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Subject: Re: MTD(F) results

Author: Richard Pijl

Date: 07:24:52 12/17/03

Go up one level in this thread

On December 17, 2003 at 09:49:12, Andrew Williams wrote:

>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.
>>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.
>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?

Moveordering is identical, but in PVS the 2nd move is only tried when the 1st
move is fully searched. In MTD(f) (as I understood it from Aske Plaat's paper)
you try all moves with the initial 0-window before, in which case the moves
ordered last are searched earlier than when using PVS.

>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.

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