specified by a mean function and a covariance
  function. These functions are specified separately, and consist of a
  specification of a functional form as well as a set of parameters
  called <em>hyperparameters</em>, see below.
  <dl>
  <dt><strong>Mean functions</strong>
  <dd>Several mean functions are available, all start with the four
    letters <tt>mean</tt> and reside in the <a
    href="../mean">mean directory</a>. An overview is provided by the <a
    href="../meanFunctions.m"><tt>meanFunctions<