ListView : getHeight() on a null object reference
What is a NullPointerException, and how do I fix it?
induction with 2 recursive sequnces I'm having trouble solving this problem. I have relation for two sequences of natural numbers.   $$a(n)+\sqrt3\cdot b(n)=\left(1+\sqrt3\right)^n$$  and I have to prove that recursions:  $$\begin{align*} &amp;a(n+1)=a(n)+3b(n)\\ &amp;b(n+1)=a(n)+b(n) \end{align*}$$  will satisfy relation mentioned above. I tried solve it using induction but I failed. Can anybody help with some other ideas? I have created a model which requires some faces to be dual sided.  I intend to import this model into Unity. Reading about this, it seems that the recommendation is to duplicate the polygons and then flip the normals.  What I have done so far is simply to duplicate the all of the relevant faces using Shift+D and then flip the normals. I don't like this method though as it hampers any future alterations to the model itself.  What is the best way of doing this? Can sum of a rational number and its reciprocal be an integer? Can sum of a rational number and its reciprocal be an integer?   My brother asked me this question and I was unable to answer it.   The only trivial solutions which I could think of are $1$ and $-1$.  As to what I tried, I am afraid not much. I have never tried to solve such a question, and if someone could point me in the right direction, maybe I could complete it on my own.  Please don't misunderstand my question.   I am looking for a rational number $r$ where $r + \frac{1}{r}$ is an integer. Trouble trying to use Windows Search to search for file with a question mark in the content It seems that Windows Search is having trouble when I specify a question mark character as the content that I'm searching for within my files.  I've tried:   content:? content:"?" content:"\?" content:\? content:%3f content:"%3f" content:\3f content:"\3f" content:\00\00\00\3F   but each of these yield no results when I do indeed have files that contain ? within the scope of the search. If I instead search for something like content:happy it will indeed find all files with the phrase "happy" within those same files.  My assumption is that Windows Search is treating some characters such as the question mark as a special character likely for the purpose of wild card expressions. To test this theory I've also searched for files containing an asterisk * and indeed I have the same issue as when searching for content of question mark. What I'm wondering is whether there is any way to get a search to work where I can search for a literal expression without any type of wildcard matching or at least a way to escape the special characters within the expression.  By the way I'm using Windows 7 Enterprise. Define $S\equiv\{ x\in \mathbb{Q}\mid x^2<2\}$. Show that $\sup S=\sqrt{2} $. How can I filter items with a certain enchantement? I am trying to build a custom Adventure Island. At this moment I am trying to limit the allowed items on this island. I'm trying to do this by filtering on a certain enchantment which is not item-specific.  For example.   When you want to filter an wooden sword with a custom name, you use this command:  /testfor @p[r=5] {Inventory:[{tag:{display:{Name:"Custom Sword"}}}]} &lt;   When you want to filter a wooden sword with a custom name and specific enchantement, you can use:  /testfor @p[r=5] {Inventory:[{tag:{display:{Name:"Custom Sword"},ench:[{id:16,lvl:1}]}}]} &lt;   But how can I filter on items with a specific enchantment on ANY item? I tried:  /testfor @p[r=5] {Inventory:[{tag:{ench:[{id:16,lvl:1}]}}]} &lt;   But this ain't work. Does anyone know how to solve this issue? I've posted a question or an answer, and I have received one or more downvotes. I am not really sure why I was down voted, or I think I know why, but I disagree.  Why did this happen, and what should I do about it? change whole font of beamer to arial bold italic? how to change the font of the content to bold italic ?  thank you   here my cool superbe example:  \documentclass[14pt,t]{beamer} \usepackage{url} \usepackage{hyperref} \usepackage{graphicx} \usepackage{grffile} \begin{frame}\maketitle\end{frame} \begin{frame} \frametitle{test0} \begin{itemize} \item test \item test \begin{itemize} \item test \end{itemize} \end{itemize} \end{frame} \end{document}   A possible solution would be to use:  \usepackage{helvet} \renewcommand{\familydefault}{\sfdefault} \renewcommand{\rmdefault}{phv} \renewcommand{\sfdefault}{phv} %\renewcommand{\mddefault}{b}   % this content bold with b \renewcommand{\bfdefault}{phv} % Helvetica has no bx series \renewcommand{\updefault}{sl}   But it does do helvel arial bold for the whole document, and maybe there are ways to have the items/text of the slides in bold italic, and to keep normal phv for the top of the slide (frame title)? Should the eigenkets be weighted in $|P\rangle = \sum\limits_{r}|\xi^r\rangle$? Page 37 of Dirac's book The Principles of Quantum Mechanics, states  The condition for the eigenstates of $\xi$ to form a complete set must thus be formulated, that any ket $|P\rangle$ can be expressed as an integral plus a sum of eigenkets of $\xi$, i.e. $$|P\rangle = \int |\xi'c\rangle\; d\xi' + \sum\limits_{r}|\xi^rd\rangle$$ where the $|\xi'c\rangle$, $|\xi^rd\rangle$ are all eigenkets of $\xi$, the labels c and d being inserted to distinguish them when the eigenvalues $\xi'$ and $\xi^r$ are equal, and where the integral is taken over the whole range of eigenvalues and the sum is taken over any selection of them.  