26 Numerics library [numerics]

26.6 Random number generation [rand]

26.6.8 Random number distribution class templates [rand.dist]

26.6.8.5 Normal distributions [rand.dist.norm]

26.6.8.5.3 Class template chi_squared_distribution [rand.dist.norm.chisq]

1

A chi_squared_distribution random number distribution produces random numbers x>0 distributed according to the probability density function\[% p(x\,|\,n) = \frac{ x^{(n/2)-1} \cdot e^{-x/2}} {\Gamma(n/2) \cdot 2^{n/2}} \; \mbox{.} \]

template<class RealType = double>
 class chi_squared_distribution{
public:
 // types
 using result_type = RealType;
 using param_type  = unspecified;

 // constructor and reset functions
 explicit chi_squared_distribution(RealType n = 1);
 explicit chi_squared_distribution(const param_type& parm);
 void reset();

 // generating functions
 template<class URBG>
   result_type operator()(URBG& g);
 template<class URBG>
   result_type operator()(URBG& g, const param_type& parm);

 // property functions
 RealType n() const;
 param_type param() const;
 void param(const param_type& parm);
 result_type min() const;
 result_type max() const;
};

explicit chi_squared_distribution(RealType n = 1);

2

Requires: 0 < n .

3

Effects: Constructs a chi_squared_distribution object; n corresponds to the parameter of the distribution.

RealType n() const;

4

Returns: The value of the n parameter with which the object was constructed.