Author: Bruce Moreland
Date: 02:09:50 09/03/00
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On September 01, 2000 at 10:21:13, Dave Gomboc wrote: >On August 31, 2000 at 13:36:54, Bruce Moreland wrote: > >>On August 30, 2000 at 05:41:01, Severi Salminen wrote: >> >>>>>>Why do you add a value depending on depth (2^depth)? Why not just increment by >>>>>>1? Just asking because I'm new to chess programming techniques and I'm >>The 2^depth thing is based upon the belief that chess programs play better if >>they use "cool" math like "^" rather than "boring" math like "+". >> >>bruce > >No, it's based on wanting to give higher increments to moves when they succeed >near the root of the search than when they succeed near the tips of the search. >An absolute shift left operation (<< ; how 2^depth is implemented) both gives >this effect and executes extremely quickly. Why are successes near the root more interesting that successes further down? You're sitting at a node and you want to try a move first that you think might kind of work. Why, if you have a draft of something small like 2, is it better to try first a move that was found to work with a large draft? If anything, that move might be less good than one that tends to cause cutoffs in positions with a draft of 2. I think this is a prime example of doing things the way they've always been done, without challenging the reasons that they are being done. "<<" is a slower operation than "+" on some important processors, and you also have to worry about messing up if the draft is somewhere around 32 and you are using 32-bit words. Drafts of 32 aren't going to happen in the middlegame, but they will happen in locked pawn endings. >As an aside, the history heuristic is something that was created 15 years ago, >and it wouldn't terribly surprise me if programs have changed enough over that >time that it's no longer valuable. I believe it's still a net win for Jonathan >in his Chinook program, though. I found it to be a little useful when I tested it a few years ago. I don't use "<<" though. bruce > >Dave
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