I tried $\min_{x \in \mathbb{R}^m, \\ y \in \mathbb{R}^n}$ but \\ doesn't create a line-break in this setting
I have the following equation, where there is a lot of stuff under the sum symbol:  \begin{equation} d(\vec{x},\vec{y})=   \sum_{Z_{xy}\in\vec{Z}_{xy},\forall x\in\vec{x},\forall y\in\vec{y}}      f(Z_{xy}) \end{equation}   In the resulting document, I find it kind of hard to read. Is there a way to write the equation to make the result more readable, e.g. putting the stuff under the sum symbol on different lines?
Extracting embedded images from a PDF Before I started using Ubuntu I used Nitro PDF reader to automatically extract images from PDF files. Is there a PDF reader for Linux that does this?  I would like to be able to extract images faster/easier than when taking a snapshot. The following code should find the appropriate project tag and remove it from the XmlDocument, however when I test it, it says:  The node to be removed is not a child of this node.  Does anyone know the proper way to do this?  public void DeleteProject (string projectName) {     string ccConfigPath = ConfigurationManager.AppSettings["ConfigPath"];      XmlDocument configDoc = new XmlDocument();      configDoc.Load(ccConfigPath);      XmlNodeList projectNodes = configDoc.GetElementsByTagName("project");      for (int i = 0; i &lt; projectNodes.Count; i++)     {         if (projectNodes[i].Attributes["name"] != null)         {             if (projectName == projectNodes[i].Attributes["name"].InnerText)             {                                                                 configDoc.RemoveChild(projectNodes[i]);                 configDoc.Save(ccConfigPath);             }         }     } }   UPDATE  Fixed. I did two things:  XmlNode project = configDoc.SelectSingleNode("//project[@name='" + projectName + "']");   Replaced the For loop with an XPath query, which wasn't for fixing it, just because it was a better approach.  The actual fix was:  project.ParentNode.RemoveChild(project);   Thanks Pat and Chuck for this suggestion. Do these define metrics on $\mathbb{R}$? Generators and relations for $\text{PSL}(2, \mathbb{F}_q)$ Is there a nice presentation for the group $\text{PSL}(2,\mathbb{F}_q)$, for every prime $q$?  (I don't have any particular definition in mind for "nice", other than, say, a small number of generators and relations.) Is it grammatical to omit the subject from "I did my work"? According to , weight decay (regularization) is not usually applied to the bias terms b why?  What is significance (intuition) behind it? Closing Reject Suggested Edit dialogue freezes review process If you go to review a suggested edit and close the Reject dialogue box, the button at the top-right will continue to say "Rejecting...". You will not be able to continue with the review process.  I have refreshed the page, and tried clearing my cache. If I refresh the page, I can continue reviewing the edit.  I'm using Chrome Version 31.0.1650.57 m. A man condemned to serve his sentence in other times I have an element that already has a class: &lt;div class=&quot;someclass&quot;&gt;     &lt;img ... id=&quot;image1&quot; name=&quot;image1&quot; /&gt; &lt;/div&gt;  Now, I want to create a JavaScript function that will add a class to the div (not replace, but add). How can I do that? If $(A-2I)^3(A+2I)^2=0$, then what are the possible Jordan canonical forms of $A$? Here is the exercise:     Let $A$ be a $5\times5$ complex matrix such that $(A-2)^3(A+2)^2=0$, where we define $A-\mu:=A-\mu I$ for scalar $\mu$. Assume that $\lambda=2$ is an eigenvalue of $A$ and its geometric multiplicity is at least $2$. What are the possibilities for the Jordan canonical form (JCF)?   What I know so far from the assumption is that    the minimal polynomial of $A$ is of the form $f(x)=(x-2)^i(x+2)^j$ where $1\leq i\leq 3$ and $0\leq j\leq 2$.  The number of blocks in the Jordan segment $J(2)$ is at least $2$.    One can write the possible minimal polynomial one by one, which gives the information of the size of the largest block in each Jordan segment, and use the possible geometric multiplicity of $\lambda=2$ to find JCF.   Here are my questions:   Is there an alternative approach?  