ccess = public, GetAccess = public)
        <span class="comment">% Formulation options</span>
        load_stiff_formula   <span class="string">uint8</span> <span class="string">=</span> <span class="string">uint8.empty</span>;   <span class="comment">% flag for type of loading stiffness formulation</span>
        unload_stiff_formula <span class="string">uint8</span> <span class="string">=</span> <span class="string">uint8.empty</span>;   <span class="comment">% flag for type of unloading stiffness formul