Fix ddof to be int
@@ -100,7 +100,7 @@ def cov(a, y=None, rowvar=True, bias=False, ddof=None):
X = core.concatenate_method((X, y), axis=0)
if ddof is None:
- ddof = not bias
+ ddof = 0 if bias else 1
fact = X.shape[1] - ddof
X -= X.mean(axis=1)[:, None]
