# 26 Numerics library [numerics]

## 26.6 Random number generation [rand]

### 26.6.9 Random number distribution class templates [rand.dist]

#### 26.6.9.6.3 Class template piecewise_­linear_­distribution[rand.dist.samp.plinear]

A piecewise_­linear_­distribution random number distribution produces random numbers x, , distributed over each subinterval according to the probability density function
The distribution parameters , also known as this distribution's interval boundaries, shall satisfy the relation for .
Unless specified otherwise, the remaining distribution parameters are calculated as for , in which the values , commonly known as the weights at boundaries, shall be non-negative, non-NaN, and non-infinity.
Moreover, the following relation shall hold:
template<class RealType = double> class piecewise_linear_distribution { public: // types using result_type = RealType; using param_type = unspecified; // constructor and reset functions piecewise_linear_distribution(); template<class InputIteratorB, class InputIteratorW> piecewise_linear_distribution(InputIteratorB firstB, InputIteratorB lastB, InputIteratorW firstW); template<class UnaryOperation> piecewise_linear_distribution(initializer_list<RealType> bl, UnaryOperation fw); template<class UnaryOperation> piecewise_linear_distribution(size_t nw, RealType xmin, RealType xmax, UnaryOperation fw); explicit piecewise_linear_distribution(const param_type& parm); void reset(); // generating functions template<class URBG> result_type operator()(URBG& g); template<class URBG> result_type operator()(URBG& g, const param_type& parm); // property functions vector<result_type> intervals() const; vector<result_type> densities() const; param_type param() const; void param(const param_type& parm); result_type min() const; result_type max() const; };
```piecewise_linear_distribution(); ```
Effects: Constructs a piecewise_­linear_­distribution object with , , , and .
```template<class InputIteratorB, class InputIteratorW> piecewise_linear_distribution(InputIteratorB firstB, InputIteratorB lastB, InputIteratorW firstW); ```
Mandates: is_­invocable_­r_­v<double, UnaryOperation&, double> is true.
Preconditions: InputIteratorB and InputIteratorW each meet the Cpp17InputIterator requirements ([input.iterators]).
If firstB == lastB or ++firstB == lastB, let , , , and .
Otherwise, forms a sequence b of length , the length of the sequence w starting from firstW is at least , and any for are ignored by the distribution.
Effects: Constructs a piecewise_­linear_­distribution object with parameters as specified above.
```template<class UnaryOperation> piecewise_linear_distribution(initializer_list<RealType> bl, UnaryOperation fw); ```
Mandates: is_­invocable_­r_­v<double, UnaryOperation&, double> is true.
Effects: Constructs a piecewise_­linear_­distribution object with parameters taken or calculated from the following values: If , let , , , and .
Otherwise, let form a sequence , and let for .
Complexity: The number of invocations of fw does not exceed .
```template<class UnaryOperation> piecewise_linear_distribution(size_t nw, RealType xmin, RealType xmax, UnaryOperation fw); ```
Mandates: is_­invocable_­r_­v<double, UnaryOperation&, double> is true.
Preconditions: If , let , otherwise let .
The relation holds.
Effects: Constructs a piecewise_­linear_­distribution object with parameters taken or calculated from the following values: Let for , and for .
Complexity: The number of invocations of fw does not exceed .
```vector<result_type> intervals() const; ```
Returns: A vector<result_­type> whose size member returns and whose operator[] member returns when invoked with argument k for .
```vector<result_type> densities() const; ```
Returns: A vector<result_­type> whose size member returns n and whose operator[] member returns when invoked with argument k for .