> In the documentation, there are no specifications for the values of nu in > the evaluation of bessel_Jnu. However after running the command for nu < 0, > a domain error was shot at me. After looking at the source code, it indeed > shows that a domain error is thrown when nu < 0. The cylinder Bessel > function however is defined when nu < 0 (for x > 0), so the documentation > should reflect that the routines only work when nu >= 0. This caused a bit > of a headache for me today and I figured I'd spare someone else from this. > > Can the case of nu < 0 be easily implemented numerically? I am going to go > through the source code and see if I can get it to work for nu < 0 over the > next day or two.
I wasn't entirely sure from your message whether you know the relationship between nu>0 and nu<0, but for Bessel functions of the first kind there is a very simple relationship - see http://mathworld.wolfram.com/BesselFunctionoftheFirstKind.html equation 51. Of course it might be better if the source code handled this explicitly, but you can very easily write a wrapper that calls through to gsl to obtain J_|m|(x) and returns J_m(x). Jonny.
