add out_flow_constraint function and private function, add unit tests #1220
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…cting duplicate terms, add unit tests
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Thanks @anthayes92 💯 Looking great, mainly left comments for the docs.
Should be able to start merging in tomorrow and will clear the backlog. Great that we've got this in so quickly!
pennylane/qaoa/cycle.py
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| hamiltonian = qml.Hamiltonian(coeffs, ops) | ||
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| return hamiltonian |
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| hamiltonian = qml.Hamiltonian(coeffs, ops) | |
| return hamiltonian | |
| return qml.Hamiltonian(coeffs, ops) |
| g = nx.complete_graph(3) # undirected graph | ||
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| with pytest.raises(ValueError): | ||
| h = out_flow_constraint(g) |
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We were also thinking of a test_net_flow_and_out_flow_constraint, perhaps we can add in a follow up PR 👍
Co-authored-by: Tom Bromley <49409390+trbromley@users.noreply.github.com>
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Thanks @anthayes92, approved! Although I left some quick suggestions. Also, don't forget to update the changelog!
Co-authored-by: Tom Bromley <49409390+trbromley@users.noreply.github.com>
For the max weighted cycle QAOA problem, the unconstrained approach requires constraints to be included in the cost Hamiltonian. An out flow constraint is introduced to the cost Hamiltonian to help ensure it's minimised by selecting edges such that each node has an out flow equal to 0 or 1.
Add a out flow constraint function.
Add a private function to calculate quadratic terms of the constraint.
Allows a user to easily introduce constraints to cost Hamiltonian.
It relies on private functions that may be redundant when changes to
qml.Hamiltonianare introduced