## Symmetry restraints

An 'S' line should look like:

    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.

For example,

    S   2   4   8   10   12   1.0   0.5

creates 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.