Computer Chess Club Archives




Subject: Re: MTD(f) and hash table size

Author: Rudolf Huber

Date: 01:27:06 08/17/03

Go up one level in this thread

On August 16, 2003 at 17:17:26, Tord Romstad wrote:

>The last few weeks I have been experimenting with MTD(f).  It still does not
>work quite as well
>as my old aspiration alpha beta search, but I intend to keep working on it for
>some more time.
>Another problem is that MTD(f) has very weird effects when combined with the
>various forward
>pruning techniques I use.  This is not entirely unexpected, because I use the
>values of alpha
>and beta for pruning decisions.  When I replace plain MTD(f) (which I haven't
>been able to
>make work very well; too many researches) with MTD(f) with a convergence
>accelerator, I
>often get entirely different search results for the same position.  If I remove
>all selectivity
>(except null move pruning) from my search, changing the test driver does not
>have any
>effect on the search results, but then my program becomes much too slow.  I
>suppose I
>will have to work out new forward pruning techniques.

First scan you source files for occurences of alpha and beta. If you
find any look hard and try to understand what you are doing there. In
mtd(f) there ist NO alpha and NO real beta. All the things (lazy eval?)
you do with alpha and beta are most likely wrong. Use the last score instead.

Also I think it is a good idea to keep it simple. Why not disabling
forward pruning and your "convergence accelerator" and first try to make
your mtd(f) implementation better than negascout.


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