The Debye functions are defined by the integral
D_n(x) = n/x^n \int_0^x dt (t^n/(e^t - 1)).
For further information see Abramowitz & Stegun, Section 27.1.
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