Author: Robert Hyatt
Date: 11:00:58 01/05/01
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On January 05, 2001 at 10:23:26, Gian-Carlo Pascutto wrote: >On January 05, 2001 at 09:45:47, Robert Hyatt wrote: >>>I notice I sometimes when I get a fail low at the root, I do a research, and >>>then get a fail high! The most likely explanation is that I am a moron and it >>is bug. Can you think of another explanation? Or an easy way to catch this >>>bug? >> >>this is not common, but perfectly normal, and it can't really be avoided. > >Since this happens a lot in my program, I spent some time tracking down >what were the minimal conditions: > >- aspiration window (no fail high/low otherwise) >- null move >- hash table used for move ordering (not for scores, not even on exact matches) > >Now it still isn't making sense to me...how can you produce a different >_score_ anywhere in the tree by just altering move ordering?? Yes. It is all about hashing and fail high/fail low... and if you overwrite the right (or wrong) thing in the hash table, things fall apart.. I haven't really noticed condition 3 above being needed. But using PVS and null-move will definitely produce fail high followed by fail low and vice versa. > >Anybody who knows an explanation here? 'You _must_ have a bug' is acceptable >too. > >-- >GCP If it is a bug, I have one. And so does every other PVS/null-move program I know of... Going all the way back to Cray Blitz...
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