How to get full element ID (path to ID) in JSF Primefaces
How to find out client ID of component for ajax update/render? Cannot find component with expression "foo" referenced from "bar"
Is there any Android XML documentation? What exactly happens to the signals hitting a common mode choke? I'm trying to better understand the principles behind the common mode choke. I made a few drawings to clarify.  &nbsp; Differential Mode Signals  Differential currents (driven by differential voltages) create equal but opposite magnetic fields B in the inductor core:    These magnetic fields cancel each other out, so the net flux in the core is zero. As such, these differential currents don't "feel" any impedance.  &nbsp; Common Mode Signals  In contrast, common mode currents generate equal and additive magnetic fields in the core. That's why they "feel" a high impedance, and cannot get through (or getting through means they are highly attenuated).    But what exactly happens? I have several theories, which I will describe below.  &nbsp; Common Mode Signals - Theory 1  My first thought would be that the common mode signal hits the choke and creates a magnetic flux inside. By doing this, lots of energy is lost (hysteresis and perhaps other effects) as heat. Only a small part gets through:      What kind of common mode choke would behave in this particular way? "Burning up" the voltage spike seems a very desirable effect to me.  &nbsp; Common Mode Signals - Theory 2  Perhaps the voltage spike doesn't really get the chance to build up much magnetic flux in the core, or maybe the core is simply not "lossy" enough. The voltage spike bounces off the core and turns back. Only small part gets through:    Although the system on the right side of the choke is protected, the system on the left has to deal with reflected signals. Nasty things like standing waves might appear.  &nbsp; My questions  I've got a few questions for you:   Do you think theory 1 or theory 2 is most plausible? Do you think certain types of common mode chokes tend to behave as described in theory 1, others like in theory 2? Perhaps both of my theories are just plain wrong. If so, what actually does happen?   Please enlighten me. Humorous time travel short story about a man's dealings with other versions of himself Okay, similar questions to this have been asked before, but not about the particular short story I am trying to find.  It was in an anthology of short sci fi stories, possibly award winning ones or at least someone's compilation of favourites. (I think)   It was a long time ago, maybe 1970s or 80s, so the story could date back to even the 1960s for all I know, but probably the 1970s.  It was the funniest story about time travel where a person meets incarnations of himself, that I have ever read. It was either derivative of 'By His Bootstraps' or the other way around, but my recollection is that this story was funnier.  Maybe my memory is playing tricks on me and it WAS 'By His Bootsraps', but I am almost certain that it wasn't, because when I read that recently it seemed unfamiliar and not as funny.  In the one I am trying to recall, the guy is also bemused and irritated by the behaviour of other incarnations of himself, like the Heinlen story, but the repartee between versions of himself and his extreme frustration is much more hilarious.  I have a vague recollection that he is in a spaceship during the story, but not absolutely sure. There seemed to be a lot of clambering around, ladders, bulkheads, etc, unlike the Heinlen story.  I'm almost certain it isn't any of the commonly suggested stories and I'm quite sure it wasn't a short film where he shoots his older self, or a full length novel. Someone will have read it and (un)remembered it fondly like me, I feel sure! Can anyone point me to a reference (preferably either something online or something a small liberal arts school would be likely to have in its library) that goes through a derivation of the minimum uncertainty wavefunction in more detail than in the Griffiths?  Edit I've moved the second part of my original question to a separate post: What is the population of the Star Wars Galaxy? I just went to install Java 8 on my ancient laptop that runs Windows XP SP3.  Java pops up a message:     Java 8 requires a newer version of Windows. You may continue with the installation, but for Java to work as specified we recommend upgrading your computer's operating system.   Will Java fail to work properly on Windows XP? Or is this just Oracle trying to be secure? Generic Parse Method without Boxing I am trying to write a generic Parse method that converts and returns a strongly typed value from a NamedValueCollection.  