The following packages have unmet dependencies:  vlc : Depends: vlc-nox (= 2.1.4+git20150226+r54594+19+11~ubuntu14.04.1) but it is not going to be installed        Depends: libsdl-image1.2 (&gt;= 1.2.10) but it is not installable        Depends: libtar0 but it is not installable        Depends: libva-x11-1 (&gt; 1.3.0~) but 1.0.15-4 is to be installed        Depends: libva1 (&gt; 1.3.0~) but 1.0.15-4 is to be installed        Depends: libvlccore7 (&gt;= 2.1.0) but it is not going to be installed        Recommends: vlc-plugin-notify (= 2.1.4+git20150226+r54594+19+11~ubuntu14.04.1) but it is not going to be installed        Recommends: vlc-plugin-pulse (= 2.1.4+git20150226+r54594+19+11~ubuntu14.04.1) but it is not going to be installed E: Unable to correct problems, you have held broken packages.  I tried  sudo apt-get install -f sudo apt-get update sudo apt-get upgrade sudo apt-get purge vlc vlc-nox libsdl-image1.2 libtar0 libva-x11-1 libva1 libvlccore7 vlc-plugin-notify vlc-plugin-pulse   But the error remains. VLC is not the only thing. many other packages I try to install gave me similar dependency errors which I finally gave up installing. I have been using Ubuntu for a while now. I just don't understand why this happens every now and then. Please help ... EDIT: Output of apt-cache policy vlc vlc-nox libsdl-image1.2 libtar0 libva-x11-1 libva1 libvlccore7   vlc:   Installed: (none)   Candidate: 2.1.4+git20150226+r54594+19+11~ubuntu14.04.1   Version table:      2.1.4+git20150226+r54594+19+11~ubuntu14.04.1 0         500 http://ppa.launchpad.net/videolan/stable-daily/ubuntu/ trusty/main i386 Packages vlc-nox:   Installed: (none)   Candidate: 2.1.4+git20150226+r54594+19+11~ubuntu14.04.1   Version table:      2.1.4+git20150226+r54594+19+11~ubuntu14.04.1 0         500 http://ppa.launchpad.net/videolan/stable-daily/ubuntu/ trusty/main i386 Packages libsdl-image1.2:   Installed: (none)   Candidate: (none)   Version table: libtar0:   Installed: (none)   Candidate: (none)   Version table: libva-x11-1:   Installed: (none)   Candidate: (none)   Version table: libva1:   Installed: (none)   Candidate: (none)   Version table: libvlccore7:   Installed: (none)   Candidate: 2.1.4+git20150226+r54594+19+11~ubuntu14.04.1   Version table:      2.1.4+git20150226+r54594+19+11~ubuntu14.04.1 0         500 http://ppa.launchpad.net/videolan/stable-daily/ubuntu/ trusty/main i386 Packages
This is what happens:  sudo apt-get install vlc Reading package lists... Done Building dependency tree        Reading state information... Done E: Unable to locate package vlc   Please help. I would also like to know when this error occurs, I've seen it before too.
I'm trying to find $\int x^x \, dx$, but the only thing I know how to do is this:  Let $u=x^x$.  $$\begin{align} \int x^x \, dx&amp;=\int u \, du\\[6pt] &amp;=\frac{u^2}{2}\\[6pt] &amp;=\dfrac{\left(x^x\right)^2}{2}\\[6pt] &amp;=\frac{x^{2x}}{2} \end{align}$$  But it's certain that this isn't the correct way to evaluate that, and the answer must be wrong. How to split a string with any whitespace chars as delimiters To make your opinion known on MSE you need both up and downvotes. Given at the moment you need 125 rep to downvote on this site, the voting patterns will be skewed positive because not everyone is active on the site.   This is to be expected for regular Stack Exchange sites as you are expected to be involved in the community before you are deemed knowledgeable enough to be part of the community voice. However, MSE is different because you are voting for the entirety of the Stack Exchange network and you shouldn't need to be active on MSE itself to have a voice on changes to the entire network.  This is especially important for questions like  because it will effect every network to do with coding at all. This was brought up in .  I would suggest reducing the rep required to downvote on MSE down to 100 (or 101) rep. This is the amount you get for the site association bonus. This is given once you achieve 200 rep on any network site and shows that you are active in at least one community. I think this would be the perfect use of the association bonus in showing that you are a member of the Stack Exchange community. How to remove comma and "and" before institutional last author after compiling BibTeX I have the following BibTeX entry:  @article{pubmed18800157,     author = {Heng, T.S. and Painter, M.W. and Immunological Genome Project Consortium},     title = {The {I}mmunological {G}enome {P}roject: networks of gene expression in immune cells.},     journal = {Nat. Immunol.