Track change in general expression API (use arg(0) and not expr).

Fixes Pyomo#2986
jsiirola · Oct 18, 2023 · 4c13589 · 4c13589
1 parent 4267cbd
commit 4c13589
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diff --git a/pyomo/core/expr/calculus/diff_with_pyomo.py b/pyomo/core/expr/calculus/diff_with_pyomo.py
@@ -328,7 +328,7 @@ def _diff_GeneralExpression(node, val_dict, der_dict):
     val_dict: ComponentMap
     der_dict: ComponentMap
     """
-    der_dict[node.expr] += der_dict[node]
+    der_dict[node.arg(0)] += der_dict[node]
 
 
 def _diff_ExternalFunctionExpression(node, val_dict, der_dict):

diff --git a/pyomo/core/tests/unit/test_derivs.py b/pyomo/core/tests/unit/test_derivs.py
@@ -230,6 +230,17 @@ def e2(m, i):
         symbolic = reverse_sd(m.o.expr)
         self.assertAlmostEqual(derivs[m.x], pyo.value(symbolic[m.x]), tol)
 
+    def test_constant_named_expressions(self):
+        m = pyo.ConcreteModel()
+        m.x = pyo.Var(initialize=3)
+        m.e = pyo.Expression(expr=2)
+
+        e = m.x * m.e
+        derivs = reverse_ad(e)
+        symbolic = reverse_sd(e)
+        self.assertAlmostEqual(derivs[m.x], pyo.value(symbolic[m.x]), tol + 3)
+        self.assertAlmostEqual(derivs[m.x], approx_deriv(e, m.x), tol)
+
     def test_multiple_named_expressions(self):
         m = pyo.ConcreteModel()
         m.x = pyo.Var()