std::piecewise_linear_distribution - cppreference.com (original) (raw)

std::piecewise_linear_distribution

| | | | | ---------------------------------------------------------------------------- | | ------------- | | template< class RealType = double > class piecewise_linear_distribution; | | (since C++11) |

std::piecewise_linear_distribution produces random floating-point numbers, which are distributed according to a linear probability density function within each of the several subintervals \(\small{[b_i, b_{i+1})}\)[bi, bi+1). The distribution is such that the probability density at each interval boundary is exactly the predefined value \(\small{p_i}\)pi.

The probability density for any \(\small{ b_i \le x < b_{i+1} }\)bi≤x<bi+1 is \(\small{p_i\frac{b_{i+1}-x}{b_{i+1}-b_i} + p_{i+1}\frac{x-b_i}{b_{i+1}-b_i} }\)pi + pi+1, where probability densities at interval boundaries \(\small{p_k}\)pk are calculated as \(\small{w_k/S}\)wk/S where \(\small{S}\)S is the sum of all \(\small{\frac{1}{2}(w_k + w_{k+1})(b_{k+1} - b_k)}\)(wk+wk+1)(bk+1−bk).

The set of interval boundaries \(\small{b_i}\)bi and the set of weights at boundaries \(\small{w_i}\)wi are the parameters of this distribution.

std::piecewise_linear_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

(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
intervalsdensities(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

[edit] Example

#include #include #include #include #include int main() { std::random_device rd; std::mt19937 gen{rd()}; // increase the probability from 0 to 5 // remain flat from 5 to 10 // decrease from 10 to 15 at the same rate std::vector i{0, 5, 10, 15}; std::vector w{0, 1, 1, 0}; std::piecewise_linear_distribution<> d{i.begin(), i.end(), w.begin()}; std::map<int, int> hist; for (int n{}; n < 1e4; ++n) ++hist[d(gen)]; for (auto [x, y] : hist) std::cout << std::setw(2) << std::setfill('0') << x << ' ' << std::string(y / 100, '*') << '\n'; }

Possible output: