this is 'beta' parameter in Brix and Diggle (2001)
mu
the mean of the latent field, if equal to NULL, this is set to -sigma^2/2
beta
ONLY USED IN case where there is covariate information.
Details
A function for setting the parameters sigma, phi and theta for lgcpPredict. Note that the returned
set of parameters also features mu=-0.5*sigma^2, gives mean(exp(Y)) = 1.