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std::piecewise_constant_distribution

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 [b
i
, b
i+1
), each with its own weight w
i
. The set of interval boundaries and the set of weights are the parameters of this distribution. The probability density for any b.


i
≤ x <b
i+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

(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
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

#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 14882:2023):
    • 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)

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