Author: Vincent Diepeveen
Date: 10:38:55 06/16/05
Go up one level in this thread
On June 15, 2005 at 22:40:22, Tor Alexander Lattimore wrote:
I wonder why there is still people using MTD in chessprograms above PVS.
In PVS you can of course easily determine the maximum number of nodes you had to
search extra on top of nullwindows. In DIEP it's just a couple of thousands at
in total millions of moves.
So the theoretic gain MTD CAN give, when you start measuring it, it is really
negative.
For material only searches or evaluation functions which have little fluctuation
and a small range it's pretty fast though to use MTD, provided you don't mind to
lose sometimes games when you hit its worse case.
The worst case you can see in the program ParSOS very well at world champs,
when it starts to doubt then it has a search depth of plies less to the others.
Nevertheless here my answers:
>Hi
>Is it possible to use a single variable in the MTD(f) search? Something like
>this:
>
>int MTD(int depth, int guess)
>{
> if (depth<1) return Evaluate();
Using hashtable in qsearch of course is a necessity for MTD because of the many
researches you're doing.
So for very fast searching software MTD is pretty expensive to use, as the
hashtable more and more gets a big overhead. Crafty (correct me if i'm wrong for
latest version) isn't hashing in qsearch for example.
> MOVE move_to_search;
> int best=-INFINITY;
> GenMoves();
> while (GetNextMove(&move_to_search))
> {
> PlayMove(move_to_search);
> val = -MTD(depth - 1, -guess + 1);
If you just search with 1 bound, then it's obvious to do:
val = -MTD(depth - 1, -guess);
> UnPlayMove(move_to_search);
> if (val>best)
> {
> best=val;
> if (val>=guess)
break;
> }
> }
> return (best);
>}
>
>perhaps there is something very wrong with this? or perhaps it's used already, I
>just noticed that on Aske Plaat's site he always uses an Alpha-Beta search with
>0 width windowed searches, but doesn't this do the same thing? Is using
>fail-soft type algorithms used in MTD(f) since it could well help zoom into the
>correct score sooner?
>
>Cheers
>Tor
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