Attribute Error from Minimizer object returned from scipy.optimize.minimize() function

Question

Using the scipy.optimize.minimize() function I went trough different results using different methods for the same objective function. To evaluate the goodness-of-fit I use to look at the reduced chi squared as a first criterion. After some time I ended with this useful guide http://newville.github.io/lmfit-py/fitting.html#Minimizer where it is specified that the reduced chi squared is set as attribute of the Minimizer object returned from the minimize() function. But if I do

minobj = scipy.optimize.minimize(...)
minobj.redchi

I get

 AttributeError: redchi

Meanwhile minobj.message and minobj.success are correctly displayed. Any guess?

Answer 1

The documentation is a little misleading --- if you look at lmfit/minimizer.py, and do a string search for "redchi" in the entire file, it only appears once, and that is in the leastsq() method. So basically, it only calculates the reduced chi squared for least-squares fitting.

If you're feeling up to it, you could add redchi to the other methods in the appropriate places, fork the lmfit github repo, and commit your changes.

Answer 2

In addition to Ashwin's answer, you could always just use:

result = lmfit.minimize(...)
x2 = result.chisqr
nfree = result.nfree
red_x2 = x2/nfree