I have an existing Stack Overflow account but somehow made another Stack Overflow account while using the StackExchange app, so now I have unpredictable behavior when I visit Stack Overflow.  Sometimes I'm using one account, sometimes I'm using another.  You can see the different reputation that I have because the Open ID links to a different account than when I actually visit Stack Overflow.  I'm not concerned with the reputation, but this makes it hard for me to manage my questions and answers because I cannot easily control which account I am using when posting.  Is there a way to delete one of my accounts?  I can provide the exact ID but not sure if posting it is safe.
I accidentally posted a question without being logged in. Is there a way to associate that question with my account?   For more information, visit &quot;&quot; in the .   a.k.a. How can you link a registered account to a cookie-based account? a.k.a. How do I merge an unregistered account with a registered account a.k.a. Merging users a.k.a. How do I associate anonymous questions I’ve asked with my registered account? a.k.a. Is there a way to claim an unregistered user? (in case anyone searches with those terms)
Connected to wifi successfully, but no internet connection How can I check if a package is installed (no superuser privileges)? At our university we can get almost any ubuntu package installed we want, but we are not superusers ourselves (we need to request packages being installed).  With some libraries it is not always easy to know whether the package is already installed or not. Is there a simple way/command to check this? Finding $\int_0^{\infty}xe^{-\lambda x} \, dx$ How to integrate:  $$\int_0^\infty x \, \lambda e^{-\lambda x} \, dx$$    I tried using integration by parts:  Let $u = x$ and $dv = \lambda e^{-\lambda x} \, dx$  Then $du = dx$  And $v = - \lambda e ^{-\lambda x}$  Correct so far?   Then   $$\begin{aligned} uv - \int v \, du &amp;= -\lambda x e^{-\lambda x} - \int (- \lambda e^{- \lambda x}) dx \\ &amp;= -\lambda x e^{-\lambda x} - \lambda e^{-\lambda x} \end{aligned}$$    The correct answer from lecture notes      UPDATE 2  Let $u=\lambda x$ and $dv = e^{-\lambda x} dx$  Then $du = \lambda \, dx$  $$dv = e^{-\lambda x} \, dx$$  Let $y = -\lambda x$  Then $dy = -\lambda \, dx$  So $dx = -\frac{1}{\lambda} dy$  $$\begin{aligned} v &amp;= \int e^u \cdot - \frac{1}{\lambda} du \\ &amp;= - \frac{1}{\lambda} e^{-\lambda x} \end{aligned}$$  But here I seem to have an extra $- \frac{1}{\lambda}$ in $v$?  If I continue using integration by parts, I get:   $$-x e^{-\lambda x} + \color{red}{\frac{1}{\lambda}} \int e^{-\lambda x} \, dx$$ When do you use the "this" keyword? I was curious about how other people use the this keyword. I tend to use it in constructors, but I may also use it throughout the class in other methods. Some examples:  In a constructor:  public Light(Vector v) {     this.dir = new Vector(v); }   Elsewhere  public void SomeMethod() {     Vector vec = new Vector();     double d = (vec * vec) - (this.radius * this.radius); } Salesforce Internal Server - What's in a GACK? Background  I have been working with Salesforce Support for several weeks now trying to get them to escalate an internal server error with GACK 2134764861-123797 (1611479512) (1611479512). After a long period of waiting I was told that in order to escalate quickly they needed to reproduce the issue in a controlled way. This was again taking them a considerable amount of time so I created a reduced test case myself () that concisely reproduces the issue with a very small amount of code. I was told that this wasn't a valid reproduction because it caused a different GACK (1291518605-518052 (1659192199) (1659192199)) despite reproducing the exact same user experience.  My Question  What makes up a GACK? Is there any information that I can take from their structure that can give me clues on which errors are related without access to the full back-end tools that Salesforce Support uses? It is not infrequent that without premier support it takes me upwards of two weeks to escalate platform bugs and I am hoping that I can somehow use the information from the GACK to reduce this time. explicit formula for recurrence relation $a_{n+1}=2a_n+\frac{1}{a_n}$ For $n\in\mathbb N$, $$a_{n+1}=2a_n+\frac{1}{a_n},\quad a_1=1. $$ Can any one give an explicit formula for all $a_n$? If such an explicit general formula doesn't exist, please explain it. I've tried to figure out the $n$-iterated function $f^{(n)}$ where $f(x)=2x+1/x$ or even $f(\tan(t))$. But in either cases, I failed.Since the recurrence isn't linear nor homogeneous,the generating function method doesn't apply here. Generate a log of all the installs on a system (whether apt-get/yum/pip/npm/...) Does Linux have the capability to use "junctioned" symbolic links? I'm not sure if this is an actual term or not, so let me explain the concept.  