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

Author: Andrew Williams

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

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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.
>>
>>anthony
>

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.

Cheers

Andrew



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