Add more informative message in verify_grad when input is not float.

theano/tensor/basic.py

@@ -5149,6 +5149,11 @@ def verify_grad(fun, pt, n_tests=2, rng=None, eps=None, abs_tol=None, rel_tol=No
     assert isinstance(pt, (list,tuple))
     pt = [numpy.array(p) for p in pt]
 
+    for i, p in enumerate(pt):
+        if p.dtype not in ('float32', 'float64'):
+            raise TypeError(('verify_grad can work only with floating point '
+                'inputs, but input %i has dtype "%s".') % (i, p.dtype))
+
     _type_tol = dict( # relativ error tolerances for different types
             float32=1e-2,
             float64=1e-4)