A function to go from Y to Gamma
GammaFromY_SPDE(Y, U, mu)
the value of Gamma for the given Y
Y
upper Cholesky matrix
the mean
Benjamin M. Taylor and Barry S. Rowlingson (2017). spatsurv: An R Package for Bayesian Inference with Spatial Survival Models. Journal of Statistical Software, 77(4), 1-32, doi:10.18637/jss.v077.i04.
Finn Lindgren, Havard Rue, Johan Lindstrom. An explicit link between Gaussian fields and Gaussian Markov random fields: the stochastic partial differential equation approach. Journal of the Royal Statistical Society: Series B 73(4)