scipy.stats.expon.fit() with no location parameter

Question

I am using scipy.stats.expon.fit(data) to fit an exponential distribution to my data. This appears to return two values where I would expect one. The documentation online doesn't seem to say what fit() returns but looking at the source, I am guessing it is both a location and scale parameter. Can you fix the location parameter to 0 when doing the fitting?

Tanagra

@mdml Thank you. I would like to run fit but have the location fixed to 0. It seems this isn't the default behaviour. (It is odd that it has a location parameter at all to be honest for the exponential distribution.) – Tanagra

Duplicate: #21610534 (Yeah, I know I already answered. Shame on me.) – Gegenschein

@WarrenWeckesser Ah well I will happily delete it but it would be great if the docs could be updated! – Tanagra

Answer 1

In the call to expon.fit, use floc=0:

In [5]: data = expon.rvs(0, 1.5, 1000)

In [6]: loc, scale = expon.fit(data, floc=0)

In [7]: scale
Out[7]: 1.4878030368336586

In [8]: loc
Out[8]: 0

Gegenschein

Thank you! Is that in the documentation anywhere? Or in other words, how did you know this? – Tanagra

You have to read the docstring of expon.fit pretty closely to find it, but it is mentioned in there. Read the description of kwds in the "Parameters" section. – Gegenschein

Oh wow. The official web page has loads less information in it than the docstring!! – Tanagra