Go to the documentation of this file.00001 #ifndef ALPHA_T_H
00002 #define ALPHA_T_H
00003
00004 #include <cmath>
00005 #include <vector>
00006 #include <numeric>
00007 #include <functional>
00008 #include <algorithm>
00009 #include "special_less.h"
00010
00011 struct alpha_T {
00012
00013 template<class LVs>
00014 double operator()(const LVs& p4s) const { typedef typename LVs::value_type LorentzV;
00015 if( p4s.size() < 2 ) return 0;
00016
00017 std::vector<double> pTs;
00018 transform( p4s.begin(), p4s.end(), back_inserter(pTs), std::mem_fun_ref(&LorentzV::Pt));
00019
00020 const double DsumPT = minimum_deltaSumPT( pTs );
00021 const double sumPT = accumulate( pTs.begin(), pTs.end(), double(0) );
00022 const LorentzV sumP4 = accumulate( p4s.begin(), p4s.end(), LorentzV() );
00023
00024 return 0.5 * ( sumPT - DsumPT ) / sqrt( sumPT*sumPT - sumP4.Perp2() );
00025 }
00026
00027 static double minimum_deltaSumPT(const std::vector<double>& pTs) {
00028 std::vector<double> diff( 1<<(pTs.size()-1) , 0. );
00029 for(unsigned i=0; i < diff.size(); i++)
00030 for(unsigned j=0; j < pTs.size(); j++)
00031 diff[i] += pTs[j] * ( 1 - 2 * (int(i>>j)&1) ) ;
00032
00033 return fabs( *min_element( diff.begin(), diff.end(), fabs_less() ) );
00034 }
00035
00036 };
00037
00038 #endif
1.7.3