Primers Coming Up

Thru my work I'm thrown into alot of technologies that i dont nearly know enough about and as with alot of tech related things, the education scene is basic basic basic..GURU with little or no gradiation, so what I'm going to do is post what i learn when i learn it and where i learn it from and hopefully it'll be useful for someone else, and I'll also take the opportunity to rehash stuff I've already done.

ATM I'll probably be doing Bash scripting, Perl Scripting, XML, and whatever UNIX stuff comes up whenever I'm writing, but for now and for a relativly simple start; X display fowarding...

This is the setup: Linux/Unix based "client" and "server"; in my case I have headless systems that i fiddle with from time to time, but after a while vim just becomes a pain, and as for viewing html files etcetc copying things back and forth is a pain in the ass.

The solution is already there; From its beginning the X server has always been client server based on some level. Basically what were gonna do is tell the server to use the client as an X display; this is controlled thru an environment variable, strangly called DISPLAY

Lets assume were using SSH. *nix SSHd has a simple system for fowarding and routing the relevent X ports (these wont show up in your "tunnels" tab if your using something like putty, but you shouldnt be using putty anyway)

Theres two versions of this fowarding ability, X and Y. in a nutshell, X is compressed and encrypted. Y isnt. On slow links, Y is probably your best bet, also some servers dont support the X flag. Also also, some sysadms disable this X fowarding.

Anyway, to the point. 

login to the server thusly

client# ssh user@server -X

then when you get a shell check to see if DISPLAY isnt already set (some servers are good enough to do this for you)

server# echo $DISPLAY

if your lucky it'll say localhost:10.0

otherwise it'll probably say :0.0 or something similar

If your in this unlucky situation, just enter

server# DISPLAY=localhost:10:0

then try it out, by running the clock and forking it into the background (&)

server# xclock &

Job done. Later

Another Uni Project

If anyone is interested in Erlang B Calculations, very relevent to any communications or engineering students, I've written a little quick piece of code to calculate them.

There are several levels of functionality in the code.
Erlang B itself only has 2 variables, System load in Erlangs, and the number of "trunks" (read: servers/call center operators/phone lines), and its output is a blocking probability from 0 to 1

All three of these variables or none atall can be defined at runtime;

• The desired blocking probability can be input to stop the calculation at that point. (default 0)
  
• The Load can be defined (See Erlang A) (default 1)
• The maximum trunks to be calculated (default 100)

The code uses the unistd.h library for argument parsing so is more or less unix only (or cygwin alternativly) and long doubles for more or less everything inside the code.

Having tested the limits, it kinda conks out then calculating large (read 1000 erlangs) on large trunks (got as far as 1234 trunks, then died)

When i get a bit of time i might optimise the factorial part so it doesnt run thru the entire factorial sequence for each number.

Anyway, the code is here. I'm not wasting my time laying out code on blogger.

Folding Code

I've been folding for a while now, and I'd previously written a really very cobbled together way of parsing my unitinfo.txt files, but, searching for something to do other than revise, I've written a similarly cobbled together but much shorter way of parsing my folding progress and telling me (as in speech) how far its going.

Required: Espeak, basic bash knowledge to adjust.

note: the espeak adjustments are just personal preference, so change them at will.

Its kinda a cheat cus it calls itself but isnt recursive. I'm just lazy


#!/usr/bin/env bash
case "$1" in
"-v")
points | espeak --stdin -s200 -v en+f4
exit
;;
"-w")
points | espeak --stdin -s200 -v en+f4 -w $2
exit
;;
*)
echo "Folding Stats at "&& date +%H:%M
echo "CPU1:" && cat /var/folding/foldingathome/CPU1/unitinfo.txt | grep Progress | cut -d'[' -f1 | cut -d' ' -f2
echo "CPU2:" && cat /var/folding/foldingathome/CPU2/unitinfo.txt | grep Progress | cut -d'[' -f1 | cut -d' ' -f2
exit
;;
esac

it doesnt look very pretty on the console but i think it sounds alright.

Better get some calculus done

::Edited for new version of code with wavfile output