Why is the suid bit having no effect on a shell or perl script?
Allow setuid on shell scripts
On a systems level, I understand that as electrons are pushed into a wire, there is a net field and a net electron velocity.  And I've read that the net electron drift is slow.  But electricity travels through the wire, essentially at c, and I want to understand that mechanism.  My apologies if my question is poorly stated, I know bare bones undergraduate quantum theory circa 1990s but it doesn't explain the motion of electricity in detail.  Here's my conception, I'm hoping someone will fill in the holes, ha ha.  An electron moves into the wire.  It's got a kinetic energy.  After travelling a short distance, it spontaneously emits a photon, which hits another electron in a valence shell.  That electron then presumably does the same.  If this conception is simply wrong, please enlighten me.  The questions that arise:   Presumably at this level, electrons are acting more like waves and less like particles, but is there any classical component in the picture, ie are electrons coming in imparting other electrons with kinetic energy through repulsion, or does it not work that way? If electrons momentarily have energy, then pass it on by a photon, what determines when that photon is emitted, and what frequency it will be?  I assume that electrons in this cloud are not limited by any kind of exclusion principal, and that any frequencies are possible? Why should a photon emitted by an electron be in the direction of travel?  Conservation of momentum tells me that if an electron is moving, the photon should be emitted in that direction, slowing the electron, but could an electron emit a photon in the opposite direction?  If it did, I assume it would somehow have had to absorb energy from elsewhere? That sounds possible by analogy with quantum tunneling. What is the mechanism by which electrons propagating increase the temperature of the material?  Are they transmitting energy to the electrons in the valence shell, which tug at the nucleus, do some photons hit the nuclei directly, or is there some other way?  Presumably, electricity travels slower than light, because there is some time in each exchange, and some time when electrons are moving at sublight speeds before emitting a photon.  By how much is this slower than light, and what is the speed of each interaction? I'm making an python script which create a lot of object and this could take a lot of time. My question is how to show to the user of my script, the "progression" of the script? For now I print an progress bar in the system console.  But you have to open the system console befor and (apparently) the system console only work with Windows.  Is there an other way to show the progression of my script with python like control the mouse percentage icon (the little icon that replace the mouse while baking) or another idea? How to get permission number by string : -rw-r--r-- I need to set the same chmod, how to get number for -rw-r--r-- ? $n$ choose $k$ where $n$ is less than $k$ I am working on parameter estimation and one of the estimators involves a summation of $_nC_k$ ($n$ choose $k$) expressions. For some iterations, I need to compute expressions like $_0C_1$, $_0C_2$, etc.  In general how do we compute $_nC_k$ when $n$ is less than $k$? Do we still use the formula $\frac{n!}{(n-k)!k!}$ and use the gamma function to compute the negative factorial?  Thanks! I am using ArcMap 10.2 and I'm looking for a way to add  a table containing certain fields from select elements from a featureclass to my map. Ive tried the add table option from the attribute table, but it doesn't quite give what I want (the table must be editable to look a certain way).   Are there any options out there for 10.2 like arcpy.mapping.tableview or will upgrading to 10.3 so I can get access to the "graphic table element" function be best? Why didn't the IF want Peter Wiggin? Why didn't the IF want Peter Wiggin?  Ender's Game implies that they didn't want him for being too violent/aggressive (I believe the quote from Graff was something like "doesn't know half the time if he wants to be a human or a jackal").  But this seems to be contradicted by two facts:   They already have specimens like that in school. Bonzo Madrid, for one, is the same except dumber.  Or Bernard, of who Alai said "I'm not Bernard, I never tortured cats for fun.". If you recall, the main signal that Peter was dangerous was his torturing small animals. Less importantly, Peter turned out way non-jackaly. We can write that off on faulty analysis during early years.   I'd prefer answers based on book sources or Card's statements if any are available. Please don't quote Graf's original statement from beginning of Ender's game as an answer - that's what I'm questioning.   IMPORTANT: Any answers that cite Peter as being a possible impediment to Ender should take into account the fact that Peter was rejected before Ender was even authorized to be born.    P.S. Just to clarify - I didn't ask why IF didn't think Peter Wigging was as genius of a commander as Ender. I am asking why he wasn't taken to the School like all the other talented bullies were. They took plenty of other kids who weren't Ender, so why wasn't Peter among them? JavaScript RegExp objects I try to write a simple Markdown parser in JavaScript. Therefore I want to check for the [link content][link id] syntax. I use the following code:  data = data.replace( /\[(.*?)\][ ]*\[([0-9]+)\]/g, '&lt;a href="$2"&gt;$1&lt;/a&gt;' );   It works well, but now I want to do this with a RegExp object. So I set up the following bit of code:  var r = new RegExp( '\[(.*?)