// std::mt19937 random number generator
// uses std::function and std::bind
#include <iostream>
#include <random>
#include <ctime> 
#include <fstream>
#include <functional>
using namespace std;
std::mt19937 gener; // define generator
void initrng(void){
  static bool first = true; 
  if(first){
    auto seed = static_cast<uint_fast32_t> (std::time(0));
    cout<<" seed = "<<seed<<endl;
    gener.seed(seed); 
    first = false; 
  }
}
double unirand(void){
  static bool first = true; 
  static function<double()> rnd ;    
  if(first){ 
    initrng();
    uniform_real_distribution<double> unif_dist(0,1);
    rnd = bind(unif_dist, gener);  
    first = false;
  } 
  return rnd();
}

double gaussrand(void){ 
  static bool first = true; 
  static function<double()> rnd ;      
  if(first) {
    initrng(); 
    normal_distribution<double> norm_dist(0,1);
    rnd = bind(norm_dist, gener);
    first = false;
  }
  return rnd();
}
double gaussrand2(void){ // warning: does not initialize generator
  static normal_distribution<double> norm_dist(0,1);
  return (norm_dist(gener));
}
double exprand(void){
  static bool first = true; 
  static function<double()> rnd ;      
  if(first) {
    initrng(); 
    exponential_distribution<double> expo;
    rnd = bind(expo, gener);
    first = false;
  }
  return rnd();
}