Gets the symmetrized wallace tensor for determining
        yield strength criteria.

        Args:
            tau (3x3 array-like): stress at which to evaluate
                the wallace tensor.

def get_symmetric_wallace_tensor(self, tau):
        """
        Gets the symmetrized wallace tensor for determining
        yield strength criteria.

        Args:
            tau (3x3 array-like): stress at which to evaluate
                the wallace tensor.
        """
        wallace = self.get_wallace_tensor(tau)
        return Tensor(0.5 * (wallace + np.transpose(wallace, [2, 3, 0, 1])))