S Num_Pairs Atom_indices1 Atom_indices2 Pair_weights
These parameters encode a single symmetry restraint, as given in Section 5.3.5. Num_Pairs is the number of atom pairs to be constrained. Atom_indices1 and Atom_indices2 are the numeric indices of the atoms in each pair, while Pair_weights are the weights for each pair.
S 2 4 8 10 12 1.0 0.5creates a symmetry restraint in which atoms 4 and 10 are constrained to be similar to each other with weight 1.0, while atoms 8 and 12 are constrained with weight 0.5.