[SciPy-dev] nbinom.ppf

Pierre GM pgmdevlist@gmail....
Mon Jul 27 14:47:44 CDT 2009


All,
I'm puzzled by this result:
 >>> from scipy.stats.distributions import nbinom
 >>>  nbinom(.3,.15).ppf(nbinom(.3,.15).cdf(np.arange(20)))
array([  1.,   2.,   2.,   3.,   5.,   5.,   6.,   8.,   9.,  10.,  11.,
         12.,  13.,  14.,  15.,  16.,  17.,  18.,  19.,  20.])

I would have naturally expected np.arange(20).
Using np.round instead of np.ceil in nbinom_gen._ppf seems to solve  
the issue.
Is there any reason not to do it ?
Thx in advance.
P.



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