Author: Robert Hyatt
Date: 10:28:48 02/26/04
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On February 26, 2004 at 04:23:01, Gerd Isenberg wrote: ><snip> >>>To avoid the white versus side to move score chaos, it makes sense to mirror all >>>>current black to move positions vertically with white to move. >>> >>>Oups, with mirror vertically i mean white pawn on e2 becomes black pawn on e7 >>>and so on. >> >>i prefer also left right mirrorring. I bet diep is one of the few programs still >>displaying the same score then :) > >A good point, with respect to castle rights of course. >In my current program there are some asymmetries in (early) middlegame :-( > >In my new approach i will implement FRC-castles, but mirroring castles (rights) >is still not possible since king/rooks target squares are still asymmetric. > >Gerd I assume he is talking about post-castling positions or mirroring makes no sense. But in Crafty, I regularly run a "flip/flop" test on my evaluation. I set up a position and compute the static evaluation, then I flip (this mirrors along the line between the 4th and 5th ranks, so that white becomes black and vice-versa. The eval should change its sign but nothing else. I then use a "flop" which mirrors along the line between the e and f files, so that a pawns move to the h-file, etc. The eval must not change at all. I have a function "ev test" that does this for me, so that it flips, flops and flips again, to produce the four different positions you can get by mirroring along the two lines given above. The scores for flops can't change, but the scores for flips much change nothing but signs. I do eliminate the two asymmetry points in the eval when I test this because crafty evaluates blocked pawns asymmetrically, and I comment that out, and the king safety asymmetry is simply set to zero with the "eval asym 0" command... It catches some bugs now and then, that might be overlooked.
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