void chint(double a, double b, double c[], double cint1[], int n)
{
	double con,sum,fac;
    con = 0.25 * (b - a);
    sum = 0.0;
    fac = 1.0;
    for (int j = 2; j<=n - 1; j++)
	{
        cint1[j] = con * (c[j - 1] - c[j + 1]) / (j - 1);
        sum = sum + fac * cint1[j];
        fac = -fac;
    }
    cint1[n] = con * c[n - 1] / (n - 1);
    sum = sum + fac * cint1[n];
    cint1[1] = 2.0 * sum;
}