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This has been tried many times before, with better-but-still-lackluster results. Sunfish is impressive because it's written in Python and in a tiny number of lines while still being readable. I LOVE Sunfish, but it is among the weakest chess engines in existence. That deep learning could not break even against Sunfish seems rather unimpressive.

The author seems to have a not-very-deep understanding of computer chess. Some examples:

>Better search algorithm. I’m currently using Negamax with alpha-beta pruning, whereas Sunfish uses MTD-f

MTD-F is not better, just a different way to accomplish more-or-less the same thing. MTD-F is a binary-search equivalent of the alpha-beta family of search. In fact, naively switching to MTD-F will probably result in worse playing ability. It takes some time to get it tuned right, and even then it is not objectively better.

>Better evaluation function...By generating “harder” training examples (ideally fed from mistakes it made) it should learn a better model

This is what every beginning chess programmer on the Computer Chess Club message boards and rec.games.chess.computer has wanted to try for the last 20+ years. It has been empirically demonstrated that for best results, the evaluation function should remain simple and fast. Improving evaluation rarely fixes "dumb mistakes". That's what search is for. Efficient search makes up for a multitude of evaluation mistakes.

>Faster evaluation function: It might be possible to train a smaller (but maybe deeper) version of the same neural network

If the evaluation function was reduced to literally take zero time to execute, it would not help significantly. It's a linear improvement being thrown at an exponential problem.

I would LOVE if there was a new approach to computer chess, but the current "smart brute force" approach is so far advanced and successful, it is hard to imagine another approach being competitive.

Thanks for the comment. I'm definitely happy to admit I have very limited understanding of computer chess and I think the likelihood of stumbling upon a new approach to chess engines is close to zero.

That being said, I'm not convinced there's anything "magic" about the fast deep search. There's a broad trend of big complex hand-tuned models being replaced by simple models with more parameters and many many orders of magnitude more training data (eg. machine translation, computer vision). There's probably a lot of domains where this approach doesn't work though. Maybe chess is one of those applications. We don't really know until we try :)

Hi Erik,

I've been associated with computer chess for a while, and was even given a shout-out by Vas Rajlich for optimization discussion prior to the release of Rybka 3.

I think this critic's view on the primacy of fast evaluation, at the expense in accuracy is off base. Looking at the two top engines today, Stockfish and Komodo, Stockfish has a great search function, but a poor eval, while Komodo's eval is better, but it's search isn't as good. It's pretty clear that bad evaluation is limiting, even at the leaves of a deep search.

Anyway, I have more basic questions about why you did what you did. First, it seems that your use of 12 x 64 sets of values to represent state information is non-optimal and even not sufficient. It seems that you are introducing a lot of unnecessary and undesirable additional degrees of freedom by duplicating the piece-square state inputs for white and black. When I've done this in the past, I used 6 x 64 sets with positive ones for squares with a white piece and negative ones for squares with a black piece. Do you see any advantage in not taking advantage of this symmetry?

Second, you really need side to move, castling state for each side, and the pesky en passant indicator (just as is required in a FEN representation). Luckily these don't significantly increase the number of inputs.

I worked on a similar project with a friend at University of Warsaw a number of years back. We generated static evals using FANN based on the complete input state, and trained with the value of the search plus eval after 30 seconds per move We used Rybka 2.2n for this, which was the strongest engine available at the time.

We both moved on after some preliminary success, mainly because there wasn't any way to conceivably make a top engine due to the closed nature of the top engines at that time. This is no longer an issue, and if someone had a black box evaluation function that produced a better eval than the current Stockfish static eval, it would be trivial to do the substitution.

Best Regards, Alan

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