Re: improving special functions in GSoC 2017

[Julien Bect]

Le 26/06/2016 à 08:08, Colin Macdonald a écrit :
> On 25/06/16 02:54, Marco Caliari wrote:
> > "Special functions are expected by users to just work".
>
> So I just found that our "besselj" gives NaNs for values like "1e10".
>
> >> besselj(1, 1e9)
> ans = -5.21042264155388e-06
> >> besselj(1, 1e10)
> ans = NaN + NaNi
>
>
> https://savannah.gnu.org/bugs/index.php?48316
>
>
> That's not some wild exotic function: its a common Bessel function!
>
>
> Why are we not just calling some free-licensed library that nails 
> these things?  For example, SciPy does:
>
> >>> scipy.special.jn(1,1e9)
> -5.2104226415538769e-06
> >>> scipy.special.jn(1,1e10)
> -7.676506113846571e-06

Another possibility is Boost : 
http://www.boost.org/doc/libs/1_61_0/libs/math/doc/html/special.html.