# std::piecewise_constant_distribution

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< cpp‎ | numeric‎ | random

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 k
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` | RealType
`param_type` | the type of the parameter set, see `RandomNumberDistribution`.

### Member functions

(constructor) | constructs new distribution (public member function)
reset | resets the internal state of the distribution (public member function)

##### Generation

operator() | generates the next random number in the distribution (public member function)

##### Characteristics

intervals densities | returns the distribution parameters (public member function)
param | gets or sets the distribution parameter object (public member function)
min | returns the minimum potentially generated value (public member function)
max | returns the maximum potentially generated value (public member function)

### Non-member functions

operator==operator!= | compares two distribution objects (function)
operator<<operator>> | performs stream input and output on pseudo-random number distribution (function template)

### Example

Run this code

    #include <iostream>
    #include <string>
    #include <map>
    #include <random>

    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=0; n<10000; ++n) {
            ++hist[d(gen)];
        }
        for(auto p : hist) {
            std::cout << p.first << ' ' << std::string(p.second/100, '*') << '\n';
        }
    }

Output:

    0 **************************************************
    10 **********
    11 *********
    12 *********
    13 **********
    14 *********

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