Given a design matrix, a subsets object and a hyperparameter object,
return the variance matrix. The app of the function name means
approximator, to distinguish it from function V.fun()
of the calibrator package.
Usage
V.fun.app(D1, subsets, hpa)
Arguments
D1
Design matrix for level 1 code
subsets
Subsets object
hpa
Hyperparameter object
References
M. C. Kennedy and A. O'Hagan 2000. Predicting the output from
a complex computer code when fast approximations are available
Biometrika, 87(1): pp1-13