Author: Uri Blass
Date: 08:21:02 03/03/03
Go up one level in this thread
On March 03, 2003 at 10:52:54, Ulrich Tuerke wrote: >On March 03, 2003 at 10:09:46, Albert Bertilsson wrote: > >>On March 03, 2003 at 09:43:24, Robert Hyatt wrote: >> >>>On March 03, 2003 at 09:13:36, Albert Bertilsson wrote: >>> >>>>Hi! >>>> >>>>During a recent game my engine reported that a mate in 2 was found, then after >>>>the next opponent move it reported that a mate in 3 was found. Does this >>>>indicate a bug in the engine? >>>> >>>>If it matters the opponent didn't followed the PV that engine displayed mate in >>>>2. But after the mate in 3 was claimed the opponent followed the PV until its >>>>defeat. >>>> >>>>/Regards Albert >>> >>> >>>It could be >>> >>>(a) a bug in hashing, where you don't adjust the mate score before storing it, >>>or you >>>don't adjust it when you hit it in the table. >>> >>>(b) your extensions make it easier to find the mate in 3 than the mate in 2 and >>>you quit >>>too soon. >>I interpret your answer as this should not happen if the engine has no bugs and >>no extensions. Since Sharper doesn't have any extensions it would be (a) then... >>alhtough I can't see how this could happen. > >I think that this can happen without extensions, too. > >It's a consequence of alpha-beta. Often some move of ply n+1 already suffices to >refute the preceeding move of ply n, instead of the checking move leading to the >mate. It's rather a matter of move ordering. > >It may for instance help a bit in some cases to prefer checking moves when >ordering moves. > >Uli I do not see how it is possible. The first mate was mate in 2 and it means that in the next position there is a mate in 1. A program should never miss mate in 1 and prefer mate in 3. The move that delivers the mate is supposed to cause an immediate cutoff. Uri
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