Author: Robert Hyatt
Date: 08:51:47 04/28/03
Go up one level in this thread
On April 28, 2003 at 11:30:08, Charles Worthington wrote: >That's an interesting question but I have one of my own. Is not the engine's >choice of continuations based soley on its eval of the line? Yes it is. However, You could take the source for Crafty, and at the top of Evaluate() where it computes the material score, you could add PAWN_VALUE*2 if white is on move, or subtract it if not, and it won't change a thing as far as the best move and the PV. The alpha/beta search simply maximizes the score, having no idea what the score really means... > Many times I have >seen Shredder follow its over optimistic evals to a dead draw as white. That's a different issue. Doing the above modification to crafty would make it always think it is doing great, even in dead drawn positions. The mistake _everybody_ makes is to take the actual displayed score from a program and think that is the gospel according to chess. The program will find what it thinks is the best move, whether the score is +1 or -1 doesn't matter. If you take its "best move" at face value, you will be happy. If you take the score as absolute, you will rarely be happy. But then again, ask two strong humans whether black or white is better in a complicated position and they will likely not agree exactly, even though they would both play the _same_ move... > I would >rather my program know where it really stands and whether or not it has >realistic winning chances. as would we all. :) > Also...I personally would like to know where it >stands as well. There is nothing quite so frustrating as to have an over >optimistic eval turn on you and bite you. I have seen numerous situations where >The King has an eval of +2 against Deep Fritz's -1 and it RARELY works out in >The Kings favor. It's hard for me to muster faith in an engine that is clueless >about it's own position and it is the one thing that keeps me from giving >Shredder a fair shot at becoming my main engine. Enough times of seeing Fritz >pull the rug out from under my Shredder eval has spooked me I guess. I just do >not see how it is possible to handle a position properly when you cannot even >eval it properly and in fast blitz time controls (3+2), I might also add that >the "optimistic" engines almost always perform more poorly than the well >balanced engines. The truth seems to perform better than the lie in this case. >Of course this discussion is about self-inflicted optimism by tampering with the >parameters so it seems even more extreme. You are taking an already-optimistic >engine and furthering it's optimism. It would likely take many thousands of >games to come to a conclusion as to which works best. Honestly though, I think >that in this case having your program lie to you (and itself) will not prove >beneficial. The program will play better if it has a full understanding of its >actual chances and not imagined ones...Optimism causes the program to >overestimate it's chances and play far too aggressively (ie. unwarranted >sacrifices) in certain positions where caution is warranted. Against a human >this may prove beneficial but against a program firmly grounded in reality it >may prove fatal. So, like in life, I think the truth has to be better than the >lie. And I think that extensive testing of these settings would show that, more >often than not, the lie would come back to bite you. > >Sincerely, Charles Again, you are making the same basic mistake everyone else makes. Ignore the fact that the program is always a half-pawn ahead. That's just some sort of bias built in most likely to make it more aggressive and as a result it skews the scores upward. If the bias was removed it would change little...
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