NAME¶

std::piecewise_linear_distribution - std::piecewise_linear_distribution

Synopsis¶

Defined in header <random>
template< class RealType = double > (since C++11)
class piecewise_linear_distribution;

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 constructs new distribution
(C++11) (public member function)
reset resets the internal state of the distribution
(C++11) (public member function)

Generation¶

operator() generates the next random number in the distribution
(C++11) (public member function)

Characteristics¶

intervals returns the distribution parameters
densities (public member function)
param gets or sets the distribution parameter object
(C++11) (public member function)
min returns the minimum potentially generated value
(C++11) (public member function)
max returns the maximum potentially generated value
(C++11) (public member function)

Non-member functions¶

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

Example¶

// Run this code

#include <iostream>
#include <iomanip>
#include <string>
#include <map>
#include <random>

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=0; n<10000; ++n) {
++hist[d(gen)];
}
for(auto p : hist) {
std::cout << std::setw(2) << std::setfill('0') << p.first << ' '
<< std::string(p.second/100,'*') << '\n';
}
}

Possible output:¶

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