<tt>hyp2.cov</tt> to zero, correspond to unit
characteristic length-scale and unit signal standard deviation. 
The likelihood hyperparameter in <tt>hyp2.lik</tt> is also
initialized. We assume that the mean function is zero, so we simply
ignore it (and when in the following we call <a href="../gp.m">gp</a>,
we give an empty argument for the mean function).</p>

<p>In the following line, we optimize over the hyperparameters, by
minimizing the negative log marginal likelihood w.r.t. the
hyperparameters. The t