Java environment broken?
How to make pdfsam work in (L)ubuntu 18.04?
It seems that a common operation needed when defining new commands is to scan over a list of arguments (separated e.g. by a comma, but maybe by something else) and do something with each argument in the list, find the last one, or whatever.  For example to write commands that look like \Command{a,b,c} or \Command{c.d.e} and do something with each a, b, and c. See e.g. questions on  and .  Some solutions have been posted there, but what would be the best idiom to perform such kind of operations? LaTeX's \@for looks very nice, but is it possible to use it to scan anything other than comma-separated lists? Do I need a Schengen visa if I have UK permanent residency? Can I convert a C# string value to an escaped string literal? In C#, can I convert a string value to a string literal, the way I would see it in code? I would like to replace tabs, newlines, etc. with their escape sequences. If this code: Console.WriteLine(someString);  produces: Hello World!  I want this code: Console.WriteLine(ToLiteral(someString));  to produce: \tHello\r\n\tWorld!\r\n Why is the electric field inside a conductor zero in equilibrium? My textbook says the field inside a conductor must be zero in order for the system to be equilibrium and therefore there must be no excess charge inside.  Their proof:  1) Place a gaussian surface inside the conductor. Since the system is at equilibrium, all points on the surface must have an electric field of zero.  2) Therefore the net flux is zero, implying the charge inside is zero.  3) If there is no charge inside, all excess charge must lie on the surface.  My problem:  "Since the system is at equilibrium, all points on the surface must have an electric field of zero."  Why?  Consider an conductor with no excess charge. To simplify things, say the conductor consists of a 100 free electrons and a 100 ions of charge 1$e^+$. The conductor is neutral and at equilibrium.  Now consider the field on one specific electron. There a total of 99 other electrons and 100  ions. So there would be a net field acting on that specific electron. So even though the system is at equilibrium, the net field on the individual particles is non-zero.  So a system can be at equilibrium, even if the net field inside is non-zero. What am I misunderstanding?  Another example: Consider a system consisting of one electron and one proton. If nothing is holding them back they will attract each other until they touch. After they touch, the force acting on them is still non-zero, yet they wouldn't accelerate. I am looking for a closed form (ideally expressed as elementary functions) of the function $\exp_n(x) = \sum_{k=0}^n x^k / k!$.  I am already aware of expressing it in terms of the gamma function. Background / Motivation When counting combinations of objects with generating functions, it is useful to be able to express the partial sum $1 + x + \cdots + x^n$ as $\frac{1-x^{n+1}}{1-x}$. For example, to count the number of ways to pick 5 marbles from a bag of blue, red, and green marbles where we pick at most 3 blue marbles and at most 2 red marbles, we can consider the generating function $f(x) = (1+x+x^2+x^3)(1+x+x^2)(1+x+x^2+\cdots)$. By using the partial sum identity, we can express it as $f(x) = \left(\frac{1-x^4}{1-x}\right)\left(\frac{1-x^3}{1-x}\right)\left(\frac{1}{1-x}\right)$.  Simplify, express as simpler product of series, and find the coefficient of the $x^5$ term. I want to be able to do the same for a generating function in the form $g(x) = \exp_{n_1}(x)^{p_1} \exp_{n_2}(x)^{p_2} \cdots \exp_{n_j}(x)^{p_j}$ The easiest way to extract the coefficient of a given term $x^p / p!$ would be to use a similar closed form expression for $\exp_n(x)$ and a similar technique to $f$. Attempted Solutions Differential equation Recall that the way to prove the identity $1+x+x^2+\cdots+x^n = \frac{1-x^{n+1}}{1-x}$ is to define $S = 1 + x + x^2 + \cdots + x^n$ and notice that: $S - Sx = 1 - x^{n+1}$. Likewise, notice that $y(x) = \exp_n(x)$ satisfies $y - y' = x^n/n!$.  Via SAGE, the solution is $y(x) = \frac{c+\Gamma(n+1,x)}{n!}e^x$.  Our initial condition $y(0) = 0$ so $c=0$.  By , $\Gamma(n+1,x) = n! e^{-x} \exp_n(x)$ so we have $y(x) = \exp_n(x)$. Recurrence Relation Notice that $\exp_n(x) = \exp_{n-1}(x) + x^n/n!$. Using the unilateral Z-Transform and related properties, we find that $\mathcal{Z}[\exp_n(x)] = (z e^{x/z})/(z-1)$. Therefore, $\exp_n(x) = \mathcal{Z}^{-1}\left[(z e^{x/z})/(z-1)\right] = \frac{1}{2 \pi i} \oint_C z^n e^{x/z}/(z-1)\;dz$. $(z^n e^{x/z})/(z-1)$ has two singularities: $z = 1$ and $z = 0$.  The point $z = 1$ is a pole of order one with residue $e^x$.  