Germ Selection Gate Penalty

[coreyostrove]

We recently ran into a scenario where it was desirable to perform germ selection in a manner which minimized the number of applications of a particularly expensive gate operation. To support that sort of use case this PR adds a new algorithm_kwarg option called gate_penalty for find_germs which is compatible with the 'greedy' and 'grasp' search algorithms which allows a user to specify and additional penalty factors for the number of instances of particular gates in a candidate germ set. Also included are some additional unit tests for both this new gate penalty as well as tests for the existing op_penalty option (which penalized the total number of gate operations overall).

[rileyjmurray]

Left several comments. Happy to iterate on them a bit!

[rileyjmurray]

Type annotation please :)

[rileyjmurray]

This text appears three times in this file. Please break it out into a helper function.

[rileyjmurray]

The keyword arguments here are hard to read. I suggest something like the following.

class GermSelectionPenaltyTester(GermSelectionData, BaseCase):

    common_kwargs  : dict[str, Any] = dict(
        randomize=True, seed=1234, candidate_germ_counts={7:'all upto'},
        assume_real=True, float_type=np.double, mode='compactEVD', algorithm='greedy'
    )

    def setUp(self):
        super(GermSelectionData, self).setUp()

    def test_op_penalty_greedy(self):
        germs_no_penalty_cevd = germsel.find_germs(self.target_model, **self.common_kwargs)
        germs_penalty_cevd    = germsel.find_germs(self.target_model, **self.common_kwargs, algorithm_kwargs={'op_penalty':.1})        
        assert count_ops(germs_no_penalty_cevd) > count_ops(germs_penalty_cevd)


    def test_gate_penalty_greedy(self):
        kwargs = self.common_kwargs.copy()
        kwargs.pop('mode')
        germs_no_penalty_alljac = germsel.find_germs(self.target_model, **kwargs, mode='all-Jac')     
        germs_no_penalty_cevd   = germsel.find_germs(self.target_model, **kwargs, mode='compactEVD')
        germs_penalty_alljac = germsel.find_germs(
            self.target_model, **kwargs, mode='all-Jac',    algorithm_kwargs={'gate_penalty':{'Gxpi2':.1}}
        )        
        germs_penalty_cevd = germsel.find_germs(
            self.target_model, **kwargs, mode='compactEVD', algorithm_kwargs={'gate_penalty':{'Gxpi2':.1}}
        )
        assert count_gate(germs_no_penalty_alljac, 'Gxpi2') > count_gate(germs_penalty_alljac, 'Gxpi2')
        assert count_gate(germs_no_penalty_cevd,   'Gxpi2') > count_gate(germs_penalty_cevd,   'Gxpi2')
                                           
    def test_gate_penalty_grasp(self):
        kwargs = self.common_kwargs.copy()
        kwargs['mode']      = 'all-Jac'
        kwargs['algorithm'] = 'grasp'
        germs_gate_penalty_grasp = germsel.find_germs(
            self.target_model, **kwargs, algorithm_kwargs={'seed':1234, 'iterations':1, 'gate_penalty':{'Gxpi2':.2}}
        )
        germs_default_grasp = germsel.find_germs(
            self.target_model, **kwargs, algorithm_kwargs={'seed':1234, 'iterations':1}
        )
        assert count_gate(germs_gate_penalty_grasp, 'Gxpi2') < count_gate(germs_default_grasp, 'Gxpi2')

[rileyjmurray]

Missing blank line at EOF

[rileyjmurray]

@coreyostrove, is this is an appropriate PR to look into the complex-dtype issues with compactEVD germ selection #659? It's fine with me if you'd like to handle that separately, but I figured I'd point out the chance.