Are large $p$ and $q$ values for ARMA models bad? I've been learning about ARMA models in my time series course and noticed that for most ARMA($p,q$) models, $p$ and $q$ never really get larger than 3 or so. Is there a reason why models don't normally have larger values?  Thanks!
Why does default auto.arima stop at (5,2,5)? The function auto.arima in the forecast package of R is a powerful tool to identify the best ARIMA(p,d,q) model for a given data series. In the   of the function, they report the following:  auto.arima(y, d=NA, max.p=5, max.q=5, max.order=5, max.d=2, start.p=2, start.q=2, ...)   According to the above function it seems that, by default, auto.arima tries to find the best model among all the combination having:   p equal or lower than 5 q equal or lower than 5 d equal or lower than 2 order equal or lower to 5, i.e. p + q + d  ≤ 5.   However, why does the default code stops at these conditions? Is there any particular reason why p, q and d should be equal or lower than 5, 5 and 2 and their sum lower than 5?
How to install the previous version of a .deb package and pin it? I am trying to install the latest version of subversion on Sid, and because it has a bug I receive a warning and I abort the installation. How do I get to locate the previous version version, install it and pin until the bug is resolved?  root@server01:~# apt-get install subversion   Reading package lists... Done                                                                                                                                                                                  Building dependency tree                                                                                                                                                                                       Reading state information... Done                                                                                                                                                                              Suggested packages:                                                                                                                                                                                              db5.3-util subversion-tools                                                                                                                                                                                  The following NEW packages will be installed:                                                                                                                                                                    subversion                                                                                                                                                                                                   0 upgraded, 1 newly installed, 0 to remove and 205 not upgraded.                                                                                                                                               Need to get 0 B/981 kB of archives.                                                                                                                                                                            After this operation, 4,844 kB of additional disk space will be used.                                                                                                                                          Retrieving bug reports... Done                                                                                                                                                                                 Parsing Found/Fixed information... Done                                                                                                                                                                        critical bugs of subversion (-&gt; 1.9.2-2) &lt;Outstanding&gt;                                                                                                                                                          b1 - #803725 - subversion: dump-load of a repository modifies verbose log output: M line lost serious bugs of subversion (-&gt; 1.9.2-2) &lt;Outstanding&gt;  b2 - #803589 - FTBFS with ruby2.2 (only) Summary:  subversion(2 bugs) Are you sure you want to install/upgrade the above packages? [Y/n/?/...] n ********************************************************************** ****** Exiting with an error in order to stop the installation. ****** ********************************************************************** E: Sub-process /usr/sbin/apt-listbugs apt returned an error code (10) E: Failure running script /usr/sbin/apt-listbugs apt I've always wondered about this and never found a good solution.  But  reminded me of it.  When I have a URL on my website it can be displayed and accessed any of the following ways:  http://www.somesite.com/subdirectory http://www.somesite.com/subdirectory/ http://www.somesite.com/subdirectory/index.htm http://www.somesite.com/subdirectory/index.html http://www.somesite.com/subdirectory/index.php http://www.somesite.com/subdirectory/index.asp http://www.somesite.com/subdirectory/some-relevant-keywords http://www.somesite.com/subdirectory/some-relevant-keywords.htm http://www.somesite.com/subdirectory/index.php?page=some-relevant-keywords http://www.somesite.com/subdirectory/?page=some-relevant-keywords http://www.somesite.com/subdirectory/?page=some-relevant-keywords&amp;even=more-keywords   etc...   Now, I can understand the merits of adding keywords in the URL. Even the most basic SEO guide will mention to do just that. ... but for the sake of sanity, clarity, ease of reading, ease of use, and so on, including web compliance ...  Is it preferred to have a file-extension or not?  Really, deep down my logic tells me: yes, it should. The reason being is this stems back to the days of the past when the internet was mostly USENET, FIDONET, FTP and GOPHER.   See, if a URL has no filename, then it normally is considered a directory. This is where index.htm came about, because this by default lists the directory if no index file is found. However, soon enough, web programmers started overriding this and using index.htm to actually serve the content of that web directory as a page. The main difference, was markup language was added in, and this was parsed in the browser. With this markup language, the Content-Type:text/html; tag in the response header became the indicator to what filetype it was for any file. HTML seems to be the only "filetype" that just doesn't have consistently named extensions, except for when they are saved.  Unfortunately, once web pages became the main thing, it became a security error to actually display the directory contents, so everything stayed hidden with only the actual URL content being displayed.   