Why do I sometimes see a user card under a question or answer which looks like the following?        Has the user been deleted?
Sometimes when reading through user comments on a particular answer, some usernames that appear like user[digit] e.g user12345 are not links. Is this a known behaviour or any other thing I am not aware of?
I forgot my username, how do I get it back? How do I install a different Python version using apt-get? How can I install a different version of Python using apt-get?  Obviously I realise I can install using the source tar ball, however I would prefer not to install from source and instead use the package manager, as that's what it's there for. Surely somewhere reputable builds .deb files for the latest Python releases (why python.org don't is beyond me) that I can reference.   What do I need to do to reference them and what issues might it create when upgrading to the next version?  If there is no way except for building from source, is there a (pseudo) package that I can can install that will provide all of the dependencies needed without having to find and install each individually? So that I don't get:  The necessary bits to build these optional modules were not found: _bz2                  _curses               _curses_panel       _dbm                  _gdbm                 _lzma               _sqlite3              _ssl                  _tkinter            readline              zlib Is there a word to describe words that can be spelled different ways? Is there a word in English to describe words that can be spelled more than one way?  For example:   colour and color favourite and favorite   However, this shouldn't be limited to words spelled differently in different dialects, though I'm not sure what other case there would be. Equivalence Relation problem $x^y = y^x$ for integers $x$ and $y$ To seek the maximum value of $S=x_1x_2+x_2x_3+\cdots+x_nx_1$ on this domain:  $x_1+x_2+\cdots+x_n=0$ and  $x_1^2+x_2^2+\cdots+x_n^2=1$.  I have made some trivial observations:  1) $S\in[-1,1)$ by the rearrangement inequality.  2) We can make $S$ arbitrarily close to $1$ by increasing $n$.  3) An equivalent problem is to minimise $(x_1-x_2)^2+\cdots+(x_n-x_1)^2$.  But does the maximum have a meaningful closed form  for each $n$? Is there a non written rule to which person to use in the PhD thesis, 5 years of using "We" in the papers have brought me to the innate necessity to do it every time I describe something.  Recently, though, one of my lab-mates told me that I should use I, since it is your work, if the thesis were co-written, then it would be a different story.  Is there any standard in your universities, or do you have any preferred practice. Can an integrated HDMI port work both ways? Say I had a laptop [Correction: notebook, don't want my thighs medium rare], any OS, and it has an HDMI port built into the side. Would it be remotely possible to hack it into an input, provided it wasn't already designed for that? I would figure all video ports operate straight off the graphics chip, however, are there ways to override that functionality on the driver level? Driver hacks already exist for plenty of things such as the classic example: Bluetooth adapters (so we can play with our PS3 controllers and save a buck) However, is HDMI one of these tamperable interfaces? As far as the interface standard is concerned, are HDMI ports designed to be either way or are they Input/Output specific? What term describes a non-offensive substitute for a swear word?   For example, Battlestar Galactica used frack instead of fuck. Another example is the use of snap instead of shit.  I think I may have heard a single-word term used to describe such alternate non-offensive words before, but I don’t know what it is. How to recover files after deleted my Ubuntu partition? Consider the  function     $$ r(x) = \mathbb{E}(Y \mid X = x) $$   This has been called the regression function in a textbook I'm using. I'm trying to figure out the relationship between this function and the classical linear regression model.  So, I know that it is a theorem* that we may write  $$ Y = r(X) + \epsilon $$  for some random variable $\epsilon$ s.t. $\mathbb{E}(\epsilon) = 0$.  Now suppose that we have     $$ Y = \beta_0 + \beta_1 X + \epsilon $$   This is the classical 1-dimensional regression function (assuming the $\beta_0$ and $\beta_1$ minimize the residual sum of squares).  Question: Is it then a mathematical theorem that if $Y$ is defined as above, that   $$ r(X) = \mathbb{E}(Y \mid X) = (\beta_0 + \beta_1 X)? $$  And is this why the function $\mathbb{E}(Y \mid X)$ is called the "regression function"?  EDIT: The theorem that I am making use of is as follows (from All of Statistics pg. 89):     Regression models are sometimes written as      $$ Y = r(X) + \epsilon $$      where $\mathbb{E}(\epsilon) = 0$. We can always rewrite a regression model this way. To see this, define $\epsilon = Y - r(X)$ and hence $Y = Y + r(X) - r(X) = r(X) + \epsilon$. Moreover, $\mathbb{E}(\epsilon) = \mathbb{E}\mathbb{E}(\epsilon \mid X) = \mathbb{E}(\mathbb{E}(Y - r(X)) \mid X) = \mathbb{E}(\mathbb{E} ( Y \mid X) - r(X)) = \mathbb{E}(r(X) - r(X)) = 0$. We know $$i^2=-1 $$then why does this happen? $$ i^2 = \sqrt{-1}\times\sqrt{-1} $$ $$ =\sqrt{-1\times-1} $$ $$ =\sqrt{1} $$ $$ = 1 $$  EDIT: I see this has been dealt with before but at least with  I'm not making the fundamental mistake of assuming an incorrect definition of $i^2$. Setting custom UITableViewCells height Sometimes we read books rather quickly and don't give them much (or any) thought, so the action 'reading' does not necessarily imply that we have given enough thoughts to any book we read.   Is there a word that describes reading a book with great care; usually but necessarily slowly over a long period of time. I'm trying to use ARIMA process to predict the behaviour of a time series, the probleme I face is that I can't get the order of each component of ARIMA, the lag is between 0 and 1, same goes for the acf. The time series has no tendency, and I guess no seasonality.     My question is : Does this mean that ARIMA orders are all 0s, and if so, is the HoltWinters a good (or the best) solution for modelling this kind of TS ? Create a book cover with spine, rear page and flaps Up to now I don't understand well what \null actually is and when we need it. I have only known that it can be used to create hypothetical anchors as follows.  \documentclass{article} \usepackage[a6paper,margin=2cm]{geometry} \parindent=0pt  \begin{document} \hfill xport \hfill\null\\ \null\hrulefill{} never \hrulefill\par \hrulefill{} dies. \hrulefill\par \hfill really? \hfill\null\par   \newpage \null \vfill \hfill The End \hfill\null \end{document}    What is \null and when do we need to use it? Why do \hrulefill and \hfill need starting \null when they follow \\ but not need \null when they follow \par? Why does \hfill always need ending \null but \hrulefill not need it? Any smart ideas on finding the area of this shaded region? Ubuntu Server 20.04 Nvidia Driver Dependencies I had a hard time installing Nvidia drivers in a fresh install of Ubuntu 20.04.  Installing via sudo apt install nvidia-driver-430 resulted in a list of 542 packages to install.  I ended up spending a bit of manual effort to get the Nvidia-provided driver installed without nearly so many dependencies (only had to install gcc and make).  Is this massive number of dependencies normal for Ubuntu Server?  I did a very vanilla install without the GUI.  Reddit suggested I ask here, as their opinion is that I should just install from the default repos, but I felt that so many packages was absurd just to install a driver.  Edit for clarity: installing the nvidia-driver-430 package appears to install the entire Gnome shell, which I feel is unnecessary on a server. I installed Ubuntu 12.04 a month ago and am using it till now. I failed to notice that all this time there was no sound at all while running Ubuntu, even while playing a game in Wine. The weird thing is that only the startup sound comes when I log in (Indian/African drum tone), then comes the utter silence.  I tested both Digital Output (S/PDIF) and the speakers in the sound settings but can hear nothing.  Any help?