Eigenvalue CAR Models
Fits Leroux model in spectral domain to estimate causal spatial effect as detailed in
Guan, Y; Page, G.L.; Reich, B.J.; Ventrucci, M.; Yang, S; (2020) .
Both the parametric and semi-parametric models are available. The semi-parametric model
relies on 'INLA'. The 'INLA' package can be obtained from < https://www.r-inla.org/>.