binder, object target, object[] args);   Complains that there is a missing ";"  go figure...  EDIT 2  Solution - was the codeDom one - it worked for as there are no security issue - only me ever going to be running the code.  Many thanks for the replies ...  And the link to the new Dragon Book  awesome   EDIT 3  Matt dataTable.Compute() also works - even better for the security conscious.  (parameter checking noted) How should a bot earn enough reputation to perform the actions necessary for that bot? We all know it: bots that chat. There are also bots that flag, or perform other actions. And usually we like them for doing that, like . So every now and then, a new bot is created, and usually you would ask a question using that bot or suggest enough edits to get the reputation necessary for that bot to operate. Instead of suggesting 100 edits, Undo has found a more efficient way, namely by . Now someone could frown on this action or not, actually it is the least intrusive way to get the bot the reputation necessary (I guess no one really likes a bot to suggest 100 edits just for the sake of earning enough reputation). The question is: is this actually the best way? Was this action allowed or should we look away because it is Smokey? Should we maybe have a special bot user status which derives the privileges from its master user? Anything else you want to share on this? Related: I have a blender file where a sphere is orbiting a force field. I want it to be more red when it's closer to the center, and more blue when it's further. I already have the math figured out, I just need to know how to get x/y coordinates in nodes.  Here's the file: I was watching the film A Game of Shadows starring Robert Downey Junior and Jude Law when this line came up, "...neither you nor I is in control..." (I can’t remember the exact words that ended the phrase; if anyone can supply them, it would be much appreciated.)   It immediately struck me as being odd. When I mentioned this to my boyfriend; an English native speaker, with a PhD in something sciency, he told me it was correct. When I asked why, he couldn't explain but put forward the following sentence as an example. "Neither of us is in control..." However, I disagreed with the wording and said the sentence should have been: "Neither one of us is in control..." The genderless third person, one, is singular, and hence, so too the verb that follows. And we say, "one is" NOT "one are".      "Neither you nor I are in control over ..."    I believe the above sounds better, but it is more logical to say:     "Neither you nor I am in control..."    because the verb agrees with the subject closest to it; however, I'm not sure if I have ever read or heard this solution. So, I tried inverting the subject and auxiliary verb order and the resulting phrase was:    "Neither you nor am I in control..."    which sounds very formal, pompous, and ... odd. Am I imagining things?  The two subjects you and I are two separate individuals who are not joined together, I agree the verb should be in the singular; but why should we use "is"? We don't say, "you is" or "I is". Before anyone rushes off to claim my question is a duplicate of a previous Stackexchange one:  I want to explain why the answer to that question fails to explain why my boyfriend and the film makers consider the  sentence below correct:     Neither you nor I is in control...   As I see it, Michael and Albert are two separate individuals, it therefore stands to reason that the verb should be singular, and "is" agrees with the subject. If I rephrase the neither and nor construction, I would get:          Michael is not correct but neither is Albert   OR          Michael is not correct and Albert isn't either.      Which have the same meaning, (either being the negative equivalent of neither) the sentences are grammatical which leads me to conclude that the verb must be singular and hence         Neither Michael nor Albert is correct      However, when I rephrase the "neither you nor I" sentence following the same procedure I have to say this:        You are not in control but neither am I (‘I am’ is ungrammatical)   OR              You are not in control and I’m not either.      which leads me to surmise that the sentence below must be grammatically correct        Neither you nor I am in control"      So, why does my boyfriend insist that the sentence ought to be:     Neither you nor I is in control   Which one of us is right and why? Energy momentum tensor from Noether's theorem in the book Quantum Field Theory by Itzykson and Zuber the following derivation for the stress-energy tensor is proposed (p.22):  Assume a Lagrangian density depending on the spacetime coordinates $x$ only through fields and their gradients. Under a translation we have $$\mathcal L (x+a)=\mathcal L[\phi_i(x+a),\partial_\mu\phi_i(x+a)].