Tuebingen music, GHMM, Partiview angles, UZ

There's been a music festival in Tuebingen the last two days. Good fun, though I only watched a couple of hours each day. In both cases I cycled down - a mental breakthrough since I've not wanted to cycle down when there are lots of people around - and of course pushed the bike up. I've given up being embarassed by having to push the bike up. It's f*ing steep, and I'm f*ing unfit. C'est la f*ing vie.

Been making a lot of progress understanding what Gunnar's been up to with his GHMM. Turns out he was anticipating a lot of the Hofmann/Altun/Tsochantriadis and Taskar et al stuff with his framework, and then settled on a method that theoretically doesn't make use of all information available, but is faster and works just as well - at least on his problems. It requires the solution of a sparse linear system with thousands (in some cases hundreds of thousands) of variables and constraints, which CPLEX is happy to solve. Unfortunately, CPLEX ain't free, so I can't use it in a general open source toolkit I plan to write in the next two weeks. We'll find out.

The Argentinians want another animation for their movie on the Pierre Auger Project, based on the past ones I've made, including ones I made in the last week. Unfortunately, this requires my being able to make smooth flypaths in Partiview. I've not known how to do that the past 18 months, as I've been stuck on the following problem:

Suppose I want to place a camera at position x1,y1,z1, looking at x2,y2,z2. Partiview requires you to specify x1,y1,z1 and some rotation angles Rx,Ry,Rz that define where the camera is looking to. Yesterday I finally figured out how to compute Rx, Ry and Rz! Here's the Matlab script. There's certainly a proper, well defined way of doing this with lots of matrices, which Stuart's tried to explain to me, so this is definitely a hack. But it works.

I'm back in touch with some people at my old undergraduate math department at the University of Zimbabwe. It's amazing how many people are still there, despite all the economic woes. (We're talking here about a country where people long to get back to the days when inflation was only in double digits, where unemployment is over 70%, life expectancy is under 40, etc.) And a couple of my friends have gone back there after getting their doctorates in the US and Norway. One of them said he was subsidizing his stay there by the money he earned lecturing in the US for three months following his graduation. Wow...