std::inclusive_scan

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Algorithm library
Execution policies (C++17)
Non-modifying sequence operations
(C++11)(C++11)(C++11)
(C++17)
Modifying sequence operations
(C++11)
(C++11)
(C++11)
(C++11)

Operations on uninitialized storage
Partitioning operations
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(C++11)
(C++11)
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Minimum/maximum operations
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Permutations
(C++11)
Numeric operations
inclusive_scan
(C++17)
(C++17)
C library
 
Defined in header <numeric>
template< class InputIt, class OutputIt >

OutputIt inclusive_scan( InputIt first,

                         InputIt last, OutputIt d_first );
(1) (since C++17)
template< class ExecutionPolicy, class InputIt, class OutputIt >

OutputIt inclusive_scan( ExecutionPolicy&& policy, InputIt first,

                         InputIt last, OutputIt d_first );
(2) (since C++17)
template< class InputIt, class OutputIt, class BinaryOperation >

OutputIt inclusive_scan( InputIt first, InputIt last,

                         OutputIt d_first, BinaryOperation binary_op );
(3) (since C++17)
template< class ExecutionPolicy, class InputIt, class OutputIt,

          class BinaryOperation >
OutputIt inclusive_scan( ExecutionPolicy&& policy,
                         InputIt first, InputIt last,

                         OutputIt d_first, BinaryOperation binary_op );
(4) (since C++17)
template< class InputIt, class OutputIt, class BinaryOperation, class T >

OutputIt inclusive_scan( InputIt first, InputIt last, OutputIt d_first,

                         BinaryOperation binary_op, T init );
(5) (since C++17)
template< class ExecutionPolicy, class InputIt, class OutputIt,

          class BinaryOperation, class T >
OutputIt inclusive_scan( ExecutionPolicy&& policy,
                         InputIt first, InputIt last, OutputIt d_first,

                         BinaryOperation binary_op, T init );
(6) (since C++17)

Computes an inclusive prefix sum operation using binary_op (or std::plus<>() for overloads (1-2)) for the range [first, last), using init as the initial value (if provided), and writes the results to the range beginning at d_first. "inclusive" means that the i-th input element is included in the i-th sum.

Formally, assigns through each iterator i in [d_first, d_first + (last - first)) the value of:

  • for overloads (1-4), the generalized noncommutative sum of *j... for every j in [first, first + (i - d_first + 1)) over binary_op
  • for overloads (5-6), the generalized noncommutative sum of init, *j... for every j in [first, first + (i - d_first + 1)) over binary_op

where generalized noncommutative sum GNSUM(op, a
1
, ..., a
N
)
is defined as follows:

  • if N=1, a
    1
  • if N > 1, op(GNSUM(op, a
    1
    , ..., a
    K
    ), GNSUM(op, a
    M
    , ..., a
    N
    ))
    for any K where 1 < K+1 = M ≤ N

In other words, the summation operations may be performed in arbitrary order.

The behavior is nondeterministic if binary_op is not associative.

Overloads (2,4,6) are executed according to policy. These overloads do not participate in overload resolution unless std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is true.

binary_op shall not invalidate iterators or subranges, nor modify elements in the ranges [first, last) or [d_first, d_first + (last - first)). Otherwise, the behavior is undefined.

Contents

[edit] Parameters

first, last - the range of elements to sum
d_first - the beginning of the destination range
policy - the execution policy to use. See execution policy for details.
init - the initial value (optional)
binary_op - binary FunctionObject that will be applied in to the result of dereferencing the input iterators, the results of other binary_op, and init (if provided).
Type requirements
-
InputIt must meet the requirements of InputIterator.
-
OutputIt must meet the requirements of OutputIterator.

[edit] Return value

Iterator to the element past the last element written.

[edit] Complexity

O(last - first) applications of the binary operation

[edit] Exceptions

The overloads with a template parameter named ExecutionPolicy report errors as follows:

  • If execution of a function invoked as part of the algorithm throws an exception,
  • if policy is std::parallel_vector_execution_policy, std::terminate is called
  • if policy is std::sequential_execution_policy or std::parallel_execution_policy, the algorithm exits with an std::exception_list containing all uncaught exceptions. If there was only one uncaught exception, the algorithm may rethrow it without wrapping in std::exception_list. It is unspecified how much work the algorithm will perform before returning after the first exception was encountered.
  • if policy is some other type, the behavior is implementation-defined
  • If the algorithm fails to allocate memory (either for itself or to construct an std::exception_list when handling a user exception), std::bad_alloc is thrown.

[edit] Example

[edit] See also

computes the differences between adjacent elements in a range
(function template)
sums up a range of elements
(function template)
computes the partial sum of a range of elements
(function template)
applies a functor, then calculates inclusive scan
(function template)
similar to std::partial_sum, excludes the ith input element from the ith sum
(function template)