[SciPy-user] problems with stats
Travis E. Oliphant
oliphant at ee.byu.edu
Tue Apr 27 16:20:38 EDT 2004
danny shevitz wrote:
> Howdy,
>
> I've encountered two problems with the binomial distribution in the
> stats module. The first is trivial and I believe just an argument
> checking problem.
>
>
>>>>binom.pdf(0,3,.5)
>
>
> bdtr domain error
> 1.#QNAN
which version are you using?
The current version 0.3 uses pmf (probability mass function) for
discrete rvs.
for me
>>> binom.pmf(0,3,.5)
0.125
>
> (the answer should be .125 of course)
>
> The second is a little more significant. I'm trying to invert the
> binomial distribution using ppf. I looked at distributions.py
>
> class binom_gen(rv_discrete):
> .
> .
> .
> def _ppf(self, q, n, pr):
> vals = ceil(special.bdtrik(q,n,pr))
> vals1 = vals-1
> temp = special.bdtr(vals1,n,pr)
> return where(temp >= q, vals1, vals)
>
> and ppf is in fact implemented, but when I try to run it I get an
> error.
>
>
>>>>binom.ppf(3,4,.95)
You uncovered a genuine bug here.
But, by the way what you expect this to return seeing how 3 is bigger
than 1.
-Travis
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