std::exponential_distribution (3) - Linux Man Pages

std::exponential_distribution: std::exponential_distribution

NAME

std::exponential_distribution - std::exponential_distribution

Synopsis


Defined in header <random>
template< class RealType = double > (since C++11)
class exponential_distribution;


Produces random non-negative floating-point values x, distributed according to probability density function:


      P(x|λ) = λe-λx


The value obtained is the time/distance until the next random event if random events occur at constant rate λ per unit of time/distance. For example, this distribution describes the time between the clicks of a Geiger counter or the distance between point mutations in a DNA strand.
This is the continuous counterpart of std::geometric_distribution
std::exponential_distribution satisfies RandomNumberDistribution

Template parameters


RealType - The result type generated by the generator. The effect is undefined if this is not one of float, double, or long double.

Member types


Member type Definition
result_type RealType
param_type the type of the parameter set, see RandomNumberDistribution.

Member functions


              constructs new distribution
constructor (public member function)
              resets the internal state of the distribution
reset (public member function)

Generation


              generates the next random number in the distribution
operator() (public member function)

Characteristics


              returns the lambda distribution parameter (rate of events)
lambda (public member function)
              gets or sets the distribution parameter object
param (public member function)
              returns the minimum potentially generated value
min (public member function)
              returns the maximum potentially generated value
max (public member function)

Non-member functions


           compares two distribution objects
operator== (function)
operator!=
           performs stream input and output on pseudo-random number distribution
operator<< (function template)
operator>>

Notes


Some implementations may occasionally return infinity if RealType is float. This is LWG_issue_2524

Example


// Run this code


  #include <iostream>
  #include <iomanip>
  #include <string>
  #include <map>
  #include <random>
  int main()
  {
      std::random_device rd;
      std::mt19937 gen(rd());


      // if particles decay once per second on average,
      // how much time, in seconds, until the next one?
      std::exponential_distribution<> d(1);


      std::map<int, int> hist;
      for(int n=0; n<10000; ++n) {
          ++hist[2*d(gen)];
      }
      for(auto p : hist) {
          std::cout << std::fixed << std::setprecision(1)
                    << p.first/2.0 << '-' << (p.first+1)/2.0 <<
                  ' ' << std::string(p.second/200, '*') << '\n';
      }
  }

Possible output:


  0.0-0.5 *******************
  0.5-1.0 ***********
  1.0-1.5 *******
  1.5-2.0 ****
  2.0-2.5 **
  2.5-3.0 *
  3.0-3.5
  3.5-4.0

External links


Weisstein,_Eric_W._"Exponential_Distribution." From MathWorld--A Wolfram Web Resource.