An 
extreme_value_distribution random number distribution
produces random numbers 
x
distributed according to
the probability density function
p(x|a,b)=1b⋅exp(a−xb−exp(a−xb)) .
template<class RealType = double>
  class extreme_value_distribution {
  public:
    
    using result_type = RealType;
    using param_type  = unspecified;
    
    extreme_value_distribution() : extreme_value_distribution(0.0) {}
    explicit extreme_value_distribution(RealType a, RealType b = 1.0);
    explicit extreme_value_distribution(const param_type& parm);
    void reset();
    
    template<class URBG>
      result_type operator()(URBG& g);
    template<class URBG>
      result_type operator()(URBG& g, const param_type& parm);
    
    RealType a() const;
    RealType b() const;
    param_type param() const;
    void param(const param_type& parm);
    result_type min() const;
    result_type max() const;
  };
explicit extreme_value_distribution(RealType a, RealType b = 1.0);