To find the residue at $z = 0$ consider the product $z^n e^{x/z} (-1/(1-z)) = -z^n \left( \sum_{m=0}^\infty x^m z^{-m} / m! \right) \left( \sum_{j=0}^\infty x^j \right)$.  The coefficient of the $z^{-1}$ term is given when $n - m + j = -1$. The residue of the point $z=0$ is then $-\sum_{m,j} x^m / m! = -\sum_{m=n+1}^\infty x^m / m!$. Let $C$ by the positively oriented unit circle centered at the origin.  By Cauchy's Residue Theorem, $\frac{1}{2 \pi i} \oint_C z^n e^{x/z}/(z-1)\;dz = \frac{1}{2 \pi i} 2 \pi i \left(e^x - \sum_{m=n+1}^\infty x^m / m!\right) = \exp_n(x)$. Finite Calculus I've tried to evaluate the sum using finite calculus, but can't seem to make much progress. C# Settings.Default.Save() not saving? sys.dm_db_index_physical_stats is extremly slow I have a database that is around 4.5TB, since we have parallel inserts (to reduce daily load time) on one table (partitioned by month) the clustered index on this table tends to be heavily fragmented. When I do a select from sys.dm_db_index_physical_stats (Limited) on this table it takes ages (> 4-5 hours). Is there a faster and better way to check the fragmentation levels on the partitions of this table, the current time this takes is completely inacceptable. With Ubuntu One shut down, is there a way to sync applications between computers? Since Ubuntu one is no longer it appears that Sync between computers no longer works.  Is there a new method to do this?  I'd like to sync the apps from one machine to another. Will I still receive OTA updates after rooting my Nexus 5? how to disconnect main service drop at service panel when upgrading to a 200 amp service panel with service drop coming from bottom underground do I need southern California Edison to come disconnect and then reconnect or can I just do it on my own. I do have a permit. I am looking for some (may be rarely know to nonnative English speakers) synonyms for  "immensely valuable" or "extremely valuable". Does the shebang determine the shell which runs the script? How to create 2D shadows I'd like to create lights and shadows in a 2D environment, like in the image below:    I did several searches but got no results. Do you have any hint? Determining size of grid cells created by vector grid tool of QGIS? I am working with QGIS 1.8.0 and Im making a vector grid on a map. Does someone know how big are the squares if the grid settings look like in the picture? How do the definitions of "irreducible" and "prime" elements differ? Separate selected UV map vertices from surrounding vertices How do I break the selected UV map from its surrounding vertices? On every use profile page the search bar on the top of the page already contains user:&lt;id&gt; text to simplify search for post of the currently visible user. But this doesn’t work correctly for the  user:        Instead of searching for posts owned by Community user I’ve got Jeff Atwood posts:        In this case minus sign was just ignored and instead of (-1, i.e. Community user), the (+1, i.e. Jeff Atwood) is used. Same happened for any other negative id for the “user:” option in the search box. How to recover a dropped stash in Git? I frequently use git stash and git stash pop to save and restore changes in my working tree. Yesterday I had some changes in my working tree that I had stashed and popped, and then I made more changes to my working tree. I'd like to go back and review yesterday's stashed changes, but git stash pop appears to remove all references to the associated commit.  I know that if I use git stash then .git/refs/stash contains the reference of the commit used to create the stash. And .git/logs/refs/stash contains the whole stash. But those references are gone after git stash pop. I know that the commit is still in my repository somewhere, but I don't know what it was.  Is there an easy way to recover yesterday's stash commit reference?  Note that this isn't critical for me today because I have daily backups and can go back to yesterday's working tree to get my changes. I'm asking because there must be an easier way! Integer reciprocals in arithmetic progression Let $m_1,m_2,\ldots,m_k$ be $k$ positive integers such that their reciprocals are in AP. Show that $k&lt;m_1+2$. Also find such a sequence.     Whatever way I tried, whichever formula I used, I could not eliminate the $m_k$ term, which I reckon would be the ideal scenario to find the solution. I am exhausted of any further ideas, please help. Thank you. I changed my Blender Units to Metric System, but when I'm building things, my meshes are transparent, i.e. I can see through faces like in wireframe even though my wireframe is turned off. All faces have a light white in non-wireframe mode, but I can still see through them.   How do I reverse this?  Another issue I get is this    Looks like clipping is not working properly.