explicit gamma_distribution( RealType alpha = 1.0, RealType beta = 1.0 );
(1) (since C++11)
explicit gamma_distribution( const param_type& params );
(2) (since C++11)

Constructs a new distribution object. The first version uses alpha and beta as the distribution parameters, the second version uses params as the distribution parameters.

[edit] Parameters

alpha - the α distribution parameter (shape)
beta - the β distribution parameter (scale)
params - the distribution parameter set