These functions compute the incomplete Gamma Function the normalization factor included in the previously defined functions: \Gamma(a,x) = \int_x\infty dt t^{a-1} \exp(-t) for a real and x >= 0.
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