Resource recommendation for rotational physics
Recommendations for good Newtonian mechanics and kinematics books
In GLM regression I have always been told to set the reference level of categorical/ordinal/dummy variables to the level with the most exposure (level with most data), because this somehow makes the model more stable. Is there any statistical reason behind this, or just historical practice without statistical reason?  I can understand that one wants a "baselevel" (reference level) in the model that are most likely to be correct, but if you are not sure about the other levels, then they surely should not be included in the regression in the first place? Find longest repeating string based on input in perl (using subroutines) A question about causality and Quantum Field Theory from improper Lorentz transformation Related post   In Peskin and Schroeder's QFT p28, the authors tried to show causality is preserved in scalar field theory.  Consider commutator $$ [ \phi(x), \phi(y) ] = D(x-y) - D(y-x) \tag{2.53} $$ where $D(x-y)$ is the two-point correlation function,  $$D(x-y):= \langle 0 | \phi(x) \phi(y) | 0 \rangle  = \int \frac{d^3 p}{ (2\pi)^3} \frac{1}{ 2E_{\mathbf{p}}} e^{-ip(x-y)}\tag{2.50}$$  P&amp;S argued that each term in the right-hand-side of (2.53) is Lorentz invariant, since $$\int \frac{d^3p }{ (2\pi)^3} \frac{1}{2E_{\mathbf{p}}} = \int \frac{ d^4 p }{ (2\pi)^4} (2\pi) \delta(p^2-m^2)|_{p^0&gt;0} \tag{2.40}$$ is Lorentz invariant.  Since there exists a continuous Lorentz transformation in the spacelike interval $(x-y)^2&lt;0 $ such that $(x-y) \rightarrow - (x-y) $ and $D(y-x)=D(x-y)$, (2.53) equals zero in the spacelike interval. In timelike interval, since such continuous Lorentz transformation does not exist, (2.53) is non-zero in general.  My question is, consider a non-continuous Lorentz transmation in the timelike interval, $PT$, namely time reversal times parity transformation. I can also let  $(x-y) \rightarrow - (x-y) $. Why (2.53) in the timelike interval is non-zero?  I guess $PT$ will let (2.40) go to $p^0&lt;0$ branch. But I am not sure if it breaks the Lorentz invariant of (2.40) and (2.50). Find the expansion for $\det(I+\epsilon A)$ where $\epsilon$ is small without using eigenvalue. I am designing gamecards in LaTeX  Everything is going pretty ok so far but when i try to insert the %-sign for a question about percentages my file keeps giving errors.  I tried putting the percentage between dollarsigns because i know just % will make it a 'remark' and that the dollarsign makes it 'mathematical data'.   Whats the reason for the error?   P.s. the error says: file ended while scanning use of \kaart. ...    Codesample:   {\kaart{Bekijk statistiek kaart F:   Schat het percentage mensen dat als lievelingseten spaghetti opgaven, je mag er slechts $ 2% $ langs zitten. } { $ 11% $}} Issue in using longtable within table environment I have an issue making a long list with wrapped text. The table can be several page long. I use longtable and assign the width for each column but as soon as I put it in the \begin{table} \end{table}, it does not work. It clips the table. I want to make a label for the table so I put it in the table environment.  And is there a way to automatically adjust the width so that I don't need to assign the value manually?  Thank you.   Tung  \begin{table} \centering \begin{longtable}{|p{6.5cm}|p{2.5cm}|p{2.5cm}|p{2.5cm}|} \hline Name                                      &amp; Company     &amp;  Catalog Number   &amp;   Comments    \\ \hline Small DNA FRAG Extract Kit-100PR          &amp; VWR         &amp;   97060-558 &amp; \\ \hline Acrylamide 40\% solution 500 mL           &amp; VWR         &amp;   97064-522 &amp;  \\ \hline Bis-acrylamide 2\% (w/v) solution 500 mL  &amp; VWR         &amp;   97063-948 &amp;  \\ \hline GeneRuler 100 bp DNA Ladder, 100-1,000 bp &amp; Fermentas   &amp;   SM0241  &amp;    \\ \hline Mini Vertical PAGE System                 &amp; VWR         &amp;   89032-300  &amp;  \\ \hline \end{longtable} \label{tab:list} \end{table} Proving the sum of two independent Cauchy Random Variables is Cauchy Is there any method to show that the sum of two independent Cauchy random variables is Cauchy? I know that it can be derived using Characteristic Functions, but the point is, I have not yet learnt Characteristic Functions. I do not know anything about Complex Analysis, Residue Theorem, etc.   I would want to prove the statement only using Real Calculus. Feel free to use Double Integrals if you please.   On searching, I found . However, I was wondering if I could get some help directly on the convolution formula:  $$f_Z(z)=\int_{-\infty}^\infty f_X(x)f_Y(z-x)\,dx=\int_{-\infty}^\infty\frac{1}{\pi^2}.\frac{1}{1+x^2}.\frac{1}{1+(z-x)^2}dx\tag{1}$$  Here I have supposed that $X,Y$ are Independent Standard Cauchy. But I think the general formula can be derived easily after some substitutions. I need some help on how to proceed from $(1)$.  EDIT: Just as what the hint in the hyperlink said, I got the answer using that hint. However, I am not quite sure that the hint is algebraically correct. Maybe there has been some typing mistake in the book. Basically, I'm trying to override some files of the Uncode theme. But this is not a theme-specific question: it can be applied to any theme. The Uncode theme has a custom dir 'partials' (/uncode/partials/) that contains some layout elements. On my child theme I created a 'partials' folder as well (my-child-theme/partials), but the inner files seem not to be overridden. Is it normal? WP docs say that any file of the same name should be overridable, but is seems that's not true. Am I doing something wrong? Installing titling.sty onto an offline Windows machine I'm trying to compile a file for which I need titling.sty:  ! LaTeX Error: File `titling.sty` not found.  