Author: Jesper Antonsson
Date: 02:39:31 07/27/02
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On July 27, 2002 at 05:30:45, Ricardo Gibert wrote: >On July 27, 2002 at 05:01:42, Jesper Antonsson wrote: > >>I thought of a simple idea of EGTB optimization and I wonder whether it's been >>tried already. Imagine we have a position that is legal on the surface, but >>unreachable in a real game, like this one: >> >>[D]8/8/8/8/8/4k3/4p3/4K3 b - - 0 1 > > >This position is reachable in a real game. Whites previous move was a move to >get out of check by the pawn. Blacks previous move before that was a capture by >his pawn giving check, etc. Oups! Sorry, of course. Bad example of me. >>I believe standard EGTB calculation algorithms will store this as a mate in n >>for black, as Kf3 or Kd3 result in wins. Wouldn't it be beneficial to mark such >>positions as broken, so as to get better compression? It can obviously be done, >>even for "deeper" unreachable positions, essentially by iterating over the EGTB, >>but perhaps it requires information about illegal positions that aren't in >>current EGTB, and then a regeneration would be necessary. >> >>Note that for five men tables, just the example position above will come up in >>many variants with two more black pieces on the board. I have no idea of the >>ratio of such broken positions to legal positions, though, but it would be >>interesting to know.
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