C++

Reference

<random>

geometric_distribution

public member function
<random>

std::geometric_distribution::operator()

(1)
template<class URNG>result_type operator()(URNG& g);
(2)
template<class URNG>result_type operator()(URNG& g, const param_type& parm);
Generate random number
Returns a new random number that follows the distribution's parameters associated to the object (version 1) or those specified by parm (version 2).

The generator object (g) supplies uniformly-distributed random integers through its operator() member function. The geometric_distribution object transforms the values obtained this way so that successive calls to this member function with the same arguments produce values that follow a geometric distribution with the appropriate probability.


Parameters

g
A uniform random number generator object, used as the source of randomness.
URNG shall be a uniform random number generator type, such as one of the standard generator classes.
parm
An object representing the distribution's parameters, obtained by a call to member function param.
param_type is a member type.

Return value

A new random number.
result_type is a member type, defined as an alias of the first class template parameter (IntType).

Example

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// geometric_distribution example
#include <iostream>
#include <chrono>
#include <string>
#include <random>

int main()
{
  // construct a trivial random generator engine from a time-based seed:
  int seed = std::chrono::system_clock::now().time_since_epoch().count();
  std::default_random_engine generator (seed);

  std::geometric_distribution<int> distribution (1.0/5);

  std::cout << "each star is 5 spaces away from the next (on average):" << std::endl;
  for (int i=0; i<100; ++i) {
    int number = distribution(generator);
    std::cout << std::string (number,' ') << "*";
  }

  return 0;
}

Possible output:
each star is 5 spaces away from the next (on average):
             *  *   *          ** *       *               *    * * **     *
*  *        *    *  *                      *    * *         *      *     ** *
*      *       *       *       *       * *       *  ****         *    **  *   **
   *     **  *      *  *  *    *   * **        *                   *     *  *
 ***   *    *   *          *   *  *       * * *           *            ** ***
 * ***          *       **              *   *  **                      *   *  *
   *  *          *   *            *  *         ***


Complexity

Amortized constant (a constant number of invocations of g.operator()).

See also

geometric_distribution::param
Distribution parameters (public member function)