Author: Carlos del Cacho
Date: 14:24:24 09/02/00
Go up one level in this thread
On September 02, 2000 at 16:49:11, Larry Griffiths wrote: >I am adding "EXACT" hashtable entries at each ply when there are no cutoffs. > This could be your mistake. You should make a difference between a PV node (a < value < b) and a fail low (when all your moves yield a value below alpha). You can't flag a fail low as an exact value value because it isn't such. Your opponent is failing high and maybe the best move wins a rook when he just needs to capture a pawn to get a beta cutoff. In those cases, all you know is that the value of the subtree searched is equal or less than what you got. If I understood you correctly this is the source of your problems. So, this is the typical hash scheme (after checking that TT depth >= actual depth) : - fail high => store value as a lower bound on the true score of the subtree from that node. If you get to one of these and the retrieved value from the table is > beta, then fail high without further search (it can only go better and we already know it's over beta). - exact => just return the value from the TT. - fail low => this is an upper bound, so if it you get here and that value is < alpha you just fail low since you know it just can get worse. carlos
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