[SciPy-User] special.kv goes from 0 to nan for large numbers

Johann Cohen-Tanugi johann.cohentanugi@gmail....
Mon Jan 23 23:28:24 CST 2012


done : http://projects.scipy.org/scipy/ticket/1589
thanks,
Johann


On 01/24/2012 01:59 AM, Pauli Virtanen wrote:
> Johann Cohen-Tanugi<johann.cohentanugi<at>  gmail.com>  writes:
> [clip]
>> In [4]: sp.kv(1./3.,1.08e+09)
>> Out[4]: nan
> [clip]
>> I guess this has to dow with a cephes and big numbers.... Is it fixed on
>> github already, or is it a known bug? Or is it a feature and not a bug?
>
> No, it's not a known bug, please file a ticket.
>
> The code for KV actually comes from Boost, so it's better quality than Cephes,
> but apparently it wasn't perfect. There's no asymptotic expansion for KV, and it
> seems the continued fraction or something else fails to converge in this limit.
>


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