Saturday, October 21, 2006

North Korea's national anthem

An old friend who is a sucker for weird sounds (he listens to Heino) today sent me the North Korea's national anthem. Having read a bit about the country, I have a hard time imagining anyone there singing such a jubilous song. You can listen to it here.

Sunday, October 15, 2006

Math problem

Dear Lazyweb!

I would like to find the symbolic solution for XT0, YT0, dSX, dSY, qX and qY to this set of equations, in a numerically stable way:

XT0 + real_X1*dSX*Cos[qX] + real_Y1*dSY*Sin[qY] == own_X1,
YT0 - real_X1*dSX*Sin[qX] + real_Y1*dSY*Cos[qY] == own_Y1,
XT0 + real_X2*dSX*Cos[qX] + real_Y2*dSY*Sin[qY] == own_X2,
YT0 - real_X2*dSX*Sin[qX] + real_Y2*dSY*Cos[qY] == own_Y2,
XT0 + real_X3*dSX*Cos[qX] + real_Y3*dSY*Sin[qY] == own_X3,
YT0 - real_X3*dSX*Sin[qX] + real_Y3*dSY*Cos[qY] == own_Y3

Mathematica seems to not come back at all when asked for a solution, Maxima (in Debian) refuses cooporation, Maple produces a solution by approximating Sin and Cos with polynoms (which is not good enough for the whole range of [-Pi .. +Pi] and furthermore is not numerically stable.

This is for finding the parameters for the transformation between two different coordinate systems of maps. The real_* and the own_* coordinates are three identical points on both maps. A numeric solution (with simulated annealing from the gnu scientific library) exists but seems to be not exact enough. See also

Wednesday, October 11, 2006

Lazyweb: notebooks

This is the reverse lazyweb: I want to share what I learned, since many have similar considerations.

Some time ago I started to use the c't hotline to inform myself before buying computer stuff. Currently I am looking for a new notebook, since my wife poured tea into her old one and the keyboard stopped working.

So today I talked with one of the notebook experts at c't. My criteria were: "small", "long battery lifetime", "reliable", "good warranty", "excellent keyboard" and "works well with Linux".

He recommended that I should look at business notebooks as they came usually in higher quality and with better warranty. He pointed out a downward trend at Lenovo, which seems to produce lower quality machines nower days. Both warranty and technology seem to get reduced in quality. Asus machines break more often then average and their repair/warranty service is bad and improves only slowly. Dell machines break more frequently but their service is good. Linux compatibility seems good at Fujitsu-Siemens notebooks, which seems to have good service/warranty, too. Keyboards have improved a lot over the last few years and he encountered no bad keyboard at any decently priced notebook nower days.

I remember that joeyh and fabbe independently from each other picked a Fujitsu-Siemens. I will look into their offerings now.