Not to mention the cross-platform file-naming wars.. windows based require a 3 or less digit extension, and unix/mac can have more. So should it be .HTM or .HTML or NONE and let the platform decide?  So in essence, I guess what I am trying to figure out is beyond SEO and dealing more with aesthetics and web compliance. Proving that a list of perfect square numbers is complete Well, I have a number  $n$ that is given by:  $$n=1+12x^2\left(1+x\right)\tag1$$  I want to find $x\in\mathbb{Z}$ such that $n$ is a perfect square.  I found the following solutions:  $$\left(x,n\right)=\left\{\left(-1,1^2\right),\left(0,1^2\right),\left(1,5^2\right),\left(4,31^2\right),\left(6,55^2\right)\right\}\tag2$$     Is there a way to prove that this a complete set of solutions? So I mean that the solutions given in formula $(2)$ are the only ones?     My work:   We know that: $$ 1 + 12x^2 \left(1+x \right) \ge 0   \space \Longleftrightarrow \space   x \ge -\frac{1+2^{-2/3}+2^{2/3}}{3}   \approx -1.07245 \tag3 $$ So we know that for $x&lt;-1$ there are definitely no solutions. My trackpad is broken so I can tap-to-click but i cannot drag and drop. This is really a problem when it comes to doing certain things.   Does anyone know how to program a sticky key to turn a click into a click-select that can then be dragged about?   I can't resize my browser or open window and I can't drag applications into the folder when installing etc.  free solutions only please.  A mid 2009 macbook-pro 13". 2.53 Ghz Intel Core 2 Due.   Running os lion (grudgingly). The product of a normal and Rademacher variables, independent from each other Let $X\sim N(0,1)$ and let $Z$ be a random variable independent of $X$ such that:  \begin{equation} \Pr(Z=z) = \begin{cases} \frac{1}{2} &amp; \mbox{if $z = -1$ or $z=1$}, \\ \\ 0 &amp; \mbox{otherwise}. \end{cases} \end{equation}   Define $Y = ZX$. Show that $Y \sim N(0,1)$. Determine $\operatorname{Cor}(X,Y)$. Are $X$ and $Y$ independent?   Progress:  I'm basically stuck at the beginning. I got as far as $P(ZX &lt; y) = P(Z &lt; y/X)$, which I'm not even sure is correct. I'm also not clear on what it means by defining $Y = ZX$ - does it mean I need to state the probability density function or something? And how do I show that $Y \sim N(0,1)$? Checking for a file and whether it is readable and writable I'm trying to write a script that will look for a certain .txt file saved to my desktop.  I want the script to be able to check if this file exists and then check to see if it is readable and writable.  Any hints? When playing with the complete elliptic integral of the first kind and its Fourier-Legendre expansion, I discovered that a consequence of $\sum_{n\geq 0}\binom{2n}{n}^2\frac{1}{16^n(4n+1)}=\frac{1}{16\pi^2}\,\Gamma\left(\frac{1}{4}\right)^4 $ is:     $$\int_{0}^{1}\frac{\arctan x}{\sqrt{x(1-x^2)}}\,dx = \tfrac{1}{32}\sqrt{2\pi}\,\Gamma\left(\tfrac{1}{4}\right)^2\tag{A}$$   which might be regarded as a sort of Ahmed's integral under steroids.  I already have a proof of this statement (through Fourier-Legendre expansions), but I would be happy to see a more direct and elementary proof of it, also because it might have some consequences about the moments of $K(x)$ of the form $\int_{0}^{1}K(x)\,x^{m\pm 1/4}\,dx$, which are associated with peculiar hypergeometric functions. Use induction to prove a product of sums of squares is a sum of squares In CSS what is the difference between "." and "#" when declaring a set of styles? What is the difference between # and . when declaring a set of styles for an element and what are the semantics that come into play when deciding which one to use? So I have an SQL dump file that needs to be loaded using mysql_query(). Unfortunately, it's not possible to execute multiple queries with it.  -> It cannot be assumed that the mysql command-line client (mysql --help) is installed -- for loading the SQL file directly  -> It cannot be assumed that the mysqli extension is installed  /* contents of dump.sql, including comments */ DELETE FROM t3 WHERE body = 'some text; with semicolons; scattered; throughout'; DELETE FROM t2 WHERE name = 'hello'; DELETE FROM t1 WHERE id = 1;   The explode() below won't work because some of the dump content's values contain semicolons.  $sql = explode(';', file_get_contents('dump.sql')); foreach ($sql as $key =&gt; $val) {     mysql_query($val); }   What's the best way to load the SQL without modifying the dump file? Block network access of a process? I read a comment under :     There are plenty of events that can occur that have zero probability.   This reminds me that I have seen similar saying before elsewhere, and have never been able to make sense out of it. So I was wondering    if zero probability and impossibility mean the same? if an event with zero probability doesn't mean that the event is impossible to occur, how probability theory represents/describes impossibility?   Thanks and regards! Installing Broadcom Wireless Drivers Is it a good practice to refer to countries, ships etc using the feminine form? While talking about ships and countries, is it a good practice to use the feminine form?  For example:  "Her economy" - while referring to a country's economy "Her flag (or deck etc)" - while referring to a ship  Is this practice common? Is it used today? 9 rows is just way too small by default. Is this a text-editor for ants? What is the different between an Normal user account and the Admin account in Ubuntu?  You must always enter your password if you want do something. Can you give a Normal account  "limitations" to do not install or remove anything or to not open any program? Can you also "hide/deactive" the terminal and console for a normal user? Are fractions with prime numerator and denominator dense? Legendre symbol: Showing that $\sum_{m=0}^{p-1} \left(\frac{am+b}{p}\right)=0$ I have a question about Legendre symbol.  Let $a$, $b$ be integers. Let $p$ be a prime not dividing $a$. Show that the Legendre symbol verifies: $$\sum_{m=0}^{p-1} \left(\frac{am+b}{p}\right)=0.$$  I know that $\displaystyle\sum_{m=0}^{p-1} \left(\frac{m}{p}\right)=0$, but how do I connect this with the previous formula?  Any help is appreciated. I have heard from people who have switched either way and who swear by the one or the other.  Being a huge Eclipse fan but having not had the time to try out IntelliJ, I am interested in hearing from IntelliJ users who are "ex-Eclipsians" some specific things that you can do with IntelliJ that you can not do with Eclipse.  Note: This is not a subjective question nor at all meant to turn into an IDE holy war. Please downvote any flamebait answers. How to load image to android and resize