[SciPy-User] Strange behavior of sph_jn

Travis Oliphant travis@continuum...
Wed Apr 11 08:48:35 CDT 2012


Thanks for this excellent feedback.    It would be very helpful if you could file a bug at

http://projects.scipy.org/scipy

That way we we don't lose track of the problem you ran in to.   The algorithm should be adjusted to handle these values. 

Best regards,

-Travis


On Apr 10, 2012, at 8:49 AM, ZIEGLER Yann (ETU EOT) wrote:

> Hi,
> 
> It seems that the bug I have with sph_jn for some values is due to scipy
> itself. I finded someone having the same kind of trouble on 
> projects.scipy.org/scipy (the website seems to have some technical problems
> at this time).
> 
> If anyone is interested in it, here is the solution I have finded to
> circumvent this bug :
> 
> Using the definition of Spherical Bessel function involving Bessel function
> (http://functions.wolfram.com/Bessel-TypeFunctions/SphericalBesselJ/02/),
> I wrote -- nothing extraordinary, this is a 2-lines function -- my own
> SphericalBessel function (naive but seemingly correct) for positive or
> negative order n and complex argument z : 
> 
> import numpy as np
> from scipy.special import jn
> 
> def SphericalBessel(n,z):
> 
>   zsqrt = np.sqrt(np.abs(z)) * np.exp(np.angle(z)/2)
> 
>   return np.sqrt(np.pi/2) / zsqrt * jn(n+0.5, z)
> 
> Yann
> 
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