Chi square numpy.polyfit (numpy)
Could someone explain how to get Chi^2/doF using numpy.polyfit?
Answer
Assume you have some data points
x = numpy.array([0.0, 1.0, 2.0, 3.0])
y = numpy.array([3.6, 1.3, 0.2, 0.9])
To fit a parabola to those points, use numpy.polyfit():
p = numpy.polyfit(x, y, 2)
To get the chi-squared value for this fit, evaluate the polynomial at the x values of your data points, subtract the y values, square and sum:
chi_squared = numpy.sum((numpy.polyval(p, x) - y) ** 2)
You can divide this number by the number of degrees of freedom if you like.