Who can change a file permission or ownership in ubuntu?
How do file permissions work?
What's wrong if I fit the auto-regression with OLS? I am doing auto-regress by usual linear regression package. e.g.  $y_t=φx+ε_t$ with $x =y_{t-1}$  My reason is that, Auto-regression does assumes iid errors, same for linear regression. Linear Regression doesn't have assumption on independent variables. What's different is merely that the independent variables is replaced with lagged dependent variable y.  But I see AR always is fitted by specific methods, I am afraid I'm doing wrong. How to make itemize/enumerate/description environment robust to missing \item elements? Is there any way to make LaTeX tolerate empty itemize/enumerate (i.e. no \item)?  Specifically, I would welcome any package/elegant hack that would gracefully "cancel" a list if no elements are found (instead of firing up a Latex Error).  Before jumping to the obvious answer (which I expect would be something along the lines of "don't use itemize if you don't have items to put in" ;)) please consider my use-case:   I want to format remotely stored elements (say, bibliographic items), which I can only access as an XML file.  &lt;elems&gt;   &lt;bibelem&gt;&lt;title&gt;Cool result 1&lt;/title&gt;&lt;author&gt;joe&lt;/author&gt;&lt;/bibelem&gt;   &lt;bibelem&gt;&lt;title&gt;Cool result 2&lt;/title&gt;&lt;author&gt;jim&lt;/author&gt;&lt;/bibelem&gt; &lt;/elems&gt;  I have a python script that downloads/parses the XML and outputs its content in a file bib.tex as a list of Latex macros-decorated data  \BibElem{Cool result 1}{joe} \BibElem{Cool result 2}{jim}  Now, I want to grant the end-user complete control over the styling of her/his produced document, so the intended usage within Latex is something like  \documentclass{article} \begin{document}   \newcommand{\BibElem}[2]{\item {\em #1} by {#2}}   \begin{itemize}     \input{bib.tex}   \end{itemize} \end{document}    The rationale behind this design choice is that the user should be restricted as little as possible in her/his styling choices. For instance, the user may either want to display the bibelems within a list as shown in the example, or may prefer a fancy-formatted tabular. On the other hand, the user should design the latex document once, and should be able to run it regardless of the amount of data produced by the source.  Therefore, the python script cannot make any assumption regarding the context in which its latex product will be included, and it should be up to the user to deal with empty bibliographies, i.e. with empty lists. How could one possibly do that?  Update: Werner proposed a nice solution that redefines the list environment to make Latex oblivious of the fact he is currently in a list. However, this only seems to work if the empty list is the last list in the document, as revealed by the following mwa:    \documentclass{article} \makeatletter \newenvironment{myitemize}   {\itemize}   {\@newlistfalse\enditemize} \makeatother \begin{document}   % Empty Itemize   \begin{myitemize}   \end{myitemize}   % Next non-nested itemize environment (can be itemize/enumerate/description)    \begin{myitemize}     \item Arghh!   \end{myitemize} \end{document} Is there any function that converts an escaped Url string to its unescaped form? System.Web.HttpUtility.UrlDecode() can do that job but I don't want to add a reference to System.Web.dll. Since my app is not a web application, I don't want to add a dependency for only using a function in an assembly.  UPDATE: Check  about the same issue. What is serial voting and how does it affect me? I just noticed that I lost a bunch of points from my reputation score, and I used the "reputation" tab on my user profile page to try and track down the cause.  During my investigation, I noticed there was an unusual event of type "reversal". In the normal place of a question title, it says "voting corrected".     What does this mean, and what caused it?  Did I do something wrong? Why did I lose all of that reputation? Is the system punishing me for leaving too many good answers?  Is there any way to earn it back? How can I prevent spam on sites which I control? This is a general, community wiki question to address all non-specific spam prevention questions.  If your question was closed as a duplicate of this question and you feel that the information provided here does not provide a sufficient answer, please open a discussion on .    