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Showing content from https://cplusplus.com/chi_squared_distribution below:

class template

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 type definition notes result_type The first template parameter (RealType) The type of the numbers generated (defaults to double) param_type not specified The 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

// 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: *