Computes a partial derivative of the covariance matrix C in function covMatrix.
covMatrixDerivative(object, X, C0, k, ...)an object specifying the covariance structure.
a matrix whose columns represent locations.
a matrix corresponding to the covariance matrix for the locations specified in the X argument, when there is no nugget effet nor observation noise.
an integer representing the partial derivative index.
additional parameters, typically an environment used for storage
A matrix representing the partial derivative of C