@classmethod
def congruent(cls, mat_1, mat_2):
    """Compute the congruent action of mat_2 on mat_1.

        This is :math: `mat_2 mat_1 mat_2^T`.

        Parameters
        ----------
        mat_1 : array-like, shape=[n_samples, n, n]
        mat_2 : array-like, shape=[n_samples, n, n]

        Returns
        -------
        cong : array-like, shape=[n_samples, n, n]
        """
    return cls.mul(mat_2, mat_1, cls.transpose(mat_2))
