where is the energy constant specified by the SCALe statement. Supppose that one observes distance restraints involving the two protons and of a particular unassigned pair; this means that there are a total of ASSIgn statements specified for this particular unassigned pair (NCOUnt has to match ). The function is then the product of two -dimensional functions, each corresponding to one of the two possible stereospecific assignments:

(20.18) |

(20.19) |

...

where the terms should be understood as atom selections. are constants that are determined internally, such that the barrier height between the two minima of is given by BHIG. The functional forms of and are similar to the soft-square function (Section 20.3.4) with a linear asymptote, except that the switching region is symmetrically arranged:

where lim is set internally to 0.1.