void chder(double a, double b, double c[], double cder[], int n)
{
	int j;
	double con;
    cder[n] = 0.0;
    cder[n - 1] = 2 * (n - 1) * c[n];
    if (n >= 3)
	{
        for (j = n - 2; j>=1; j--)
		{
            cder[j] = cder[j + 2] + 2 * j * c[j + 1];
        }
    }
    con = 2.0 / (b - a);
    for (j = 1; j<=n; j++)
	{
        cder[j]= cder[j] * con;
    }
}