Please can somebody advise on using gsl_sf_bessel_Jn_array for small z?
I need to generate Bessel functions up to some n_max (of order 50) for arbitrary z. I run into problems for small z because the function uses a downward recurrence to populate the array, and suffers underflow for large n.
It is not a problem for me if underflow occurs at high n: I am computing a sum, and if underflow occurs for some n then that will definitely not affect the overall result.
What I presume I need to do is to determine what n (<= n_max) I need to pass to gsl_sf_bessel_Jn_array in order to avoid underflow. Unfortunately that doesn't seem to be trivial to compute (which is not really surprising). The best strategies I can come up to are to use a lookup which gives the minimum z which works for a given cutoff n, or to just try calling gsl_sf_bessel_Jn_e for some trial n and then reducing n if I get an error. That is not ideal, though, as I'll need to install an error handler and I want to do this in threaded code.
Can anybody suggest a better strategy to take? It seems like this should be a relatively simple thing to ask, but I can't come up with a simple way of achieving it...
Thanks Jonny _______________________________________________ Help-gsl mailing list [email protected] http://lists.gnu.org/mailman/listinfo/help-gsl
