## Rigid bodies

A 'B' line should look like:

    B Scale_factor Atom_indices

These parameters encode the rigid body information as given in Section 5.3.4. `Atom_indices` are the numeric indices of all atoms in the rigid body, and `Scale_factor` the scaling factor from system state to body orientation.

For example,

    B   5   10  25   30

creates a rigid body containing atoms 5, 10, 25 and 30.