[SciPy-Dev] Deprecate planck distribution?

[Robert Kern]

On Wed, Jan 2, 2019 at 1:36 AM Christoph Baumgarten <
christoph.baumgarten at gmail.com> wrote:
>
> Hi all,
>
> happy new year!
>
> I noted that the Planck distribution is a geometric distribution with a
different parametrization, see Issue #9359:
>
> import numpy as np
> from scipy.stats import planck, geom
>
> a = 0.5
> k = np.arange(20)
> sum(abs(geom.pmf(k, 1-np.exp(-a), loc=-1) - planck.pmf(k, a))) # 1.30e-18
>
> I don't know if there is a specific reason to have the Planck
distribution in addition to the geometric. If not, I would propose to
deprecate it.
>
> Any views? Thanks

If we were to turn back time, and the question was whether to *add* the
Planck distribution given that we had the geometric distribution, I would
probably be convinced by this. However, given that the Planck distribution
has already been added, I don't think that it's worth removing it. The
marginal cost to having this alternate parameterization is likely less than
the cost of anyone changing their code.

The collection of probability distributions are also a place where some
nontrivial duplication actually has some positive value. People typically
come to `scipy.stats` with a distribution (with a name and specific
parameterization conventions) already in mind. Having more than one
parameterization available helps people recognize the distribution that
they want; having an alternate present doesn't impair the search task while
not having one they are looking for (or burying it in the Notes of the
docstring of the canonical version) can make the search task much harder.
It's a common complaint that `scipy.stats` doesn't expose certain common
parameterizations of distributions, so we should probably be working to
expand the collection of parameterizations rather than collapsing them.

--
Robert Kern
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