What should I look for in a wide angle lens?
What to look for in a wide angle lens?
How to access a SQL Server database from other computer connected to the same workgroup? "You can only post once every 40 minutes" on different sites This morning I posted a question on a SE site. Then realized a different SE site would be more appropriate.   I proceeded to delete the question on the first site and copied it to the second, but I got the dreaded "You can only post once every 40 minutes.", even if the question was deleted from a different SE site.   I have only the affiliation reputation on both of those sites. Now I'm sitting here waiting for the 40 minutes to pass.  Paradoxically, as a trusted user in SO, I'm more likely to come to other SE sites to ask a few things about topics that are new to me (as opossed to answering in SO), yet I feel more limited.   Maybe trusted users from other sites should have slightly lower restrictions than &lt;125 on the fellow communities? In particular in order to ask a couple of questions. How can I solve "Be aware that removing the lock file is not a solution and may break your system"? I did: sudo apt-get update  I got this: Reading package lists... Done E: Could not get lock /var/lib/apt/lists/lock. It is held by process 1131 (packagekitd)  N: Be aware that removing the lock file is not a solution and may break your system.  E: Unable to lock directory /var/lib/apt/lists/  I used to just remove the lock file, but I've never seen that note before (did it break my system?)?? What do I do? $\displaystyle\int_{0}^{2\pi}\frac{1}{a+ \cos\theta}\,d\theta$ What is the best solution for database connection pooling in python? I have developed some custom DAO-like classes to meet some very specialized requirements for my project that is a server-side process that does not run inside any kind of framework.    The solution works great except that every time a new request is made, I open a new connection via MySQLdb.connect.    What is the best "drop in" solution to switch this over to using connection pooling in python?  I am imagining something like the commons DBCP solution for Java.    The process is long running and has many threads that need to make requests, but not all at the same time... specifically they do quite a lot of work before brief bursts of writing out a chunk of their results.  Edited to add: After some more searching I found  which looks decent, but as I'm relatively new to python I guess I just want to make sure I'm not missing a more obvious/more idiomatic/better solution. A current I flows through a solenoid (with n turns). Self inductance is $L$. If the magnetic flux is $\phi$, I am taught that $-n\phi=LI$  I dont understand the part with $n$, why do we have multiply by $n$? $\phi$ itself represents the whole magnetic flux there, if $\phi$ implied the flux only occurred by one coil, then it would be correct.   Moreover, flux change by a coil ($n$ turns) in $dt$ time is $d\phi$, so the induced electromagnetic force is   $$dE=n \cdot \frac{d\phi}{dt}$$   Why do we multiply by $n$ here? If $\phi$ means the whole flux, then why multiply? Show that:  If $U$ is a principal ultrafilter, then the canonical inmersion $j$ is an isomorphism between $\mathcal A$ and $Ult_{U}\mathcal A$ How to break out of multiple loops? In my past experiences, I have almost never typeset my manuscripts according to the formats required by the journals to which I would like to submit. I leave my manuscripts as produced by the LaTeX article documentclass.  Recently I am wondering: Would such a behavior generally give handling editors a negative first impression? Find all natural numbers $x,y$ such that   $$3^x=2y^2+1$$  solutions are $(1,1)$, $(2,2)$, $(5,11)$. I found that parity of both is same and If $x$ Is odd it is of the form $4k+1$. Is Pauli-repulsion a "force" that is completely separate from the 4 fundamental forces? Limit point versus limit and implications for convergence I understand that similar questions to this have been asked  and  but I believe my question is different because with regards to (1) I am not asking about the set $X$ that contains the points of my sequence and with regard to (2) because I have the distinct definitions of limit and limit point in mind. That said:  My Question: My textbook, Fundamental Ideas of Analysis by Michael Reed, defines a limit point as:     Definition: Let $(a_n)$ be a sequence of real numbers. A number $d$ is called a limit point if, given $\epsilon &gt; 0$ and an integer $N$, there exists $\color{red}{\mathrm{ an }} \ n \ge N$ so that $|a_n - d| \le \epsilon$.    The definition of a limit is as follows:     Definition: We say that a sequence $(a_n)$ converges to a limit $a$ if, for every $\epsilon \ge 0$, there is an integer $N(\epsilon)$ so that $|a_n - a| \le \epsilon \color{red}{\text{  for all  }} n \ge N$.    From these definitions, and given this question:     If a sequence converges it has exactly one limit point. Is the converse true? If not, provide a counterexample   Can I conclude that the converse is indeed true simply by appealing to the definitions, or do I need a tighter proof. And if I do, I'm a little stuck on how to refine this proof. Three-columns text with figures of 2\columnwidth Stopping to eat is tedious, is there any way to automate the process? While I've managed to optimize and automate almost everything, constantly having to stop and eat is annoying (I run around a lot, so I get hungry quickly). Is there any device or tool that will keep me well fed at all times without having to stop and feed? How do I submit a form via AJAX? What are the differences between 32-bit and 64-bit, and which should I choose? Mapping ManyToMany with composite Primary key and Annotation: Convergence of $\int_0^\infty $sin$ (x^p) dx$ Error when using TikZ-Feynman package Today I downloaded and installed the new  package to draw Feynman diagrams. I included the packages   \usepackage{tikz}  \usepackage{tikz-feynman} \tikzfeynmanset{compat=1.0.0} \usetikzlibrary{shapes,arrows,positioning,automata,backgrounds,calc,er,patterns}   into my preamble (changed them already many times).  However, already a simple sample code like  \begin{tikzpicture} \begin{feynman} \vertex (a) {\(\mu^{-}\)}; \vertex [right=of a] (b); \vertex [above right=of b] (f1) {\(\nu_{\mu}\)}; \vertex [below right=of b] (c); \vertex [above right=of c] (f2) {\(\overline \nu_{e}\)}; \vertex [below right=of c] (f3) {\(e^{-}\)}; \diagram* { (a) -- [fermion] (b) -- [fermion] (f1), (b) -- [boson, edge label'=\(W^{-}\)] (c), (c) -- [anti fermion] (f2), (c) -- [fermion] (f3), }; \end{feynman} \end{tikzpicture}   directly gives the error:     Package pgfkeys Error: I do not know the key '/graph drawing/node distance'.   Can you please help me? Thanks in advance! In general, in most places, it is said that using TeX defaults is the best. However, TeX does provide things like \, and \quad etc. When one should use them? Both in general and in math mode in particular.