for very flexible and interesting
  structures. <br> Examples are given below and in the 
  <a href="usageMean.m"><tt>usageMean</tt></a> and <a href="usageCov.m">usageCov</a> functions.
<dt><strong>Hyperparameters</strong>
<dd>GPs are typically specified using mean and covariance functions
 which have free parameters called <em>hyperparameters</em>. Also
 likelihood functions may have such parameters. These are encoded in
 a struct with the fields <tt>mean</tt>, <tt>cov</tt> and
 <tt>lik</tt> (some of which