// std::mt19937 random number generator
// uses std::function and std::bind
#include <iostream>
#include <random>
#include <ctime> 
#include <fstream>
#include <functional>

using namespace std;


// define generator
std::mt19937 gener;

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(0,1);
    rnd = bind(unif, gener);  
    first = false;
  } 
  return rnd();
  
}

double gaussrand(void){
  static bool first = true; 
  static function<double()> rnd ;      
  if(first) {
    initrng(); 
    normal_distribution<double> gaussian(0,1);
    rnd = bind(gaussian, gener);
    first = false;
  }
  return rnd();
}



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();
}