Support trivial constraints in SCIP interfaces

Author: xueyuan

pyomo/contrib/solver/solvers/scip/base.py

@@ -46,6 +46,7 @@
     EqualityExpression,
     InequalityExpression,
     RangedExpression,
+    TrivialRelationalExpression,
 )
 from pyomo.core.expr.visitor import StreamBasedExpressionVisitor
 from pyomo.gdp.disjunct import AutoLinkedBinaryVar
@@ -218,6 +219,12 @@ def _handle_inequality(node, data, opt, visitor):
     return data[0] <= data[1]
 
 
+def _handle_trivial_inequality(node, data, opt, visitor):
+    # Keep the constant relation symbolic so that PySCIPOpt creates a
+    # constraint instead of Python evaluating it to a bool.
+    return scip.Expr() + data[0] <= data[1]
+
+
 def _handle_named_expression(node, data, opt, visitor):
     return data[0]
 
@@ -244,6 +251,7 @@ def _handle_unit(node, data, opt, visitor):
     EqualityExpression: _handle_equality,
     RangedExpression: _handle_ranged,
     InequalityExpression: _handle_inequality,
+    TrivialRelationalExpression: _handle_trivial_inequality,
     ScalarExpression: _handle_named_expression,
     ExpressionData: _handle_named_expression,
     VarData: _handle_var,

pyomo/contrib/solver/tests/solvers/test_scip_direct.py

@@ -243,6 +243,26 @@ def test_infeasible_raises_no_feasible_solution_error(self):
                 m, load_solutions=True, raise_exception_on_nonoptimal_result=False
             )
 
+    def test_trivial_constraints(self):
+        m = pyo.ConcreteModel()
+        m.x = pyo.Var(bounds=(0, 1))
+        m.feasible = pyo.Constraint(expr=pyo.Constraint.Feasible)
+        m.obj = pyo.Objective(expr=m.x)
+
+        opt = ScipDirect()
+        res = opt.solve(m)
+        self.assertEqual(res.solution_status, SolutionStatus.optimal)
+        self.assertAlmostEqual(m.x.value, 0)
+
+        m.infeasible = pyo.Constraint(expr=pyo.Constraint.Infeasible)
+        res = opt.solve(
+            m, load_solutions=False, raise_exception_on_nonoptimal_result=False
+        )
+        self.assertEqual(
+            res.termination_condition, TerminationCondition.provenInfeasible
+        )
+        self.assertEqual(res.solution_status, SolutionStatus.noSolution)
+
     def test_timer(self):
         m = self.create_lp_model()
         timer = HierarchicalTimer()

pyomo/contrib/solver/tests/solvers/test_scip_persistent.py

@@ -289,3 +289,24 @@ def test_infeasible_raises(self):
             opt.solve(
                 m, load_solutions=True, raise_exception_on_nonoptimal_result=False
             )
+
+    def test_trivial_constraints(self):
+        m = pyo.ConcreteModel()
+        m.x = pyo.Var(bounds=(0, 1))
+        m.feasible = pyo.Constraint(expr=pyo.Constraint.Feasible)
+        m.obj = pyo.Objective(expr=m.x)
+
+        opt = ScipPersistent()
+        res = opt.solve(m)
+        self.assertEqual(res.solution_status, SolutionStatus.optimal)
+        self.assertAlmostEqual(m.x.value, 0)
+
+        m.infeasible = pyo.Constraint(expr=pyo.Constraint.Infeasible)
+        opt.add_constraints([m.infeasible])
+        res = opt.solve(
+            m, load_solutions=False, raise_exception_on_nonoptimal_result=False
+        )
+        self.assertEqual(
+            res.termination_condition, TerminationCondition.provenInfeasible
+        )
+        self.assertEqual(res.solution_status, SolutionStatus.noSolution)