For purposes of this question, spam will include:   Any automated post Manually-posted content which includes links to spammers' sites Manually-posted content which includes instructions to visit a spammer's site byte[] to hex string How do I convert a byte[] to a string? Every time I attempt it, I get      System.Byte[]    instead of the value.  Also, how do I get the value in Hex instead of a decimal? Given that $x^y=y^x$, what could $x$ and $y$ be? It's not too difficult to figure out that $x$ and $y$ can both be 1, and also $x$ can be 2 and $y$ can be 4 (and vice versa). But I can't rule out if there are other solutions. Does it have anything to do with inverse functions? Is there a way to see the solutions by graphing, or algebraically? Not sure if someone else has already raised this - I've got eleven notifications that I've received a Caucus badge on English Language Learners. Perhaps one notification for each community that I'm a member of?  I am a member of the community, and did visit the election. Also, the badge hasn't been awarded more that once (so I think it's just the notification that's at fault).  Note that this seems to happen for other badges, it has been reported for: Caucus, Nice Answer, Enthusiast. Connection between rank and matrix product I have a problem understanding the following:     Let $A$ be an $m \times n$ matrix and let t $\in \mathbb{N}$. Prove that   $\operatorname{rank}(A)\leq t$ if and only if there exists an $m \times t$ matrix $B$ and a $t \times n$ matrix $C$ so that $A = BC$.   I know what a rank is but I can't make a connection between the rank and the existence of two matrices such that $A = BC$. sed : Ignore line starting whitespace for match Fancy chapter headings What happens to the second Marty at the end of Back to the Future? In  (the original movie), Marty comes back from 1955 10 mins early to prevent Doc from being shot (which he fails at). He then rolls up to the Lone Pine Mall and sees himself hit 88 mph and shoot back to 1955 (again). Marty then carries on with this life as usual. What happens to the Marty that goes back to 1955 at the end of the film?  This obviously is a recursive problem where it would create another timeline and Marty would keep coming back 10 mins early to view another Marty zip back to 1955? Why does the sizeof operator return a size larger for a structure than the total sizes of the structure's members? Saudi Arabia Transit Visa I am travelling to Rome along with five other members (all in a family) from Bengaluru via Jeddah. My layover in Jeddah is 13.5 hours before i catch a connecting Flight to Rome. I won't be moving out of airport in Jeddah. Do I still need a Transit visa in Saudi Arabia. Difference between 2 numbers I need the perfect algorithm or C# function to calculate the difference (distance) between 2 decimal numbers.  For example the difference between: 100 and 25 is 75 100 and -25 is 125 -100 and -115 is 15 -500 and 100 is 600  Is there a C# function or a very elegant algorithm to calculate this or I have to go and handle every case separately with ifs.  If there is such a function or algorithm, which one is it? SQL Server Escape an Underscore How do I escape the underscore character?  I am writing something like the following where clause and want to be able to find actual entries with _d at the end.  Where Username Like '%_d' Control custom properties How can I add remove and create a callback/event for a custom property using bpy. I have a scene, called scene, and I want to add a custom property named x, defulat value 2 (as intereger), and a callback foo, to run when it is changed. I also need to be able to read the value from it, and delete it. How do I do this? I wonder if there is any difference between mapping and a function. Somebody told me that the only difference is that mapping can be from any set to any set, but function must be from $\mathbb R$ to $\mathbb R$. But I am not ok with this answer. I need a simple way to explain the differences between mapping and function to a lay man together with some illustration (if possible).  Thanks for any help. How to find $ f(x)$ if $f(1-f(x))=x$ for all $x$ $\in \mathbb{R}$ How can I determine $ f(x)$ if $f(1-f(x))=x$ for all real $x$?  I have already recognized one problem caused from this: it  follows that $ f(f(x))=1-x $, which is discontinuous. So how can I construct a function $f(x)$?  Best regards and thanks, John In convex optimization, the feasible region is convex if equality constraints $h(x)$ are linear or affine, and inequality constraints $g(x) \leq 0$ are convex. Does this mean that if $h(x)$ is nonlinear, then the optimization problem is non-convex? Is there any special case where $h(x)$ is nonlinear and the feasible region is still convex?