— Function: double gsl_sf_bessel_Knu (double nu, double x)
— Function: int gsl_sf_bessel_Knu_e (double nu, double x, gsl_sf_result * result)

These routines compute the irregular modified Bessel function of fractional order \nu, K_\nu(x) for x>0, \nu>0.

— Function: double gsl_sf_bessel_lnKnu (double nu, double x)
— Function: int gsl_sf_bessel_lnKnu_e (double nu, double x, gsl_sf_result * result)

These routines compute the logarithm of the irregular modified Bessel function of fractional order \nu, \ln(K_\nu(x)) for x>0, \nu>0.

— Function: double gsl_sf_bessel_Knu_scaled (double nu, double x)
— Function: int gsl_sf_bessel_Knu_scaled_e (double nu, double x, gsl_sf_result * result)

These routines compute the scaled irregular modified Bessel function of fractional order \nu, \exp(+|x|) K_\nu(x) for x>0, \nu>0.