Author: Uri Blass
Date: 23:48:11 12/25/03
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On December 25, 2003 at 20:32:24, Christophe Theron wrote: >On December 25, 2003 at 14:35:53, Uri Blass wrote: > >>On December 25, 2003 at 14:04:47, Christophe Theron wrote: >><snipped> >>>By experience, no smart evaluation can compensate for the loss of one ply of >>>search. In theory evaluation could compensate, but in practice I don't think >>>anybody has ever managed to do it. >> >>I think that evaluation can compensate easily for loss of one ply of search and >>not only in theory because it is easy to tell your evaluation to calculate the >>result of 2 ply search. >> >>Evaluation by definition is a function that get a position and returns a number. >>If the target is not to play better but to prove that evaluation can compensate >>for 1 ply search then you simply tell your evaluation to perform 2 plies search. >> >>Note that some kind of search is already needed in smart evaluation even if you >>do not make moves. >> >>For example you cannot detect trapped pieces in evaluation without checking that >>every square that they can go is threatened by the opponent. >> >>You cannot detect forks in your evaluation without doing some kind of search. >> >>Uri > > > >Why did I *know* you would say that? :) > >In this case (positional evaluation doing a search), it's going to be a very >expensive (computationally) evaluation. And what it does is... a search. So it >just proves that nothing beats searching deeper... > >You can quibble on the definition of what positional is, of course. I have >already stated myself several times that simple evaluation terms are able, given >enough depth, to understand more complex concepts. So search is able to extract >some positional information that is not explicitely described in the evaluation >function, yes. > >Basically, positional evaluation is the kind of information you extract without >doing a search, which is not material bean-couting, and which tries to evaluate >how well your pieces are positioned. A SEE for example is not a positional >evaluator: a SEE is doing some kind of move search (it searches a degenerated >capture tree) and it does material bean-counting... On the other hand, a penalty >for a weak pawn is a positional term, for example. > > > > Christophe The point is that there may be important evaluation that is based on doing some small search and there are positions when this evaluation can save more than the plies that it searches. Take for example the case of trapped piece when the piece is not threatened by the opponent but every square that it can go is controlled by the oponent. search with simple evaluation may need many plies to find out that the piece is lost when some selective one ply search(you search every square that the piece can go) can help to avoid the problem(of course you cannot be sure if the piece is really trapped but it may be better not to go to the trouble of risking it in the first place if there is a logical alternative). Uri
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