},     pages = {1091-1094},     volume = {9},     number ={10},     year = {2008}, }, %\bibliographystyle{unsrt}   When the bibliography is generated, it puts comma a the end of the author:   Notice the comma after M.W. Painter. Is there a way to remove it? How can I stop Lollipop ignoring my wifi network? Android 5.0 has a new "feature": If a wifi network has no connection to the internet, it will remain connected to it but route traffic over mobile data instead. A small exclamation mark shows in the status bar over the wifi symbol.  Unfortunately, for some reason Android has decided that my home wifi does not have a good internet connection - which is not true, as I'm using it to access Stackexchange at the moment - and is, instead, trying to send everything over GPRS.  With mobile data disabled, things work over wifi just fine, despite the exclamation mark - so it isn't a problem with the wifi not working, per se.  Is there any way to override this "smart" feature? The only way I have found to make things work at the moment is to disable mobile data while I am in my house - which is not a practical long-term solution.   EDITING to add that I have now solved this problem by buying a new router! I was using something very old... But, I'll leave the question here for the benefit of anybody else with the same difficulty. has been, have been , had been How to lock compiled Java classes to prevent decompilation? How do I lock compiled Java classes to prevent decompilation?  I know this must be very well discussed topic on the Internet, but I could not come to any conclusion after referring them.  Many people do suggest obfuscator, but they just do renaming of classes, methods, and fields with tough-to-remember character sequences but what about sensitive constant values?  For example, you have developed the encryption and decryption component based on a password based encryption technique. Now in this case, any average Java person can use  to decompile the class file and easily retrieve the password value (defined as constant) as well as  and in turn can decrypt the data by writing small independent program!  Or should such sensitive components be built in native code (for example, VC++) and call them via ? How do I close a terminal without saving the history? More than once I've accidentally run a number of commands and polluted my bash history. How do I close my terminal without saving my bash history? I'm using Fedora. How to deserialize a JSON String to Apex The axiom of choice asserts that for any set $X$ there exists a function $f : (2^X − \{\emptyset\}) \rightarrow X$ such that for any nonempty $A \subseteq X$, $f(A) \in A$. Show that this is equivalent to the assertion that every relation includes a function with the same domain. I am given this problem in my assignment. My approach is following. I have a set $X$. Then it has a choice function $g : \mathcal{P}(X) \setminus \left\{\emptyset\right\} \rightarrow X$. Suppose $X$ has a relation $R \subseteq X \times X$. $dom(R) \subseteq X$. Then the required function $f : dom(R) \rightarrow X$ is $$f(x) = g(\{y\ |\ (x, y) \in R\})$$ Conversely, suppose $X \supseteq Y$ is a non-empty subset. Let $$R_Y = \{(x, y)\ |\ y \in Y, x \in Y, (p, q) \in R_Y \Rightarrow p = x\}$$ Then there is a function $f_Y : dom(R_Y) \rightarrow X$. But $dom(R_Y)$ is singleton from the definition of $R_Y$. Then $im(f_Y)$ is also singleton. We define our choice function as $f = \{(Y, y)\ |\ y \in im(f_Y)\}$ Are my arguments correct?  Edit.1: what I tried to do for converse is, for any subset $Y$, I construct a relation $Y_1 \times Y$ where $Y \supseteq Y_1 = \{y\}$. Then there is a function $f_Y : Y_1 \rightarrow Y$. Then if $f$ is my choice function I define $f(Y) = f_Y(y)$. May be I should define $R_Y$ as $$R_Y = \{(x, y)\ |\ y \in Y; x \in Y; (p, q), (p', q) \in R_Y \Rightarrow p = p'\}$$ I understand there may be multiple $R_y$'s. But can't I define a singleton set as $\{s\in S\ |\ a, b \in S \Rightarrow a = b\}$? This can be $\{s\}$ $\forall s \in S$. But isn't it a valid specification?  Edit.2: This is the final solution with the help from @Asaf.  If we assume axiom of choice then for any $X$ there is a choice function $f : \mathcal{P}(X) \setminus \left\{\emptyset\right\} \rightarrow X$ such that $f(A) \in A$. Suppose $R$ is a relation between $P$ and $Q$. Then we have a choice function $f_Q$ for $Q$. Let $f_R(p) = f_Q(\{q\ |\ pRq\})$. The function $f_R : P \rightarrow Q$ and $dom(f_R) = dom(R)$. So this is our required function.  Conversely, if every relation includes a function with same domain. Let $R$ be a relation between $\mathcal{P}(X) \setminus \left\{\emptyset\right\}$ and $X$ such that $aRb \Rightarrow b \in a$. Now $R$ includes a function $f : \mathcal{P}(X) \setminus \left\{\emptyset\right\} \rightarrow X$. Then $xRf(x) \Rightarrow f(x) \in x$. So $f$ is the choice function for $X$. Can a plan "age" reach zero? Where did dedicated.abac.net. come from in my rDNS and PTR records? So I followed this guide to the letter:   I did so for 3 domains.  