void chstwo(double bins1[], double bins2[], int nbins, int knstrn, 
			double& df, double& chsq, double& prob)
{
	int j;
    df = double(nbins - 1 - knstrn);
    chsq = 0.0;
    for (j = 1; j<=nbins; j++)
	{
        if (bins1[j] == 0.0 && bins2[j] == 0.0)
		{
			df = df - 1.0;
		}
        else
		{
			chsq = chsq + (bins1[j] - bins2[j]) * (bins1[j] - bins2[j])
				  / (bins1[j] + bins2[j]);
        }
    }
    prob = gammq(0.5 * df, 0.5 * chsq);
}