I came across broken dependency trying to install wine. This happens after I try to install Intel Linux driver. Somehow it uninstalled wine and I couldn’t reinstall it. The problem is probably due to the “newer version” of applications I installed before I upgrade the machine from 10.04. It took me many hours finding a…
It takes me quite a while for me to figure out how to clone my screen to the projector. The default setting (two separate screens) may be reasonable for power point presentation. But I would like to take advantage of the stylus during my presentation. Cloning the display is of course a better choice for…
Got my cheap used X61 but the touchscreen is way off. I tried to calibrate it with this and this post but it just doesn’t work in my case. To be fair, xinput-calibrator suggested by the posts is very useful. Just the calibrated data is not registered. After some more search, find the command xsetwacom….
Just installed another 12.04 to a X61 tablet from ebay. It is one of my favorite machine as I can write notes on that and it is cheap ($150 from ebay). And with xournal, I don’t even need to print out stuff and rescan if I need to sign some document (just use the annotate…
My ubuntu box does not always configure wireless connection correctly. Luckily, setting connection on command line is rather easy. I followed the comment by Savage for this guide (or I guess this one is kind of the same). It didn’t work the first shot for me. But it worked after some slight modifications. You may have a different device,…
A very intuitive yet powerful inequality in information theory is the data processing inequality. Lemma: If random variable $latex X$, $latex Y$ and $latex Z$ form a Markov chain $latex X \rightarrow Y \rightarrow Z$, then $latex I(X;Y) \ge I(X;Z)$. The great thing about the inequality is that unlike some results in information theory, it…
Lemma 1: All eigenvalues of a Hermitian matrix are real. Proof: Let $latex A$ be Hermitian and $latex \lambda$ and $latex x$ be an eigenvalue and the corresponding eigenvector of $latex A$. We have $latex \lambda^* x^H x = (x^H A^H) x = x^H (A x)=\lambda x^Hx$. Thus we have $latex \lambda^*=\lambda$ as $latex x^H…
For a matrix $latex M = \begin{pmatrix} A &B\\C&D\end{pmatrix}$, we call $latex S\triangleq D -CA^{-1}B$ the Schur complement of $latex A$ in $latex M$. Note that $latex S$ naturally appear in block matrix inversion. Note that when $latex M$ is symmetric and $latex A$ is positive definite, $latex M$ is positive definite if and only…
Here are some formula for matrix inversion. Lemma 1: For a block matrix $latex M=\begin{pmatrix}A & B \\C &D\end{pmatrix}$, $latex M^{-1}=\begin{pmatrix}(A-B D^{-1} C)^{-1}& -A^{-1}B(D-CA^{-1}B)^{-1}\\-(D-CA^{-1}B)^{-1}CA^{-1}&(D-CA^{-1}B)^{-1}\end{pmatrix}$ $latex =\begin{pmatrix}A^{-1}+A^{-1}BS^{-1}CA^{-1}& -A^{-1}BS^{-1}\\-S^{-1}CA^{-1}&S^{-1}\end{pmatrix}$, where $latex S=D-CA^{-1}B$ is basically the Schur’s complement of block $latex A$. Proof: Let $latex M^{-1}=\begin{pmatrix}E&F\\G&H\end{pmatrix}$, $latex M M^{-1}=1$ gives us $latex AE+BG=I$ $latex AF+BH=0$ $latex CE+DG=0$ $latex…
After some trial and error and reading some other posts, I finally manage to capture screencast of a selected window with ffmpeg under 10.04. I am using the native ffmpeg from ubuntu and so recompiling is not needed. The command I’m using is as below. ffmpeg -f alsa -ac 2 -i pulse -f x11grab -r…