Pawn structure evaluation

Lately I spent some efforts trying to improve the evaluation of pawn structures. A pawn structure is a rather long lasting feature of a position. A good understanding of strength and weaknesses of those structures helps the engine to better understand the position.

I'm not so happy with the current evaluation of iCE in that area so I tried to improve it. I studied some of the theory e.g. Pawn Power in Chess by Hans Kmoch and tried to deduct meaningful patters like different kinds of double pawns (the closely shielded central double pawn which is not necessarily a weakness), isolated and backward pawns, levers etc.

I modified my evaluation with those patterns but unfortunately none of the regression tests succeeded. The best version was still a minor regression of about -4 ELO although I noticed that the playing style of the engine changed a lot. Usually if I test a new version against the old one I have a draw ratio of more than 50%. Here I only experienced a draw ratio of only about 30% which is the usual draw ratio of unrelated engines. So the changed pawn structure code had a significant impact. To bad it was not stronger.

So I went back to my old evaluation.

Nevertheless it was not a complete waste of time. Not my engine but I did learn something along the way about pawn structures and I got an impression what terms to target next. But overall of course I hoped for a better outcome.