scale named expressions; don't remove from constraints when applying …

…transformation

pyomo/core/plugins/transform/scaling.py

@@ -10,7 +10,7 @@
 #  ___________________________________________________________________________
 
 from pyomo.common.collections import ComponentMap
-from pyomo.core.base import Block, Var, Constraint, Objective, Suffix, value
+from pyomo.core.base import Block, Var, Constraint, Objective, Suffix, value, Expression
 from pyomo.core.plugins.transform.hierarchy import Transformation
 from pyomo.core.base import TransformationFactory
 from pyomo.core.base.suffix import SuffixFinder
@@ -174,7 +174,7 @@ def _apply_to(self, model, rename=True):
 
         already_scaled = set()
         for component in model.component_objects(
-            ctype=(Constraint, Objective), descend_into=True
+            ctype=(Constraint, Objective, Expression), descend_into=True
         ):
             if component.is_reference():
                 # Skip any references - these should get picked up when
@@ -187,13 +187,13 @@ def _apply_to(self, model, rename=True):
                     continue
                 already_scaled.add(id(c))
                 # perform the constraint/objective scaling and variable sub
-                scaling_factor = component_scaling_factor_map[c]
                 if c.ctype is Constraint:
+                    scaling_factor = component_scaling_factor_map[c]
                     body = scaling_factor * replace_expressions(
                         expr=c.body,
                         substitution_map=variable_substitution_dict,
-                        descend_into_named_expressions=True,
-                        remove_named_expressions=True,
+                        descend_into_named_expressions=False,
+                        remove_named_expressions=False,
                     )
 
                     # scale the rhs
@@ -218,11 +218,22 @@ def _apply_to(self, model, rename=True):
                         c.set_value((lower, body, upper))
 
                 elif c.ctype is Objective:
+                    scaling_factor = component_scaling_factor_map[c]
                     c.expr = scaling_factor * replace_expressions(
                         expr=c.expr,
                         substitution_map=variable_substitution_dict,
-                        descend_into_named_expressions=True,
-                        remove_named_expressions=True,
+                        descend_into_named_expressions=False,
+                        remove_named_expressions=False,
+                    )
+                elif c.ctype is Expression:
+                    # Note that we don't have a scaling factor for Expression objects.
+                    # If we want to add this, Expressions would need to be added to
+                    # component_scaling_factor_map, defined above.
+                    c.expr = replace_expressions(
+                        expr=c.expr,
+                        substitution_map=variable_substitution_dict,
+                        descend_into_named_expressions=False,
+                        remove_named_expressions=False,
                     )
                 else:
                     raise NotImplementedError(

pyomo/core/tests/transform/test_scaling.py

@@ -690,6 +690,21 @@ def test_get_float_scaling_factor_intermediate_level(self):
         sf = ScaleModel()._get_float_scaling_factor(m.b1.b2.b3.v3)
         assert sf == float(0.3)
 
+    def test_scaled_named_expressions(self):
+        m = pyo.ConcreteModel()
+        m.x = pyo.Var(initialize=10)
+        m.y = pyo.Var(initialize=0.1)
+        m.inner_expr = pyo.Expression(expr=3 + m.x**2 + m.y)
+        m.sum = pyo.Expression(expr=m.x + m.y + m.inner_expr)
+        m.scaling_factor = pyo.Suffix(direction=pyo.Suffix.EXPORT)
+        m.scaling_factor[m.x] = 0.1
+        m.scaling_factor[m.y] = 10
+        m_scaled = pyo.TransformationFactory('core.scale_model').create_using(
+            m, rename=False
+        )
+        self.assertAlmostEqual(pyo.value(m.sum), 113.2)
+        self.assertAlmostEqual(pyo.value(m_scaled.sum), 113.2)
+
 
 if __name__ == "__main__":
     unittest.main()