C++

Reference

<random>

chi_squared_distribution

public member function
<random>

std::chi_squared_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 chi_squared_distribution object transforms the values obtained this way so that successive calls to this member function with the same arguments produce floating-point values that follow a Chi-squared distribution with the appropriate parameters.

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 (RealType).

Example

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// chi_squared_distribution example
#include <iostream>
#include <chrono>
#include <random>

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

  std::chi_squared_distribution<double> distribution (4.0);

  std::cout << "some chi-squared-distributed(4.0) results:" << std::endl;
  for (int i=0; i<5; ++i)
    std::cout << distribution(generator) << std::endl;

  return 0;
}

Possible output:
some chi-squared--distributed(4.0) results:
6.67422
2.31487
12.7602
5.29782
6.76836


Complexity

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

See also

chi_squared_distribution::param
Distribution parameters (public member function)