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Subject: Re: MTD(F) results

Author: Anthony Cozzie

Date: 07:23:20 12/17/03

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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.
>>>>
>>>>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

Suppose there are 3 moves, A, B, C.

C is a losing capture according to see, so it is tried last.  So in PVS(), we
get:

A B C++ <- c fails high
C A B

in mtd(F) we get

A B C
A B C++
C A B
C A B
C A B
C A B

in other words, it figures out that the score is higher very rapidly, and plays
move C relatively earlier.

anthony



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