Author: Tord Romstad
Date: 14:17:26 08/16/03
The last few weeks I have been experimenting with MTD(f). It still does not work quite as well as my old aspiration alpha beta search, but I intend to keep working on it for some more time. One of my biggest worries right now is that the search slows down almost to a full stop when the hash table starts getting full. For instance, here are the time (in seconds) needed to finish a 11-ply search from the starting position for different hash table sizes from 5 to 320 MB: 5MB: 102 seconds 10MB: 88 seconds 20MB: 78 seconds 40MB: 55 seconds 80MB: 47 seconds 160MB: 34 seconds 320MB: 27 seconds Is this normal, or do I have some kind of bug? I really hope I don't need a 320MB hash table to play decently at slow time controls. Should I take a look at my hash table replacement scheme? Currently I always replace if the depth of the new position is >= dept of old position. Another problem is that MTD(f) has very weird effects when combined with the various forward pruning techniques I use. This is not entirely unexpected, because I use the values of alpha and beta for pruning decisions. When I replace plain MTD(f) (which I haven't been able to make work very well; too many researches) with MTD(f) with a convergence accelerator, I often get entirely different search results for the same position. If I remove all selectivity (except null move pruning) from my search, changing the test driver does not have any effect on the search results, but then my program becomes much too slow. I suppose I will have to work out new forward pruning techniques. Tord
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