class template
<random>

std::chi_squared_distribution

template <class RealType = double> class chi_squared_distribution;
Chi-squared distribution
Random number distribution that produces floating-point values according to a chi-squared distribution, which is described by the following probability density function:



This distribution produces random numbers as if the square of n independent standard normal random variables (Normal with μ=0.0 and σ=1.0) were aggregated, where n is the distribution parameter, known as degrees of freedom.

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

Template parameters

RealType
A floating-point type. Aliased as member type result_type.
By default, this is double.

Member types

The following aliases are member types of normal_distribution:

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

Member functions

(constructor)
Construct Chi-squared 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:

chi_squared_distribution::n
Degrees of freedom (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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// chi_squared_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::chi_squared_distribution<double> distribution(3.0);

  int p[10]={};

  for (int i=0; i<nrolls; ++i) {
    double number = distribution(generator);
    if ((number>=0.0)&&(number<10.0)) ++p[int(number)];
  }

  std::cout << "chi_squared_distribution (3.0):" << std::endl;

  for (int i=0; i<10; ++i) {
    std::cout << i << "-" << (i+1) << ": ";
    std::cout << std::string(p[i]*nstars/nrolls,'*') << std::endl;
  }

  return 0;
}


Possible output:
chi_squared_distribution (3.0):
0-1: *******************
1-2: ***********************
2-3: ******************
3-4: ************
4-5: *********
5-6: *****
6-7: ***
7-8: **
8-9: *
9-10: *

See also

normal_distribution
Normal distribution (class template )
lognormal_distribution
Lognormal distribution (class template )
cauchy_distribution
Cauchy distribution (class template )
fisher_f_distribution
Fisher F-distribution (class template )
student_t_distribution
Student T-Distribution (class template )

C++