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std::extreme_value_distribution

From cppreference.com
< cpp‎ | numeric‎ | random
 
 
Numerics library
 
Pseudo-random number generation
 
 
Defined in header <random>
template< class RealType = double >
class extreme_value_distribution;
(since C++11)

Produces random numbers according to the Generalized 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.

[edit] 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.

[edit] Member types

Member type Definition
result_type (C++11) RealType
param_type (C++11) the type of the parameter set, see RandomNumberDistribution.

[edit] Member functions

constructs new distribution
(public member function) [edit]
(C++11)
resets the internal state of the distribution
(public member function) [edit]
Generation
(C++11)
generates the next random number in the distribution
(public member function) [edit]
Characteristics
(C++11)
returns the distribution parameters
(public member function) [edit]
(C++11)
gets or sets the distribution parameter object
(public member function) [edit]
(C++11)
returns the minimum potentially generated value
(public member function) [edit]
(C++11)
returns the maximum potentially generated value
(public member function) [edit]

[edit] Non-member functions

(C++11)(C++11)(removed in C++20)
compares two distribution objects
(function) [edit]
performs stream input and output on pseudo-random number distribution
(function template) [edit]

[edit] Example

Run this code
#include <algorithm>
#include <cmath>
#include <iomanip>
#include <iostream>
#include <map>
#include <random>
#include <vector>
 
template<int Height = 5, int BarWidth = 1, int Padding = 1, int Offset = 0, class Seq>
void draw_vbars(Seq&& s, const bool DrawMinMax = true)
{
 static_assert(0 < Height and 0 < BarWidth and 0 <= Padding and 0 <= Offset);
 
 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(*std::cbegin (s)) V; V e : s)
 qr.push_back(std::div (std::lerp (V(0), 8 * Height,
 (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)
 if (const float x = p * (1.0f / norm); 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

[edit] External links

Weisstein, Eric W. "Extreme Value Distribution." From MathWorld — A Wolfram Web Resource.
Retrieved from "https://en.cppreference.com/mwiki/index.php?title=cpp/numeric/random/extreme_value_distribution&oldid=160839"

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