I tried two methods but both of these methods are going through boxing and unboxing to get the value.  Does anyone know a way to avoid the boxing?  If you saw this in production would you not like it, how bad is it for performance?  Usuage:  var id = Request.QueryString.Parse&lt;int&gt;("id");   Attempt #1:  public static T Parse&lt;T&gt;(this NameValueCollection col, string key) {     string value = col[key];      if (string.IsNullOrEmpty(value))         return default(T);      if (typeof(T) == typeof(int))     {         //return int.Parse(value); // cannot convert int to T         //return (T)int.Parse(value); // cannot convert int to T         return (T)(object)int.Parse(value); // works but boxes     }     if (typeof(T) == typeof(long))     {         return (T)(object)long.Parse(value); // works but boxes     }     ...      return default(T); }   Attempt #2 (using reflection):  public static T Parse&lt;T&gt;(this NameValueCollection col, string key) {     string value = col[key];      if (string.IsNullOrEmpty(value))         return default(T);      try     {         var parseMethod = typeof(T).GetMethod("Parse", new Type[] { typeof(string) });          if (parseMethod == null)             return default(T);          // still boxing because invoke returns an object         var parsedVal = parseMethod.Invoke(null, new object[] { value });         return (T)parsedVal;     }     // No Proper Parse Method found     catch(AmbiguousMatchException)      {     }      return default(T); } How to prove $\,x^a-1 \mid x^b-1 \iff a\mid b$ How to prove $x^a-1\mid x^b-1 \iff a \mid b$, where $x \ge 2$ and $a,b,x \in \Bbb Z$.  I've tried the following in attempting to solve this:  $$a\mid b \Rightarrow aq=b \Rightarrow x^{aq}=x^b \Rightarrow x^ax^q=x^b$$  Because $x^q \in \Bbb Z$, it follows that $x^a\mid x^b$.  This is as far as I have gotten; any help getting further is appreciated.  Note: It may be that this identity is not true at all? When is JavaScript's eval() not evil? I'm writing some JavaScript code to parse user-entered functions (for spreadsheet-like functionality). Having parsed the formula I could convert it into JavaScript and run eval() on it to yield the result.  However, I've always shied away from using eval() if I can avoid it because it's evil (and, rightly or wrongly, I've always thought it is even more evil in JavaScript, because the code to be evaluated might be changed by the user).  So, when it is OK to use it? I just upgraded my texlive distribution and can no longer insert space in table rows using \\[x pt] syntax when colortbl is loaded.  It seems that recent changes to array.sty might be the problem as this is the only package to change recently.  Can anyone suggest a workaround?  MWE  \listfiles \documentclass{article} \usepackage{colortbl} \begin{document} \begin{tabular}{l}   \hline   No space below with \texttt{colortbl.sty} loaded. \\[10mm]   \hline \end{tabular} \end{document}   File versions in use:   article.cls    2014/09/29 v1.4h Standard LaTeX document class   size10.clo    2014/09/29 v1.4h Standard LaTeX file (size option) colortbl.sty    2012/02/13 v1.0a Color table columns (DPC)    array.sty    2018/04/07 v2.4g Tabular extension package (FMi)    color.sty    2016/07/10 v1.1e Standard LaTeX Color (DPC)    color.cfg    2016/01/02 v1.6 sample color configuration   pdftex.def    2018/01/08 v1.0l Graphics/color driver for pdftex I have the name of a function in JavaScript as a string. How do I convert that into a function pointer so I can call it later?  Depending on the circumstances, I may need to pass various arguments into the method too.  Some of the functions may take the form of namespace.namespace.function(args[...]). When solving this issue (  ), I did a function so that the plugin would auto-hide from all users except one (me:).  The flaw is that it only auto-hides when active.  At first, it was a mu-plugin, but I had to enable/disable it manually. It really doesn't need to run all the time, as it may slow the site (?) or even contain some sensitive manipulation of the site's language (another question mark).  But mainly the motivation is that I don't want the client activating/deactivating/deleting this plugin (is for my own use), and don't want it cluttering her own plugins list.  So, decided to split the functions in two plugins:   One is a Must-Use used to hide the regular one.  The other will be activated/deactivated upon necessity and is the one from the above linked issue.   But now I run into another question: how to hide one plugin from the Must-Use listing? Why is there an electric field in a wire even though it is a conductor? If you take a perfect conductor, there cannot be a field across it since if there were, the particles would arrange themselves in a way to cancel out the field right?  