C++

Reference

<random>

geometric_distribution

class template
<random>

std::geometric_distribution

template <class IntType = int> class geometric_distribution;
Geometric distribution
Random number distribution that produces integers according to a geometric discrete distribution, which is described by the following probability mass function:



This distribution produces positive random integers where each value represents the number of unsuccessful trials before a first success in a sequence of trials, each with a probability of success equal to p.

The distribution parameter, p, is set on construction.

To produce a random value following this distribution, call its member function operator().

Its analogous continuous distribution is the exponential_distribution.

Template parameters

IntType
An integer type. Aliased as member type result_type.
By default, this is int.

Member types

The following aliases are member types of geometric_distribution:

member typedefinitionnotes
result_typeThe first template parameter (IntType)The type of the numbers generated (defaults to int)
param_typenot specifiedThe type returned by member param.

Member functions

(constructor)
Construct geometric distribution (public member function)
operator()
Generate random number (public member function)
reset
Reset distribution (public member function)
param
Distribution parameters (public member function)
min
Minimum value (public member function)
max
Maximum value (public member function)

Distribution parameters:

p
Probability of success (public member function)

Non-member functions

operator<<
Insert into output stream (function template)
operator>>
Extract from input stream (function template)
relational operators
Relational operators (function template)

Example

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// geometric_distribution
#include <iostream>
#include <random>

int main()
{
  const int nrolls = 10000; // number of experiments
  const int nstars = 100;   // maximum number of stars to distribute

  std::default_random_engine generator;
  std::geometric_distribution<int> distribution(0.3);

  int p[10]={};

  for (int i=0; i<nrolls; ++i) {
    int number = distribution(generator);
    if (number<10) ++p[number];
  }

  std::cout << "geometric_distribution (0.3):" << std::endl;
  for (int i=0; i<10; ++i)
    std::cout << i << ": " << std::string(p[i]*nstars/nrolls,'*') << std::endl;

  return 0;
}

Possible output:
geometric_distribution (0.3):
0: *****************************
1: *********************
2: **************
3: *********
4: *******
5: *****
6: ***
7: **
8: *
9: *


See also

exponential_distribution
Exponential distribution (class template)
bernoulli_distribution
Bernoulli distribution (class)
binomial_distribution
Binomial distribution (class template)