Author: Gian-Carlo Pascutto
Date: 15:31:18 11/21/01
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On November 21, 2001 at 18:23:08, Michel Langeveld wrote: >I build nullmove in my chessprogram and received a problem. > >The example which is on Bruce side seems not to work in certain positions. >Especially positions where it's possible to give mate: > >[D] rnbq1bnr/pp2k3/2p1p1B1/3pP1p1/7p/4PQ2/PPPN1PPP/R3K1NR b KQ > >After Qc7 white doesn't see Qf7 anymore. > >It seems to be that the line: > >val = -AlphaBeta(depth - 1 - R, -beta, -beta + 1); > >Must be changed into: > >val = -AlphaBeta(depth - 1 - R, -beta+1, -beta); Nope. Due to the negamax recursive call, (-beta, -beta+1) becomes (beta-1, beta) at the next level, which is correct. (-beta+1, -beta) would become (beta, beta-1). These last bounds are false. What is effectively beta there (the second value), is smaller than alpha. I hope that makes sense. I'm not as good an explainer as Bruce is. -- GCP
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