Author: Vincent Diepeveen
Date: 08:56:40 04/10/01
Go up one level in this thread
On April 10, 2001 at 11:15:50, Robert Hyatt wrote:
>On April 09, 2001 at 23:40:21, Jon Dart wrote:
>
>>>On April 09, 2001 at 17:04:09, Vincent Diepeveen wrote:
>>
>>> An interesting thing is lazy evaluation, as the problems of it are
>>> very similar to futility pruning.
>>
>>As another poster has said, it is not really risky to exit the eval early if
>>you're certain you are going to be have a score outside the search bounds. I
>>have a test mode where it goes through the full eval always but also checks to
>>see if it would have done a lazy exit, and if so, if it would have done so in
>>error. I run it once in a while and expect no errors.
>>
>>> A possible compromise i found in tests was to increase the margin.
>>
>>Yes. Crafty apparently uses a 1 pawn margin for futility pruning in the qsearch.
>>I tried this and didn't like the results. Mine is almost 2 pawns.
>
>I do this because a _single_ move should not produce _huge_ score swings. The
>futility pruning is based on the stand-pat score, which means that the current
>position is evaluated, and the only possible change will be from the piece
>being captured, or the positional score the single capture can produce. I tried
>several values and have had good luck with the current one.
classical example: tossing a pawn and then i keep left with a passer
somewhere because of the tossing which is unstoppable.
If that doesn't increase score :)
>
>
>>
>>I also account for trade bonuses and other adjustments to the material score
>>that would be made as a result of the capture. So I'm pretty conservative, at
>>least in the qsearch (I do other somewhat riskier pruning in the main search).
>>I've been trying some alternative strategies lately but haven't found reason to
>>make major changes so far.
>>
>>> My big question was: what score to return for example if evaluation in this
>>> position is e and e+ 3.5 pawns <= alfa ?
>>
>>> Must one return alpha, estimated evaluation or evaluation+3.5 pawns,
>>> when talking about e+margin <= alfa (idem story for e-margin >= beta) ?
>>
>>I return the estimated evaluation. But I fail to see that it makes a lot of
>>difference. If it's below alpha, you're not going to propagate this evaluation
>>up the tree, anyway.
>>
>>--Jon
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