[Scipy-tickets] [SciPy] #583: negative binomial fails with 0 < r < 1

SciPy scipy-tickets@scipy....
Fri Jan 11 16:31:27 CST 2008


#583: negative binomial fails with 0 < r < 1
-------------------------+--------------------------------------------------
 Reporter:  danhs        |       Owner:  somebody                 
     Type:  defect       |      Status:  new                      
 Priority:  normal       |   Milestone:                           
Component:  scipy.stats  |     Version:  none                     
 Severity:  normal       |    Keywords:  nbinom, negative binomial
-------------------------+--------------------------------------------------
 With r < 1 it seems that the negative binomial function has some
 noteworthy failures.

 Example:

 {{{
 nbinom = scipy.stats.nbinom(0.88, 0.42)


 # These will have errors:
 nbinom.rvs()
 nbinom.cdf()
 nbinom.ppf()

 # Strangely this does not:
 nbinom.isf()
 }}}

 My purpose was to create a random sample from the negative binomial so, I
 was able to use the following code successfully:

 {{{
 nbinom.isf(random.random())
 }}}


 Negative binomial is defined for r greater than 0 (real numbers), and for
 p in range 0 to 1 according to wikipedia

 So these should be acceptable inputs.

 This was observed on scipy 0.6.0.

-- 
Ticket URL: <http://www.scipy.org/scipy/scipy/ticket/583>
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