 computing test probabilities, we call <tt>gp</tt>
 with additional test inputs, and as the last argument a vector of
 targets for which the log probabilities <tt>lp</tt> should be
 computed. The fist four output arguments of the function are mean and
 variance for the targets and corresponding latent variables
 respectively. The test set predictions are computed using algorithm
 3.6 from the <a href="http://gaussianprocess.org/gpml/">GPML
 book</a>. The contour plot for the predictive distribution is
 show