when perform   $ sudo apt-get update  Err http://security.ubuntu.com trusty-security/main Sources             Connection failed [IP: 91.189.92.201 80] Err http://security.ubuntu.com trusty-security/restricted Sources                 Connection failed [IP: 91.189.91.13 80]
Occasionally, when I'm installing stuff, I get an error like the following:  Some packages could not be installed. This may mean that you have requested an impossible situation or if you are using the unstable distribution that some required packages have not yet been created or been moved out of Incoming. The following information may help to resolve the situation:  The following packages have unmet dependencies:  package1 : Depends: package2 (&gt;= 1.8) but 1.7.5-1ubuntu1 is to be installed E: Unable to correct problems, you have held broken packages.   How can I resolve this?
How to set up USB for Virtualbox? I'm using Ubuntu Maverick and Virtual Box 3+. I have Windows 7 Ultimate. The problem is that it doesn't detect USB drives in Windows 7, but USB peripherals (mouse + keybord) are working.  I followed , but I can't find the user group vboxusers. How can I continue? I would also like to upgrade to the latest version without any risk (without losing my virtual hard disk drive). I've been reading , and I would like to know why the Lasso provides variable selection and ridge regression doesn't.  Both methods minimize the residual sum of squares and have a constraint on the possible values of the parameters $\beta$. For the Lasso, the constraint is $||\beta||_1 \le t$, whereas for ridge it is $||\beta||_2 \le t$, for some $t$.  I've seen the diamond vs ellipse picture in the book and I have some intuition as for why the Lasso can hit the corners of the constrained region, which implies that one of the coefficients is set to zero. However, my intuition is rather weak, and I'm not convinced. It should be easy to see, but I don't know why this is true.  So I guess I'm looking for a mathematical justification, or an intuitive explanation of why the contours of the residual sum of squares are likely to hit the corners of the  $||\beta||_1$ constrained region (whereas this situation is unlikely if the constraint is $||\beta||_2$). Alt-Tab shows two application switchers on Unity I started to have problems with my Ubuntu application switcher (Alt +  Tab) this morning. When I press Alt +  Tab, not only one, but two application switchers show up. Last night I customized some stuff using the Unity Tweak Tool. I thought I didn't touch the application switcher. So now it looks like this: Install pandas to python3.5 instead of 2.7 I've recently installed pgAdmin 1.18.1 and noticed a strange thing:  Long json query results are shortened to 256 symbols and then ' (...)' is added.  Could someone help me disable this shortening? Why is XOR preferred over XNOR? The XOR operator seems to be a frequently used building block inside many cryptographic primitives.  As far as I can see, its most desirable properties seem be that for the XOR of two bits $a\oplus b=c$:   The information is preserved.  Either $a$ or $b$ can be recovered from $c$ and the other bit. The information is hidden.  An adversary can not learn anything about $a$ or $b$ from $c$ alone.   Neither AND nor OR has these properties but XNOR does.  It seems like any cryptographic application using XOR could be constructed equivalently with XNOR, without incurring any loss in security.  One possible reason to prefer XOR might be that XOR is equivalent to addition modulo 2, whereas XNOR would be addition plus 1 modulo 2, but this seems to be entirely mathematical, and I'm not sure if it actually results in any additional hardware complexity in practice.  Is the choice of XOR then an arbitrary one, made for historical reasons, or is there any tangible underlying motivation for using it over XNOR? Partitions of $n$ into distinct odd and even parts proof How do I add VBA in MS Office? I've seen posts showing answers which use VBA () code/macros, however, I've also noted additional comments afterwards about how to use the VBA (how to implement and execute it). I'm hoping this will help just to get the code executed.   So, my question is:  I have some VBA code. How do I add VBA to my MS Excel or Word or Outlook project? Why do a lot of questions from around 2008 seem to have really high upvotes? Automatically building a database of forward and backward citations My goal is to produce a graph showing the linkages (and lack there of) between several fields that share a common subproblem by showing who cites whom.  There are many databases that show citations between papers: , , and Google Scholar.  However none allows me to download even part of their database.  Is there some database I have overlooked?  Has someone written a scrapper for one of these websites?    For reference, the fields I'm considering are Mechanics, Magnetic Resonance Imaging, Signal Processing, Geophysics, and several others. I have a Student object and have a pick list field  "Student Status" in this object. Status can be Full-Time OR Part Time. Now my requirement is i want this student status list, Part-Time or Full-Time in apex controller. how can i do this?  If i get a student record it will only give me that particular student status Full-Time or Part-Time. But i need all options that are available in student status field.  Please help me How to install Skype 4.3? Plotting recursive function using pgfplots \addplot Is it possible to plot a recursive function using pgfplots \addplot command?  I tried like this;  \documentclass{article} \usepackage{pgfplots}  \pgfmathdeclarefunction{fac}{1}{   \pgfmathparse{(#1&lt;=1)+                 (#1&gt;1)*#1*fac(#1-1)   } }  \begin{document} fac(5) is \pgfmathparse{fac(5)}\pgfmathresult  \end{document}   But the result seems to be an infinite recursion, as the entire function is being evaluated. I want to prove that if we have a commutative integral domain $D$ with field of fractions $F\neq D$ then $F$ is not finitely generated as a $D$-module. (In this question it may be the case that $1\not\in D$.)    My original plan was to localize at a maximal ideal and then use Nakayama's lemma but as we don't have a $1$ our localization may not be local (in fact we need not have maximal ideals).  So I'm a bit lost as to where to go?  Thanks for any help. How many solutions has the equation $\sin x= \frac{x}{100}$ ? How many solutions has the equation $\sin x= \frac{x}{100}$ ?   Usually when I was asked to solve this type of problem, I would solve it graphically but this one seems to be trickier. It doesn't seem wise to put $f(x)=\sin x$ and $g(x)=\frac{x}{100}$ in the same graph and then counting all the intersection points.  What would be some algebraic methods to solve this? Git ignore file for Xcode projects Which files should I include in .gitignore when using Git in conjunction with Xcode? cardinality of the Borel $\sigma$-algebra of a second countable space Second countability by itself doesn't restrict the cardinality of a topological space, since every set with the trivial topology is a second countable space, but it seems natural to ask whether second countability restricts the cardinality of the Borel $\sigma$-algebra of the space.  Can the cardinality of the Borel $\sigma$-algebra of a second countable space be arbitrarily big? If this is the case is there a simple construction for a second countable space with an arbitrarily big Borel $\sigma$-algebra? What is the proof that a force applied on a rigid body will cause it to rotate around its center of mass? How do simulacra behave? Declare global variables in Visual Studio 2010 and VB.NET