[Numpy-discussion] multinomial question

Robert Kern robert.kern@gmail....
Wed Dec 5 20:34:41 CST 2007


Alan G Isaac wrote:
> I would think that
>     multinomial(1,prob,size=ntrials).sum(axis=0)
> would be equivalent to
>     multinomial(ntrials,prob)
> but the first gives a surprising result.  (See below.)
> Explanation?

A bug in rk_binomial_inversion(). Unfortunately, this looks like a logical bug
in the sources I was deriving this code from. The "safety bound" on the search
inversion search cuts out too early. Now that I re-examine it, it looks the
bound (whichever of the multiple choice of bounds one could use) could always be
legitimately exceeded, so there shouldn't be a bound at all. I'll have to dive
deeper to figure out what is going on. This makes me grumpy.

-- 
Robert Kern

"I have come to believe that the whole world is an enigma, a harmless enigma
 that is made terrible by our own mad attempt to interpret it as though it had
 an underlying truth."
  -- Umberto Eco


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