gamma_distribution::operator()

Returns a random value.

template<class Engine>
    result_type operator()(Engine& eng);
template<class Engine>
    result_type operator()(Engine& eng,
        const param_type& par0);

Parameters

• Engine
  The type of the random engine.

• eng
  The random engine.

• par0
  The parameter package used to return the random value.

Remarks

The first member function uses the engine eng as a source of uniformly distributed random values and returns values with a probability density of pr(x) = 1 / gamma(stored_alpha) * x^(stored_alpha - 1) * e^(-x).

The second member function behaves the same, except that it uses the parameters stored in par0.

Example

// std_tr1__random__gamma_distribution_operator_fn.cpp 
// compile with: /EHsc 
#include <random> 
#include <iostream> 
 
typedef std::ranlux64_base_01 Myeng; 
typedef std::gamma_distribution<double> Mydist; 
int main() 
    { 
    Myeng eng; 
    Mydist dist(1.5); 
    Mydist::input_type engval = eng(); 
    Mydist::result_type distval = dist(eng); 
 
    distval = distval;  // to quiet "unused" warnings 
    engval = engval; 
 
    std::cout << "alpha == " << dist.alpha() << std::endl; 
 
    dist.reset(); // discard any cached values 
    std::cout << "a random value == " << dist(eng) << std::endl; 
    std::cout << "a random value == " << dist(eng) << std::endl; 
    std::cout << "a random value == " << dist(eng) << std::endl; 
 
    return (0); 
    } 
 

alpha == 1.5
a random value == 1.69867
a random value == 0.555659
a random value == 0.609713

Requirements

Header: <random>

Namespace: std

See Also

Reference

<random>

gamma_distribution Class