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Subject: Re: MTD(F) results (sorry forgot to add this...)

Author: Andrew Williams

Date: 23:15:40 12/16/03

Go up one level in this thread

On December 17, 2003 at 02:12:08, Andrew Williams wrote:

>On December 16, 2003 at 21:22:56, Anthony Cozzie wrote:
>>Recently I experimented with adding MTD(F) into Zappa.  It has been an
>>interesting experiment, but I am going back to PVS().
>>I thought that since Zappa has a [UL,LL] paired transposition table and an
>>evaluation granularity of only 1/100 of a pawn, MTD(f) would work quite well,
>>but that does not seem to be the case.  The MTD(f) version of Zappa does
>>slightly better on test suites (113/183 @ecmgcp v 106 @ 10s/move) but in the
>>positional test suites it averaged about 3/4 of a ply less than the PVS()
>>version.  My guess is that because MTD(F) tries all moves, some of the
>>"ridiculously losing captures" ordered near the end by PVS() are tried earlier,
>>which accounts for the increased test suite performance.
>I don't understand the last part of this paragraph. Why would "ridiculously
>losing captures" be tried earlier (than what?) in MTD?
>>If anyone has any suggestions, I'm keeping the MTD(F) code in Zappa (just turned
>>off) and I'm willing to try anything.

One thing to look at is alpha- or beta-dependent pruning. In an MTD-based
search, you don't have *bounds*, you just have an *estimate* of the score, and
you can't use this is in pruning decisions. Instead you should use the bounds
which you have established in the MT Driver for your forward pruning tricks.



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