 to get help), and an example is
    the <a href="../cov/covSEard.m"><tt>covSEard</tt></a> "Squared Exponential
    with Automatic Relevance Determination" covariance function.
  </dl>
  For both mean functions and covariance functions, two types exist:
  simple and composite. Whereas simple types are specified by the
  function name (or function pointer),
  composite functions join together several components using cell
  arrays. Composite functions can be composed of other composite
  functions, allowing 