Feature Request: Custom Excitation List

[osamarais]

Is there a method to create the UCJ ansatz by passing a list of excitations to keep while ignoring the rest? It seems like the only way to do this would be to zero out t1, t2 amplitudes when creating the UCJ ansatz from parameters.

Something like:

ffsim.UCJOpSpinBalanced.from_t_amplitudes(t2, *, t1=None, n_reps=None, interaction_pairs=None, excitation_list=None)

where excitation_list is a list of single and double excitations e.g. [ ( (1) , (2) ) , ( (2) , (3) ) , ( (1,2) , (3 ,4) ) ]
would be more convenient.

[kevinsung]

For now, I suggest writing your own helper function to zero out certain entries of the t2 and t1 amplitudes. Before we consider adding such a function to ffsim, may I ask, what is the motivation?