Author: Robert Hyatt
Date: 15:26:29 11/26/98
Go up one level in this thread
On November 26, 1998 at 09:36:38, Dusan Dobes wrote: >On November 25, 1998 at 13:35:13, Robert Hyatt wrote: > >>Here is another one: >> >> +---+---+---+---+---+---+---+---+ >> 8 | *K| | | | | | | | >> +---+---+---+---+---+---+---+---+ >> 7 | *P| *P| | | | | | | >> +---+---+---+---+---+---+---+---+ >> 6 | | | | | | | | | >> +---+---+---+---+---+---+---+---+ >> 5 | | | | | | *Q| | | >> +---+---+---+---+---+---+---+---+ >> 4 | | *P| | | | | | | >> +---+---+---+---+---+---+---+---+ >> 3 | *P| P | *R| | | | | | >> +---+---+---+---+---+---+---+---+ >> 2 | P | | P | R | | | | | >> +---+---+---+---+---+---+---+---+ >> 1 | | B | K | | | | | | >> +---+---+---+---+---+---+---+---+ >> a b c d e f g h >> >>fen: k/pp//5q/1p/pPr/P1PR/1BK b >>This is another zug case... Qf1+ Rd1 Qf4+ Rd2 is the key stuff. > >This is also mate in 2, no checks needed: Qf4 Kd1 Qf1# >Your two examples can be solved if you dont do null moves in positions >where side to move has less than (e.g.) five legal moves, this works >for most zugzwangs. You must generate all legal moves before trying >null move, however, and that costs time. that's the issue... the only time this normally happens is when you are in check, and nulls aren't done there anyway... But when it happens it crashes things... > >>Other serious cases happen in a different way... >> >>suppose black has played g6 after castling kingside... if you reach a position >>in the tree with white having a queen at h6 and a pawn/bishop at f6, with no >>way for black to defend g7, this is a mate in 1. But if you reach this position >>with black to move, near the depth limit on the tree, black can play a >>null-move, which reduces the depth by 2 extra plies, which can take you right >>to the capture search where you don't find Qg7#. This used to kill me until >>I got my speed up to the point where I don't do 4-5 ply searches, even in >>bullet, any longer. If you do a 5 ply search, and reach this at ply=2, you are >>dead, because white's next move will be a quiesce() move... and it will likely >>overlook Qg7# unless you include non-captures in the q-search... > >Here is an example of the g7 weakness: years ago i killed MChessPro 3.5 >(on a 486/50, i think) in a slow TC game with this simple mate in 6: >r4rk1/4npp1/p1b1p3/qpp1P1P1/4NBQ1/2PP2P1/P4P2/R3R1K1 w Ne4f6+ >Phalanx on a P90 needs 37 seconds to find the move. With null move off, >it's only 3 seconds. I do try some interesting checks in quiescence and >that helps too. > >Dusan this will not be so bad if you do checks in q-search. Cray Blitz did and I never saw this as a problem... But for my simplistic q-search, it can be a killer... So I catch this positionally so that it won't fail high with such a position on the board...
This page took 0 seconds to execute
Last modified: Thu, 15 Apr 21 08:11:13 -0700
Current Computer Chess Club Forums at Talkchess. This site by Sean Mintz.