Author: scott farrell
Date: 01:57:19 09/17/02
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On September 16, 2002 at 09:15:16, Simon Finn wrote: >On September 14, 2002 at 23:41:55, scott farrell wrote: > >>Does anyone know what implications fail-soft might have on hashing? >> >>If you do a search say from 1 to 2, and under fail soft it returns 2.5 >>(fail-high / beta cutoff). I am currently storing the score as a beta cuttoff of >>2.5. If I see this position again, and the depth is good enough, I return the >>value from the hash table, so this is fail-soft as well. >> >>if (mainTable.flag[te] == flagBeta) >> if (mainTable.value[te] >= beta) >> return mainTable.value[te]; >> >>I was tracking IID failures, and came up with some debugging that shows >>occaisonally no entry in the hashtable after a score of >= beta. > >Is this surprising? > >If you arrive at the same position by different routes, >you may have different alpha-beta windows. > >This means that a fail-soft value (generated with a narrow >window) is not necessarily reusable (for a search with a >wider window). > >When you search a node at greater depth, you may also have >a different alpha-beta window (because preceding nodes, >also searched at greater depth, now return different values). > >When you start IID from a node, you may encounter a >high-draft/small-window/fail-soft node (generated by IID >from some other node) in the hash table. Depending on >the actual fail-soft value, this may or may not lie >outside the current alpha-beta window. > >If the stored fail-soft value is within the current >(wider) window, you will get a "hash table failure". > >Does this explain what you are seeing, or have I misunderstood >the problem? Simon, thanx for that. It sounds like you know your stuff, I'll re-read it a few times, and it sounds like it might answer it. thanks again Scott > >Simon > > >>I am still >>trying to trace it down. It seems lots more of these occured nearer to the >>terminal nodes (search horizon). I stopped IID recursing nearer the terminal >>nodes, and many of the failures stopped. I guess I might not be hashing enough >>details near the terminal nodes. I have tried turning on and off storing values >>from the qsearch, but it didnt seem to effect things.
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