Can we use the characteristic polynomial of $A$ here? Sum of the alternating harmonic series $\sum_{k=1}^{\infty}\frac{(-1)^{k+1}}{k} = \frac{1}{1} - \frac{1}{2} + \cdots $ Given a real, skew-symmetric matrix $\mathbf{A}\in\mathbb{R}^{m\times m}$, and a nonzero vector $X\in\mathbb{R}^{m}$, classify the scalar $\lambda$ (real, complex, imaginary, etc.) in the eigenvalue equation $$ \mathbf{A}X = \lambda X $$  The matrix $\mathbf{A}$ is skew symmetric if $\mathbf{A}^{T}=-\mathbf{A}$.  My try : I am new to matrices , so can not get a idea how to deal with it , Any hint will help Given: $\operatorname{gcf}(x,36)=9$ and $\operatorname{lcm}(x,36)=108$. Find $x$.   p.s I tried $54$ but although the $\operatorname{lcm}$ of $54$ and $36$ is $108$ the GCF is $18$ and it has to be $9$. Help me please. I remember (vaguely) reading somewhere that it is wrong to use the present perfect when the subject of a sentence is someone who is long dead:     *Einstein has visited the Philippines.   My question is, What if the dead person is not the subject but an object:     Leo is the best president our country has/had ever had. (The ones who   succeeded him were inferior, even our current president.)   Which tense is proper here Entire function and the series of its successive derivatives I recently came across the result that if $g$ is holomorphic in a neighbourhood of a point $z_0$ and  $$\sum_{n=0}^{\infty }{g^{(n)}(z_0)} $$ converges then $g $ is an entire function. Now, my doubt is if the above series is absolutely convergent then can we say something more about $g$, like say $g$ is a polynomial? I could not find any non-polynomial  entire function( I tried with functions like $e^z$, $\sin z $, et al), whose successive derivatives converge absolutely as series. Any help please? Chrome S3 Cloudfront: No 'Access-Control-Allow-Origin' header on initial XHR request I recently traveled from India to USA. I am on H1B. I entered USA on 29th December 2016. As my Visa extension is due in August 2017, I was gathering documents for Visa Extension. It was required to provide a scanned copy of passport page with all entry and exit stamps.  Myself and my wife both travelled back from India. My wife's passport has a entry stamp with date as 29th December 2016. But the same is missing from my passport. I guess the officer missed putting the entry stamp on my passport. My I 94 reflects the correct date of entry as 29th December. Somehow I still have my boarding pass from this trip (usually I throw them once trip is complete).   Want to know what could be implications of missing entry stamp when I travel to India next time (somewhere towards early next year)? Does this impact my H1B Visa extension ? Also what can I do to correct this information on my passport? Profile avatar lost on several sites after profile edit (Gravatar replaced with Identicon) I have had the same network-wide profile avatar for many years; it's a custom image which I installed nework-wide soon after I registered for Stack Overflow back in 2011. I still see that image e.g. on  and  but not, for instance, on this site, or e.g. on   (The example originally linked to my Unix &amp; Linux profile instead of Super User but I experimentally changed my profile back to the gravatar one there.)  I routinely update my profile presentation text every few months, and did so again a few days ago. Comments below seem to indicate that others who recently edited their profile are experiencing the same problem.  My preferred avatar is a Gravatar which is connected to my email address, which has always been the same (MD5 091f411d57db5be8298e057a32e5ad72). The replacement seems to be a generic identicon with a different MD5. I don't recall seeing this identicon as an option in my profile before:    You'll notice that the gravatar is still visible as an option, but I can find no way to replace it on all sites in one go. I switched back to the gravatar one on Unix &amp; Linux and noticed that the help next to the "Save" button says     Your profile will be updated on all public communities.   but alas, that did not in fact happen. Do I really have to go over 170+ member sites and manually select my gravatar on each? Easy way to write contents of a Java InputStream to an OutputStream How are one-time pads distributed? It seems that OTP encryption is unbreakable. I have read some articles (Wikipedia, Blogpost, etc.), but I could not find any information about how they are used.  If I wanted to create a messenger service, how would I distribute the OTP keys? Both the sender and the receiver need this key before the message is sent, right?   And how do I make sure no one else gets these keys?