Computes the transport function J(2,x).
The transport functions J(n,x) are defined by the integral representations J(n,x) := \int_0^x dt t^n e^t /(e^t - 1)^2.
err contains an estimate of the absolute error in the value z.
This function is from the GNU Scientific Library, see http://www.gnu.org/software/gsl/ for documentation.
Package: gsl