public static void FitOrigin(double[] x, double[] y, double[] sig,
out double b, out double sigb, out double chi2, out double q)
{
int ndata = x.Length;
if (x.Length != y.Length)
{
throw new Exception("x.Length != y.Length: " + x.Length + " " + y.Length);
}
if (sig != null && x.Length != sig.Length)
{
throw new Exception("x.Length != sig.Length: " + x.Length + " " + sig.Length);
}
double t;
double st2 = 0.0;
b = 0.0;
if (sig != null)
{
for (int i = 0; i < ndata; i++)
{
t = (x[i]) / sig[i];
st2 += t * t;
b += t * y[i] / sig[i];
}
}
else
{
for (int i = 0; i < ndata; i++)
{
t = x[i];
st2 += t * t;
b += t * y[i];
}
}
b /= st2;
sigb = Math.Sqrt(1.0 / st2);
chi2 = 0.0;
if (sig == null)
{
for (int i = 0; i < ndata; i++)
{
double tmp = y[i] - b * x[i];
chi2 += tmp * tmp;
}
q = 1.0;
double sigdat = Math.Sqrt((chi2) / (ndata - 2));
sigb *= sigdat;
}
else
{
for (int i = 0; i < ndata; i++)
{
double tmp = (y[i] - b * x[i]) / sig[i];
chi2 += tmp * tmp;
}
q = NumericalRecipes.Gammq(0.5 * (ndata - 1), 0.5 * (chi2));
}
}
