Add example of replicate draws from the posterior?

[cboettig]

To illustrate the point that the GP posterior contains a family of possible curves, might be useful to include a few example draws from the posterior rather than just the mean path and variance.

Need to reconstruct the covariance kernel from bgp first...

[cboettig]

set zcov=TRUE, and the *.s2 and, instead of being vectors, the outputs will be matrices containing the posterior mean covariance matrices at the X and XX locations respectively. It is, unfortunately, not possible to obtain samples from the posterior covariance matrix directly from tgp

[cboettig]

This is now done for Figure 1b, the "goodness-of-fit", e.g.:

Could be done on Figure 1a (state-space) but less interesting, and already cluttered.

• [ ] Consider doing in Figure 1a context in which prior on L is not quite so long?
• [ ] Consider doing in Figure 1b over a range of points outside the observed data