#include "genlib.h"
#include <math.h>
#include <stdio.h>
#include <time.h>

/*cubic covariance function*/
double cubic(double h) {
    double z;

    if (h >= 1.) {
        z = 0.;
    } else {
        z = 1. - 7. * (double)(h * h) + (35. / 4.) * (double)(h * h * h) - 3.5 * (double)(h * h * h * h * h) + .75 * (double)(h * h * h * h * h * h * h);
    }
    
    return z;
}