$$  Consider an infinitesimal $x$-dependent transformation $$\delta\phi_i=\delta a^\mu(x)\partial_\mu\phi_i(x),$$ $$\delta\partial_u\phi_i(x)=\delta a^\nu \partial_\nu\partial_\mu\phi_i(x)+\partial_\mu[\delta a^\nu (x)]\partial_\nu \phi_i(x).$$  The proof then proceeds with variation of the action and integration by parts. But why do we consider an $x$-dependent local transformation instead of a global transformation? Contacting prospective advisors before graduate school applications - courtesy or annoyance? Last year, rather late during the MSc application cycle (after one round of funding was allocated - tardiness due to an abrupt change in my life situation), I emailed two professors from two schools that I most wanted to go to. I had perused their webpages and decided these professors had the specific research interests closest to my own.  My reason for contacting them before finishing my applications for their respective schools was that the applications included a large section for specific research questions that I wanted to investigate. So, I emailed these professors asking a bit about their work, because their webpages of course featured surface-level stuff.  One professor was very receptive and invited me to Skype with her so she could better explain herself and I could ask her questions. With her support, I was able to write an application that met her standards quite quickly.  The other professor told me - paraphrasing, of course - that he was too far into the process of choosing a new student for his research group to spend time helping me finish the application.  Let me be clear that the latter professor didn't say any harsh words and I have nothing bad to say about him. That said, the purpose of my question is to decide whether it's better for me as a prospective MSc student to email professors ahead of time like this. Was the latter's rejection likely due to my tardiness rather my emailing him? The more receptive professor made the point that she always wanted to have prospective MSc students write their own research proposals and get her approval before submitting the application. Is this common? If so, then I guess reaching out beforehand is a good thing to do, but earlier in the application cycle?  Thank you. Reinstall software-center in Ubuntu 16.04 Adobe Illustrator: strange behavior while aligning objects I am creating icons with Adobe Illustrator during which process I use the Align tool quite frequently.  All of a sudden, the align tool started behaving quite strangely.  When I select two objects and specify that I want to align to a key object, when I press align it seems to only align halfway to where it should be.  When I press align again it aligns halfway again - after I press it several more times, it finally gets to where it needs to be.  Also, when I try to align to artboard, it pushes the object out to a seemingly random place.  Here is a video showing exactly what I mean:   What setting did I accidentally set to make align behave like this? Why does bool(xml.etree.ElementTree.Element) evaluate to False? How can I insert a newline in a framebox? Finding value of an expression If $x^2-3x-1=0$ then find the value of $(x^6+1)/x^3$ I tried to solve the quadratic but it became too complicated any way of doing this without a calculator Proposing Windows as its own Stack Exchange site? Is there a reason why we have a "Unix and Linux" Stack Exchange and an "Apple" Stack Exchange but no "Windows" Stack Exchange? (Hell even Ubuntu got its own)  I couldn't find it anywhere so I'm asking.  Since Windows has many users it would be a potent Stack Exchange. I've got `PDOException: SQLSTATE[HY000] [2002] No such file or directory` when using drush I installed Drush for the first time (so it may be a configuration error) and I'm trying to update to the latest core version of Drupal.  Drush is giving me this error - I'm on an OSX box.  dev5:clientnamedirectory my.name$ drush pm-update projects drupal-7.25 &lt;h1&gt;Additional uncaught exception thrown while handling exception.&lt;/h1&gt;  &lt;h2&gt;Original&lt;/h2&gt;&lt;p&gt;PDOException: SQLSTATE[HY000] [2002] No such file or directory in drupal_get_installed_schema_version() (line 155 of /Users/my.name/Sites/proface/includes/install.inc).&lt;/p&gt;  &lt;h2&gt;Additional&lt;/h2&gt;  &lt;p&gt;PDOException: SQLSTATE[HY000] [2002] No such file or directory in system_list() (line 165 of /Users/my.name/Sites/clientnamedirectory/includes/module.inc).&lt;/p&gt;&lt;hr /&gt;  Drush command terminated abnormally due to an unrecoverable error. How to start/stop/restart a thread in Java? I am developing firefox extension and wanted to count total number of text box of webpage so how to count text box? Why does Ubuntu create a file ending in ~ for every file I create with a text editor like GNU Emacs? Biblatex: submitting to a journal Taking screenshot of a specific area from the command line "Congratulation" vs. "congratulations"