  We investigate average case tractability of approximation of additive random
fields with marginal random processes corresponding to the Korobov kernels for
the non-homogeneous case. We use the absolute error criterion (ABS) or the
normalized error criterion (NOR). We show that the problem is always
polynomially tractable for ABS or NOR, and give sufficient and necessary
conditions for strong polynomial tractability for ABS or NOR.
