Author: Heiner Marxen
Date: 10:35:59 08/14/00
Go up one level in this thread
On August 14, 2000 at 10:20:59, Uri Blass wrote: >On August 14, 2000 at 08:43:08, Enrique Irazoqui wrote: > >>This one is a MES position: >> >>[D]3B4/1r2p3/r2p1p2/bkp1P1p1/1p1P1PPp/p1P1K2P/PPB5/8 w - - 0 1 >> >>After 6.f5, all programs I tried evaluate it from +11 to +17. >> >>Enrique >> >>[Event "?"] >>[Site "?"] >>[Date "????.??.??"] >>[Round "?"] >>[White "MES.941"] >>[Black "?"] >>[Result "*"] >>[SetUp "1"] >>[FEN "3B4/1r2p3/r2p1p2/bkp1P1p1/1p1P1PPp/p1P1K2P/PPB5/8 w - - 0 1"] >>[PlyCount "11"] >> >>1. Ba4+ Kxa4 2. b3+ Kb5 3. c4+ Kc6 4. d5+ Kd7 5. e6+ Kxd8 6. f5 * > >This example proves that programs do not know to search the right lines. >It is possible to prove that white has at least a draw by search+hash tables if >you search the right lines. > >The number of relevant positions that programs needs to look at in order to >prove by a tree that white has at least a draw is >4*(22*21)/2*19*17*2=78*231*34<1000000 so it is not a problem for the right >program to prove the draw. > >4 is the number of squares for the black bishop. >19 is an the number of squares of the black king(after choosing a square for the >bishop). > >22*21/2 is the number of squares of the black rooks(after choosing the squares >for the black bishop and the black king). >17 is the number of squares for the white king. >2 is the number of sides to move. > > >The only problem is that programs need to be selective in searching white moves >and to avoid searching captures of white and chess programs do not know to do it >(the first move that they analyze is capturing the rook in case that it is >possible). > >Uri That is not enough. The program also has to find that white can force a "draw by repetition". When you try to do this as part of the normal search, the minimum search depth needed to recognize it is the length of the longest cycle that the opponent can manage to set up. Here it is in the order of 4*(22*21)/2*19, = 17556. That if far too much for a search depth. I.e. you also have to have a special detection algorithm. The normal search is not sufficient to recognize such large loops. Of course, it can be done ;-) it is just not very easy. Heiner
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