[Scipy-tickets] [SciPy] #1502: lognorm pdf produces incorrect values
SciPy Trac
scipy-tickets@scipy....
Thu Aug 25 15:13:14 CDT 2011
#1502: lognorm pdf produces incorrect values
--------------------------+-------------------------------------------------
Reporter: rgrout | Owner: somebody
Type: defect | Status: closed
Priority: high | Milestone: Unscheduled
Component: scipy.stats | Version: 0.9.0
Resolution: worksforme | Keywords: lognorm, pdf
--------------------------+-------------------------------------------------
Changes (by rkern):
* status: new => closed
* resolution: => worksforme
Comment:
No, it's correctly calculated, it just follows a different convention than
you may be used to. For a uniform interface to all of the distributions,
they all take a location and scale parameter. In this case, exp(m) is the
scale parameter. Take a look at the docstring for scipy.stats.lognorm.
Thus, you don't specify the mean directly, you specify scale=exp(m) in the
arguments to the various methods. ._pdf() is an internal method that
computes the PDF for loc=0, scale=1.0. The .pdf() method will normalize
its input by the location and scale parameter, call the ._pdf() method
with the normalized input, then do the appropriate adjustment for the
scale.
http://docs.scipy.org/doc/scipy/reference/generated/scipy.stats.lognorm.html#scipy.stats.lognorm
http://docs.scipy.org/doc/scipy/reference/tutorial/stats/continuous.html
#continuous-random-variables
If you still think there is a bug, please reopen this ticket and show us
exactly what example you tried, the results that you obtained from scipy,
as well as the corresponding examples and results from the other software
that you are comparing against. Thanks!
--
Ticket URL: <http://projects.scipy.org/scipy/ticket/1502#comment:1>
SciPy <http://www.scipy.org>
SciPy is open-source software for mathematics, science, and engineering.
More information about the Scipy-tickets
mailing list