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https://issues.apache.org/jira/browse/MATH-1373?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15338637#comment-15338637
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Gilles commented on MATH-1373:
------------------------------
I think that it's a documentation issue.
{quote}
* MathWorld's M being equivalent to Commons Math's scale
* MathWorld's S being equivalent to Commons Math's shape
{quote}
In [MathWorld|http://mathworld.wolfram.com/LogNormalDistribution.html], {{M}}
and {{S}} above are respectively named {{mu}} and {{sigma}}.
But CM uses the names {{scale}} and {{shape}} (in that order), whereas
[Wikipedia|https://en.wikipedia.org/wiki/Log-normal_distribution#Location_and_scale]
refers to them as {{location}} and {{scale}} (in that order).
IIUC, CM uses the [NIST convention
|http://www.itl.nist.gov/div898/handbook/eda/section3/eda3669.htm] (where
{{sigma}} is referred to as {{shape}}) but the Javadoc links to sites that use
other conventions.
The API would be less confusing if we'd use {{meanLog}} (a.k.a. {{mu}} or
{{scale}}) and {{standardDeviationLog}} (a.k.a. {{sigma}} or {{shape}}).
Do you agree?
> In LogNormalDistribution.java, it appears shape & scale are
> reversed/mis-labelled.
> ----------------------------------------------------------------------------------
>
> Key: MATH-1373
> URL: https://issues.apache.org/jira/browse/MATH-1373
> Project: Commons Math
> Issue Type: Bug
> Affects Versions: 3.6.1
> Reporter: Karl D. Gierach
> Priority: Minor
> Attachments: MATH-1373.patch
>
> Original Estimate: 1h
> Remaining Estimate: 1h
>
> When I compute the logshape and log scale based on the formulas on
> wikipedia's lognormal distribution page that use empirical mean and variance,
> I found that the getNumericalMean() method was not returning the empirical
> mean.
> However, upon just trying to reverse the shape and scale parameters in the
> constructor proved to fix the problem, and the object then returns the
> correct empirical mean.
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