void vander(double x[], double w[], double q[], int n)
{
    const int nmax = 100;
    double zero = 0.0;
    double one = 1.0;
    double c[100];
	int i,j,k,k1;
	double xx,t,b,s;
    if (n == 1)
	{
        w[1] = q[1];
	}
    else
	{
        for (i = 1; i<=n; i++)
		{
            c[i] = zero;
        }
        c[n] = -x[1];
        for (i = 2; i<=n; i++)
		{
            xx = -x[i];
            for (j = n + 1 - i; j<=n-1; j++)
			{
                c[j] = c[j] + xx * c[j + 1];
            }
            c[n] = c[n] + xx;
        }
        for (i = 1; i<=n; i++)
		{
            xx = x[i];
            t = one;
            b = one;
            s = q[n];
            k = n;
            for (j = 2; j<=n; j++)
			{
                k1 = k - 1;
                b = c[k] + xx * b;
                s = s + q[k1] * b;
                t = xx * t + b;
                k = k1;
            }
            w[i] = s / t;
        }
    }
}