I've gone through the following questions:   From those posts, I learned that, when my question/answer gets too many downvotes or deleted, I'll be banned from Q&amp;A. To lift the ban, I have to earn more reputation by creating or editing a question or answer to attract upvotes. However, it is unclear to me that:  Will asking questions which are neither downvoted nor upvoted make me banned? Will upvoting too many answers make me banned? Will accepting answers increase my rep and then help to get unblocked? Or, will getting upvoted comments (no rep increase) help me get out of the ban?  I am asking because, a few days ago, I upvoted a few of the answers I got and later I find my upvotes are reversed. I upvoted again and then get reversed again and again. Then my account is banned. PS: I think this site must fully disclose its banning mechanism. I never learn about it until I got banned. For downvoters: please let me know what I did wrong; it is much appreciated.  Ok, now I realized that upvoting has nothing to do with a question ban (this is the ban I got). I'll now work on my previous questions. One likely reason of getting instant voting reversal is probably the Internet/Wi-Fi/data instability.
If you are reading this, you may have been affected by one of our post quality bans. If so, it is important that you  to understand what has happened and how to regain the permissions that you lost. While trying to ask a question, one could see:  We are no longer accepting questions from this account. See  to learn more.  Likewise, for answers:  We are no longer accepting answers from this account. See  to learn more.   Why am I getting this message? Are deleted posts taken into account too? Is a question/answer ban the same as a suspension? How do I avoid getting a question ban? How long do I have to wait before I can post again? What can I do to release the ban? How can I reactivate my account? Can I simply create a new account? I'll just ask somewhere else on the SE network, and they'll migrate my question to the correct site! Will a ban on one Stack Exchange site affect my standing on other sites in the network? Does this apply to meta sites too? My account is in good standing. Why am I still blocked?
Statistics interview questions Method for batch layout of images into PDF sheets I have 100,000 identically-sized, but unique, PNG/JPG images which I want to automatically layout onto A4 sheets which can then be exported as print-ready PDFs.  So assuming I can fit 8 of these images per page in a 4x2 grid, I'm looking to input my 100,000 images and output 12,500 PDFs.  I'm a programmer so I could probably write a script to do this myself (e.g. PHP/Python), but I was wondering whether there are any tools/scripts/software that already exists that can do this automatically. Access pictures from Pictures app in my android app Just like the iPhone has a UIImagePickerController to let the user access pictures stored on the device, do we have a similar control in the Android SDK?  Thanks. How to get parent process in .NET in managed way I was looking a lot for method to get parent process in .NET, but found only P/Invoke way. I have a group $G$ with $p^2$ elements, where $p$ is a prime number. Some (potentially) useful preliminary information I have is that there are exactly $p+1$ subgroups with $p$ elements, and with that I was able to show $G$ has a normal subgroup $N$ with $p$ elements.   My problem is showing that $G$ is abelian, and I would be glad if someone could show me how.   I had two potential approaches in mind and I would prefer if one of these were used (especially the second one).   First: The center $Z(G)$ is a normal subgroup of $G$ so by Langrange's theorem, if $Z(G)$ has anything other than the identity, it's size is either $p$ or $p^2$. If $p^2$ then $Z(G)=G$ and we are done. If $Z(G)=p$ then the quotient group of $G$ factored out by $Z(G)$ has $p$ elements, so it is cylic and I can prove from there that this implies $G$ is abelian. So can we show theres something other than the identity in the center of $G$?  Second: I list out the elements of some other subgroup $H$ with $p$ elements such that the intersection of $H$ and $N$ is only the identity (if any more, due to prime order the intersected elements would generate the entire subgroups). Let $N$ be generated by $a$ and $H$ be generated by $b$. We can show $NK= G$, i.e every element in G can be wrriten like $a^k b^l $. So for this method, we just need to show $ab=ba$ (remember, these are not general elements in the set, but the generators of $N$ and $H$).   