Computer Chess Club Archives




Subject: Re: Deep Search Extension

Author: Heiko Mikala

Date: 13:48:50 01/22/98

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On January 22, 1998 at 12:50:45, Bruce Moreland wrote:

>On January 22, 1998 at 05:03:38, Ernst A. Heinz wrote:
>>>>I tried Bruce's mate threat extension (everyone did, I guess...), and it
>>>>works fine.
>>I just gave it a quick shot but then put it on my to-do list because the
>>quick implementation made our search trees *explode* ... :-(
>For me it doesn't explode, but this could be coincidence.  I could have
>a hard time return values for mate in N where N is > 1, so this might
>not be activating unless there is a mate in 1 present.

Yes, I also do it only for mates in 1, and my trees don't explode. And
it helps with WAC 141.

But there was another reason for me to use this extension, which I would
like to share. There is a position in the BT2630 test suite (number 1),
which my program normally would solve in a 7 ply search, but using
null-moves this problem seemed to be unsolvable for my program. For
a very long time now I was searching for a way to be able to solve this
problem without changing my null-move implementation.
Then I implemented the mate-threat and the one-reply-to-check extension
and voila - the problem is solved in 7 plies again! Using only one of
two extensions alone doesn't help, but using both together does.
So the mate-threat-extension seems not only to help in finding difficult
solutions to some problems but it also seems to help against some
drawbacks of the null-move.


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