Merge pull request #3566 from bknueven/issue-3565

Fix bug in `XpressPersistent.update_var`

Author: jsiirola

pyomo/solvers/plugins/solvers/xpress_persistent.py

@@ -110,8 +110,8 @@ def update_var(self, var):
         qctype = self._xpress_chgcoltype_from_var(var)
         lb, ub = self._xpress_lb_ub_from_var(var)
 
-        self._solver_model.chgbounds([xpress_var, xpress_var], ['L', 'U'], [lb, ub])
         self._solver_model.chgcoltype([xpress_var], [qctype])
+        self._solver_model.chgbounds([xpress_var, xpress_var], ['L', 'U'], [lb, ub])
 
     def _add_column(self, var, obj_coef, constraints, coefficients):
         """Add a column to the solver's model

pyomo/solvers/tests/checks/test_xpress_persistent.py

@@ -128,6 +128,31 @@ def test_basics(self):
         del m.z
         self.assertEqual(opt.get_xpress_attribute('cols'), 2)
 
+    @unittest.skipIf(not xpress_available, "xpress is not available")
+    def test_vartype_change(self):
+        # test for issue #3565
+        m = pyo.ConcreteModel()
+        m.x = pyo.Var(bounds=(0, 1))
+        m.o = pyo.Objective(expr=m.x)
+
+        opt = pyo.SolverFactory('xpress_persistent')
+        opt.set_instance(m)
+
+        m.x.fix(1)
+        opt.update_var(m.x)
+
+        x_idx = opt._solver_model.getIndex(opt._pyomo_var_to_solver_var_map[m.x])
+        lb = []
+        opt._solver_model.getlb(lb, x_idx, x_idx)
+        self.assertEqual(lb[0], 1)
+
+        m.x.domain = pyo.Binary
+        opt.update_var(m.x)
+
+        lb = []
+        opt._solver_model.getlb(lb, x_idx, x_idx)
+        self.assertEqual(lb[0], 1)
+
     @unittest.skipIf(not xpress_available, "xpress is not available")
     def test_add_remove_qconstraint(self):
         m = pyo.ConcreteModel()