The two biggest issues are 1) it's on a Windows machine (I'm really only &quot;comfortable&quot; with the Unix command line) and 2) the machine cannot be connected to the internet (so automatic approaches are impossible). Assuming the error means I'm missing a package and following some related advice (e.g., ), I downloaded the file , transferred it to the offline machine, and unzipped it, then tried to run: latex titling.ins  But this gave me an error (given I can't copy-paste, I'm including what I think may be relevant):  ******************************************************** * No Configuration file found, using default settings. * ******************************************************** ! ************************************************** * Could not find your \batchfile=titling.ins. **************************************************. \processbatchFile ...****************************}                                                  \fi \else \ifDefault \Msg ... 1.1092 \process@first@batchfile  I have no idea how to proceed from this. How can I install titling.sty on this machine? What are the highest DC and AC voltages or currents that can be considered as safe? Why isn't an upgrade to 20.04 from 18.04 available yet? I want to use do-release-upgrade to upgrade from 18.04 to 20.04, but I can't do that do-release-upgrade Checking for a new Ubuntu release There is no development version of an LTS available.  It seems that  is used, and it still points to 18.04. Do you know when (or how?) can I upgrade to 20.04? What happened to the Dursleys? As last seen, the Dursleys are forced to move by the ministry of magic, put into protective custody by the ministry. However, the ministry fell only a few weeks later, and there was evidence that it couldn't be trusted, even then. Are they still alive, and if so, how did they survive the purge from the ministry? An inequality from Littlewood's Miscellany How do I get label of the selected item from a lightning:select drop down list? I would like to get the value of the label of the selected drop down item.  In this case, the label is the Name of the Contact.  &lt;aura:component&gt;  &lt;aura:attribute name="contacts" type="Contact[]"/&gt;  &lt;lightning:select label="Contact" aura:id="contactList" name="contactList"&gt;     &lt;aura:iteration items="{!v.contacts}" var="c" indexVar="index"&gt;        &lt;option value="{!c.Id}"&gt;{!c.Name}&lt;/option&gt;    &lt;/aura:iteration&gt;  &lt;/lightning:select&gt;  &lt;/aura:component&gt;   I know how to get the value:  component.find("contactList").get("v.value");   But how do I get the label? Capitalize fields of study? Do I say "I study computer science," or "I study Computer Science"? Similarly, "I really liked that computer science course," vs. "I really liked that Computer Science course." How to add sysadmin to user in SQL Server 2008 when no sysadmin accounts exist I have a SQL server 2008 instance running. Unfortunately during testing I deselected the sysadmin rights for my login and now can't readd it (because I don't have sysadmin rights).  There are no other sysadmin accounts for the instance except SA.  I was set up for just Windows Authentication so I hacked the LoginMode in the registry to 2 so I could login as SA using Sql Authentication. This does indeed set the login mode to Mixed, however the SA user is disabled by default and I can't reenable it because I am don't have sysadmin rights.  How do I enable the SA login so I can get in and reassign the sysadmin to my normal account? Is there a registry setting for this too or is it stored in the master database? Annoying flickering in 16.04 LTS - Chrome I've upgraded from 4.4.0 to 4.4.8 and then 4.5.2 on Ubuntu 16.04 LTS 64-bit, and it's still happening.   At 4.5.2 it's even more frequent, and mainly in Chrome (haven't tried firefox or opera just yet). Every time I open a new web page. Any way to fix that, or is it a bug?  00:02.0 VGA compatible controller: Intel Corporation HD Graphics 5500 (rev 09) 04:00.0 Display controller: Advanced Micro Devices, Inc. [AMD/ATI] Venus XTX [Radeon HD 8890M / R9 M275X/M375X] (rev 81)   Cheers. One page website - Effect on SEO I'm considering re-designing my personal website to promote my web services in my local area.  My issue is whether to do a one page website with a scroll-to navigation system. What effect does this have on SEO. As i understand it, you set stuff like h1's and meta description on specific page content. How does this work when all of your different content is on one page? Is there a rule for pronouncing “th” at the beginning of a word? How do I backup a LVM partition to an image for recovery purposes?  I am trying to run dd on /dev/sda2, but it crashes after ca 8 hours, at around 380G   sudo lvmdiskscan   /dev/centos/swap [       3.89 GiB]    /dev/sda1        [     500.00 MiB]    /dev/centos/root [      50.00 GiB]    /dev/sda2        [     465.27 GiB] LVM physical volume   /dev/centos/home [     411.38 GiB]    /dev/sdb1        [     931.51 GiB]    3 disks   2 partitions   0 LVM physical volume whole disks   1 LVM physical volume   Anyway, could running from a stick make any difference?