Multi column table in latex

You want a table the spans across pages and raps in 2 columns. You need supertabular and to stick everything in a \twocolumn. Do it:

\pagebreak
\twocolumn
\begin{supertabular}{ |l|c|l| }
\hline
stuff1 & stuff2 & stuff3 \\
1 & 2 & 3 \\
1 & 2 & 3 \\
1 & 2 & 3 \\
1 & 2 & 3 \\
1 & 2 & 3 \\
1 & 2 & 3 \\
1 & 2 & 3 \\
1 & 2 & 3 \\
1 & 2 & 3 \\
1 & 2 & 3 \\
1 & 2 & 3 \\
1 & 2 & 3 \\
\hline
\end{supertabular}
\onecolumn
\pagebreak

latex "File ignored" not found on nfs ( isilon )

You are unable to compile latex files (i.e. latex myreport.tex) on an nfs drive but they compile correctly from the local disk. You receive errors such as "File ignored" or "no found". In my case this occurred when using an Isilon. The solution is to switch file ID size from 64bit to 32bit on the isilon configuration. "File Sharing"->NFS->"Edit Settings" on the Isilon web configuration.

Growing a VM

I started a VM with the default 8Gb for a linux install. I have successfully added additional HDD to the VM but eventually I hit a problem that required editing the actual size of the main disk. I used the vmware-vdiskmanager (-x 12Gb Kubuntu.vmdk) to successfully resize the VM disk. Then I booted the VM into a gparted image using the ISO as a CD (option in the VMware server). This worked fine. I then edited the partition. First increase the size of the swap. Then shift it to the right and then make it smaller again, before resizing the main partition. Click apply changes and then wait. Or in my case head up to the terrace and enjoy beer and "Schnittchen". The KDE session does appear borked after all this. It complains about some DCOP setting not running. I tried changing permissions on the tmp dir and following general advice on the internet - however moving .kde to .kde_old solved the problem for me. The partition is now showing up as 12 gigs and all the files seem to be okay.

Aluminium Mac Keyboard disassembly

This post has been moved here

avr-gcc read I/O on single port with AT90USB162

I want to repeatedly read from and write to a single port on a AT90USB162. This is to implement a key matrix scanner and pins will be repeated reconfigured as input or output. I ran in to trouble, reads seems to overlap as if they were being cached.



For example, I have pins 1 and 2 shorted.

pin 1 is set as an output. pin 2 an input.

pin 2 is set to pullup.

I output logic 0 on pin 1.

I read the value from pin 2 and store the result in a variable VAL1.



Now I set pin 1 as a input (and pullup).

I set another pin, say pin 3 to logic 0 (not shorted to anything).

I output logic 0 on pin 3.

I read the value from pin 2 in to a variable VAL2.





Now logically VAL1 should be 0 and VAL2 1. However that doesn't seem to be the case. If I do this I often read 1 for both VAL1 and VAL2. Removing the second read however makes VAL1 revert to it's correct value, EVEN THOUGH BOTH READS SHOULD BE INDEPENDENT!! I've not seen this with the AT90USBKey so it's a bit odd.


The solution I've found is to place a delay loop after the port configuration but before the read, in my code:

inline unsigned char get_scan(unsigned char pin) {

  unsigned char p = 1 << pin;

  DDR = 0x00 ^ p;
  PORTD = 0xFF ^ p;

  for(volatile int i=0;i<100;i++);

  return ~p & PIND;
}

The volatile is important, if you omit that it doesn't work. I guess the compiler optimizes it out. (volatile tells the compiler some other external code could change this variable so explicitly check it where ever it's referenced).

jvterm: text based cut and based

I've been trying to rid myself of the mouse. The final thing holding me back is cut and paste for terminal applications. Turns out that most Linux terminal programs don't have any support for keyboard based cut and paste. And in fact the only mainstream terminal app I've seen it in the The OS X Tiger Terminal.app (it seems to have been removed from later versions).



Anyway, after some hunting I found a Linux terminal program that does text based cut and paste. It's called jvterm. The downside is that though it's an X11 application it's not really designed to run in concert with X. It only works full screen and you can't alt-tab between it and X applications. Anyway, I couldn't find the documentation for text based selection so here's typically how you might use it:


Press Shift twice to enter selection mode

Use the cursor keys to move to the start of the selection region

Press Shift again

Move to the end of the selection region (text will be highlighted)

Press space


The text will now be on the clipboard. To paste it press Shift Twice and then Enter.


This is a really neat feature, and I hope it finds its way in to other terminal applications.



(protip: Read the man page. I found this out from guessing, but it's actually in the man page).





AHHH! You can do something similar with screen but how do I get it to share the X clipboard?!?




There's a urxvt (rxvt-unicode) perl script for this!

I found it in google cache and have copied it here:

HERE

To use it press alt-y to activate. Move using vi style keystrokes (hjkl) then press space to start selection and space to end. The text appears on you x buffer via xclip! Neato!

To install the script copy it to ~/.urxvt The copy the following in to you ~/.Xdefaults:

URxvt.keysym.M-y: perl:mark-and-yank:activate_mark_mode
URxvt.keysym.M-u: perl:mark-and-yank:activate_mark_url_mode
URxvt.perl-lib: /home/new/.urxvt/
URxvt.perl-ext-common: tabbed,mark-and-yank
URxvt.urlLauncher: firefox

Gaussian and Binomial distributions

I'm most probably being entirely stupid here...

I've been trying to understand the Gaussian distribution and it's relation to the Binomial distribution. I've kind of decided that the Gaussian distribution is a continuous representation of the Binomial distribution. Is this correct?

Anyway, here is some C++ which creates a binomial distribution by adding n random values (-1,0 or 1) to a fixed initial value. I think for this as a kind of 2D random walk. Here's the code:

#include <vector>
#include <iostream>
#include <math.h>

using namespace std;

int main(void) {

  vector<size_t> space(100,0);

  size_t tries=1000000;
  size_t offset=50;
  for(size_t n=0;n<tries;n++) {

    size_t moves=1000;

    int final=50;
    for(size_t t=0;t<moves;t++) {
      int val = rand()%3;
      val -= 1;

      final +=val;
    }
    space[final]++;
  }

  for(int n=0;n<space.size();n++) {
    cout << n << " " << space[n] << endl;
  }

  return 0;
}

Here's the gnuplot generated from the output:



If you have any pointer on the link between Binomial and Gaussian distributions explained in a way a computer scientist can understand please add them below.