std::piecewise_linear_distribution

 

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Random number 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)

 

std::piecewise_linear_distribution

Member functions

piecewise_linear_distribution::piecewise_linear_distribution

piecewise_linear_distribution::reset

Generation

piecewise_linear_distribution::operator()

Characteristics

piecewise_linear_distribution::intervalspiecewise_linear_distribution::densities

piecewise_linear_distribution::param

piecewise_linear_distribution::min

piecewise_linear_distribution::max

Non-member functions

operator==operator!= (C++11)(C++11)(until C++20)

operator<<operator>> (C++11)(C++11)

 

Defined in header <random>
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

bi+1-x

bi+1-bi

+ pi+1

x-bi

bi+1-bi

, 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 \(\small{\frac{1}{2}(w_k + w_{k+1})(b_{k+1} - b_k)}\)

1

2

(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.

Template parameters

RealType

-

The result type generated by the generator. The effect is undefined if this is not one of float, double, or longdouble.

Member types

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

Member functions

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

Non-member functions

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

Example

Run this code

#include <iomanip>#include <iostream>#include <map>#include <random>#include <string>   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 ratestd::vector<double> i{0, 5, 10, 15};std::vector<double> 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:

00 * 01 *** 02 **** 03 ****** 04 ********* 05 ********* 06 ********* 07 ********** 08 ********* 09 ********** 10 ********* 11 ******* 12 **** 13 *** 14 *