Author: José Carlos
Date: 07:27:21 10/22/03
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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.
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