std::piecewise_linear_distribution

 

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std::piecewise_linear_distribution

Member functions

piecewise_linear_distribution::piecewise_linear_distribution (C++11)

piecewise_linear_distribution::reset (C++11)

Generation

piecewise_linear_distribution::operator() (C++11)

Characteristics

piecewise_linear_distribution::intervalspiecewise_linear_distribution::densities (C++11)(C++11)

piecewise_linear_distribution::param (C++11)

piecewise_linear_distribution::min (C++11)

piecewise_linear_distribution::max (C++11)

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 \(\small{[b_i, b_{i+1})}\)[b
i, b
i+1). The distribution is such that the probability density at each interval boundary is exactly the predefined value \(\small{p_i}\)p
i.

The probability density for any \(\small{ b_i \le x < b_{i+1} }\)b
i≤x<b
i+1 is \(\small{p_i\frac{b_{i+1}-x}{b_{i+1}-b_i} + p_{i+1}\frac{x-b_i}{b_{i+1}-b_i} }\)p
i

b i+1-x

b i+1-b i

+ p
i+1

x-b i

b i+1-b i

, where probability densities at interval boundaries \(\small{p_k}\)p
k are calculated as \(\small{w_k/S}\)w
k/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

(w
k+w
k+1)(b
k+1−b
k).

The set of interval boundaries \(\small{b_i}\)b
i and the set of weights at boundaries \(\small{w_i}\)w
i 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 long double.

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 rate
    std::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 *