Author: Stan Arts
Date: 08:13:47 03/23/04
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On March 23, 2004 at 09:43:31, Jaime Benito de Valle Ruiz wrote: >If you're using a small aspiration window at the root, and it fails low (this is >a score below the lower window value, right?), is there any chance that the REAL >score is actually above the window value? If this is possible, could you give me >an example? >Thank you, > > Jaime Hi Jaime There's a chance, if it happens it's because of instability. Caused for instance by using the hashtable as transportationtable, and pruning (for instance null-move, that's alpha-beta dependant) and other such techniques. In Neurosis I have complicated aspirationsearchwindow things at the root, and before I wouldn't do anything about these instabilities (that luckily don't happen often in my program, once or twice a game, and mostly after I started using the hashtable as transportationtable.) but now I detect them by looking if, when researching and expecting a lower score a higher comes back and the other way around, and try to resolve them, by researching the entire iteration (not just that (best move, uptill then anyway) move, because it could be after getting rid of the instability the score for that move is actually very bad, and needs to find a better one, that might be further infront in the move-list.) and research starting with that move, and with different alpha-beta values at the root, and try this a few times, and if it's still not resolved then, I again do some researches with different alpha-beta values, but then with clearing (clearing the scores) the hashtable everytime. And if all that fails..I go on..but this seems to (at some point..) always solve the instability. :) It's not so slow, as these instabilities usually return right away, and seem to happen mostly on lower depths in my program, for instance by re-using hashtable information from previous (actual game) moves. Greetings and goodluck, Stan
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