29 Numerics library [numerics]

29.8 Generalized numeric operations [numeric.ops]

29.8.3 Reduce [reduce]

template<class InputIterator> typename iterator_traits<InputIterator>::value_type reduce(InputIterator first, InputIterator last);

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#

Effects: Equivalent to: 

return reduce(first, last,
              typename iterator_traits<InputIterator>::value_type{});

template<class ExecutionPolicy, class ForwardIterator> typename iterator_traits<ForwardIterator>::value_type reduce(ExecutionPolicy&& exec, ForwardIterator first, ForwardIterator last);

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Effects: Equivalent to: 

return reduce(std::forward<ExecutionPolicy>(exec), first, last,
              typename iterator_traits<ForwardIterator>::value_type{});

template<class InputIterator, class T> T reduce(InputIterator first, InputIterator last, T init);

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Effects: Equivalent to: 

return reduce(first, last, init, plus<>());

template<class ExecutionPolicy, class ForwardIterator, class T> T reduce(ExecutionPolicy&& exec, ForwardIterator first, ForwardIterator last, T init);

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Effects: Equivalent to: 

return reduce(std::forward<ExecutionPolicy>(exec), first, last, init, plus<>());

template<class InputIterator, class T, class BinaryOperation> T reduce(InputIterator first, InputIterator last, T init, BinaryOperation binary_op); template<class ExecutionPolicy, class ForwardIterator, class T, class BinaryOperation> T reduce(ExecutionPolicy&& exec, ForwardIterator first, ForwardIterator last, T init, BinaryOperation binary_op);

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Requires:

  • (5.1)

    T shall be MoveConstructible (Table 23).

  • (5.2)

    All of binary_­op(init, *first), binary_­op(*first, init), binary_­op(init, init), and binary_­op(*first, *first) shall be convertible to T.

  • (5.3)

    binary_­op shall neither invalidate iterators or subranges, nor modify elements in the range [first, last].

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Returns: GENERALIZED_­SUM(binary_­op, init, *i, ...) for every i in [first, last).

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Complexity: O(last - first) applications of binary_­op.

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[ Note: The difference between reduce and accumulate is that reduce applies binary_­op in an unspecified order, which yields a nondeterministic result for non-associative or non-commutative binary_­op such as floating-point addition.  — end note ]