Author: Robert Hyatt
Date: 07:25:52 06/07/00
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On June 06, 2000 at 23:51:54, Bruce Moreland wrote: >On June 06, 2000 at 23:32:51, Robert Hyatt wrote: > >>What would be dangerous is to say "in a R+P ending, if _all_ pawns are on one >>side of the board, divide the eval by 2, making it more drawish." The danger >>is that the program is a _full-width_ searcher. It will search so many >>different positions that it will guarantee itself to search positions where that >>bit of advice is wrong. Yet it will rely on it to "save itself" from losing a >>game that it will suddenly think is kind of drawish. >> >>The think to keep in mind is how fast these thing are searching. On my quad >>xeon, I see 1M nodes per second. That is a _bunch_ of positions. If only .01% >>of the positions is mis-evaluated, that is still a big number when you factor >>in the search speed. The idea here is that the eval terms you use really do >>have to be accurate nearly 100% of the time. Otherwise the program will force >>those inaccurate cases to happen and then use them to skew the eval and fool >>itself about what is going on. >> >>It is a very dangerous tightrope to walk... I can't count the number of times >>I have written code that works almost all the time... and then am amazed to >>see how many times the silly search can make those exceptions occur, when they >>will do the most damage. > >It's not true that any error in the tree is inevitably fatal. And it's not true >that it's wrong to add knowledge if the knowledge can be wrong. > I'm not saying "any" error is fatal. I am saying that if the error condition is wide enough, the search will make it happen, because of the speed/depth we are now seeing. That means that a bunch of sloppy rules-of-thumb will wreck things quickly and effortlessly. I try to come up with rules of thumb that work, and then qualify the rules so that they are not applied in the wrong positions. But if I am not careful, wham... >You already have anti-knowledge by not having the term. There's no reason to >assume that this is any better than knowledge. That is a good point. You are wrong if you don't have it, you might be wrong some percentage of the time if you do add it. Which is better? The thing to watch out for is the case where when you are wrong, it changes the game result, where when you don't have the knowledge, you still might have a chance. catch-22 of course. > >What you want in these cases is to reflect tendencies, not to just say "return >0". I think it's possible to do this safely. > >bruce I agree, although the word "safely" might need a very precise definition. :)
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