std::fisher_f_distribution
From cppreference.com
| Defined in header <random>
|
||
| template< class RealType = double > class fisher_f_distribution; |
(since C++11) | |
Produces random numbers according to the f-distribution:
- p(x;m,n) =
(m/n)m/2 x(m/2)-1 (1+Γ((m+n)/2) Γ(m/2) Γ(n/2)
)-(m+n)/2mx n
m and n are the degrees of freedom.
std::fisher_f_distribution satisfies all requirements of RandomNumberDistribution
Contents |
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 RandomNumberDistribution. |
Member functions
| (C++11) |
constructs new distribution (public member function) |
| (C++11) |
resets the internal state of the distribution (public member function) |
Generation | |
| (C++11) |
generates the next random number in the distribution (public member function) |
Characteristics | |
| (C++11) |
returns the distribution parameters (public member function) |
| (C++11) |
gets or sets the distribution parameter object (public member function) |
| (C++11) |
returns the minimum potentially generated value (public member function) |
| (C++11) |
returns the maximum potentially generated value (public member function) |
Non-member functions
| (C++11)(C++11)(removed in C++20) |
compares two distribution objects (function) |
| (C++11) |
performs stream input and output on pseudo-random number distribution (function template) |
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, bool DrawMinMax = true, class Sample> void draw_vbars(Sample const& s) { static_assert((Height > 0) && (BarWidth > 0) && (Padding >= 0) && (Offset >= 0)); auto cout_n = [](auto const& v, int n) { 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 (float e : s) { qr.push_back(std::div(std::lerp(0.f, Height*8, (e - *min)/(*max - *min)), 8)); } for (auto h{Height}; h-- > 0 ;) { cout_n(' ', Offset); for (auto [q, r] : qr) { char d[] = "█"; // == { 0xe2, 0x96, 0x88, 0 } 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) h == Height - 1 ? std::cout << "┬ " << *max: h != 0 ? std::cout << "│" : std::cout << "┴ " << *min; cout_n('\n', 1); } } int main() { std::random_device rd{}; std::mt19937 gen{rd()}; auto fisher = [&gen](const float d₁, const float d₂) { std::fisher_f_distribution<float> d{ d₁ /* m */, d₂ /* n */}; const int norm = 1'00'00; const float cutoff = 0.002f; 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 (float x = p * (1.0/norm); cutoff < x) { bars.push_back(x); indices.push_back(n); } } std::cout << "d₁ = " << d₁ << ", d₂ = " << d₂ << ":\n"; draw_vbars<4,3>(bars); for (int n : indices) { std::cout << "" << std::setw(2) << n << " "; } std::cout << "\n\n"; }; fisher(/* d₁ = */ 1.0f, /* d₂ = */ 5.0f); fisher(/* d₁ = */ 15.0f, /* d₂ = */ 10.f); fisher(/* d₁ = */ 100.0f, /* d₂ = */ 3.0f); }
Possible output:
d₁ = 1, d₂ = 5:
███ ┬ 0.4956
███ │
███ ▇▇▇ │
███ ███ ▇▇▇ ▄▄▄ ▂▂▂ ▂▂▂ ▁▁▁ ▁▁▁ ▁▁▁ ▁▁▁ ▁▁▁ ▁▁▁ ▁▁▁ ▁▁▁ ┴ 0.0021
0 1 2 3 4 5 6 7 8 9 10 11 12 14
d₁ = 15, d₂ = 10:
███ ┬ 0.6252
███ │
███ ▂▂▂ │
▆▆▆ ███ ███ ▃▃▃ ▁▁▁ ▁▁▁ ▁▁▁ ┴ 0.0023
0 1 2 3 4 5 6
d₁ = 100, d₂ = 3:
███ ┬ 0.4589
███ │
▁▁▁ ███ ▅▅▅ │
███ ███ ███ ▆▆▆ ▃▃▃ ▂▂▂ ▂▂▂ ▁▁▁ ▁▁▁ ▁▁▁ ▁▁▁ ▁▁▁ ▁▁▁ ▁▁▁ ▁▁▁ ▁▁▁ ▁▁▁ ┴ 0.0021
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16External links
Weisstein, Eric W. "F-Distribution." From MathWorld--A Wolfram Web Resource.
