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Subject: Re: Futility Pruning

Author: Tony Werten

Date: 14:36:20 12/20/02

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On December 20, 2002 at 17:20:26, Uri Blass wrote:

>On December 20, 2002 at 16:30:32, Vincent Diepeveen wrote:
>
>>On December 20, 2002 at 12:02:23, Uri Blass wrote:
>>
>>>On December 20, 2002 at 11:26:28, Richard Pijl wrote:
>>>
>>>>On December 20, 2002 at 10:54:01, Vincent Diepeveen wrote:
>>>>
>>>>>On December 20, 2002 at 08:23:59, Russell Reagan wrote:
>>>>>
>>>>>No futility is 100% different from lazy evaluation.
>>>>>
>>>>>Futility in fact selects less moves (in qsearch)
>>>>>based upon alfa or beta and lazy evaluation gives
>>>>>back a quick score a lot of the times.
>>>>
>>>>They are still related in a sense that both 'cut-off' the work to be done by
>>>>saying that it can't get good enough to improve alpha, so better stop working on
>>>>it.
>>>>>
>>>>>If you search a ply deeper a futile pruned move should not
>>>>>get pruned, whereas a lazy evaluated position will give problems
>>>>>no matter what depth you search.
>>>>>
>>>>>In contradiction to draughts where everything is seen fullwidth,
>>>>>in computerchess the effect of futility can be very bad too,
>>>>>because last 3 to 4 plies (R=2 versus R=3) the qsearch is returning
>>>>>back a score instead of a full search.
>>>>>
>>>>>If that misses major problems then you are in trouble.
>>>>>
>>>>>The argumentation of Heinz that futility is correct, is using the
>>>>>assumption that an evaluation doesn't get a big score for positional
>>>>>matters. The problem is that todays top programs do give big scores
>>>>>though.
>>>>
>>>>Although Baron is not a top program yet I'm starting to feel this.
>>>>To be sure that the wrong nodes aren't getting pruned I wrote a little piece of
>>>>test code. It returned the highest difference it found between the lazyeval
>>>>score and the full eval score (but not with passers on the board, and not in the
>>>>endgame). I added 20% to this and that was the threshold used for both lazyeval
>>>>and futility pruning. It turned out that with every release of the Baron this
>>>>value increased.
>>>>Now I'm working on 0.99.4 and the margin was getting very large, more than 5
>>>>pawns.
>>>
>>>I think that it may be interesting to see the position that you talk about
>>>
>>>When do you see a difference of more than 4 pawns between the static evaluation
>>>and the lazy evaluation?
>>
>>define lazy evaluation in this case. Just material component or
>>a function that quickly estimates lazy eval?
>
>I think that the definition of lazy evaluation may be a function that quickly
>estimates the real evaluation(not just material)
>
>The estimate can also say that the big evaluation need to be done in small part
>of the cases (for example you can decide that if there are no pawns near the
>king then king safety can get big scores so you cannot trust fast evaluation).
>
>>
>>Note that just a diff of > 4 pawns is not interesting, only when it
>>would modify alfa or beta it is;
>>
>>if lazy eval is 2 pawns white up and actual score is 3 pawns white up
>>and beta is 1.5, then obviously it is not interesting. A cutoff is
>>a cutoff, isn't it?
>>
>>Idem for <= alfa.
>>
>>The interesting thing is when your quick eval with a margin is
>>at the other side of the bound (alfa or beta) than the real eval.
>>
>>In diep i produced a big graph and found out that 1% was wrong.
>
>If I understand correctly in 99% of the cases when lazy without margin was in
>the wrong side of the bound lazy with margin was right.
>
>I am still surprised to read it
>My question is if you evaluate tactical stuff like pins or forks because my
>opinion is that positions when positional stuff worth more than 3 pawns are
>rare.

Don't forget that one side only has to be 1,5 pawn up and the other 1,5 pawn
down.

Tony

>
>You say that you worked 3 monthes about your fast evaluation so the question is
>in how many cases only material+margin of +3 is wrong.
>
>
>Uri



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