 may be empty). When specifying
  hyperparameters, it is important that the number of elements in each
  of these struct fields, precisely match the number of parameters expected
  by the mean function, the covariance function and the likelihood
  functions respectively (otherwise an error will result). Hyperparameters whose
 natural domain is positive are represented by their logarithms.
<dt><strong>Likelihood Functions</strong>
<dd>The <a href="../likFunctions.m">likelihood function</a> specifies
  the pr