* (1+1/beta^2);
            <span class="keyword">end</span>

            <span class="comment">% Unloading stiffness coefficient</span>
            <span class="keyword">switch</span> this.unload_stiff_formula
                <span class="keyword">case</span> this.CONSTANT
                    this.unload_stiff = this.stiff / e2;
                <span class="keyword">case</span> this.VARIABLE
                    fmax = this.stiff * v0 * sqrt(m/this.stiff);
                    this.unload_stiff = this.stiff 