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I thought people would be working on little code projects together, but I don't see them, so here's an easy one:  Code that validates a valid US Zip Code. I know there are ZIP code databases out there, but there are still uses, like web pages, quick validation, and also the fact that zip codes keep getting issued, so you might want to use weak validation.  I wrote a little bit about zip codes in a side project on my wiki/blog:    There is also a new, weird type of zip code.     I can do the javascript code, but it would be interesting to see how many languages we can get here. I accidentally set an object as camera, how do I undo this? I have a problem with rendering in cycles. In blender render my object is rendering fine, but in cycles when I pushed F12 I got only this:    One more thing: when I click 0 on keyboard I'm not in camera persp, but in object as camera, it looks like invisible layer, I don't know how to undo this, and be in camera persp again.  Does anybody have any idea how to fix this? Show that if $u$ is harmonic in $\mathbb R^n$ and $u=o(|x|)$, then $u$ is a constant.(Hint: use the solid version of the mean value property $u(x)=\frac{1}{\omega R^n} \int _{B_{R(x)}} u(y)dy$, and estimate $|u(x)-u(x')|$.)  Can anyone tell me how to use this hint? Multivariate linear regression vs. several univariate regression models In the univariate regression settings, we try to model   $$y = X\beta +noise$$  where $y \in \mathbb{R}^n$ a vector of $n$ observations and $X \in \mathbb{R}^{n \times m}$ the design matrix with $m$ predictors. The solution is $\beta_0 = (X^TX)^{-1}Xy$.  In the multivariate regression settings, we try to model   $$Y = X\beta +noise$$  where $y \in \mathbb{R}^{n \times p}$ is a matrix of $n$ observations and $p$ different latent variables. The solution is $\beta_0 = (X^TX)^{-1}XY$.  My question is how is that different than performing $p$ different univariate linear regression? I read  that in the latter case we take into consideration correlation between the dependent variables, but I don't see it from the math. Question  I want to write a book in Arabic (I have an Arabic keyboard, so I don't need a converter). By Arabic book I mean literally Arabic:    title, table of contents  etc    all in Arabic.   The equations, however, I want to write them in English/Latin.  Related    This link helped a lot but it was for Arabic texts in an English main document.    I already checked these two (and plenty other sites). How to make a LAMP server accessible from the internet? Hi I want to make my own SNS (Social Networking Site), so I installed LAMP on my Ubuntu 14.04. But its not accessible from the internet! I can run the server only on my computer by typing "https:\localhost" on my browser.  I don't want any domains; I just want that whosoever from any part of the world wants to use my SNS he/she just have to type the ip-address and my SNS opens i.e. I want my server accessible from the internet.  My router is Binatone DT 850W. Can you please tell me what should I do? I was wondering how far in imaging physics had gotten. Do we hold the technology to actually take a picture of, say, an alpha particle, or even a single atom?  I realise we aren't talking about camera pictures, so what kind of imaging techniques have taken images/is most likely to be the technique to take an image of a single atom? What do I need to get photos with a unifom black background (not with post)? Often i see portraits such as the one below and like the way they look. I wanted to know can I get this look in my shots.  I am sure there are professional materials you can get to outfit a studio that will deliver such results. I have no clue what these items would be, can i get clued in?  Also, I was wondering if there is a DIY way to achieve this as well. Maybe with a black bed sheet or something?  I want to set something up in a room in my house for studio type shots. I am looking to get an idea of what items I need to get this done and how the setup should go. I want to write a query like this:  SELECT o.OrderId, MAX(o.NegotiatedPrice, o.SuggestedPrice) FROM Order o   But this isn't how the MAX function works, right?  It is an aggregate function so it expects a single parameter and then returns the MAX of all rows.     Does anyone know how to do it my way? Word to describe someone who goes to all the events in town! I'm looking for a short word that could describe people who are always going to every event in town. It doesn't need to be an existing word, feel free to create one of your own. It can also be made of words related to events and parties. (ex: club, event, guest list, etc.)  Edit  The word will serve as a new term to describ these people in a favorable way. It will probably be used for an app name so it need to be catchy and fun. ( Preferably ) Does every Abelian group admit a ring structure? Given some Abelian group $(G, +)$, does there always exist a binary operation $*$ such that $(G, +, *)$ is a ring? That is, $*$ is associative and distributive:  \begin{align*} &amp;a * (b * c) = (a*b) * c \\ &amp;a * (b + c) = a * b + a * c \\ &amp;(a + b) * c = a * c + b * c \\ \end{align*}  We also might have multiplicative identity $1 \in G$, with $a * 1 = 1 * a = a$ for any $a \in G$. Multiplication may or may not be commutative.  Depending on the definition, the answer could be no in the case of the group with one element: then $1 = 0$. But the trivial ring is not a very interesting case. For cyclic groups the statement is certainly true, since $(\mathbb{Z}_n, +, \cdot)$ and $(\mathbb{Z}, +, \cdot)$ are both rings. What about in general? Is there some procedure to give arbitrary abelian groups ring structure? Factorial sum estimate $\sum_{n=m+1}^\infty \frac{1}{n!} \le \frac{1}{m\cdot m!}$ Prove that:  $$\displaystyle \sum_{n=m+1}^\infty \dfrac{1}{n!} \le \dfrac{1}{m\cdot m!}$$  I have tried induction on $m$ but it does not work very well. Any suggestion? Calendar.getInstance(TimeZone.getTimeZone("UTC")) is not returning UTC time 10 servers to administer and I'm a history major Through reasons that don't warrant exhaustive discussion, I find myself in charge of 10 servers:   A domain controller-~500 hosts/~350 users IIS web server-This is where we make our money SQL server-The crown jewels Exchange server Linux box for data entry AV server Backup server A few others tossed around   The company where I work believes everybody is replaceable and therefore believes they can pay a minimum wage for any position. The IT manager and Sysadmin quit recently and I think I was the only person who did not take a big step backward when the call went out for volunteers. This also explains why someone with my background is in this position. That is the reality, as much as I wish it otherwise.  What are the things I should be doing to keep those systems running? There is no written procedure left behind and I crammed the A+ and Network+ certs in the last two months but that leaves me with some theory and no practical experience.  I am in the process of teaching myself powershell but from here to there is a long way. I have no scripting or programming experience.  What tasks should I be performing? What practices should I implement?  I understand I am probably hosed but a lifeline to get me through would be helpful. How can I have colored and underlined links with hyperref? Expanding GCDs Reasoning: $\gcd(a,c) \cdot \gcd(b,c) = \gcd(ab,bc,ac,cc)$ I'm just wondering the reason behind being able to do this:  $$\gcd(a,c) \cdot \gcd(b,c) = \gcd(ab,bc,ac,cc)$$  Is there an elementary proof to the reasoning behind this? Counterspelling a counterspell Evaluating $\int_{0}^{\infty}\frac{\sin^{2n+1}x}{x}\mathrm{d}x$ What issues / pitfalls must be considered when overriding equals and hashCode? Where do executables look for shared objects at runtime? I understand how to define include shared objects at linking/compile time. However, I still wonder how do executables look for the shared object (*.so libraries) at execution time.  For instance, my app a.out calls functions defined in the lib.so library. After compiling, I move lib.so to a new directory in my $HOME.  How can I tell a.out to go look for it there?