Re: [Boost-users] spherical bessel functions

Subject: Re: [Boost-users] spherical bessel functions
From: John Maddock (boost.regex_at_[hidden])
Date: 2012-03-23 06:10:16

>It doesn't matter if I define double x = a*kw and pass this into the 
>interface, what seems to matter is the value of the index,
>when n = 8 it doesn't work. It works for 9 and 10 and all integers before 
>8.
>I can replace x with a, lambda or pi and it works for n = 8, so it seems to 
>be this combination of numbers or something I'm doing
>wrong w/r to type casting variables etc.

OK I can reproduce here, and it's very specific to the calculation of 
Y[8.5](4*Pi), if you change nu at all, or add a tiny increment to the 4PI 
arg then it all works OK.  The problem BTW is exquisite cancellation inside 
the algorithm, which leads me to suspect there's something "special" about 
this value.  Unfortunately I don't have a fix at present (or understand the 
root cause yet), more investigation needed....

Thanks for the report, John.