Computes Int(kappa_i(X, design) . kappa_j(design, X)). This function is preferred for updates
W_kappa_ij_up(W, design, theta, i1, i2, start, ct)W is modified in-place.
The matrix to store the computation in
matrix of design points
lengthscales
index of the derivatives (WARNING: starts at 0)
The column/row index at which to start the computation (doesn't touch the start by start submatrix).
Covariance type, 1 means Gaussian, 2 means Matern 3/2, 3 means Matern 5/2