What is the meaning of $d$? Is is Delta? If it is Delta, why is it then not $\Delta$? I am still confused with that. Can someone help explain it to me?
I have read the thread regarding , but it does not answer my question.  I am confused about the notation for change in Physics. In Mathematics, $\delta$ and $\Delta$ essentially refer to the same thing, i.e., change. This means that $\Delta x = x_1 - x_2 = \delta x$. The difference between $\delta$ and $d$ is also clear and distinct in differential calculus. We know that $\frac{dy}{dx}$ is always an operator and not a fraction, whereas $\frac{\delta y}{\delta x}$ is an infinitesimal change.   In Physics, however, the distinction is not as clear. Can anyone offer a clearer picture?
Cardinality of separable metric spaces Are we inside a black hole? Button that triggers modal Citing a range of papers using numeric keys as in \cite{a, b, c} -> [1-3] What is the ideal data type to use when storing latitude / longitude in a MySQL database? Bearing in mind that I'll be performing calculations on lat / long pairs, what datatype is best suited for use with a MySQL database? A standard proof for press needs crop marks and color bars as below    With the package crop, the crop marks can be easily added.  But how about the color bar ?  Is there a way or a package to make it ?  An example is   \documentclass[b5paper,10pt]{article} \usepackage[utf8]{inputenc} \usepackage[cross,a4,center,info,axes]{crop}  \title{Test} \author{User} \begin{document} \maketitle \section{Fox} The quick brown fox jumps over a lazy dog. \end{document} Find the set of $x>0$ such that the series $\sum\limits_n x^{\ln{n}}$ converges If $x&gt;0$, find the set of all values of $x$ such that series is convergent$$\sum_{n=1}^{\infty} x^{\ln{n}}$$   My attempt:- I used Ratio test for finding the set of all values of $x$ such that series is convergent.   $$\lim_{x\to\infty}\frac{x^{\ln{n+1}}}{x^{\ln{n}}}$$  $$=\lim_{x\to\infty}x^{\ln\frac{n+1}{n}}$$ This quantity must be less than one for getting a convergent series, I am not able to judge. Can you please help me to find the interval of convergence? We are working on a service that is quite new and unknown to people. It's is oriented on small business. The target audience is divided into 3 specific different groups. As for now, we have one landing page, which communicates to 3 groups.   We have very low conversion mainly because people don't understand how they can use the service and benefit from it.  So, we decided to change the logic:  There will be one entrance page, where user will have to choose his group (1 of 3) and then he will be forwarded to the page of the group he chose before, where all the explanations how to use the service are provided.  So instead of one page we will have four pages. Will it improve the communication with users and are there any suggestions how to deal with 3 different target audiences? Probability of first actor winning a "first to roll seven with two dice" contest? Two players P and Q take turns, in which they each roll two fair and independent dice. P rolls the dice first.  The first player who gets a sum of seven wins the game. What is the probability that player P wins the game? How does the Doctor know how old he is? I've often wondered, how does the Doctor know how old he is? He not only travels through time, but also through space, and visits planets where days can be shorter or longer than 24 hours. How does he 'keep score'?  Also, does he count his age in Earth years or Gallifrey years? They might be completely different in length. Everytime I sudo apt-get update it always not complete and will say in the end  E: Read error - read (5: Input/output error) E: The package lists or status file could not be parsed or opened.   Same goes, when I try to install something and do sudo apt-get install &lt;some app&gt;  What should I do ? I admit, that my drive has bad sectors, could that be the reason? Is there anything else I can do? Solving the matrix equation $AP=PB$, where $A$ and $B$ are similar Currently I'm stuck with this problem:     The following matrices are similar to each other.      $$A=\begin{bmatrix}-3&amp;0\\8&amp;4\end{bmatrix},\qquad B=\begin{bmatrix}-4&amp;4\\-2&amp;5\end{bmatrix},\qquad C=\begin{bmatrix}k&amp;1\\m&amp;-2\end{bmatrix}.$$      How do you find the matrix $P$ such that $AP = PB$?       And how can you calculate the values of $k$ and $m$?      Thank you in advance. What does an icon on the tag mean, for example the "rg" before the sql-server tag as pictured below? Can you supply arguments to the map(&:method) syntax in Ruby? Colored borders around windows after update split file lines based on first field How do I alter a message in the message queue independent of site language? I want to programatically alter a message in the message queue. The message I want to alter is set in the message queue by function comment_form_submit() in comment.module, i.e.:  if ($comment-&gt;status == COMMENT_NOT_PUBLISHED) {   if (!user_access('administer comments')) {     drupal_set_message(t('Your comment has been queued for review by site administrators and will be published after approval.'));   } }   Instead of this, I want the call to drupal_set_message() to be this:  drupal_set_message(t('Your comment will be published when you validate your e-mail address.'));   How do I do this?  Postscript: Based on the answer below by Topsitemakers, I got this working for any language by using array_search() inside a custom MYMODULE_comment_submit to search the message array, and then compare the translated strings to identify the key of the string to alter.  This is the working code I ended up with:  $mm = drupal_get_messages('status', TRUE); $key = array_search(t('Your comment has been queued for review by site administrators and will be published after approval.'), $mm['status']); if (FALSE !== $key) {   $mm['status'][$key] = t('Your comment will be published when you validate your e-mail address.'); } foreach ($mm['status'] as $msg) {   drupal_set_message($msg, 'status'); } Several times now I have inadvertently lost the .tex file that generated a PDF file with pdflatex. Given what I know of the internal structure of PDF files, it should be possible to embed a text file containing the original LaTeX file into the PDF file so that it can be extracted later.   I am aware of no technology for doing this, but perhaps you are. Does anybody have something like this? How do you return to the default view (the one you see when blender starts)? I need to repair my Windows 10 installation. Where can I get a clean ISO (with install.wim, no Install.ESD, so that I can run DISM against the WIM) of the specific Windows 10 build required for this?  In my case, I need the Anniversary update (Build 14393), Creators Update (Build 15063) or Fall Creators Update (Build 16299.15).