Checking GP predictive accuracy on-the-fly

[dflemin3]

Checking GP predictive accuracy on-the-fly

[dflemin3]

Accidentally closed the wrong issue!

[dflemin3]

This task can be accomplished in a few ways:

1. k-folds cross-validation
   At any point in the algorithm, I can partition the training set, {theta, y}, into k folds, training on k-1 folds and predicting on the kth fold. This procedure yields a pretty decent estimate of the the accuracy and uncertainty of the predictions that can be compared to the GP's own uncertainty from its conditional predictive distribution.

2. on-the-fly
   Before the GP evaluates the forward model, I can use it to predict the functional value at that point, with uncertainties under the GP model, to assess the accuracy of the prediction.

Both of these methods should be implemented, and both should not be too computationally-expensive as re-training the GP for a given set of hyperparameters is decently quick with george given that be design, our training set sizes are small.