def _find_permutation(a, b):
 t = np.argsort(a)
 u = np.argsort(b)
 u_ = _inverse_permutation(u)
 return t[u_]

def _find_permutation ( a , b ) : t = np . argsort ( a ) u = np . argsort ( b ) u_ = _inverse_permutation ( u ) return t [ u_ ]
find the permutation from a to b .