2. The method as set forth in claim 1 , further comprising: after the estimating, iteratively adjusting the partitioning to increase the number of soft bin regions and repeating the estimating over the increased number of soft bins until a stopping criterion is met.
4. The method as set forth in claim 2 , wherein the soft bin regions are defined by products of sigmoid functions and the adjusting comprises: splitting a selected soft bin region defined by a product of sigmoid functions into two smaller soft bin regions each defined by a product of sigmoid functions in which the two smaller soft bin regions together span the selected soft bin region.