Function to create singles and doubles transitions.

[MarcoBarroca]

What should we add?

It would be useful to give users functions to create singles and doubles transitions instead of asking them to code it themselves like in this tutorial.

Supposing one has the code to calculate the transitions it could work something like this:

import numpy as np
from qiskit_addon_sqd.fermion import create_transitions_doubles_within_same_spin, create_transitions_doubles_across_spin, create_transitions_single

transitions_single = create_transitions_single(norb)
transitions_doubles_same = create_transitions_doubles_within_same_spin(norb)
transitions_doubles_across= ccreate_transitions_doubles_across_spin(norb)
    
# Create the identity transition
identity_transition = np.array([['I'] * (2 * norb)], dtype='<U1')
    
# Combine all transitions
transitions_combined = np.vstack([transitions_single, transitions_doubles_same,transitions_doubles_across, identity_transition])

Then a user could easily create whichever transitions it wanted and include then with enlarge_batch_from_transitions.

I could work on this if people think it would be useful.

[caleb-johnson]

@MarcoBarroca , thanks for submitting this! I could see a couple of helper functions like this making sense in the counts module.

We'd need:

• 3 new public functions (I think in counts module).
• Tests to ensure the functions produce the right output for some given inputs.
• Release note
• Update relevant notebook(s) to use the functions instead of doing it manually