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[rand.dist.samp.discrete]

C++17 → C++20 3.3 KB 43 lines
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tmp/tmp7pap463v/{from.md → to.md} RENAMED
@@ -1,19 +1,16 @@
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  ##### Class template `discrete_distribution` <a id="rand.dist.samp.discrete">[[rand.dist.samp.discrete]]</a>
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  A `discrete_distribution` random number distribution produces random
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  integers i, 0 ≤ i < n, distributed according to the discrete probability
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- function $$%
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- P(i\,|\,p_0,\ldots,p_{n-1})
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- = p_i
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- \; \mbox{.}$$
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  Unless specified otherwise, the distribution parameters are calculated
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- as: $p_k = {w_k / S} \; \mbox{ for } k = 0, \ldots, n\!-\!1$ , in which
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- the values wₖ, commonly known as the *weights* , shall be non-negative,
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- non-NaN, and non-infinity. Moreover, the following relation shall hold:
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- 0 < S = w₀ + ⋯ + wₙ₋₁.
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  ``` cpp
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  template<class IntType = int>
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  class discrete_distribution {
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  public:
@@ -59,15 +56,18 @@ p₀ = 1.
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  ``` cpp
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  template<class InputIterator>
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  discrete_distribution(InputIterator firstW, InputIterator lastW);
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  ```
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- *Requires:* `InputIterator` shall satisfy the requirements of an input
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- iterator ([[input.iterators]]). Moreover,
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- `iterator_traits<InputIterator>::value_type` shall denote a type that is
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- convertible to `double`. If `firstW == lastW`, let n = 1 and w₀ = 1.
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- Otherwise, [`firstW`, `lastW`) shall form a sequence w of length n > 0.
 
 
 
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  *Effects:* Constructs a `discrete_distribution` object with
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  probabilities given by the formula above.
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  ``` cpp
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  ``` cpp
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  template<class UnaryOperation>
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  discrete_distribution(size_t nw, double xmin, double xmax, UnaryOperation fw);
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  ```
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- *Requires:* Each instance of type `UnaryOperation` shall be a function
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- object ([[function.objects]]) whose return type shall be convertible to
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- `double`. Moreover, `double` shall be convertible to the type of
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- `UnaryOperation`’s sole parameter. If `nw` = 0, let n = 1, otherwise let
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- n = `nw`. The relation 0 < δ = (`xmax` - `xmin`) / n shall hold.
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  *Effects:* Constructs a `discrete_distribution` object with
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  probabilities given by the formula above, using the following values: If
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  `nw` = 0, let w₀ = 1. Otherwise, let wₖ = `fw`(`xmin` + k ⋅ δ + δ / 2)
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  for k = 0, …, n - 1.
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- *Complexity:* The number of invocations of `fw` shall not exceed n.
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  ``` cpp
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  vector<double> probabilities() const;
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  ```
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  ##### Class template `discrete_distribution` <a id="rand.dist.samp.discrete">[[rand.dist.samp.discrete]]</a>
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  A `discrete_distribution` random number distribution produces random
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  integers i, 0 ≤ i < n, distributed according to the discrete probability
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+ function $$P(i \,|\, p_0, \dotsc, p_{n-1}) = p_i \text{ .}$$
 
 
 
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  Unless specified otherwise, the distribution parameters are calculated
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+ as: pₖ = {wₖ / S} for k = 0, …, n - 1, in which the values wₖ, commonly
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+ known as the *weights* , shall be non-negative, non-NaN, and
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+ non-infinity. Moreover, the following relation shall hold:
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+ $0 < S = w_0 + \dotsb + w_{n - 1}$.
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  ``` cpp
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  template<class IntType = int>
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  class discrete_distribution {
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  public:
 
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  ``` cpp
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  template<class InputIterator>
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  discrete_distribution(InputIterator firstW, InputIterator lastW);
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  ```
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+ *Mandates:*
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+ `is_convertible_v<iterator_traits<InputIterator>::value_type, double>`
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+ is `true`.
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+
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+ *Preconditions:* `InputIterator` meets the *Cpp17InputIterator*
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+ requirements [[input.iterators]]. If `firstW == lastW`, let n = 1 and
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+ w₀ = 1. Otherwise, [`firstW`, `lastW`) forms a sequence w of length
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+ n > 0.
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  *Effects:* Constructs a `discrete_distribution` object with
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  probabilities given by the formula above.
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  ``` cpp
 
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  ``` cpp
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  template<class UnaryOperation>
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  discrete_distribution(size_t nw, double xmin, double xmax, UnaryOperation fw);
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  ```
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+ *Mandates:* `is_invocable_r_v<double, UnaryOperation&, double>` is
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+ `true`.
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+
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+ *Preconditions:* If `nw` = 0, let n = 1, otherwise let n = `nw`. The
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+ relation 0 < δ = (`xmax` - `xmin`) / n holds.
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  *Effects:* Constructs a `discrete_distribution` object with
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  probabilities given by the formula above, using the following values: If
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  `nw` = 0, let w₀ = 1. Otherwise, let wₖ = `fw`(`xmin` + k ⋅ δ + δ / 2)
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  for k = 0, …, n - 1.
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+ *Complexity:* The number of invocations of `fw` does not exceed n.
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  ``` cpp
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  vector<double> probabilities() const;
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  ```
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