discrete_distribution.hh

#ifndef LOCARNA_DISCRETE_DISTRIBUTION
#define LOCARNA_DISCRETE_DISTRIBUTION

#ifdef HAVE_CONFIG_H
#  include <config.h>
#endif

namespace LocARNA {
    
    // ------------------------------------------------------------
    class DiscreteDistribution {
    private:
        std::vector<double> distrib_acc_;
    public:
        DiscreteDistribution(const std::vector<double> &distvec)
        {
            if (distvec.size()==0) return;
        
            distrib_acc_.resize(distvec.size());

            distrib_acc_[0] = distvec[0];
            for (size_t i=1; i<distvec.size(); i++) {
                distrib_acc_[i]+=distrib_acc_[i-1]+distvec[i];
            }
            double max_acc = distrib_acc_[distvec.size()-1];
            for (size_t i=0; i<distvec.size(); i++) {
                distrib_acc_[i]/=max_acc;
            }
        }
    
        size_t
        operator () (size_t x) {
            double y=x/(double)RAND_MAX;
        
            size_t i=0;
            for (; i<distrib_acc_.size() && y>distrib_acc_[i]; ++i)
                ;
        
            assert(i<=distrib_acc_.size());
            return i;
        }
    };

} // end namespace LocARNA

#endif //LOCARNA_DISCRETE_DISTRIBUTION