Custom version of _square_dist that allows sc to provide per-datapoint length
        scales. sc: N x M x D.

def _cust_square_dist(A, B, sc):
        """
        Custom version of _square_dist that allows sc to provide per-datapoint length
        scales. sc: N x M x D.
        """
        return tf.reduce_sum(tf.square((tf.expand_dims(A, 1) - tf.expand_dims(B, 0)) / sc), 2)