I’m happy to announce updates to both chess engines. Prophet 4.2 is approximately 50 elo stronger than 4.1, and 150 elo stronger than 4.0. (I missed a release announcement or two while this development blog was offline.) The most significant change, and the reason the chess4j major version number has been incremented, is that chess4j now includes an auto tuner! The tuner uses logistic regression with gradient descent to optimize evaluation terms. I’ll write more detail about that in a separate post. Those optimized weights have been added into Prophet, so it benefits from that work as well. Tapered evaluation has been fully implemented as well which added a few elo. I say “fully” because the king evaluation was already tapered, but now both programs fully evaluate the position with a middle game and an endgame score, and weight them based on material on the board. Some concept of mobility has been added as well – a simple count of available squares for both bishops and queens.
Here is how Prophet 4.2 stacks up against its current sparring partners in 1+0.5 games: