Author: Jaime Benito de Valle Ruiz
Date: 09:37:30 12/21/03
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>I don't mean to pry, but I am curious to know the criteria your software uses to >select the PV line to be displayed. Do you somehow identify a critical path >leading to a leaf node where the leaf node chosen is no worse than any other >evaluated leaf node? How can you be satisfied that the PV line displayed meets >your criteria? As a user, can I "believe" your PV? > >Generally, I assume that the first move in any PV is most reliable and that the >next move is less reliable, etceteras, due to some sort of horizon effect. For >example, the evaluation of a leaf node position must be done without the normal >searching process. [This is true in spite of the fact that the position >evaluation is necessarily sequential because that's the nature of >microprocessors, ignoring multithreading.] I would expect that leaf node >evaluations would be less reliable than the evaluations of internal nodes since >branches are evaluated. > >Bob D. The "criteria" is basically the same for all programs (although the pruning and other things are different, of course): The engine reaches the current max. depth, and chooses the "best move" for the side to move by trying and analysing all available moves, and then it assign it a score. Then it goes down one ply, undo the last move, tries another one, and then chooses the "best move" for the side to play in that new position again. Repeating this process recursively, it eventually comes up with a PV and with a score associated to it. If the analysis at the leaves is assumed to be perfect, then the PV is also perfect. The analysis is far from being perfect for any engine, so the PV.... Most programs -I guess- update the PV as they search, so if there are no bugs, you'll be able to see the real PV associated with the score; any other line will give (according to the engine judgement) a worse score (or maybe the same, but not better). Shredder is probably extracting the PV from the hash tables, so if any position has been re-written during the search for some reason, you get the wrong PV. This is just a guess. Obviously, a bad evaluation function will lead to stupid PVs in most cases. A material-based-only evaluation function will lead to absurd PVs most of the time, except for when you blunder.... and then they will find the way to win you a pawn or whatever. Regards, Jaime
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