I have a git repository containing all my configuration dot files in ~/dotfiles. I use symbolic links into this directory in order to "activate" them. For example, by executing ln -s ~/dotfiles/bash/bash_profile ~/.bash_profile to produce the link:  ~/.bash_profile -&gt; ~/dotfiles/bash/bash_profile   However, I find myself in a situation where I want to combine the contents of multiple files. For example, I want the ~/.bash_profile symbolic link to point to two separate files, one for each project. E.g.:  ~/.bash_profile (1) -&gt; ~/dotfiles/bash/bash_profile (2) -&gt; ~/dotfiles/proj/bash_profile   I know I can simply concatenate the two files (e.g., cat ~/dotfiles/{bash,proj}/bash_profile &gt; ~/.bash_profile), but if I can do the same thing with symbolic links, I would prefer to.  I imagine that if such a feature exists (Nix is pretty huge), then under the hood it would have to map the two different files together, hiding all sorts of complexities under the hood (mapping file offsets of all non-first "mapped" files, locking all files when writing to the junctioned symbolic link, etc, etc).  If such a feature doesn't exist, are there are plans to implement it? How do you deserialize json properties that are reserved words in apex? What is the difference between ++i and i++? In C, what is the difference between using ++i and i++, and which should be used in the incrementation block of a for loop? Number of monic irreducible polynomials of prime degree $p$ over finite fields Suppose $F$ is a field s.t $\left|F\right|=q$. Take $p$ to be some prime. How many monic irreducible polynomials of degree $p$ do exist over $F$?   Thanks! Say I have two strings,  String s1 = "AbBaCca"; String s2 = "bac";   I want to perform a check returning that s2 is contained within s1. I can do this with:  return s1.contains(s2);   I am pretty sure that contains() is case sensitive, however I can't determine this for sure from reading the documentation. If it is then I suppose my best method would be something like:  return s1.toLowerCase().contains(s2.toLowerCase());   All this aside, is there another (possibly better) way to accomplish this without caring about case-sensitivity? If $k>0$ is a positive integer and $p$ is any prime, when is $\mathbb Z_p[\sqrt{k}] =\{a + b\sqrt k~|~a,b \in\mathbb Z_p\}$ a field. Effective Refractive Index in Paper I am reading the paper, entitled "Artificial uniaxial and biaxial dielectrics with use of two-dimensional subwavelength binary gratings" by Eric B. Grann, M. G. Moharam, and Drew A. Pommet.   In the paper they mention this formula:        Do you know how it can be derived and where it comes from ? Does python optimize modules when they are imported multiple times? If a large module is loaded by some submodule of your code, is there any benefit to referencing the module from that namespace instead of importing it again?  For example: I have a module MyLib, which makes extensive use of ReallyBigLib. If I have code that imports MyLib, should I dig the module out like so  import MyLib ReallyBigLib = MyLib.SomeModule.ReallyBigLib   or just  import MyLib import ReallyBigLib Running tcpdump starts ssh flood I have runtime Linux running in a PLC. My development machine is running Ubuntu 14.04. The PLC and the development machine are connected through a five port switch. I ssh to PLC from my development machine to transfer executable of a networking application that I develop on my development machine.   I run tcpdump on PLC to debug the kind of packets my network application is receiving BUT as soon as I start tcpdump, there starts a flood of ssh sync and acks back and forth from my ubuntu machine to the PLC. The LED lights of ethernet controller of PLC as well on the switch start blinking rapidly. The flood overwhelms the PLC and it almost dies down while all other packets get dropped. It feels like a DOS attack whenever I run tcpdump but as soon as I stop tcpdump, everything calms down and gets back to the normal.   I would like know remedy on this problem and why it happens?     Any help would be appreciated. Reasons not to use a 741 op-amp? Get file size before uploading I want to update ubuntu 11.04 throught apt-get. So I added the following lines in apt.conf  export http_proxy=http://username:password@proxyserver.net:port/ export ftp_proxy=http://username:password@proxyserver.netport/  export http_proxy=http://deepak:Deepak@123@12.1.1.1:3128   My question is: how do I insert special characters to a username or password?  For instance: my password for proxy is Deepak@123 and it is getting an error. What are the current travel restrictions on individuals entering the United States from regions affected by Covid-19? This community wiki explains the current restrictions by the United States of America on the entry of individuals who may pose a risk of transmission of the SARS-Cov2, the virus which causes the Covid-19 disease.