Computes the covariance matrix at a set of locations for a spatial random process with a given covariance structure.
covMatrix(object, X, noise.var = NULL)an object specifying the covariance structure.
a matrix whose columns represent locations.
for noisy observations : an optional vector containing the noise variance at each observation
a list with the following items :
a matrix representing the covariance matrix for the locations specified in the X argument, including a possible nugget effect or observation noise.
a vector of length n (X size) containing a replication of the nugget effet or the observation noise (so that C-diag(vn) contains the covariance matrix when there is no nugget effect nor observation noise)