Author: Robert Hyatt
Date: 11:18:41 04/16/03
Go up one level in this thread
On April 15, 2003 at 17:23:09, Will Singleton wrote:
>[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.
It takes me until depth 11 to see that Ne5 is not +2:
8 0.81 0.12 1. ... Ne5 2. Qb4 Nfg4 3. f4 exf3 4.
Nb5 Qb7 5. Qa5
8-> 1.23 0.12 1. ... Ne5 2. Qb4 Nfg4 3. f4 exf3 4.
Nb5 Qb7 5. Qa5
9 2.31 ++ 1. ... Ne5!!
9 3.27 -1.65 1. ... Ne5 2. Qb4 Nxc4 3. Nb5 Qc6 4.
Qxc4 Rd5 5. Nxa7 Rxa7
9-> 4.02 -1.65 1. ... Ne5 2. Qb4 Nxc4 3. Nb5 Qc6 4.
Qxc4 Rd5 5. Nxa7 Rxa7
10 6.14 -1.75 1. ... Ne5 2. Qb4 Nxc4 3. Nb5 Qc6 4.
Qxc4 Rd5 5. Nxa7 Rxa7 6. Qxd5 Nxd5
7. Bxa7 Nxc3
10-> 7.59 -1.75 1. ... Ne5 2. Qb4 Nxc4 3. Nb5 Qc6 4.
Qxc4 Rd5 5. Nxa7 Rxa7 6. Qxd5 Nxd5
7. Bxa7 Nxc3
11 9.52 -- 1. ... Ne5
11 17.27 -0.10 1. ... Ne5 2. Qb4 Nxc4 3. Nb5 Qc6 4.
Qxc4 Nd7 5. Rfd1 Bb7 6. Rxd7 Qxd7 7.
Nxa7
That was on a quad 400 machine using 4 processors. My dual 2.8 would likely
find
that 2-3 seconds.
>
>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
This page took 0 seconds to execute
Last modified: Thu, 15 Apr 21 08:11:13 -0700
Current Computer Chess Club Forums at Talkchess. This site by Sean Mintz.