Review spectral_radius_bound: added other exceptions for the exponent

theano/sandbox/linalg/ops.py

@@ -695,6 +695,10 @@ def spectral_radius_bound(X, log2_exponent):
     """
     if X.type.ndim != 2:
         raise TypeError('spectral_radius_bound requires a matrix argument', X)
+    if not(isintance(log2_exponent,int)):
+        raise TypeError('spectral_radius_bound requires a integer exponent', log2_exponent)
+    if log2_exponent<=0:
+        raise ValueError('spectral_radius_bound requires a strictly positive exponent', log2_exponent)
     XX = X
     for i in xrange(log2_exponent):
         XX = tensor.dot(XX, XX)