Don't test sum with a mix of complex and scalar.

Sum with a complex input and scalar output doesn't work because of the ambiguity of casting complex to scalar. The reverse doesn't work because of the ambiguity of the casting in the gradient. Therefore disallow both.

Don't test sum with a mix of complex and scalar.
0a531470 · Arnaud Bergeron · 7da49941 · 0a531470
--- a/theano/tensor/tests/test_elemwise.py
+++ b/theano/tensor/tests/test_elemwise.py
@@ -854,11 +854,10 @@ class T_reduce_dtype(unittest.TestCase):
            for input_dtype in self.dtypes:
                x = tensor.matrix(dtype=input_dtype)
                for output_dtype in self.dtypes:
-                    # If the output is a complex, the gradient of the reduce will
-                    # cast the complex to the input dtype. We can't call the normal
-                    # cast on a complex to a not complex as this is ambiguous.
-                    if (not input_dtype.startswith('complex') and
-                            output_dtype.startswith('complex')):
+                    # Only tests case where both input and output are complex.
+                    icomplex = input_dtype.startswith('complex')
+                    ocomplex = output_dtype.startswith('complex')
+                    if icomplex != ocomplex:
                        continue

                    axis = self.axes[idx % len(self.axes)]