Calculate's a given elastic tensor's contribution to the
        stress using Einstein summation

        Args:
            strain (3x3 array-like): matrix corresponding to strain

def calculate_stress(self, strain):
        """
        Calculate's a given elastic tensor's contribution to the
        stress using Einstein summation

        Args:
            strain (3x3 array-like): matrix corresponding to strain
        """
        strain = np.array(strain)
        if strain.shape == (6,):
            strain = Strain.from_voigt(strain)
        assert strain.shape == (3, 3), "Strain must be 3x3 or voigt-notation"
        stress_matrix = self.einsum_sequence([strain]*(self.order - 1)) \
                / factorial(self.order - 1)
        return Stress(stress_matrix)