cppdraft_translate/cppdraft/rand/dist/pois/gamma.md

[rand.dist.pois.gamma]

29 Numerics library [numerics]

29.5 Random number generation [rand]

29.5.9 Random number distribution class templates [rand.dist]

29.5.9.4 Poisson distributions [rand.dist.pois]

29.5.9.4.3 Class template gamma_distribution [rand.dist.pois.gamma]

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A gamma_distribution random number distribution produces random numbers x>0 distributed according to the probability density function in Formula 29.10.

p(x|α,β)=e−x/ββαâ‹Î“(α)â‹xα−1(29.10)

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namespace std {templateclass gamma_distribution {public:// typesusing result_type = RealType; using param_type = unspecified; // constructors and reset functions gamma_distribution() : gamma_distribution(1.0) {}explicit gamma_distribution(RealType alpha, RealType beta = 1.0); explicit gamma_distribution(const param_type& parm); void reset(); // equality operatorsfriend bool operator==(const gamma_distribution& x, const gamma_distribution& y); // generating functionstemplate result_type operator()(URBG& g); template result_type operator()(URBG& g, const param_type& parm); // property functions RealType alpha() const; RealType beta() const; param_type param() const; void param(const param_type& parm); result_type min() const; result_type max() const; // inserters and extractorstemplate<class charT, class traits>friend basic_ostream<charT, traits>&operator<<(basic_ostream<charT, traits>& os, const gamma_distribution& x); template<class charT, class traits>friend basic_istream<charT, traits>&operator>>(basic_istream<charT, traits>& is, gamma_distribution& x); };}

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explicit gamma_distribution(RealType alpha, RealType beta = 1.0);

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Preconditions: 0<alpha and 0<beta.

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Remarks: alpha and beta correspond to the parameters of the distribution.

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RealType alpha() const;

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

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RealType beta() const;

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