std:: piecewise_linear_distribution

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piecewise_linear_distribution
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std::piecewise_linear_distribution
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 [b i , b i+1 ) . The distribution is such that the probability density at each interval boundary is exactly the predefined value p i .

The probability density for any b i ≤x<b i+1 is 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 p k are calculated as w k /S where S is the sum of all
1
2
(w k +w k+1 )(b k+1 −b k ) .

The set of interval boundaries b i and the set of weights at boundaries 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

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

Non-member functions

(C++11) (C++11) (removed in C++20)
compares two distribution objects
(function)
(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 *
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