_2&amp;x_4&amp;x_2+x_3&amp; 0\cr 0&amp;x_2+x_3&amp; x_4&amp;x_3\cr 0&amp;0&amp;x_3&amp;x_1}\succeq 0$"></p>
         <p>To define this example, we can again use Matlab's anonymous functions:</p><pre class="codeinput"><span class="keyword">function</span> [penm] = bex3()
  B = sparse(4,4);
  A{1} = sparse([1 0 0 0; 0 0 0 0; 0 0 0 0; 0 0 0 1]);
  A{2} = sparse([0 1 0 0; 1 0 1 0; 0 1 0 0; 0 0 0 0]);
  A{3} = sparse([0 0 0 0; 0 0 1 0; 0 1 0 1; 0 0 1 0]);
  A{4} = sparse([0 0 0 0; 0 1 0 0; 0 0 1 0; 0 0 0 0]);
  