def _has_converged(centroids, old_centroids):
return (set([tuple(a) for a in centroids]) == set([tuple(a) for a in old_centroids]))<EOL>
Stop if centroids stop to update
Parameters
-----------
centroids: array-like, shape=(K, n_samples)     
old_centroids: array-like, shape=(K, n_samples)
------------    
returns
True: bool