Author: Peter McKenzie
Date: 23:17:26 05/02/00
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On May 02, 2000 at 06:26:34, Michael Neish wrote: > >Hello, > >I wonder whether anyone could help me, or offer any suggestions as to the >following little problem. > >The program I'm writing needs two ply to see what I think should take only one >ply. > >In the position below White wins material by the blindingly obvious Bg5. > >[D]6k1/pp1nrppp/5rb1/P2P4/5BP1/5P2/4BK1P/R3R3 b - - > >However, if I set my program to look only one ply deep, it doesn't see this >move, and prefers Bb5. At two ply, though, it sees it all right. I think one >ply should be enough, as the Qsearch ought to take care of the ensuing >exchanges. Indeed, other programs I have tried manage to find it easily enough >in one ply. > >This might be a trivial position, but if it's taking longer than it should to >see these tactics then I could be wasting plies in my search. Most traditional 'brute force' style programs won't see the tactical win in 1 ply. The reason of course is because after 1.Bg5 our 1 ply is used up and we hit q-search. In q-search, you have the option of standing pat so black will be able to take the static evaluation after 1.Bg5 without being forced to lose the exchange. There are ways to solve this position in 1ply, but its debatable whether it is worthwhile. You could extend 1 ply for 'special' Bg5 type moves or you could evaluate the skewer in your eval function. There is no right answer here, it just depends on your design philosophy. cheers, Peter > >By the way, in case anyone asks, I'm not doing anything unusual in Qsearch. I >call Eval() first, return if it fails high, otherwise set alpha to the Eval() >score if it's greater than alpha, and then search through the available >captures. > >Thanks for your help. > >Mike.
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