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[ENH] set_cover Python: expose the lower bound accessors directly #5277

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[ENH] set_cover Python: expose the lower bound accessors directly #5277

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3 changes: 3 additions & 0 deletions ortools/set_cover/python/set_cover.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -291,6 +291,9 @@ PYBIND11_MODULE(set_cover, m) {
*invariant.model() = model;
})
.def("cost", &SetCoverInvariant::cost)
.def("lower_bound", &SetCoverInvariant::LowerBound)
.def("cost_or_lower_bound", &SetCoverInvariant::CostOrLowerBound)
.def("is_cost_consistent", &SetCoverInvariant::is_cost_consistent)
.def("num_uncovered_elements", &SetCoverInvariant::num_uncovered_elements)
.def("is_selected",
[](SetCoverInvariant& invariant) -> std::vector<bool> {
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27 changes: 27 additions & 0 deletions ortools/set_cover/python/set_cover_test.py
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Expand Up @@ -222,6 +222,33 @@ def test_knights_cover_trivial(self):
inv.check_consistency(set_cover.consistency_level.FREE_AND_UNCOVERED)
)

def test_dual_ascent_lower_bound(self):
model = create_knights_cover_model(8, 8)
self.assertTrue(model.compute_feasibility())

primal = set_cover.SetCoverInvariant(model)
self.assertTrue(set_cover.GreedySolutionOptimizer(primal).optimize())
upper_bound = primal.cost()

dual = set_cover.SetCoverInvariant(model)
self.assertTrue(set_cover.DualAscentOptimizer(dual).optimize())
lower_bound = dual.lower_bound()

# The dual ascent bound is a valid lower bound on the optimum, so it
# cannot exceed the cost of any feasible cover.
self.assertGreaterEqual(lower_bound, 0.0)
self.assertLessEqual(lower_bound, upper_bound)

def test_cost_or_lower_bound(self):
model = create_knights_cover_model(4, 4)
inv = set_cover.SetCoverInvariant(model)

self.assertTrue(set_cover.GreedySolutionOptimizer(inv).optimize())
if inv.is_cost_consistent():
self.assertEqual(inv.cost_or_lower_bound(), inv.cost())
else:
self.assertEqual(inv.cost_or_lower_bound(), inv.lower_bound())

# TODO(user): KnightsCoverGreedyAndTabu, KnightsCoverGreedyRandomClear,
# KnightsCoverElementDegreeRandomClear, KnightsCoverRandomClearMip,
# KnightsCoverMip
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