[quote=“moneta”]Have you done before
using namespace ROOT::Math;
or called the function with
ROOT::Math::expint(1)
Otherwise if it does not work, please tell me the ROOT version and the platform you are using
Lorenzo[/quote]
I called the function with the command ROOT::Math::expint(1)
Actually I am working with ROOT version 5.10 on a SLC 4.4 x86_64 platform, but I also tried on a Linux Mandrake platform with an older ROOT version 4.