STS(v15.0) AT.005

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

Category 15.0 is "Avoid Pointless Exchange". This category was never added to the original web page for STS. The designation "AT" meaning "attacked"? I don't know why it is named "AT".

The intent of the position is that the engines should avoid the pointless exchange of Queens.

Stockfish 14 failed to find the best move in the 3 second test. Stockfish 14 suggested 1.Rfe1/25. That actually is not a bad move from a human perspective, or for an engine to play. Often you can gain tempi in such a situation by defending the piece being attacked. Compare this to the alternate move in the EPD, 1.Qd4. The EPD gives this a 9 out of 10 score. However, that move is not very good. Best is the intended 1.Qb4.

My study on this position is here:

The Human Perspective

Black is threatening to play ...Qxe4, capturing White's Queen. Exchanging Queens would truly be pointless; the response would be for the Black Bishop to recapture, and so White has helped Black develop that Bishop. The intended best move of 1.Qb4 threatens 2.Qxf8+, winning, and also 2.Re1, winning. The move 1.Rfe1 does not avoid the exchange, but does not initiate it either. If Black then exchanges Queens, then White gains tempi for the development of the f1-Rook. Attempting to gain tempi in this way with 1.Nc5 does not work out as well - it takes analysis or experience to see that.

Stockfish's Perspective

Stockfish evaluates many White alternatives as close to zero. Stockfish does not like 1.Qd4 at all. It gives 1.Qd4 -1.0/31; basically cooking that move. Stockfish at a depth of 23 and 42 evaluates 1.Rfe1 and 1.Qb4 as 0.0. This explains why Stockfish chose 1.Rfe1. From Stockfish's point of view it is "pointless" to prefer either of two moves which both lead to a draw!

EPD Changes Needed

Despite the intent of the EPD, 1.Rfe1 is a very reasonable move. On the other hand, the EPD move of 1.Qd4, and its score of 9, is wrong. After 1...Ba7, the Queen has to move again. As the analysis shows, the best move at that point is 2.Qd6 and the Queens get exchanged; however White has gained nothing and Stockfish says -1.0/22 at the end of the line. I'd leave Qg2 as an alternate with a low score. It is the right idea; just not the best square for the Queen.
Changes to the EPD: Qb4=10, Rfe1=9, Qg2=2, and remove Qd4 as an alternate.

Links

- The Strategic Test Suite (STS) home page.
https://sites.google.com/site/strategictestsuite/
- The STS-rating code.
https://github.com/fsmosca/STS-Rating