When I "test" the records and enter: host 64.150.176.81 on my linux machine, it shows me 81.172.150.64.in-addr.arpa domain name pointer 64-150-172-81.dedicated.abac.net.  when it should be showing me 81.176.150.64.in-addr.arpa domain name pointer 64-150-172-81.example.com.  Has anybody encountered a similar problem?  I am hosting with codero, not abac.net btw. How can I delete my account? How can I delete everything from my MacBook Pro before selling it? I have a Mac that runs Snow Leopard and I intend to upgrade it to Mountain Lion and sell it on ebay. However, I only have one hard-drive, and I'm sure I can't use something in my OS to delete my OS and all user data.  Is there something for this that's built into the firmware that I can do on boot, or otherwise?   I have source code on my Mac for multiple corporations' proprietary software and I can't risk somebody gaining access through the use of any sort of disk recovery tool. I plan to use a 7 pass erase rather than simply deleting the directory. My keyboard has no "media" keys; can I control media without them? My USB keyboard does not have "media" keys -- that is, dedicated keys for play, stop, next, prev, volume up/down, etcetera.    For the sake of this question, I would prefer not to install additional software if I can avoid it.  Is it possible to issue some standard key sequence on a generic USB keyboard that emulates these play, stop, etc. multimedia keys?  Like Ctrl+Alt+Shift+F12 or something obscure like that? How can Kitty Pryde achieve time travel with her phasing abilities? In X-Men: Days of Future Past, how does Kitty Pryde suddenly get the power to send people's minds back in time? Initially she was only able to phase through objects and could extend this power to other people. The explanation of this cited molecular spaces.  How does she go from there to time travel all of a sudden?? which vectors are perpendicular to each other?  $\vec a = (1, -2, 3)$, $\vec b = (5, 4, 1)$, $\vec c = (1, 0, -5)$  Do i just take the dot product of 2 of them. If the dot product they are at $90^\circ$? But how do i know if there perpendicular? Inheritance in Java - creating an object of the subclass invokes also the constructor of the superclass. Why exactly? I have a question about inheritance in Java.  I have two classes A and B , and class B, inherits from A:  public class A {      public A() {          System.out.println("Hi!");      } }   public class B extends A {      public B() {          System.out.println("Bye!");      }       public static void main(String[] args) {          B b = new B();      } }   When I run program B, the output is:  Hi! Bye!      Question : why the constructor of class A is invoked, when I create and object of class B ?    I know that B inherits everything from A - all instance or class variables, and all methods, and in this sense an object of B has all characteristics of A plus some other characteristics defined in B. However, I didn't know and didn't imagine that when I create an object of type B, the constructor of A is also invoked. So, writing this:  B b = new B();   creates Two objects - one of type B, and one of type A.  This is getting interesting,   can somebody explain why exactly this happens? Why not always present logistic regression estimates in the response scale (probablity)? There's a lot of discussion in epidemiology around the relative merits of odds ratios vs risk ratios. Proponents of the former cite the mathematical qualities of odds (not constrained to be between 0 and 1) and their suitability for examining common outcomes. Proponents of the latter believe that RR's are often more interpretable, and match how clinicians and the public tend to think. Some have suggested methods to model risk ratios directly (in multivariable models). For instance, the log binomial model and poisson regression with robust standard errors. What I don't understand is - why don't we just fit the model using standard logistic regression and perform the inverse logit transformation on the fitted estimates? For instance, lets say we are trying to predict coronary heart disease using BMI (exposure) and age (confounder). We could fit the model and estimate the odds of CHD across the range of values of BMI (adjusted for age), according to the model. We then take the inverse-logit of those fitted odds to transform them onto the probability scale. Seemingly this way we now have an idea of the risk of the outcome across all values of the exposure, which we can plot or otherwise describe. But i've never seen this method recommended. Which makes me think there must be a conceptual issue with it?? p.s. lets assume we are performing a cross-sectional or cohort study (not a case-control study). How do I create a D&D character correctly as a total newbie?