export PREFIX="/path/to/your/prefix"; mkdir -p $PREFIX

export REPO="<enter the git repository here>"

mkdir -p ${PREFIX}/src && cd ${PREFIX}/src
git clone --recurse-submodules ${REPO}
mkdir -p pythia6m/BUILD && cd pythia6m/BUILD
cmake .. -DCMAKE_INSTALL_PREFIX=${PREFIX} -DCMAKE_PREFIX_PATH=${PREFIX}
make -j4
make install

export PATH=${PREFIX}/bin:${PATH}
echo "export PATH=\${PREFIX}/bin:\${PATH}" >> ${HOME}/.bash_profile

pythia6m -h

// event level
int32_t evnum;   // the event index
int32_t evgen;   // the total number of generated events sofar. 
                 // this includes generated events that were somehow cut out
double xsec;     // the total generated cross section
                 // the last stored value is the best estimate of the total
                 // cross section. 
                 // To obtain the cross section for a subset of n events:
                 //     xsec_n = n * xsec / evgen;
int32_t process; // PYTHIA process number
double s;        // s for this event
// particle level
std::vector<int32_t> index;     // The index of this track, equal to the fortran 
                                // index, so the C-index is (index - 1)
std::vector<int32_t> status;    // LUND track status (see pythia manual)
std::vector<int32_t> type;      // LUND particle type
std::vector<int32_t> parent;    // fortran index of the parent, 0 if initial
std::vector<int32_t> daughter1; // fortran index of first daughter, 0 if none
std::vector<int32_t> daughter2; // fortran index of last daughter, 0 if none
std::vector<int32_t> charge;    // charge
std::vector<ROOT::Math::XYZTVector> vertex; // vertex 4-vector
std::vector<ROOT::Math::XYZTVector> mom;    // momentum 4-vector
std::vector<double> mass;       // mass
std::vector<bool> init;         // is this an initial particle?
std::vector<bool> lund;         // is this a final particle produced by PYTHIA?

// event level
double Q2;          // Generated Q2
double nu;          // Generated nu
double x;           // Generated Bjorken-x
double y;           // Generated y
double W2;          // Generated W2
int32_t scat_index; // the C-index of the scattered (NOT THE FORTRAN INDEX)
                    // of the scattered lepton