Author: Tord Romstad
Date: 03:59:20 12/03/03
Go up one level in this thread
On December 02, 2003 at 18:32:08, macaroni wrote: >this is the analasys from the re-write of my engine from the first position in >WAC. >[D]2rr3k/pp3pp1/1nnqbN1p/3pN3/2pP4/2P3Q1/PPB4P/R4RK1 w - - 0 1 >-->"WAC001", best=Qg6 >stage=middlegame, playing as WHITE, nullmove is ON, Using >ply=1, value=-200, nodes=113, kNps=0, best=Ne5xc6 >ply=2, value=-200, nodes=2546, kNps=11, best=Ne5xc6 >ply=3, value=-200, nodes=7708, kNps=18, best=Ne5xc6 >ply=4, value=10000, nodes=129225, kNps=88, best=Qg3-g6 >ply=5, value=100, nodes=224379, kNps=105, best=Nf6-e8 >ply=6, value=10000, nodes=658686, kNps=125, best=Qg3-g6 >ply=6, value=10000, nodes=1012767, kNps=129, best=Qg3-g6 > >it's a very easy mate in 2, and the computer, as expected, finds it at ply 4, >but then disregards it at ply 5, for Ne8, which also just about wins. It is >nullmoving that has caused this, is there any way I can avoid this sort of >problem? it arises, because after playing Qg6, it nullmoves, and calls a 1 ply, >or 0 ply search, in both of these searches, black is better by 200 points, it >doesn't fail in the ply 4 search because there is nothing better, it DOES fail >in the ply 5 search because Ne8 is also good, so beta is 100, not -200. It must be a bug, I'm afraid. As others have mentioned, allowing checks at least at the first ply in the qsearch (I do it at all levels in the qsearch) helps greatly in positions like this. It is also a good idea to try to detect simple mate threats in the evaluation function, and avoid doing a null move (and perhaps make an extension) when such a threat is found. In WAC001, after white's move 1. Qg6, my program notices that the black king is on the back rank, that the square directly in front of it is attacked by a white queen and knight, and that this square is not defended by any black pieces except the king. The program knows that this means that there is almost certainly a mate threat on h7, and therefore avoids doing a null move. The move 1. Qg6 is found already at the first iteration. Tord
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