I have some confusion regarding how may I define my trial function according to this literature. Here, u is the actual degrees of freedom which consists of translational dof zeta, and rotational dofs theta. However, these dofs can be divided into curvature vector and distortion vector. And in the final variational form the left hand side will be expressed in terms of translational dof zeta, as well as curvature and distortion vector. I would like some help which might guide me on how should I make the mixed element in this purpose.