Author: Dieter Buerssner
Date: 06:50:52 01/21/01
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On January 20, 2001 at 10:43:30, Robert Hyatt wrote: >On January 20, 2001 at 10:10:30, Dieter Buerssner wrote: > >>On January 20, 2001 at 00:10:45, Robert Hyatt wrote: >> >>>Two things. 1. You have to correct mate scores to be relative to the current >>>ply when you store them. 2. You only do this if you are storing an EXACT score. To clarify. I am speaking of adjusting mate values for exact scores, lower bounds and upper bounds values, while storing and retrieving those values to/from the hash table. From the above, I understand, that you think, that adjusting upper/lower bound mate values is wrong. >>I cannot see, why adjusting lower bound or upper bound scores is wrong. >>If you have a lower bound score, that says, that this is a mate to 10 or better >>from the root position, and you are 2 plies down in the search, this means, >>that the score is a mate in 9 or better from this position. If you later >>hit the same position 4 plies down from the root position, you know, that >>this line yields a mate in 11 or better from the root. > >If the lower bound is mate in 30, and you correct this to mate in 20 because >you are at ply=20, you just changed the bound, which is wrong. I do not know, what you mean by "you changed the bound" here. I changed the value, that will be stored in the hashtable. Yes, I will store the value as mate in 20 for this position, just as if it were an exact value. When I later retrieve it at the same ply, I will readjust it to mate in 30 from the root. Nothing interesting here. Interesting it gets, when you hit a transposition at a deeper ply. Say at ply 30 (That the plys may be unreallistically high should not matter for the argument). Say also, I have a beta of mate in 32. I will retrieve the value mate in 20 from the hash table and adjust it to mate in 35 from the root. Now this value is smaller than beta, and a beta cutoff will not be allowed. This looks totally correct to me. All I know, is that from this position, there is at least a mate in 20, and this is not enough for a beta cutoff at this ply. When you don't adjust the mate score for the lower bound value, you will retrieve mate in 30, and get a wrong beta cutoff. Regards, Dieter
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