I am testing the bessel function boost::math::cyl_bessel_j in gnu compiler with boost 1.51.0, I am testing

boost::math::cyl_bessel_j(2000, 0.9) boost::math::cyl_bessel_j(4000, 0.9)

the first one give zero but the second one gives infinity while it should give zero also. I wonder why it doesn't work when the order is bigger than 4000?

Works for me with 1.54 - can you please update your Boost version and try again as there have been some fixes and improvements to the Bessel functions over the last couple of releases. Thanks, John.