quested with keywords in the second argument
to plot: <br>
<ul style="color: rgb(204, 51, 204);">
  <li>contour3<span style="color: rgb(0, 0, 0);"> (a countour in 3D)</span><br>
  </li>
  <li>surfl<span style="color: rgb(0, 0, 0);"> (surface with light)</span><br>
  </li>
  <li>pcolor<span style="color: rgb(0, 0, 0);"> (a flat matrix/image
view, may be advantageously coupled with the <span style="color: rgb(204, 51, 204);">hide_axis</span> option)</span><br>
  </li>
  <li>stem3<span style="color: rgb(0, 0, 