std::fisher_f_distribution - cppreference.com (2024)

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C++

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Numerics library

Common mathematical functions
Mathematical special functions (C++17)
Mathematical constants (C++20)
Floating-point environment (C++11)
Complex numbers
Numeric arrays
Pseudo-random number generation
Factor operations
gcd (C++17)
lcm (C++17)
Interpolations
midpoint (C++20)
lerp (C++20)
Generic numeric operations
iota (C++11)
ranges::iota (C++23)
accumulate
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reduce (C++17)
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Bit operations
bit_cast (C++20)
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countr_one (C++20)
popcount (C++20)
endian (C++20)

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[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

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

[edit] Non-member functions

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

[edit] Example

Run this code

#include <random>#include <iomanip>#include <map> #include <algorithm>#include <iostream>#include <vector>#include <cmath>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(*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()}; 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 (auto const& [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"; for (draw_vbars<4, 3>(bars); 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 14d₁ = 15, d₂ = 10: ███ ┬ 0.6252 ███ │ ███ ▂▂▂ │▆▆▆ ███ ███ ▃▃▃ ▁▁▁ ▁▁▁ ▁▁▁ ┴ 0.0023 0 1 2 3 4 5 6d₁ = 100, d₂ = 3: ███ ┬ 0.4589 ███ │▁▁▁ ███ ▅▅▅ │███ ███ ███ ▆▆▆ ▃▃▃ ▂▂▂ ▂▂▂ ▁▁▁ ▁▁▁ ▁▁▁ ▁▁▁ ▁▁▁ ▁▁▁ ▁▁▁ ▁▁▁ ▁▁▁ ▁▁▁ ┴ 0.0021 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

[edit] External links

Weisstein, Eric W. "F-Distribution." From MathWorld — A Wolfram Web Resource.

Uniform random bit generators
uniform_random_bit_generator (C++20)
Engines and engine adaptors
linear_congruential_engine (C++11)
mersenne_twister_engine (C++11)
subtract_with_carry_engine (C++11)
discard_block_engine (C++11)
independent_bits_engine (C++11)
shuffle_order_engine (C++11)
Non-deterministic generator
random_device (C++11)
Distributions
Uniform distributions
uniform_int_distribution (C++11)
uniform_real_distribution (C++11)
generate_canonical (C++11)
Bernoulli distributions
bernoulli_distribution (C++11)
binomial_distribution (C++11)
negative_binomial_distribution (C++11)
geometric_distribution (C++11)
Poisson distributions
poisson_distribution (C++11)
exponential_distribution (C++11)
gamma_distribution (C++11)
weibull_distribution (C++11)
extreme_value_distribution (C++11)
Normal distributions
normal_distribution (C++11)
lognormal_distribution (C++11)
chi_squared_distribution (C++11)
cauchy_distribution (C++11)
fisher_f_distribution (C++11)
student_t_distribution (C++11)
Sampling distributions
discrete_distribution (C++11)
piecewise_constant_distribution (C++11)
piecewise_linear_distribution (C++11)
Seed Sequences
seed_seq (C++11)
C library
rand
srand
RAND_MAX

Member functions
fisher_f_distribution::fisher_f_distribution (C++11)
fisher_f_distribution::reset (C++11)
Generation
fisher_f_distribution::operator() (C++11)
Characteristics
fisher_f_distribution::mfisher_f_distribution::n (C++11)(C++11)
fisher_f_distribution::param (C++11)
fisher_f_distribution::min (C++11)
fisher_f_distribution::max (C++11)
Non-member functions
operator==operator!= (C++11)(C++11)(until C++20)
operator<<operator>> (C++11)(C++11)