Razoring

In chess programming Razoring describes a forward pruning algorithm. In order to process the huge search tree some "uninteresting" branches are not searched as deep as others. This simulates a bit the human behavior where obviously bad lines are not considered as carefully as promising lines.

When thinking ahead and the engine finds itself in a position that is worse than a position it already knows it can get to it will stop searching the moves into that direction and consider other moves.

Of course this means the engine can also miss some good moves that it would have found if it searched just a bit more into that direction. So this is a bit gambling. If the engine gains more from skipping bad moves than it loses from missing some good ones overall it is a gain.

In the past iCE did not use razoring, I tried it and it did not work. I also read hat Bob Hyatt tried it extensively and it did not work for him either.

Anyway from time to time I retest some features. Recently I got history heuristics working that also failed in the past. So now I retested razoring and it also seems that it now works. Even without tuning the razor conditions iCE got another small improvement.

It seems the time for the big jumps is gone, so progress means piling up small gains. But in total a lot of small steps gets you as far as a big jump. It is just more work.