[Numpy-discussion] numpy.random.multinomial() cannot handle zero's
Christopher Barker
Chris.Barker at noaa.gov
Mon Aug 27 14:07:00 EDT 2007
Stefan van der Walt wrote:
> For some reason, the kahan_sum of [0.2,0.0,0.8,0.0] is ever so
> slightly larger than 1.0 (in the order of 1e-16), but I'm not sure
> why, yet (this isn't specific to kahan summation -- normal summation
> shows the same behavior).
Just to make sure -- is the khan_sum "compensated summation"?
Is the kahan_sum closer? -- it should be, though compensated summation
is really for adding LOTS of numbers, for 4, it's pointless at best.
Anyway, binary floating point has its errors, and compensated summation
can help, but it's still not exact for numbers that can't be exactly
represented by binary.
i.e. if your result is within 15 decimal digits of the exact result,
that's as good as it gets.
-Chris
--
Christopher Barker, Ph.D.
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