Author: Will Singleton
Date: 14:23:09 04/15/03
[D]r1br2k1/p1q2ppp/2n2n2/2B5/P1BNp3/1QP1P3/5PPP/R4RK1 b - - Some programs never show an elevated score, others show +2 or so before figuring it out. It has to do with a piece that is guarding a pinned piece at the end of the pv. Ruffian and Yace 99.5 exhibit the problem, while Tao doesn't. I'm wondering if this problem is due to a lack of extensions in the pv, or a qsearch artifact, or something else. ruffian: 9 119 220 3044077 Ne5 Qb4 Nxc4 Qxc4 Rd5 Nb3 Rb8 Rad1 Rxd1 Rxd1 Rxb3 Qxb3 Qxc5 10 224 695 9490320 Ne5 Qb4 Nxc4 Nb5 Qc6 Nxa7 Qa6 Nxc8 Raxc8 Rfd1 Nd5 11 36 1278 16931060 Ne5 Qb4 Nxc4 Nb5 Qc6 Qxc4 Nd7 Rad1 Bb7 Rxd7 Rxd7 Nxa7 If you look at Ruffian's ply 10 pv with a +2.24 score (Ne5 Qb4 Nxc4 Nb5 Qc6 Nxa7 Qa6 Nxc8 Raxc8 Rfd1 Nd5), white plays Nxa7, giving up the bishop for a pawn. The reason can be seen in Amateur's ply 10 pv below, which is that if Qxc4 instead of Nxa7, the bishop looks lost due to Rd5, without any compensation. 10 216 736 3122242 Ne5 Qb4 Nxc4 Nb5 Qc6 Qxc4 Rd5 Rd1 Rxc5 Rd8 Ne8 However, at the end of that pv, you get the following position: [D]r1bRn1k1/p4ppp/2q5/1Nr5/P1Q1p3/2P1P3/5PPP/R5K1 w - - Clearly, white can just take the rook for free. Apparently, a lot of programs cannot see this. Just speculating: in the qsearch the move Qxc5 would be tossed out, since a typical SEE would score it a losing capture. If this is indeed the problem, it would be helpful to know how some programs avoid it. It's possible that some programs just extend the relevant pv more than others. Mine only would have 1 extension, since the recapture Qxc4 doesn't follow the first capture. Or, perhaps there's a qsearch method that doesn't toss out Qxc5. Will
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