std::piecewise_constant_distribution

 

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std::piecewise_constant_distribution

Member functions

piecewise_constant_distribution::piecewise_constant_distribution

piecewise_constant_distribution::reset

Generation

piecewise_constant_distribution::operator()

Characteristics

piecewise_constant_distribution::intervalspiecewise_constant_distribution::densities

piecewise_constant_distribution::param

piecewise_constant_distribution::min

piecewise_constant_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_constant_distribution;		(since C++11)

std::piecewise_constant_distribution produces random floating-point numbers, which are uniformly distributed within each of the several subintervals [bi, bi+1), each with its own weight wi. The set of interval boundaries and the set of weights are the parameters of this distribution.

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

wi

S (bi+1 - bi)

, where S is the sum of all weights.

std::piecewise_constant_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	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 <map>
#include <random>
#include <string>
 
int main()
{
    std::random_device rd;
    std::mt19937 gen(rd());
    // 50% of the time, generate a random number between 0 and 1
    // 50% of the time, generate a random number between 10 and 15
    std::vector<double> i {0, 1, 10, 15};
    std::vector<double> w {1, 0, 1};
    std::piecewise_constant_distribution<> d(i.begin(), i.end(), w.begin());
 
    std::map<int, int> hist;
    for (int n {}; n < 1e4; ++n)
        ++hist[d(gen)];
 
    for (std::cout << std::hex << std::uppercase; auto [x, y] : hist)
        std::cout << x << ' ' << std::string(y / 100, '*') << '\n';
}

Possible output:

0 **************************************************
A **********
B *********
C *********
D **********
E *********

References

• C++23 standard (ISO/IEC 14882:2024):

• 28.5.9.6.2 Class template piecewise_constant_distribution [rand.dist.samp.pconst] (p: 1421-1422)

• C++20 standard (ISO/IEC 14882:2020):

• 29.6.9.6.2 Class template piecewise_constant_distribution [rand.dist.samp.pconst] (p: 1207-1208)

• C++17 standard (ISO/IEC 14882:2017):

• 29.6.8.6.2 Class template piecewise_constant_distribution [rand.dist.samp.pconst] (p: 1098-1100)

• C++14 standard (ISO/IEC 14882:2014):

• 26.5.8.6.2 Class template piecewise_constant_distribution [rand.dist.samp.pconst] (p: 962-964)

• C++11 standard (ISO/IEC 14882:2011):

• 26.5.8.6.2 Class template piecewise_constant_distribution [rand.dist.samp.pconst] (p: 955-957)