Do any of these methods seem viable? I understand one can give very strong theorems using Sylow theorems and related facts, but I am looking for an elementary solution (no Sylow theorems, facts about p-groups, centrailzers) but definitions of centres and normalizers is fine. How can I improve Ubuntu overall system performance? What are your tips for improving overall system performance on ubuntu? Inspired by this  I realized that some default settings may be rather conservative on Ubuntu and that it's possible to tweak it with little or no risk if you wish to make it faster.  This is not meant to be application specific (e.g. make firefox load pages faster), but system wide.  Preferably 1 tip per answer, with enough detail for people to implement it.  A couple of mine would be:   Install  (via Software Center or sudo apt-get install preload); Change  value - "which controls the degree to which the kernel prefers to swap when it tries to free memory";   What are yours?  PS: Since this is not intended to have a unique answer but rather, several useful tips, I'm making this community wiki out-of-the-box. Python Ctypes - loading dll throws OSError: [WinError 193] %1 is not a valid Win32 application how to install drivers for wifi adaptor Ralink 148f:7601 on ubuntu? Delete all lines in Notepad++ except lines containing a word I need? Would fewer Jedi be more powerful? How to get domain name from URL I'm trying to prove whether or not the Laurent polynomials $\mathbb{Z}[x, x^{-1}]$ with coefficients in $\mathbb{Z}$ form a principal ideal domain.    I know that $\mathbb{F}[x, x^{-1}]$ is a PID when $\mathbb{F}$ is a field, but clearly $\mathbb{Z}$ is not a field so I cannot appeal to this result. And my intuitions are not serving me very well at the moment. Can anyone provide a hint or direction to take? How to get my own IP address and save it to a variable in a shell script? I've just gotten through replacing capacitors on a trio of dead LCD screens (nothing's blown up yet, so far) - they either had one or two capacitors on their inverter circuit SLIGHTLY bloated, and not quite leaky. I ended up replacing all capacitors of the same brand/'colour', even the ones that looked fine, in case.  Now, checking a bad resistor is simple - i can use a standard multimeter to test it, and i tend to check my solders with the continuity testing option of the multimeter.  How would i test a capacitor ? Is there some standard, common way to test one? prove $\lim_{n\to\infty}{\frac{a^n}{n!}}=0$ I have the proof but i don't understand one part. The proof (for $a&gt;1$) goes as follows:  there exists $k \in N$ such that$a&lt;k, \frac{a}{k}&lt;1$ and since $\frac{a}{k+i}&lt;\frac{a}{k}, i \in N$ $$\frac{a^n}{n!}=\frac{a}{1} \cdot \frac{a}{2} \cdot...\cdot\frac{a}{k}\cdot\frac{a}{k+1}\cdot...\cdot\frac{a}{n}&lt;\frac{a^k}{k!}(\frac{a}{k})^{n-k}=\frac{a^k}{k!}\cdot \frac{a^na^{-k}}{k^nk^{-k}}$$  $$0&lt;\frac{a^n}{n!}&lt;\frac{k^k}{k!}(\frac{a}{k})^n$$  then $$0 \leq \lim_{n\to\infty}{\frac{a^n}{n!}}\le\frac{k^k}{k!}\lim_{n\to\infty}{(\frac{a}{k})^n}$$  Now, the part I don't understand is in the expansion of $\frac{a^n}{n!}$. How does one come with $&lt;\frac{a^k}{k!}(\frac{a}{k})^{n-k}$ part, to be more precise, how does one come up with $(\frac{a}{k})^{n-k}$ part of the inequality? How to disable the keyring for SSH and GPG? Add folder to PATH How to add something to PATH ? I have added like   PATH=$PATH:/home/example export PATH   and it works until I restart , after that when  I type env in PATH there is no /home/example. SharePoint People.aspx Page is Visible for All Users The SharePoint People.aspx page is visible for all users by default. Is there any way to restrict this page from certain readers? Merge array items into string Remove the flag notification in the top bar when I have done my job with it I have the moderator privileges on .  Even though it's quite rare that flags appear over there, it is still quite annoying that once I have done my job with a flag and therefore cannot do anything else with it, the flag in the top bar remains there. Why do I have to keep seeing that flag when in fact, I can't do anything about it?  Images, with free-hand circles:  A flag exists in the notification bar:    I have already done my part of the flag handling:    And yet the flag remains in the notification bar.