This documentation is archived and is not being maintained.

gamma_distribution::operator()

Returns a random value.

template<class Engine>
    result_type operator()(Engine& eng);

Engine

The type of the random engine.

eng

The random engine.

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

 

// std_tr1__random__gamma_distribution_operator_fn.cpp 
// compile with: /EHsc 
#include <random> 
#include <iostream> 
 
typedef std::tr1::ranlux64_base_01 Myeng; 
typedef std::tr1::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

Header: <random>

Namespace: std::tr1

Show: