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mambofish wrote:Ermintrude playing black, recently got itself into this position against a human player in a blitz game (6 seconds per move):

[d] r1bqr1k1/pp2bpp1/5n1p/3p2N1/3B3P/2PB1Q2/PP3PP1/R4K1R b - - 1 15

Having declined playing hxg5 for some moves, ermintrude wrongly judged it was now safe to do so, and lost a few moves later. When it played the knight capture it considered the PV to be

1. ... hxg5 2. hxg5 Ne4 3. Qh5 f6 4. Qh8+ Kf7 5. g6+ Ke6 7. Qxg7 with a score of +1.26 for black.

What it failed to consider after f6 was g6! which a human player would find very easily, and which leads to mate.

When I looked into this I realised what had happened. Ermintrude considers g6 to be a "quiet" move, and as black is a knight up at this point, the evaluation after g6 is short-circuited - no king safety check is done.

In fact, even if it had been done, it wouldn't have made any difference as the maximum value of all positional factors in the "slow eval" is only 75 centipawns and the knight capture would still have been played.

In fact the only way ermintrude could have detected the problem earlier was if it had extended the search after g6. To do this, it would have to somehow recognise that g6 is a deadly threat. The problem is that many such moves might appear to threaten the king, but only a few actually are genuine threats, so I don't do a specific king threat analysis for extensions as it is too expensive.

So I was wondering what do other people do? And how many of the other engines out there would also greedily make the capture at blitz time controls... !

1 212 0 10 hxg5
1 212 0 40 hxg5
2 212 0 109 hxg5 Bxf6
2 212 0 269 hxg5 Bxf6
3 212 1 726 hxg5 Bxf6 Bxf6
3 212 1 1940 hxg5 Bxf6 Bxf6
4 212 3 3965 hxg5 Bxf6 Bxf6 hxg5
4 212 4 6531 hxg5 Bxf6 Bxf6 hxg5
5 129 7 15336 hxg5 hxg5 Ne4 Bxe4 dxe4
5 129 21 45391 hxg5 hxg5 Ne4 Bxe4 dxe4
6 129 26 55465 hxg5 hxg5 Ne4 Bxe4 dxe4 Qxe4
6 129 57 124035 hxg5 hxg5 Ne4 Bxe4 dxe4 Qxe4
7 24 75 169747 hxg5 hxg5 Ne4 Qh5 f6 Qh7+ Kf7 g6+ Ke6
7 24 209 482723 hxg5 hxg5 Ne4 Qh5 f6 Qh7+ Kf7 g6+ Ke6
8 -124 282 655991 hxg5 hxg5 Qd6 gxf6 Bxf6 Qh5 Kf8 Qh8+ Ke7 Re1+ Be6
8 3 618 1487489 Bg4 Qg3 Qd7 Bxf6 Bxf6 Nh7 Rac8 f3
8 3 807 1910470 Bg4 Qg3 Qd7 Bxf6 Bxf6 Nh7 Rac8 f3
9 6 1276 3045963 Bg4 Qg3 Qc8 f3 Bf5 Bxf5 Qxf5 Bxf6 Qd3+ Kg1
9 6 1806 4276445 Bg4 Qg3 Qc8 f3 Bf5 Bxf5 Qxf5 Bxf6 Qd3+ Kg1
10 6 2973 7103384 Bg4 Qg3 Qd7 Bxf6 Bxf6 Nf3 d4 Nh2 Bh5 Rc1
10 6 4053 9382479 Bg4 Qg3 Qd7 Bxf6 Bxf6 Nf3 d4 Nh2 Bh5 Rc1
11 25 5948 13828369 Bg4 Qg3 Qd7 Nf3 Nh5 Qh2 Bxf3 gxf3 Bf6 Rc1 g6
11 25 7598 17435452 Bg4 Qg3 Qd7 Nf3 Nh5 Qh2 Bxf3 gxf3 Bf6 Rc1 g6
12 22 11317 26578754 Bg4 Qg3 Qd7 Nf3 Nh5 Qh2 Bxf3 gxf3 g6 Re1 Bd6

Pradu wrote: Buzz seems to see it. Not quite sure what makes it work but probably try check extensions, singular-reply extensions, and perhaps checks in qsearch. Also recapture extensions might work on this position.

mambofish wrote:Ermintrude playing black, recently got itself into this position against a human player in a blitz game (6 seconds per move):

[d] r1bqr1k1/pp2bpp1/5n1p/3p2N1/3B3P/2PB1Q2/PP3PP1/R4K1R b - - 1 15

Having declined playing hxg5 for some moves, ermintrude wrongly judged it was now safe to do so, and lost a few moves later. When it played the knight capture it considered the PV to be

1. ... hxg5 2. hxg5 Ne4 3. Qh5 f6 4. Qh8+ Kf7 5. g6+ Ke6 7. Qxg7 with a score of +1.26 for black.

What it failed to consider after f6 was g6! which a human player would find very easily, and which leads to mate.

When I looked into this I realised what had happened. Ermintrude considers g6 to be a "quiet" move, and as black is a knight up at this point, the evaluation after g6 is short-circuited - no king safety check is done.

In fact, even if it had been done, it wouldn't have made any difference as the maximum value of all positional factors in the "slow eval" is only 75 centipawns and the knight capture would still have been played.

In fact the only way ermintrude could have detected the problem earlier was if it had extended the search after g6. To do this, it would have to somehow recognise that g6 is a deadly threat. The problem is that many such moves might appear to threaten the king, but only a few actually are genuine threats, so I don't do a specific king threat analysis for extensions as it is too expensive.

So I was wondering what do other people do? And how many of the other engines out there would also greedily make the capture at blitz time controls... !

Gerd Isenberg wrote:

Pradu wrote: Buzz seems to see it. Not quite sure what makes it work but probably try check extensions, singular-reply extensions, and perhaps checks in qsearch. Also recapture extensions might work on this position.

Some may even trigger extensions by some trojan-pattern and/or switch the eval in some take-care mode...