Yet, why does the same not hold true for a wire. A wire is essentially a long, thin conductor yet electrons do indeed flow so there must be an electric field.  Does this not contradict with what happens in a conductor? Why don't the electrons re-arrange to cancel out the electric field? Non-Root Package Managers From my research, I seem to notice that all package managers insist on being used as a privileged user and must be installed into /.  Typically, what I like to do is create a throwaway account, compile some software, and install to $HOME for that account. I can try a variety of setups and then when I'm done, just destroy the account.  However, compiling software becomes tedious.  My experience is really just limited to yum, but I don't understand why I wouldn't be able to drop a repo file into ~/etc/yum.repos.d and have yum install everything into a home account.  Is there any reason why package managers must be used as a privleged user to install software? How to place a .png texture with transparency over a material I am trying to create a low poly face with a face from a .png file. The issue is I already have material placed for hair and skin, as shown in the picture below.   I have created a .png file with a face which I would like to overlay over the skin material on the front of the head.    All examples I searched so far assume I also want the color of the material from the .png texture.  Update:  I added UVMapping, changed view to texture, made sure one face is on the eye but nothing is displayed..... see image... I don't know what is going on. Is it better in C++ to pass by value or pass by constant reference?  I am wondering which is better practice.  I realize that pass by constant reference should provide for better performance in the program because you are not making a copy of the variable. Images are escaping from the help center privilege page Images included in the fully expanded privilege pages are escaping from the body.    This is most noticeable on the  (which I know is going away soon anyway):    But is also apparent on:       In the edit page preview, the images sit correctly within the borders.  Chrome 27, Windows 7 Probability that uniform random variables equal the natural numbers I have random variables $X_{1}, X_{2}, \dots X_{n}$ that are each Unif$\{1, \dots, n\}$, and I want to calculate $$P(\{X_{1}, X_{2}, \dots X_{n}\}=\mathbb{N})$$  My intuition is that this means each $X_{n} = n$, which occurs with probability $\frac{1}{n!}$.  Does this seem correct? In a preadditive category, products are coproducts $\renewcommand{\phi}{\varphi}$ $\require{AMScd}$ My question is different from .  I want to see how in a preadditive category $\mathcal{C}$ a product is a coproduct, following . I'll write the proof up to the point where I get stuck.  Let $A=A_1,B=A_2$ be objects and suppose their product $P$ does exist, with projections $\pi_i:P\rightarrow A_i$. By considering a wedge  $$\begin{CD}A @&lt;{id_A}&lt;&lt;  A @&gt;{0_{AB}}&gt;&gt;  B\end{CD}$$  and the obvious analogous one with $A$ and $B$ exchanged, where $0_{A,B}$ is the zero morphism, we see that the product property implies the existence of two unique morphisms $k_i\in\mathcal{C}[A_i,P]$ s.t.  \begin{align*} \pi_j\circ k_i=\begin{cases} \mathrm{id}_i &amp;\text{if }i=j\\ 0_{A_i, A_j} &amp;\text{if }i\neq j \end{cases}. \end{align*} Using these equations and the definition of zero morphism, it's easy to see that the morphism $m\equiv k_1\circ \pi_1+ k_2\circ \pi_2$ satisfies $\pi_i\circ m=\pi_i$.   This is where I get stuck: In the linked proof, they now state that this implies $m=\mathrm{id}_P.$ But I don't see why this should be true.   Specifically, if $\phi\in\mathcal{C}[S,P]$ for some arbitrary object $S$, it is not apparent why $m\circ\phi=\phi$. All that we know is that there are some morphisms $x_i\in\mathcal{C}[S,A_i]$ that factor through $P$ via the universal property, but these are not necessarily unique.  And we learn even less about $m$ by looking at morphisms in $\mathcal{C}[P,S]$.  What am I missing here? Getting MAC Address I need a cross platform method of determining the MAC address of a computer at run time.  For windows the 'wmi' module can be used and the only method under Linux I could find was to run ifconfig and run a regex across its output.  I don't like using a package that only works on one OS, and parsing the output of another program doesn't seem very elegant not to mention error prone.   Does anyone know a cross platform method (windows and linux) method to get the MAC address?    If not, does anyone know any more elegant methods then those I listed above?