Author: Gerd Isenberg
Date: 11:29:44 10/22/03
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On October 22, 2003 at 10:27:21, José Carlos wrote: >On October 22, 2003 at 09:42:50, Gerd Isenberg wrote: > >>On October 22, 2003 at 06:30:13, Sergei S. Markoff wrote: >> >>>Hello All! >>> >>>DS - is a term for using some features of classical evaluation that consists of >>>two parts - material and positional. >>>There are a lot of positions in that for one side material evaluation is >0 but >>>positional evaluation is <0 or vice versa. The root of big part of mistakes made >>>by modern engines is underestimating of positional eval because the positional >>>evaluation is constructed of several "atomic" factors. The _sum_ of this factors >>>frequently isn't good positional evaluation (anyway there are a lot of >>>"palliative" methods to avoid this problem like evaluation the relationship >>>between several factors). We can't fully trust positional evaluation and that's >>>why most of modern programs using a small values for a lot of factors. >>>The idea of DS is to use disagreement between positional and material >>>evaluation. There are a lot of ways how to use it. For example we can check >>>nodes in which sum_eval < alpha, but positional eval is large (for example we >>>sacrificed a pawn for attack e.t.c.). For this nodes we can: >>>1. Rebuild quiescence to include checks e.t.c. >>>2. Extend search >>>3. Change eval for the case of losing pawn or quality (trade bishop or knight >>>for rook) for big passed pawn / king attack eval. >>>4. Do assymetric eval. >>>5. Something else? >>> >>>Do you have some ideas in this area? >>> >>>Best wishes, >>>Sergei >> >>Hi Sergei, >> >>very interesting stuff. I'm currently using some feedback from eval to control >>search's behaviour, mainly (leaf node) extensions. Even if huge positional terms >>compensate each other, e.g. passers versus king safety. >> >>May be other search algorithms than alpha-beta are more convenient to handle >>such DS stuff to back it up to the root. >> >>Gerd > > I'm doing something like that in Anubis. The eval determines the "uncertainity >degree" of the position. A highly uncertain position is never pruned, while a >clear position is easily pruned against beta (or other prunning and reductions >stuff I'm experimenting with). I use static threats, king safety, something >similar to DS, and other concepts. For example, a passed pawn in pawn endings >makes a position highly uncertain unless I statically detect it's lost... > DS, as defined by Sergei, is interesting and can fit very well in my schema. I >will test it. > > José C. Hi José, yes, same for me. The DS is an interesting indicator to trigger something with. One may try to add (or subtract) some fractions of one to a fixed point score, so that otherwise equal scores got a bit different and backupped to the root. Gerd
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