Merge pull request Pyomo#3281 from kutlay/issue-3127

Sort indices while removing constraints to fix Pyomo#3127
Jtramey · Jul 9, 2024 · 86aa282 · 86aa282
2 parents e01e74b + 072c2c5
commit 86aa282
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diff --git a/pyomo/contrib/appsi/solvers/highs.py b/pyomo/contrib/appsi/solvers/highs.py
@@ -481,7 +481,7 @@ def _remove_constraints(self, cons: List[ConstraintData]):
             indices_to_remove.append(con_ndx)
             self._mutable_helpers.pop(con, None)
         self._solver_model.deleteRows(
-            len(indices_to_remove), np.array(indices_to_remove)
+            len(indices_to_remove), np.sort(np.array(indices_to_remove))
         )
         con_ndx = 0
         new_con_map = dict()

diff --git a/pyomo/contrib/appsi/solvers/tests/test_highs_persistent.py b/pyomo/contrib/appsi/solvers/tests/test_highs_persistent.py
@@ -80,6 +80,43 @@ def test_mutable_params_with_remove_vars(self):
         res = opt.solve(m)
         self.assertAlmostEqual(res.best_feasible_objective, -9)
 
+    def test_fix_and_unfix(self):
+        # Tests issue https://github.com/Pyomo/pyomo/issues/3127
+
+        m = pe.ConcreteModel()
+        m.x = pe.Var(domain=pe.Binary)
+        m.y = pe.Var(domain=pe.Binary)
+        m.fx = pe.Var(domain=pe.NonNegativeReals)
+        m.fy = pe.Var(domain=pe.NonNegativeReals)
+        m.c1 = pe.Constraint(expr=m.fx <= m.x)
+        m.c2 = pe.Constraint(expr=m.fy <= m.y)
+        m.c3 = pe.Constraint(expr=m.x + m.y <= 1)
+
+        m.obj = pe.Objective(expr=m.fx * 0.5 + m.fy * 0.4, sense=pe.maximize)
+
+        opt = Highs()
+
+        # solution 1 has m.x == 1 and m.y == 0
+        r = opt.solve(m)
+        self.assertAlmostEqual(m.fx.value, 1, places=5)
+        self.assertAlmostEqual(m.fy.value, 0, places=5)
+        self.assertAlmostEqual(r.best_feasible_objective, 0.5, places=5)
+
+        # solution 2 has m.x == 0 and m.y == 1
+        m.y.fix(1)
+        r = opt.solve(m)
+        self.assertAlmostEqual(m.fx.value, 0, places=5)
+        self.assertAlmostEqual(m.fy.value, 1, places=5)
+        self.assertAlmostEqual(r.best_feasible_objective, 0.4, places=5)
+
+        # solution 3 should be equal solution 1
+        m.y.unfix()
+        m.x.fix(1)
+        r = opt.solve(m)
+        self.assertAlmostEqual(m.fx.value, 1, places=5)
+        self.assertAlmostEqual(m.fy.value, 0, places=5)
+        self.assertAlmostEqual(r.best_feasible_objective, 0.5, places=5)
+
     def test_capture_highs_output(self):
         # tests issue #3003
         #