I find it inconsistent that the eigenkets under the integral are weighted by what appears to be a differential eigenvalue $d\xi'$, yet all the eigenkets under the summation are weighted by the value 1. Is this correct? How to prevent freehub body damage? I feel like this is poor design. I have two wheelsets that are less than a year old which have damaged freehub bodys due to cogs digging in to the splines on the freehub. It's so bad that I can't remove the cassette spacer without filing down the splines. I had to use  pliers and chain whip to remove the cogs that were embedded in the freehub when trying to remove the cassette.  Most of the damage is on the center of the cassette as the largest 3 cogs are held together by carrier. I'm using a shimano 105 cassette and  Novatec disc hub and Velocity ATB convertible disc hubs (which were somewhat damaged in the same fashion, but not as bad as the novatec).  I'm using this bike for cyclocross, offroad exploring, light singletrack use, Rail trails and some road riding.    How can I prevent this damage to the freehub from happening? How does the CS:GO ranking system work? What happens when you put a Portable Hole inside a Bag of Holding while on the Astral plane? What would happen if someone were to place a Portable Hole within a Bag of Holding while being within the Astral Plane? Would it be the reverse effect? Remove completed reminders in OS X and iOS Cardinality of the Cartesian Product of Two Equinumerous Infinite Sets Is the cardinality of the Cartesian product of two equinumerous infinite sets the same as the cardinality of any one of the sets? I couldn't find this explicitly stated in any handout or text. This certainly seems to be true from the examples I have seen:  The Cartesian product of two infinitely countable sets is again infinitely countable. The Cartesian product of two sets with cardinality of continuum again has cardinality of continuum. Ubuntu halts after few seconds of starting and nothing works command, virtual terminal, GUI garamondx ligatures no longer work crossfade between 2 videos using ffmpeg I've been trying to achieve a crossfade transition between 2 video clips using ffmpeg but have failed so far. I'm new to ffmpeg and am mostly relying on tweaking what I can find in the documentation and existing examples online. From what I read so far, using either the blend or overlay filter should help in achieving what I'm after but I can't figure out the command line details to get it to work.  The fade and concat filters are great for fade-out of video 1, fade-in to video 2 and concat the 2 into 1 clip type transitions but I'd appreciate help in getting a command to transition from video 1 to video 2 without any going to black in between. I couldn't find any examples for exactly this problem anywhere, maybe I'm looking for the wrong keywords...?  More speficially, my videos are mp4s (h264 video, no sound, in case that matters), each is 5 seconds long and I'm after a transition from approx. 4.5s of video 1 to 0.5s of video 2.  Similar to what this tutorial does using MLT and frames (see 2:25 for an example fade), though I'm looking for a way to do this just in ffmpeg without calling any other progs.   Any pointers or maybe a command line to get a fade like this would be much appreciated, thanks very much! The ls -al command shows the following output;  -rwxrw-r--    10    root   root 2048    Jan 13 07:11 afile.exe   What are all the fields in the preceding display? Why did Voldemort stop employing Occlumency against Harry in Deathly Hallows? Converting Linux into a Router- Traffic from eth0:0 to eth0 So I have been trying to convert my linux box which is running Mint into an router. eth0 has a public address that has 71.xx.xx.xx for an IP addr. I created an eth0:0 and set it an IP address , 10.0.0.100. I started a DHCP server that is on eth0 ( because it wont use eth0:0) and that's giving out addresses between 10.0.0.101 and 10.0.0.200. I can ping between eth0 and eth0:0 on the same machine. I have a another laptop connected to the linux via a switch and its able to receive an ip addr via the DHCP server. Problem is how do I route traffic from and to eth0:0 to eth0 and vice versa so that computers on the private network that is 10.0.0.x can access internet via the static IP on eth0.