std::piecewise_linear_distribution

 

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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 [bi, bi+1). The distribution is such that the probability density at each interval boundary is exactly the predefined value pi.

The probability density for any bi≤x<bi+1 is pi

bi+1-x

bi+1-bi

+ pi+1

x-bi

bi+1-bi

, where probability densities at interval boundaries pk are calculated as wk/S where S is the sum of all

1

2

(wk+wk+1)(bk+1−bk).

The set of interval boundaries bi and the set of weights at boundaries 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 long double.

Member types

Member type	Definition
result_type	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 <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 *