std::piecewise_constant_distribution

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Pseudo-random number generation
 
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
w
i
S (b
i+1 - b
i)
, 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

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)
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