  ddgk = [<span class="keyword">...</span>
        0 x(3)*x(4) x(2)*x(4) x(2)*x(3) 0 0;
        x(3)*x(4) 0 x(1)*x(4) x(1)*x(3) 0 0;
        x(2)*x(4) x(1)*x(4) 0 x(1)*x(2) 0 0;
        x(2)*x(3) x(1)*x(3) x(1)*x(2) 0 0 0;
        0 0 0 0 0 0;
        0 0 0 0 0 0];
  <span class="keyword">case</span> (2)
    ddgk = [<span class="keyword">...</span>
        2 0 0 0 0 0;
        0 2 0 0 0 0;
        0 0 2 0 0 0;
        0 0 0 2 0 0;
        0 0 0 0 0 0;
        0 0 0 0 0 0];
  <span class="keyword">end</span>