def face_mass(self, vec): return pt.matmul(self._face_mass_mat, vec.T).T
def inv_mass(self, vec): return pt.matmul(self._inv_mass_mat, vec.T).T
def stiffness(self, vec): return pt.matmul(self._stiffness_mat, vec.T).T
def interp(self, vec): return pt.matmul(self._interp_mat, vec.T).T