IPOPT now returns Lagrange multpliers using the same sign convention as SNOPT.

pyoptsparse/pyIPOPT/pyIPOPT.py

@@ -296,7 +296,7 @@ def eval_intermediate_callback(*args, **kwargs):
             sol_inform["text"] = self.informs[status]
 
             # Create the optimization solution
-            sol = self._createSolution(optTime, sol_inform, obj, x)
+            sol = self._createSolution(optTime, sol_inform, obj, x, multipliers=-constraint_multipliers)
 
             # Indicate solution finished
             self.optProb.comm.bcast(-1, root=0)

pyoptsparse/pyOpt_optimization.py

@@ -1577,7 +1577,7 @@
         con_opt = self._mapContoOpt(con)
         return self.processContoDict(con_opt, scaled=False, natural=True)
 
-    def summary_str(self, minimal_print=False):
+    def summary_str(self, minimal_print=False, print_multipliers=False):
         """
         Print Structured Optimization Problem
 
@@ -1588,6 +1588,8 @@
             variables and constraints with a non-empty status
             (for example a violated bound).
             This defaults to False, which will print all results.
+        print_multipliers : bool
+            If True, print the Lagrange multipliers associated with the constraints.
         """
         TOL = 1.0e-6
 
@@ -1656,7 +1658,7 @@
 
         if len(self.constraints) > 0:
             # must be an instance of the Solution class
-            if not isinstance(self, Optimization) and self.lambdaStar is not None:
+            if print_multipliers and self.lambdaStar is not None:
                 lambdaStar = self.lambdaStar
                 lambdaStar_label = "Lagrange Multiplier"
             else:
@@ -1716,7 +1718,7 @@
         return text
 
     def __str__(self):
-        return self.summary_str(minimal_print=False)
+        return self.summary_str(minimal_print=False, print_multipliers=False)
 
     def __getstate__(self) -> dict:
         """

pyoptsparse/pyOpt_solution.py

@@ -75,7 +75,7 @@ def __str__(self) -> str:
         """
         Print Structured Solution
         """
-        text0 = super().__str__()
+        text0 = self.summary_str(minimal_print=False, print_multipliers=True)
         text1 = ""
         lines = text0.split("\n")
         lines[1] = lines[1][len("Optimization Problem -- ") :]

tests/test_hs071.py

@@ -213,6 +213,17 @@ def test_optimization(self, optName):
         self.assert_solution_allclose(sol, self.tol[optName])
         # Check informs
         self.assert_inform_equal(sol)
+        # Check the lagrange multipliers in the solution text
+        lines = str(sol).split("\n")
+        constraint_header_line_num = [i for i, line in enumerate(lines) if "Constraints" in line][0]
+        con1_line_num = constraint_header_line_num + 2
+        con2_line_num = constraint_header_line_num + 3
+        lambda_con1 = float(lines[con1_line_num].split()[-1])
+        lambda_con2 = float(lines[con2_line_num].split()[-1])
+        if optName in ("IPOPT", "SNOPT", "ParOpt"):
+            assert_allclose([lambda_con1, lambda_con2], self.lambdaStar[0]["con"], rtol=1.0e-5, atol=1.0e-5)
+        else:
+            assert_allclose([lambda_con1, lambda_con2], [9.0e100, 9.0e100], rtol=1.0e-5, atol=1.0e-5)
 
 
 if __name__ == "__main__":