[SciPy-Dev] doc inconsistency at http://docs.scipy.org/doc/scipy/reference/generated/scipy.stats.lognorm.html

josef.pktd@gmai... josef.pktd@gmai...
Mon Mar 5 11:47:02 CST 2012


On Mon, Mar 5, 2012 at 10:57 AM,  <keith.briggs@bt.com> wrote:
> http://docs.scipy.org/doc/scipy/reference/generated/scipy.stats.lognorm.html defines lognorm as having a location parameter and a scale parameter, but later on it says:
>
> "... shape paramter [sic] sigma and scale parameter exp(mu)."
>
> The same name should be used throughout.

lognormal is always a bit tricky

the ... in your quote refer to sigma and mu for the normal
distribution or log(x), while scale and shape in the second half refer
to the parameters of the log-normal (conditional statement)

except for the typo it looks correct to me

>>> stats.norm.cdf(np.log(5.5), loc=5, scale=2)   #mu=5 sigma=2
0.049714725582938914
>>> stats.lognorm.cdf(5.5, 2, scale=np.exp(5))
0.049714725582938914
>>> stats.lognorm.cdf(5.5, 2, loc=0, scale=np.exp(5))  #shape=sigma=2, scale=exp(mu)=exp(5)
0.049714725582938914

We should add an example like this to the docstring

Josef

>
> Keith
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