Author: Robert Hyatt
Date: 13:03:06 09/06/02
Go up one level in this thread
On September 06, 2002 at 15:46:53, Tony Werten wrote: >On September 06, 2002 at 14:45:11, Dann Corbit wrote: > >>Did anyone notice his cutoff idea in the evaluation function? >> >>It seems to me to be a very good idea, and I don't know if others have tried it >>out. >> >>Basically, it consists of three modes with two early exits... >> >>1. If the material + structure score alone is dominant enough, it exits right >>away. >>2. Otherwise, it processes the piece list. If that score is dominant, it exits. >>3. Otherwise, it does a full board control scan for all 64 squares. >> >>It is described starting on page 62 under the section "3.3.2 Multi Staged >>Design" >>He gets roughly 71% evals returning in stage #1, 13% in stage #2 and 7% in stage >>#3. >> >>It seems like it might be a big win to do it that way. > >It's called lazy eval and is not a good idea. The times it is wrong happen to be >the important ones. > >Tony Two things... First, you _can_ do a lazy eval with zero error. I did it in Cray Blitz and I explained the idea here before... You can compute the possible "positional error" (the amount the score will change max and min) for each type of piece. When you do a lazy eval, you can use this min/max and sum 'em up (or do it incrementally as we did, which can be a headache) so that you know the "independent piece max/min scores". If you lazy eval based on that, you get _zero_ errors because you will _really_ know that the individual piece scores can't produce a number larger than X or smaller than Y, so you can make an informed decision. I don't do that today because each time you change the eval, you have to update those min/max values which is something I would continually forget. 2. You can get good results with remembering the min/max positional scores during a real game. yes, the scores will continue to "widen" and reduce lazy eval exits, but the error rate is not that bad. Compared to the cost.
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