Add support for float16 for stability opts.

theano/tensor/opt.py

@@ -5140,7 +5140,8 @@ def local_log_erfc(node):
                    T.log(1 - 1 / (2 * x ** 2) + 3 / (4 * x ** 4)
                          - 15 / (8 * x ** 6)))
 
-    if node.outputs[0].dtype == 'float32':
+    if (node.outputs[0].dtype == 'float32' or
+            node.outputs[0].dtype == 'float16'):
         threshold = 10.0541949
     elif node.outputs[0].dtype == 'float64':
         threshold = 26.641747557
@@ -5287,7 +5288,7 @@ def local_grad_log_erfc_neg(node):
                             3 / (4 * (x ** 4)) - 15 / (8 * (x ** 6)), -1)
                   * T.cast(T.sqrt(numpy.pi), dtype=x.dtype))
 
-    if x.dtype == 'float32':
+    if x.dtype == 'float32' or x.dtype == 'float16':
         threshold = 9.3
         #threshold = 10.1
     elif x.dtype == 'float64':