Author: Gerd Isenberg
Date: 12:19:56 02/26/04
Go up one level in this thread
On February 26, 2004 at 13:28:48, Robert Hyatt wrote: >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. I have that features too, even rotating a->h or h->a, which is particular interesting with some endings. Anyway, i still have some slight left-right asymmetries in post-castling positions. Exactly as Vincent pointed out. Queen- and kingside issues even in late middlegame and probably isolated d- versus e-pawn in middlegame. [D]8/k1p1r3/p2b3p/5ppq/1np5/6P1/1R1N1P1P/R4QK1 b - - ; am c3 [D]8/3r1p1k/p3b2p/qpp5/5pn1/1P6/P1P1N1R1/1KQ4R b - - difference: 0.04 similar search behaviour... Gerd
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