std::gamma_distribution
From cppreference.com
Defined in header <random>


template< class RealType = double > class gamma_distribution; 
(since C++11)  
Produces random positive floatingpoint values x, distributed according to probability density function:
 P(xα,β) =
· xα1ex/β βα
· Γ(α)
where α is known as the shape parameter and β is known as the scale parameter. The shape parameter is sometimes denoted by the letter k and the scale parameter is sometimes denoted by the letter θ.
For floatingpoint α, the value obtained is the sum of α independent exponentially distributed random variables, each of which has a mean of β
std::gamma_distribution
satisfies RandomNumberDistribution
Template parameters
RealType    The result type generated by the generator. The effect is undefined if this is not one of float, double, or long double.

Member types
Member type  Definition 
result_type

RealType 
param_type

the type of the parameter set, see RandomNumberDistribution .

Member functions
constructs new distribution (public member function)  
resets the internal state of the distribution (public member function)  
Generation  
generates the next random number in the distribution (public member function)  
Characteristics  
returns the distribution parameters (public member function)  
gets or sets the distribution parameter object (public member function)  
returns the minimum potentially generated value (public member function)  
returns the maximum potentially generated value (public member function) 
Nonmember functions
compares two distribution objects (function)  
performs stream input and output on pseudorandom number distribution (function template) 
Example
This section is incomplete Reason: no example 
External links
Weisstein, Eric W. "Gamma Distribution." From MathWorldA Wolfram Web Resource.