jomega
STS(v10.0) Simplification.018
Continue the kingside attack, or not?A continuation of the discussion started here:
jomega's Blog • Strategic Test Suite (STS): The EPD file's best and alternate best moves. • lichess.org
Another interesting position for which Stockfish 14 failed to find the best move in the 3 second (depth 21) test.
Stockfish simply did not have enough time to compute a reasonable move. At depth 21, it came up with 1.Kh1. At higher depths, Stockfish prefers to prepare for the White Queen's retreat, with a complex position. A human would prefer the simple approach.
The Human Perspective
White is attacking kingside and Black is defending. White's Queen is severely restricted, but participating in the kingside attack. White can either continue the kingside attack or get the White Queen some air.
In terms of positional features, Black has the "hanging pawns". See my study
https://lichess.org/study/y1wA1JDw/
Black has weak dark squares on the kingside. White is already occupying some of those with Knight and Queen and so Black has to maintain a second rank defense. White has a backward b-pawn on a half-open file.
In the plan to continue the kingside attack, White does not want to immediately play h5 because Black would exchange Rooks; pulling the d1-Rook off the attack of the d5-pawn. Hence, 1.Rxe7 is best first for that plan. In the plan to get the White Queen some air, the best move for that plan is 1.Nf3, so that the Queen can come back on the diagonal.
The first plan is the simplest approach. I think most humans would prefer the clear cut position obtained in the mainline variation of 1.Rxe7, to the complex positions arising after 1.Nf3. In the position at the end in the mainline variation, White is a clear passed pawn up, and the Queens have been exchanged.
Stockfish's Perspective
Stockfish wants to play 1.Nf3 so that the White Queen is not restricted. One can get some clue that this is what is going on inside Stockfish by the variation given, and by looking at the Graph tab on hxim.github.io/Stockfish-Evaluation-Guide/ for this position. If you want to do this yourself, paste in the FEN for the initial position on that page.
On that Graph tab page, there is displayed a static evaluation of the position by Stockfish using equivalent code. There are 50 categories displayed on the far left. Each of those can be clicked and you are then taken to a page that explains that category. The bars extending to the right are indicating a White advantage, while the ones extending to the left are indicating a Black advantage. Notice the category 'Restricted'. This measures the restriction of the opponent's pieces; in the case the White Queen.
Stockfish calculates that the attack on the hanging pawns will succeed despite complexities.
EPD Changes Needed
The move 1.h5 is premature as pointed out in the study. The other suggested moves by Stockfish, except for 1.Nxh7, and in particular 1.Kh1, are clearly inferior. The move 1.Nxh7, sacrifices the Knight for 3 pawns giving White 3 connected passed pawns - an interesting choice for an engine that is very aggressive.
The scores in the EPD should be Rxe7=10, Nf3=8, Nxh7=3.
Links
- The Strategic Test Suite (STS) home page.
https://sites.google.com/site/strategictestsuite/
- The STS-rating code.
https://github.com/fsmosca/STS-Rating
