Author: Robert Hyatt
Date: 20:24:02 05/26/99
Go up one level in this thread
On May 26, 1999 at 23:18:09, Robert Hyatt wrote: >On May 26, 1999 at 23:14:59, Robert Hyatt wrote: > >>On May 26, 1999 at 20:22:28, Paul Richards wrote: >> >>>On May 26, 1999 at 19:32:02, José de Jesús García Ruvalcaba wrote: >>> >>> >>>> The main problem is that no program will see the repetition, as white >can easily make 50 moves without allowing a third repetition. The program >>>>would need to detect the 50-moves draw with the search, and that would not >>>>be enough as white can make five pawn advances, resetting the count. >>>> Then the program needs to search 50x5x2=500 plies to detect the draw, >and that is quite far from what current programs reach on current hardware. >>> >>>Crafty completely ignores gxh6?? as an option, and if forced to make the move, >>>realizes the position is drawn at 16 ply (this is within the Fritz GUI, >>>no tablebase access enabled. So what is the code that allows it to avoid >>>gxh6?? immediately, and how does it determine the draw after making the move >>>gxh6? This would be rather easy for Dr. Hyatt to explain, hence the use of >>>the word Crafty in the subject to draw his attention. :)) In any case most >>>programs do see the draw, and without resorting to tablebases. >> >>To see a draw, in this kind of case, you need two circumstances: The side >>that is 'seeing' the draw hopefully thinks it is better. The other side, >>therefore, thinks it is losing. >> >>Given those two, the side trying to win discovers that if it doesn't play the >>move leading to a draw it loses outright. But by playing the move that does >>lead to a possible draw, the opponent can't find any way to win, and since that >>side thinks it is losing, it heads to the draw a.s.a.p. Not knowing that it >>can also play a much longer draw if it wants. >> >>Cray Blitz would handle this far differently, but it would produce the same >>result. If the other side (in this position) was well ahead, then the other >>would not be able to force a draw it could see, because the winning side would >>try like mad to avoid the draw and push it off so far into the future that it >>would not be seen. In essence this is a position where the drawing move is the >>only move that doesn't lose, and by playing this the other side becomes >>convinced that taking the draw is the right thing to do. >> >>Almost like _both_ sides think they are losing, but not quite. :) > > >also I didn't look at the position, but there are many positions that Crafty >knows about... ie bishop + rookpawn of the wrong color. So that it can >evaluate something as drawn even though it is way up in material. Perhaps >Fritz doesn't know about this. It is amazing how many programs don't know >about not playing Bxa7 if black can play b6 and trap the bishop. But I watched >Crafty spring this trap on two well-known programs yesterday and today on ICC. >B+RP is just another important piece of knowledge that will save a game here >and there at nominal execution time cost. OK.. I read the whole thread, and tried it. It is the piece of knowledge that says K + B + RP on wrong color draws if the opposing king can get to the queening square before the pawn. That is why Crafty plays Nh6 as black and _never_ considers gxh6. If you play Nh6, a 1 ply search rejects gh because it evaluates to DRAW. Very simple answer after looking at it.. so forget my first answer. That happens, but not in this case...
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