Skip site navigation (1)Skip section navigation (2)

FreeBSD Manual Pages

  
 
  

home | help 
std::extrem...distribution(3) C++ Standard Libarystd::extrem...distribution(3)

NAME
       std::extreme_value_distribution - std::extreme_value_distribution

Synopsis
	  Defined in header <random>
	  template< class RealType = double >  (since C++11)
	  class	extreme_value_distribution;

	  Produces  random numbers according to	the extreme value distribution
       (it is also
	  known	as Gumbel Type I, log-Weibull, Fisher-Tippett Type I):

		  \({\small    p(x;a,b)	   =	\frac{1}{b}	\exp{(\frac{a-
       x}{b}-\exp{(\frac{a-x}{b})})}
		  }\)p(x;a,b) =

		  1
		  b

		  exp

		  a-x
		  b

		  - exp

		  a-x
		  b

	  std::extreme_value_distribution satisfies all	requirements of
	  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(C++11)  the  type	of  the	 parameter set,	see RandomNum-
       berDistribution.

Member functions
	  constructor	constructs new distribution
	  (C++11)	(public	member function)
	  reset		resets the internal state of the distribution
	  (C++11)	(public	member function)

Generation
	  operator()	generates the next random number in the	distribution
	  (C++11)	(public	member function)

Characteristics
	  a		returns	the distribution parameters
	  b		(public	member function)
	  param		gets or	sets the distribution parameter	object
	  (C++11)	(public	member function)
	  min		returns	the minimum potentially	generated value
	  (C++11)	(public	member function)
	  max		returns	the maximum potentially	generated value
	  (C++11)	(public	member function)

Non-member functions
	  operator==
	  operator!=		    compares two distribution objects
	  (C++11)		    (function)
	  (C++11)(removed in C++20)
	  operator<<		     performs  stream  input  and  output   on
       pseudo-random number
	  operator>>		    distribution
	  (C++11)		    (function template)

Example
       // Run this code

	#include <random>
	#include <map>
	#include <iomanip>
	#include <algorithm>
	#include <iostream>
	#include <vector>
	#include <cmath>

	template  <int Height =	5, int BarWidth	= 1, int Padding = 1, int Off-
       set = 0,	class Seq>
	void draw_vbars(Seq&& s, const bool DrawMinMax = true) {
	    static_assert((Height > 0) && (BarWidth > 0) && (Padding >=	0)  &&
       (Offset >= 0));
	    auto  cout_n = [](auto&& v,	int n =	1) { while (n--	> 0) std::cout
       << v; };
	    const  auto	 [min,	max]   =   std::minmax_element(std::cbegin(s),
       std::cend(s));
	    std::vector<std::div_t> qr;
	    for	(typedef decltype(*cbegin(s)) V; V e : s)
		qr.push_back(std::div(std::lerp(V(0),	  Height*8,    (e    -
       *min)/(*max - *min)), 8));
	    for	(auto h{Height}; h-- > 0; cout_n('\n'))	{
		cout_n(' ', Offset);
		for (auto dv : qr) {
		    const auto q{dv.quot}, r{dv.rem};
		    unsigned char d[] {	0xe2, 0x96, 0x88, 0 }; // Full	Block:
       ''
		    q  < h ? d[0] = ' ', d[1] =	0 : q == h ? d[2] -= (7	- r) :
       0;
		    cout_n(d, BarWidth), cout_n(' ', Padding);
		}
		if (DrawMinMax && Height > 1)
		    Height - 1 == h ? std::cout	<< " " << *max:
				  h ? std::cout	<< " "
				    : std::cout	<< " " << *min;
	    }
	}

	int main()
	{
	    std::random_device rd{};
	    std::mt19937 gen{rd()};

	    std::extreme_value_distribution<> d{-1.618f, 1.618f};

	    const int norm = 10'000;
	    const float	cutoff = 0.000'3f;

	    std::map<int, int> hist{};
	    for(int n=0; n<norm; ++n) {
		++hist[std::round(d(gen))];
	    }

	    std::vector<float> bars;
	    std::vector<int> indices;
	    for(const auto& [n,p] : hist) {
		float x	= p*(1.0f/norm);
		if (x >	cutoff)	{
		    bars.push_back(x);
		    indices.push_back(n);
		}
	    }

	    draw_vbars<8,4>(bars);

	    for	(int n : indices) {
		std::cout << " " << std::setw(2) << n << "  ";
	    }
	    std::cout << '\n';
	}

Possible output:

       0.2186

			 0.0005
	 -5   -4   -3	-2   -1	   0	1    2	  3    4    5	 6     7     8
       9   10

External links
	  Weisstein,  Eric  W. "Extreme	Value Distribution." From MathWorld--A
       Wolfram Web
	  Resource.

http://cppreference.com		  2022.07.31	 std::extrem...distribution(3)

Want to link to this manual page? Use this URL:
<https://man.freebsd.org/cgi/man.cgi?query=std::extreme_value_distribution&sektion=3&manpath=FreeBSD+Ports+15.0>

home | help