Author: Russell Reagan
Date: 14:55:53 01/15/03
Go up one level in this thread
On January 15, 2003 at 17:04:35, David Rasmussen wrote:
>On your site, you describe some problems of different repetition detection
>schemes. Could you post example positions to show these problems? I guess they
>ought to be on the page itself too.
>
>/David
[D]8/2p5/b4p2/8/8/2N1k3/8/4K3 w - - 0 1
This is similar to one of Bruce's examples. If black had just played 1. ... Ke3
(from f3), and white (your program) only had time for a shallow search, it would
see that 2. Kd5+ <any> 3. Nxf6 would win a pawn, and so it would play Nd5+. If
black plays Kf3 to get out of check, and your program thinks that if a position
is repeated it must be a draw (only two repetitions, instead of three), it will
see that Nc3 is a draw, and Nxf6 gives a score of -1.00 (based on material), so
the program would play Nc3.
The method TSCP uses can sometimes incorrectly claim a draw. For example, from
the opening position you can do this:
tscp> new
tscp> g1f3
tscp> g8f6
tscp> f3e5
tscp> f6e4
tscp> e5g4
tscp> e4g5
tscp> g4h6
tscp> g5h3
tscp> h6g8
tscp> h3g1
tscp> g8h6
tscp> g1h3
tscp> h6g8
tscp> h3g1
1/2-1/2 {Draw by repetition}
tscp>
Or in SAN...
1. Nf3 Nf6 2. Ne5 Ne4 3. Ng4 Ng5 4. Nh6 Nh3 5. Ng8 Ng1 6. Nh6 Nh3 7. Ng8
Ng1
[D]rnbqkbNr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBnR w KQkq - 0 8
The method TSCP uses is that if all of the same squares are empty, it thinks the
position is the same, which is not correct, of course.
[D]4K3/2R3QQ/8/qp6/5q2/3r4/8/4k3 w - - 0 1
In this position, if the computer was playing black, and white (for some reason)
wants to exchange rooks, so he plays Rd7. Your program doesn't want to and has
to play a move quickly in time pressure, so it moves its hanging rook to c3,
Rc3. White really wants to exchange rooks, so he plays Rd3. Now your program
could play Rc7! and win a queen for a rook, but since your program uses the same
method as TSCP and thinks two repetitions is a draw (instead of three), it
thinks that Rc7 is a draw, since the same squares are empty as the initial
position, so it exchanges rooks.
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