Author: Stuart Cracraft
Date: 07:04:58 09/11/04
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On September 11, 2004 at 05:34:37, Richard Pijl wrote: >On September 10, 2004 at 21:35:58, Stuart Cracraft wrote: > >>I read, somewhere, and I forget who, about >>if 1 legal move, extend 2 ply, >>2 or more legal moves, then 1 ply. >>Anyone have any stats on the effects >>on play of the above instead of >>always extend 1 legal move. Does it >>blow up? > >I do this in two steps: extend 1 move for giving check, extend 1 move for a >single reply, so in fact that is extending 2 moves on the single reply on check. >Because I've spread it out over two moves, no other extensions can fire during >these two moves (the move giving check, and the move out of check). If you >extend 2 ply on one move you might extend the next move for e.g. recaptures or >threats. I also limit the extensions when the tree is getting too deep. >> >>How do people get around the cost >>of determining that there is only >>1 legal move? >> >>For me, that's an expensive operation >>involving usually dozens of makemove/unmakemove's >>with a test to see if the king is attacked, >>at every single node, before doing the search >>of the 1 move with the increased depth. > >It is not really expensive. In a semi-legal move generator you will have to >iterate over every move in the regular search loop anyway. When in check, I loop >over every move in the movelist and remove the illegal ones, and determine the >number of legal replies. When I start the search loop only the legal moves are >left, that are usually not many. >Besides determining the number of replies, some other thinks can be done as well >while determining the number of replies (e.g. ETC, or perhaps also repetition >checks (when beta < 0 so a repetition would give a beta cutoff)) >Richard. > >>Only rarely is it just 1 legal move to get >>out of check. But the determination of that >>is not rare. It has to be done for every >>sweep of the moves at each node. >> > >>Thanks, >> >>Stuart Thanks -- I found your message very well written and understandable.
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