Used apt-get to install chromium but how to start it?
Where are my installed applications?
Greatest common divisor of two positive integers I know that Greatest common divisor of two positive integers $a$ and $b$ is the largest positive integer that divides both $a$ and $b$, but how can I use that to prove that $\gcd(a, b) = \gcd(a, b-a)$. I almost always want the profile correct applied, but it's an extra step. Any ideas on how to apply these automatically? Best way to list files in Java, sorted by Date Modified? I want to get a list of files in a directory, but I want to sort it such that the oldest files are first.  My solution was to call File.listFiles and just resort the list based on File.lastModified, but I was wondering if there was a better way.  Edit: My current solution, as suggested, is to use an anonymous Comparator:  File[] files = directory.listFiles();  Arrays.sort(files, new Comparator&lt;File&gt;(){     public int compare(File f1, File f2)     {         return Long.valueOf(f1.lastModified()).compareTo(f2.lastModified());     } }); Looking for a function $f$ that is $n$-differentiable, but $f^{(n)}$ is not continuous I am looking for a real valued function of real variable that is $n$-differentiable, but whose $n$th derivative is not continuous.  This is my function:  $f_n(x) = x^{n+1} \cdot \sin{\frac{1}{x}}$, if $x \neq 0$ and 0, if $x=0$. $n\in \{0,1,2,\ldots\}$ For example, if $n=0$, $f_0$ it's continuous and non diferentiable in $0$. Update from 14.04 to 16.04 failed with GPG error Chain-calling parent initialisers in python How to install software or upgrade from an old unsupported release? Recently I have installed an older version of Ubuntu on my old machine. Whenever I try to install any software, I get an error saying it couldn't be found:  $ sudo apt-get install vlc Reading package lists... Done                Building dependency tree        Reading state information... Done     E: Couldn't find package vlc Let $V$ be spherically symmetric and $W$ i.i.d. Gaussian. Then $E[V|V+W=t]=g(\|t\|)$ A random vector $V \in \mathbb{R}^n$ is said to be spherically symmetric. If for every orthogonal matrix  $A$   the distribution of $AV$ is the same as the distribution of $V$.   My question: Let $W$ be  i.i.d. zero mean Gaussian random variable.     Can we show that  for a spherically symmetric $V$ the conditional expectation  \begin{align} E[V|V+W=t]=   g(\|t\|).  \end{align}  That is the conditional expectation is only a function of the magnitude.   My attempt:  \begin{align} E[V|V+W=t]= \int  V  \frac{f_W(t-v)}{f_{V+W}(t)} dP_V(v)= \frac{\int  v  f_W(t-v) dP_V(v)}{f_{V+W}(t)}= \frac{E[ V  f_W(t-V) ]}{f_{V+W}(t)} \end{align}  Therefore, we can show that the two functions in the above ratio only depend on $\|t\|$.   Observe that we can write $t= \|t\| u_t$  where $u_t$ is a unit vector. Then, for any orthogonal matrix $A$ \begin{align} f_{V+W}(t)=f_{V+W}(\|t\|, u_t)&amp;= \frac{1}{(2\pi)^{n/2}} E[ e^{-\frac{\|t-V  \|^2}{2}} ]\\ &amp;= \frac{1}{(2\pi)^{n/2}} E[ e^{-\frac{\|t-AV  \|^2}{2}} ]\\ &amp;= \frac{1}{(2\pi)^{n/2}} E[ e^{-\frac{\|tA^{-1}-V  \|^2}{2}} ]\\ &amp;= \frac{1}{(2\pi)^{n/2}} E[ e^{-\frac{\|t A^T-V  \|^2}{2}} ]\\ &amp;= f_{V+W}(tA^T)\\ &amp;= f_{V+W}(\|t\|,  u_t A^T) \end{align}  Since, $A$ was arbitrary  we have that $f_{V+W}(t)=h(\|t\|)$(i.e., only depends on the magnitute).  Now I am not sure how to show that $E[ V  f_W(t-V) ]$ only depends on $\|t\|$? Why is the Converse to Lagrange's Theorem False? Do synonyms have exactly the same meanings as each other in all contexts? I have a question about synonyms: I'm wondering for quite a while if synonyms always stand exactly for the same thing. Is there sometimes a little difference in meaning? Let's use clumsy and clunky for example. Can I always replace clunky with clumsy? Since I'm not a native speaker, as you may have noticed, I cannot tell them apart. According to my dictionary, they mean exactly the same. Is it always true?  If the question has already been ask, sorry I couldn't find it.  Edit: Thank you very much! Every answer has helped a lot and thank you so much for it. I really appreciate it. I've voted all your answer because every answer helped me in a different way. I've accepted Barrie England's answer because it was the best one in my case. But all of yours were really good and helpful :) 2 different passports with different surnames com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure How to contact professors for PhD vacancies? I know many master's students who get an opportunity to talk to their potential PhD advisors well before applying. In most cases this opportunity is available by the professors with whom they worked for their master's. Moreover, there are many others who establish a contact with professors by mailing them and enquiring about PhD vacancies.   My questions are:   How important is knowing an advisor prior to applying for PhD?  Does an email interaction play a vital role when the department makes its admit decisions? If email contact is important, can a student send out mails to 2-3 professors (working in the same area) in case one of them does not bother to reply? To sum up, is applying of any use (especially in top universities) when you have no contacts and only your credentials to bank on? Suppose that G is a group and N &lt; G a normal subgroup. Assume that there is no normal subgroup M &lt; G with N &lt; M. Prove that G/N is simple.  This problem is really throwing me for a loop. The concept of quotient groups and how they relate to simple subgroups is confusing me, and so I am not really sure how to begin. If a simple subgroup's only normal subgroup is itself (and the trivial group), then G/N being simple would be proving that when multiplying the entire subgroup N by an element g for all g in G, that the collection of those sets cannot be broken into smaller normal subgroups? Why is.vector on a data-frame doesn't return TRUE? What happens with lethargy when Haste is cast again on a creature before first cast runs out? Use a .jar java library API in C#? I'm an entry level programmer so please be descriptive in your responses.  I am trying to use a Java API given as a .jar file in my C# .net application.  I don't know much Java, but this .jar file says "no main-class manifest attribute" when I try to run it so this means its a library?  This Java API also comes with a .java file which shows how to use the library but I cannot see the code inside the .jar.  I found  on this site, and one of the answers reads, "In simple way you can pack your java classes to jar file then In C# use Process class for execute and map IO stream."  I am semi-familiar with the Process class in C# but I don't understand how I could use it to use a Java library in my C# .net project.  Is this possible? or was that answer incorrect?  If so, could you explain how I can use the .jar library in my C# app. Smooth transition between two materials The sum of powers of two and two's complement – is there a deeper meaning behind this? What is the inverse of CoefficientList?