Computer Chess Club Archives




Subject: Re: MTD: an observation and a question

Author: Dieter Buerssner

Date: 13:50:38 09/12/02

Go up one level in this thread

On September 12, 2002 at 16:10:38, martin fierz wrote:

>bestvalue = -mate;
>for all moves do
>  {
>  value = -search(-beta,-alpha,etc);
>  bestvalue = max(value, bestvalue);
   alpha = max(value, alpha);
>  if(value>beta)
>     break;
>  }
>return bestvalue;
>is there anything wrong with this?

Pehaps you left it out on purpose - but this code snipped is missing an update
of alpha. For example at the place, I suggested above.

I see the same problem as you. Even when using strict fail soft search (I also
consider other points mentioned in this thread, like lazy eval), I typically
(but not allways) get back a score of X+1 for search, that fails high in the
window X, X+1. I think, your suggestions "alpha-beta tries to do the least work"
explains this. With a deep depth, and a complicated search tree, the X+1 score
will be easiest to prove and most probably be proven first.


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