Author: Robert Hyatt
Date: 16:50:51 03/24/99
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On March 24, 1999 at 09:30:19, Inmann Werner wrote: >Hello. > >My question sure is a little dumb, but anyway.... > >When in Qsearch a check occurs, and the opponent can not come out of the check >(cause he only tries capture moves!) a position is evaluated to be mate, >although this is not right. >I am worried about this, but looking at the play of my program, it seems to >never occur. >In normal search, when a check comes, I extend. I also extend on the way to the >Qsearch. But if I am really in Qsearch I seem to ignore the problem. > >Is it a problem or am I seeing Ghosts? > >Werner Here are some choices: 1. ignore (don't detect) checks. This is what I do. 2. Detect them, and when you do, do a normal move generation, and not a capture-only generation. Then try all the moves and if none are legal, you can safely declare 'mate'. (2) has a problem, in that suppose you are 6 plies into the q-search, and you find mate. You back this up to the previous ply and your opponent can choose to 'stand pat' rather than try a capture that leads to getting mated. And you can't see/force the mate. There are a couple of solutions to this (if you check your opponent at the first ply of q-search, he _has_ to try all moves in (2). Then if you check him again at ply=3, he has to try all moves, so that as long as he is in check, from the front of the q-search until you mate him, you _know_ he couldn't stand pat. But it isn't 'free'...
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