Author: Robert Hyatt
Date: 06:31:34 06/24/99
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On June 24, 1999 at 04:50:01, Ed Schröder wrote: >>Posted by Robert Hyatt on June 03, 1999 at 22:44:02: > >From an older posting.... > >>>Should a hash table move precede the PV? > >I always understood "PV move" = "hash table move". > >What is the difference? > >>I don't have a "PV" option. After each iteration, the first thing I do >>is 'stuff' the PV moves into the hash table... which means that following the >>hash table move will suck me right down the PV as I want... all without having >>to have _any_ special code in the move ordering stuff... > >"Stuff the PV moves into the hash table", what does this mean? > When you search the first move, the PV from that search _should_ be in the hash table. But by the time the rest of the moves are searched, it is more than just probable that some of those positions have been overwritten as the rest of the tree is searched... To make _sure_ that the PV moves are in the hash table when the next iteration is started, I 'stuff' them in. I do this by following the PV, looking up each position, and if I don't find it in the hash table, I store what should be there again... so that when the next iteration starts, I will find every PV position and run down that path first... If you don't 'stuff' you will not always follow the PV from the last search, because if _any_ hash entry (for the PV moves) was overwritten, you have to revert to normal move ordering, which likely won't be the "pv move".. >Maybe we have you can explain about your definition of PV as we >might have a different one :) PV = principle variation. PV moves are those moves from the previous search, best path, as displayed when the best score was found. But it is not guaranteed that these positions (which are definitely stored in the hash table as the PV is backed up) will survive to the start of the next iteration. They can easily be overwritten, particularly those near the end of the PV as they will have a shallow 'draft' and be likely candidates for replacement. > >Ed Schroder > > >>The other answer is 'yes' pv should come first... but if done right, the >>PV should be in the hash table, so there should never be a 'choice' anyway...
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