Author: GeoffW
Date: 14:06:23 03/06/04
Hi
Here is a position I found interesting, white has just played Rf6, black to move
[D]r3qnk1/rb2bppp/4pR2/pp1pP1PP/2pP3N/P1P1P1Q1/1PB5/4B1RK b - - 0 1
My programs analysis for this position is horrid
Ply Eval Time Nodes Principle Variation
1 433 0 17 g7f6 e5f6
2 433 0 290 g7f6 e5f6
3- 393 1 4782 g7f6
3 204 1 8053 e7a3 b2a3 g7f6 e5f6
4 204 3 18575 e7a3 b2a3 g7f6 e5f6
5 204 6 44876 e7f6 g5f6 g7g6 h4f3 f8d7 h5g6 h7g6
6 192 10 97670 e7f6 e5f6 g7g6 h5g6 h7g6 h4f3
7 194 21 193103 e7f6 e5f6 g7g6 h4f3 a8d8 h5g6 h7g6
8 187 60 564304 e7f6 e5f6 g7g6 h4f3 g6h5 g3h4 f8d7 h4h5
9 188 132 1263805 e7f6 e5f6 g7g6 h4f3 f8d7 e1d2 a8b8 g3h2 e8d8
10 176 396 3783030 e7f6 e5f6 g7g6 h4f3 f8d7 g3h2 a8d8 e1g3 d7b6 f3e5
11 176 942 8062241 e7f6 e5f6 g7g6 h4f3 e8c6 g3h2 f8d7 e1g3 a8d8 f3e5
d7e5 g3e5
12- 136 3984 35236639 e7f6
12 102 144954 868931003 b5b4 a3b4 a5b4 f6f4 a7a2 g3g2 b4b3 c2b1 a2a1 e1d2
f8d7 e3e4
It firstly thinks it has won a rook by taking it with Pxf6, then it realises
this is bad, and avoids the Rook sacrifice by coming up with its own weird
bishop sacrifice Bxa3. Two plies later then decides it had better take the rook
after all with the obvious looking Bxf6. It takes 40 seconds to get to ply 12
before it realises that this is also a hopeless losing move.
Then it takes almost 25 minutes to resolve the fail low with a branching factor
of 24 !!
I am not sure why it struggles to resolve this specific fail low so badly, this
is probably the trickiest fail low I have seen so far, at least for my program.
It was taking so long I was convinced it was locking up in an infinite search
bug. I guess it probably isnt a bug as it finally does come up with a reasonable
move, all be it far too late.
What do other programs make of this, daresay Crafty et al. will have it all
worked out and resolved in about 5 seconds flat ;-(
P.S it finally managed ply 13 as I was typing this up
13 102 327723 2072998497 b5b4 a3b4 a5b4 f6f2 b4b3 c2b1 f8d7 e1d2 a7a1 h5h6
g7g6 h4f3 a8a7
54 minutes to decide white is a pawn up after avoiding the sac.
Regards Geoff
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