Merge pull request #2763 from michaelbynum/highs_fix

Better handling of mutable parameters with values of 0 in Highs interface

pyomo/contrib/appsi/solvers/highs.py

@@ -343,6 +343,7 @@ def _add_constraints(self, cons: List[_GeneralConstraintData]):
             for ndx, coef in enumerate(repn.linear_coefs):
                 v = repn.linear_vars[ndx]
                 v_id = id(v)
+                coef_val = value(coef)
                 if not is_constant(coef):
                     mutable_linear_coefficient = _MutableLinearCoefficient(pyomo_con=con, pyomo_var_id=v_id,
                                                                            con_map=self._pyomo_con_to_solver_con_map,
@@ -352,8 +353,10 @@ def _add_constraints(self, cons: List[_GeneralConstraintData]):
                     if con not in self._mutable_helpers:
                         self._mutable_helpers[con] = list()
                     self._mutable_helpers[con].append(mutable_linear_coefficient)
+                    if coef_val == 0:
+                        continue
                 var_indices.append(self._pyomo_var_to_solver_var_map[v_id])
-                coef_values.append(value(coef))
+                coef_values.append(coef_val)
 
             if con.has_lb():
                 lb = con.lower - repn.constant

pyomo/contrib/appsi/solvers/tests/test_persistent_solvers.py

@@ -1089,6 +1089,29 @@ def test_variables_elsewhere2(self, name: str, opt_class: Type[PersistentSolver]
         self.assertIn(m.y, sol)
         self.assertNotIn(m.z, sol)
 
+    @parameterized.expand(input=all_solvers)
+    def test_bug_1(self, name: str, opt_class: Type[PersistentSolver]):
+        opt: PersistentSolver = opt_class()
+        if not opt.available():
+            raise unittest.SkipTest
+
+        m = pe.ConcreteModel()
+        m.x = pe.Var(bounds=(3, 7))
+        m.y = pe.Var(bounds=(-10, 10))
+        m.p = pe.Param(mutable=True, initialize=0)
+
+        m.obj = pe.Objective(expr=m.y)
+        m.c = pe.Constraint(expr=m.y >= m.p*m.x)
+
+        res = opt.solve(m)
+        self.assertEqual(res.termination_condition, TerminationCondition.optimal)
+        self.assertAlmostEqual(res.best_feasible_objective, 0)
+
+        m.p.value = 1
+        res = opt.solve(m)
+        self.assertEqual(res.termination_condition, TerminationCondition.optimal)
+        self.assertAlmostEqual(res.best_feasible_objective, 3)
+
 
 @unittest.skipUnless(cmodel_available, 'appsi extensions are not available')
 class TestLegacySolverInterface(unittest.TestCase):