Author: Dezhi Zhao
Date: 12:51:53 12/03/02
Go up one level in this thread
On December 03, 2002 at 04:26:50, scott farrell wrote:
>I choose to start the story now ...
>
>A few months ago I added code to show "mate in 4" rather than just mate. It uses
>mate-depthTree in order to document the mate depth.
>
>This helped alot in actually mating opponents, as it can choose the shortest
>route to mate. rather than as it was just doing lots of checks, that all lead to
>mate, and randomly actually mating the opponent.
>
>This worked well, EXCEPT, in deep checking lines, it actually fails slower, as
>it tries to look for a better mate. So it actually blew nodes out somewhat on
>some test positions.
>
>I still go a few more plies during iterative deepening to try to find shorter
>mates - due to null move and pruning etc. But these searches seem to be slow
>also.
>
>I recently added a nice piece of code:
>
>if (alpha>INFINITY/2){
> matein= INFINTY-alpha; //or whatever you use to calc mate depth in plies
> if (depthTree>matein)
> return alpha;
>}
>
>Do others think this is valid? fail low if you are already too deep, and just
>fail low.
>
>It sure verifies the mates about 1000 times faster.
This does cause some problems. You could notice the problem of producing longer
than necessary mate sequence if you test more positions.
Worse than that, sometimes your modification may cost much more nodes in some
positions. Your trick sounds logical at first sight. However, you must take
transposition into account, which makes the seemingly futile search productive
instead sometimes. I realized this when I played with such idea 2 or 3 years
ago.
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