On 21/07/2017 21:23, Rainer wrote:
On 21/07/2017 17:14, Martin Brown wrote:
I have stumbled upon a position where quite a few engines - I
thought at first it was just x64 types but Fritz 10 also sees
the same phantom "Good move" which evaluates as a draw where
none exists. The position is hopelessly lost but that isn't the
point. Something is wrong.
I found it analysing a lost game where there was a clear and
bizarre discontinuity in the evaluation function that made no
sense to me.
Crafty x64 23.05 also sees the wrong right move but x32 20.14 is
OK.
r2r4/1p2p1kp/p5p1/3BNbPn/8/2N4P/PPP2P2/R3K2R b KQ - 0 21
It is a close run thing between 22. ... Rac8, or 22 ... Nf4 but
the phantom move which evaluates as a draw is 22. ... Bc8
If you actually play this move Bc8 then the evaluation becomes
correct again with white to move. There is something odd about
this position that breaks some engines. Any ideas what it might
be?
My guess is that it is some sort of draw by repetition bug
common to several of the engines since the offending thread
displays as just a single move with no continuation line : [...]
You didn't post the game, so I have to ask: is there a position
repetition after 21...Bc8? If so, a zero score would be
acceptable.
The material balance is such that the winning side should not be
looking for a draw and the losing side has no way to force perpetual
check. The score for the move 22. ... Bc8 is totally anomolous (as
is the fact that it does not have any continuation line in the
annotation).
It might be relevant that the strongest continuation for white is
0-0-0 and there may be a bug in the logic around queens side
castling somewhere. Almost none of the engines see anything other
than "best" is 21. ... Bc8 0.0 (and see no further than that)
This is the result of applying blundercheck threshold 20cp 4s to the
entire game (opening blunder in blitz) but played on in the hope of
winning something back.
[...]
Sysop: | Keyop |
---|---|
Location: | Huddersfield, West Yorkshire, UK |
Users: | 296 |
Nodes: | 16 (2 / 14) |
Uptime: | 91:39:19 |
Calls: | 6,658 |
Files: | 12,203 |
Messages: | 5,334,171 |