— Function: double gsl_sf_bessel_Jnu (double nu, double x)
— Function: int gsl_sf_bessel_Jnu_e (double nu, double x, gsl_sf_result * result)

These routines compute the regular cylindrical Bessel function of fractional order \nu, J_\nu(x).

— Function: int gsl_sf_bessel_sequence_Jnu_e (double nu, gsl_mode_t mode, size_t size, double v[])

This function computes the regular cylindrical Bessel function of fractional order \nu, J_\nu(x), evaluated at a series of x values. The array v of length size contains the x values. They are assumed to be strictly ordered and positive. The array is over-written with the values of J_\nu(x_i).