Set the domain label for the alignment tensor.
tensor: The alignment tensor to assign the domain label to.
domain: The domain label.
Prior to optimisation of the N-state model or Frame Order theories, the domain to which each alignment tensor belongs must be specified.
To link the alignment tensor loaded as `chi3 C-dom' to the C-terminal domain `C', type:
[numbers=none] relax> align_tensor.set_domain(tensor='chi3 C-dom', domain='C')