\][ ]*\[([0-9]+)\]', 'g' ); data = data.replace( r, '&lt;a href="$2"&gt;$1&lt;/a&gt;' );   But it doesn't work. It even says that my regular expression (which works since the first example does a good job) is invalid:     unmatched ) in regular expression   I think it must have to do with some RegExp-object peculiarities I am not aware of. What am I doing wrong and how can the problem be solved? Proposition      Let $\mathcal{P_e}$ be the set of functions $p_e(x) = a_o + a_2x^2 +  \cdots + a_{2n}x^{2n}$, $p_e : \mathbb{R} \to \mathbb{R}$      Show that all $f:[0,1]\to\mathbb{R}$ can be uniformly approximated by   elements in $\mathcal{P_e}$   Attempt:    Since we are talking about polynomials let's try play with Weierstrass Theorem  By definition $\mathcal{P_e}$ is dense in  $C^0([0,1], \mathbb{R})$ , if for every funciton $f \in C^0([0,1], \mathbb{R})$, $\exists p_e \in \mathcal{P_e}$ such that $\forall \epsilon &gt; 0, \forall x \in [0,1], ||p_e-f||&lt; \epsilon$  So we want to show $\|p_e - f\| &lt; \epsilon$  Try something like...since every continuous function is approximated by polynomials i.e. $\forall \epsilon &gt; 0,\ \|f - p\| &lt; \epsilon$, therefore let $p$ be a polynomial, $p = a_0 + a_1x + a_2x^2 + a_3x^3 + \cdots$  $$\|p_e - f\| \leq \|f - p\| + \|p - p_e\|$$  $$\Rightarrow \|p_e - f\| &lt; \epsilon + \|p_o\|,$$ where $p_o$ is an odd polynomial  $$\Rightarrow \|p_e - f\| &lt; \epsilon + \sup_x|a_1+a_3+\cdots+a_{2_n+1}|$$  Stuck.   In any case, $p$ and $p_o$ is poorly defined. What would be the standard approach to prove the proposition? Gravitational wave solutions to the Einstein field equations It is well known that general relativity predicts gravitational waves, but I would like to know how. What solution(s) to the Einstein field equations yield something which can be interpreted as a wave(-like) phenomenon? Difference between myself and by myself a, b are integers. p is prime. I want to prove: $(a+b)^{p} \equiv a^p + b^p \pmod p$  I know about Fermat's little theorem, but I still can't get it I know this is valid: $(a+b)^{p} \equiv a+b \pmod p$ but from there I don't know what to do.  Also I thought about $(a+b)^{p} = \sum_{k=0}^{p}\binom{p}{k}a^{k}b^{p-k}=\binom{p}{0}b^{p}+\sum_{k=1}^{p-1} \binom{p}{k} a^{k}b^{p-k}+\binom{p}{p}a^{p}=b^{p}+\sum_{k=1}^{p-1}\binom{p}{k}a^{k}b^{p-k}+a^{p}$ Any ideas?  Thanks! Redirect the output using `sudo` I have a small question regarding using sudo with output redirect &gt;. To enable IP forwrding, someone can use the command:  echo 1 &gt; /proc/sys/net/ipv4/ip_forward   Executing this command will give permission denied as it requires root privileges. However, executing the same command with sudo gives also permission denied error! It seems that output redirect &gt; does not inherit the permissions of the preceding command echo. Is this right?  As a workaround I do:  echo 1 | sudo tee /proc/sys/net/ipv4/ip_forward   Is this the best way to do it? Am I missing something?  Please, note that this is an example and it applies to all commands that use output redirect. Evaluate the integral $\int_{-1}^1\frac{dx}{(e^x+1)(x^2+1)}$. Evaluate:      $$\int_{-1}^1\frac{dx}{(e^x+1)(x^2+1)}$$ Does a Nikon DX lens on a FX camera get subjected to the 1.5X crop factor? "sudo -u postgres psql postgres" does not ask for password remove locked by android device manager message I have played with Android device manager and I have blocked my phone. I have deblocked but everytime my phone enters into standyby it apears me the message "locked by android device manager" and I have to enter the password again.  Do you know how to remove this message? Prove $GL_n(\Bbb{R})/SL_n(\Bbb{R}) \cong \Bbb{R}^\times$ $$GL_n(\Bbb{R})/SL_n(\Bbb{R}) \cong \Bbb{R}^\times$$  This is trivial to prove with the first isomorphism theorem - by using the determinant as a endomorphism, then as $SL_n(\Bbb{R})$ is $1$ under the determinant, it is the kernel, and by FIT, the above is proved.  I was wondering how to prove this without the isomorphism theorem ? In Python, how can I parse a numeric string like "545.2222" to its corresponding float value, 545.2222? Or parse the string "31" to an integer, 31?  I just want to know how to parse a float str to a float, and (separately) an int str to an int. Relation bewteen Hessian Matrix and Curvature According to ,  It describes the local curvature of a function.   AFAIK, for one-variable function $f(x)$, its local curvature is  $$\kappa = \frac{|f''|}{(1 + f'^2)^{3/2}},$$ and its Hessian matrix is  $$\mathcal{Hess}(f) = [f''],$$ right? And here is my problem, I think the local curvature is not just described by its Hessian matrix, because $f'$ also has its role in it, doesn't it?  And furthermore, for 2-variable function $f(x,y)$, its Hessian matrix is  $$\mathcal{Hess}(f) = \left[ \begin{array}{cc} f_{xx}'' &amp; f_{xy}'' \\ f_{xy}'' &amp; f_{yy}'' \end{array} \right].$$ How does it relate to the local curvature of $f(x,y)$? Should spam posts be edited? I noticed that the posts of the recent spam surge on Ask Ubuntu were all edited by community members into something like     EDITED - REMOVED SPAM ANSWER   or similar.  While I understand why the users have done this and I too don't want to leave the spam content visible for longer than absolutely necessary, it made flagging more time consuming for me.  I had to check the revision for every of those possible spam posts to check if it is actually spam, instead of being able to flag directly from the review site. Spam flags carry a serious penalty, I'm not willing to add my spam flag without checking that it's really spam.  I see the benefit of editing spam, but it also causes some more effort for the later flaggers. Should we as a general policy edit out the content of spam posts, or should we deal with them solely by flagging?