Merge pull request #928 from Kenneth-T-Moore/ken4

Better reporting of relative error when fd is zero during drivative checks.

openmdao/core/problem.py

@@ -1770,7 +1770,16 @@ def _assemble_derivative_data(derivative_data, rel_error_tol, abs_error_tol, out
             derivative_info['magnitude'] = magnitude = MagnitudeTuple(fwd_norm, rev_norm, fd_norm)
 
             if fd_norm == 0.:
-                derivative_info['rel error'] = rel_err = ErrorTuple(nan, nan, nan)
+                if fwd_norm == 0.:
+                    derivative_info['rel error'] = rel_err = ErrorTuple(nan, nan, nan)
+
+                else:
+                    # If fd_norm is zero, let's use fwd_norm as the divisor for relative
+                    # check. That way we don't accidentally squelch a legitimate problem.
+                    derivative_info['rel error'] = rel_err = ErrorTuple(fwd_error / fwd_norm,
+                                                                        rev_error / fwd_norm,
+                                                                        fwd_rev_error / fwd_norm)
+
             else:
                 if totals:
                     derivative_info['rel error'] = rel_err = ErrorTuple(fwd_error / fd_norm,

openmdao/core/tests/test_check_derivs.py

@@ -1485,6 +1485,39 @@ def test_bug_local_method(self):
         for key, val in iteritems(data['comp3']):
             assert_rel_error(self, val['rel error'][0], 0.0, 1e-15)
 
+    def test_rel_error_fd_zero(self):
+        # When the fd turns out to be zero, test that we switch the definition of relative
+        # to divide by the forward derivative instead of reporting NaN.
+
+        class SimpleComp2(ExplicitComponent):
+            def setup(self):
+                self.add_input('x', val=3.0)
+                self.add_output('y', val=4.0)
+
+                self.declare_partials(of='y', wrt='x')
+
+            def compute(self, inputs, outputs):
+                # Mimics forgetting to set a variable.
+                pass
+
+            def compute_partials(self, inputs, partials):
+                partials['y', 'x'] = 3.0
+
+        prob = Problem()
+        prob.model = Group()
+
+        prob.model.add_subsystem('p1', IndepVarComp('x', 3.5))
+        prob.model.add_subsystem('comp', SimpleComp2())
+        prob.model.connect('p1.x', 'comp.x')
+
+        prob.setup(check=False)
+
+        stream = cStringIO()
+        data = prob.check_partials(out_stream=stream)
+        lines = stream.getvalue().splitlines()
+
+        self.assertTrue("Relative Error (Jfor  - Jfd) : 1." in lines[8])
+
 
 class TestCheckPartialsFeature(unittest.TestCase):