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Subject: Re: mate threat extension/null move

Author: Rick Bischoff

Date: 20:56:39 09/25/04

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Hi,

But this is what Bob Hyatt does in crafty-- quote verbatim from search.c:

      if (depth - null_depth >= INCPLY)
        value =
            -Search(tree, -beta, 1 - beta, Flip(wtm), depth - null_depth,
            ply + 1, NO_NULL, 0);
      else
        value = -Quiesce(tree, -beta, 1 - beta, Flip(wtm), ply + 1);

    ... snip ...

    if (value >= beta) {
        HashStore(tree, ply, depth, wtm, LOWER, value, mate_threat);
        return (value);
      }
      if (value == -MATE + ply + 2)
        mate_threat = 1;
    }


>
>if (x >= beta) return beta
>
>means that you don't return the actual scores, just the cutoff. This is fine
>until you try to detect threats. Then you need to return the actual scores
>because only those will have the mate in them.
>
>In WAC 141 you should hit a bunch of mate threat extensions on the way to the
>lowest ply because each time your Rooks take a pawn, and then the bishop, you
>should trigger one. In my search it still isn't enough to counteract the drop
>into qsearch where I don't consider checks. I've given up on generating the mate
>score in a short time right now (I have plenty of other problems!). It's enough
>that the first few plies in the PV are correct so if it actually hit it, it
>would find it. Of course that only works here because it turns out that the
>Queen sacrifice is good more material as well as mate!
>
>Andy.



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