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Subject: Re: MTD is a big disaster

Author: Vincent Diepeveen

Date: 23:25:44 07/20/99

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On July 20, 1999 at 23:57:13, Dan Homan wrote:

>On July 20, 1999 at 20:35:49, Vincent Diepeveen wrote:
>>On July 20, 1999 at 11:25:07, Dan Homan wrote:
>>>On July 20, 1999 at 08:52:18, Vincent Diepeveen wrote:
>>>>Let's however write down some facts why my prog is unhappy with MTD.
>>>>It's up to others to generalize it to their progs:
>>>>  - the huge number of researches needed. In DIEP my evaluation is nowadays
>>>>    in 1/1000 of a pawn. For a long time i had 1/200 of a pawn (in the time
>>>>    i experimented with MTD), but now i have 1/1000 of a pawn. So a drop
>>>>    of 0.20 pawn, which is a normal drop in DIEP, is in fact a drop of 200
>>>>    points. Happy researching!
>>>Even if the score dropped a whole pawn (1000 points in DIEP), this would
>>>only be 10 or 11 zero-width searches (2^10 = 1024) assuming that you
>>>bound the score in an efficient manner.  Also,  I can understand having
>>>a high resolution within the eval routine itself, but does it really help
>>>to have the output of the eval be in 1/1000 pawn units?  I wouldn't trust
>>>the sum total of any eval routine to 0.001 pawns! Maybe you could
>>>output the total eval in units of 1/100 of a pawn (or even less).
>>>Actually, that is an interesting question.  Does anyone know what the
>>>optimum eval unit is for searching?  I am talking here only about what
>>>the eval outputs - not the unit used internally for calculating the eval.
>>>I know that most programs use the same unit for both purposes, but I
>>>wonder if that is really optimum.
>>Every time i get to a draughts tournament i have to laugh a little when
>>playing a certain program. It has a stone at 1000 points worth,
>>yet he has no positional eval in 1/1000 of a stone. Only in 1/10 of a
>>pawn. So he's either at +0.100 or -0.100 or a multiple of that.
>>If you only count material in chess
>>you can of course simply use 10 for a pawn.
>>a pawn = 1, knight=3,bishop = 3, rook=5, queen=10
>>and you're ready. MTD will rock i bet.
>>Start with window 0 from root,
>>and end the game with a window -100.
>>Hope that answers, as your question is kind of retoric.
>My question was serious.  I have a way of going from one idea
>to another - sorry about that.  I started by pointing out that
>you didn't need to do as many researches as you thought, to
>wondering what benefit you got from using 1/1000 of a pawn
>during your search, to the general question of whether it
>is a good idea to use different eval resolutions internal
>to the eval routine and when you return a value to the search.
>I wasn't suggesting anything as crazy as setting the eval
>resolution as coarse as one pawn.  What I was curious about was
>whether the search was improved by having you eval output results
>in 1/1000ths of a pawn.  I can understand the benefit of having
>1/1000 internal to the evaluation routine - this way small
>positional benefits can add up to something significant, but
>might is it useful to return the value to the search with
>less resolution than 1/1000th?  Do you see what I mean here?
>Lets say the eval works in 1/1000 units.  Add all the scores
>up for pawn structure, king safety, piece placement, etc...  Now
>we have a total score in 1/1000 units of a pawn, but do we trust
>this total score to this accuracy?  Should we return this raw score
>directly to the search or should we round it down to 1/100 of a pawn
>or perhaps even less?  Is there benefit in keeping the 1/1000
>resolution when we return the total score to the search?  Is there
>benefit to the searching routines in rounding the score down to a
>coarser resolution?
>I don't know the answers to these questions.  I tried it briefly with
>my program (which works in 1/100 of a pawn normally) by simply
>bit shifting the eval result so the resolution was 1/25 of a pawn.
>I noticed a (small) speed-up in the search, but I worried that this
>resolution was too coarse and took the changes out.

before my eval returns to the search i can obviously lose knowledge
by shifting my score of 1000 pawn units to 10 pawn units,
but it won't play well then.

Idem for 100
> - Dan
>>Sorry to bother you, forgot the name of your program and the number of
>>nodes a second you get with it.
>>> - Dan

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