Calculate the normalized (regularized) upper incomplete gamma function

Dear all,
do you know how to calculate the normalized (regularized) upper incomplete gamma function with root (given two input double)?

I tried something like this

double p;
double D;
double B;
p = ROOT::Math::inc_gamma_c(D,B);

or

p = TMath::inc_gamma_c(D,B);

(I have found it in http://arxiv.org/pdf/1111.2062v4.pdf, plus that’s exactly what it says in http://project-mathlibs.web.cern.ch/project-mathlibs/sw/html/group__SpecFunc.html#ga0d41b67be213ef7e49a3722acb316ed5)

But, in both cases, I could NOT compile my program.

The error I get is the following:
error: ‘inc_gamma_c’ is not a member of ‘ROOT::Math’
or
error: ‘inc_gamma_c’ is not a member of ‘TMath’

FYI, the command I use to compile is:
g++ -Wl,–no-as-needed myprogram.cxx root-config --cflags --libs -o exec
and I am using root 5.34.34

Thank you in advance for your help
Mat

Do you:
#include “Math/SpecFunc.h”

Of course I did not. Thanks. It’s working.
Sorry for your time
Cheers