d coordinate
    system (Y axis pointing downwards). Figure generated
    by <code/>vl_demo_frame</code>.
  </span>
 </div>
</div>

<div class="highlight"><pre><span class="n">radius</span> <span class="p">=</span> <span class="mi">1</span> <span class="p">;</span>
<span class="n">theta</span> <span class="p">=</span> <span class="nb">pi</span><span class="o">/</span><span class="mi">4</span> <span class="p">;</span>
<span class="n">f</span> <span class="p">=</span> <span class="p">[</span><span class="n">T