STK_RBF_MATERN32 computes the Matern correlation function of order 3/2.

 CALL: K = stk_rbf_matern32 (H)

    computes the value of the Matern correlation function of order 3/2 at
    distance H. Note that the Matern correlation function is a valid
    correlation function for all dimensions.

 CALL: K = stk_rbf_matern32 (H, DIFF)

    computes the derivative of the Matern correlation function of order 3/2, at
    distance H, with respect the distance H if DIFF is equal to 1. (If DIFF is
    equal to -1, this is the same as K = stk_rbf_matern32(H).)

 See also: stk_rbf_matern, stk_rbf_matern52