Author: Ernst A. Heinz
Date: 13:47:38 12/06/00
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On December 06, 2000 at 12:45:30, Leen Ammeraal wrote: >I have the impression that most chess programmers >use their hashtables to store >only one evaluation value, along with a flag >denoting Lower, Upper, or Exact. >Why not store both a lower and an upper bound, >where lower = -inf or upper = +inf if only one >real bound is available? A flag is then >superfluous, since this follows from >the two bound values. >For example: >LB UB Flag value (not stored) >-inf 100 Upper >-20 +inf Lower >30 30 Exact >This also offers the possibility to store >two different bounds at the same time, as in >LB = -50, UB = 70. >This is the way I do it, but, unfortunately, >my program is weaker than most others. >Could this be because this idea of storing >two bounds and no flag is wrong? >Leen Ammeraal Hi Leen, It is fine to do what you suggest but consumes far more memory than the standard flagged approach. Moreover, the additional information stored does not seem to help much in the context of PVS/NegaScout. With MTD(f), however, it is a whole different story. There you seem to need *both* bounds to achieve decent performance. =Ernst=
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