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Subject: Re: MTD(F) results

Author: Andrew Williams

Date: 06:49:12 12/17/03

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On December 17, 2003 at 07:48:55, Anthony Cozzie wrote:

>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
>>
>>Andrew
>
>
>In most test suites the winning move is evaluated as losing by the SEE.  So in
>PVS() it gets tried last.  In MTD(f) it goes through all the moves every time.
>
>anthony

Sorry, I still don't understand? I would have thought that move ordering would
be pretty much identical for both methods? Am I missing something?

My engine is MTD(f) but if I were to convert it to PVS I think it would still
try all the moves in the same order, all things being equal. You should look at
Tord's message as he has some very good advice in there. The convergence
accelerator thing is *very* important.

Andrew



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