Residues and Threads

I'm slowly changing all my algorithms to work on either raw data or residue data. Because raw data are integer values in the range of 1 to 5, and thus enabling some performance optimizations and shortcuts, but residue data are essentially floats, all my algorithms took a performance hit.

At the same time, I'm adding multi-threading support to speed things up. The improvement is significant, but I'm already seeing diminishing returns: on a quad-core systems, matrix factorization using 4 cores runs at only 3.27x the speed of using one core.

Back to Basics

New year, now I'm playing with the most basic stuff: global effects. This time I'll try to be more patient and take a more systematic approach, instead of the "hack anything that looks promising" approach I've been taking.

Right now I've a nice number for my qualifying RMSE: 0.8888. Hey, it takes real skill to hit such a nice number by chance ! I'll try to resist the urge to submit better results until I'm sure I've made a big improvement.