std::inclusive_scan (3) - Linux Man Pages

std::inclusive_scan: std::inclusive_scan

NAME

std::inclusive_scan - std::inclusive_scan

Synopsis


Defined in header <numeric>
template< class InputIt, class OutputIt >
OutputIt inclusive_scan( InputIt first, (1) (since C++17)
InputIt last, OutputIt d_first );
template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2 >
ForwardtIt2 inclusive_scan( ExecutionPolicy&& policy, ForwardIt1 first, (2) (since C++17)
ForwardIt1 last, ForwardIt2 d_first );
template< class InputIt, class OutputIt, class BinaryOperation >
OutputIt inclusive_scan( InputIt first, InputIt last, (3) (since C++17)
OutputIt d_first, BinaryOperation binary_op );
template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2,
class BinaryOperation >
ForwardIt2 inclusive_scan( ExecutionPolicy&& policy, (4) (since C++17)
ForwardIt1 first, ForwardIt1 last,
ForwardIt2 d_first, BinaryOperation binary_op );
template< class InputIt, class OutputIt, class BinaryOperation, class T >
OutputIt inclusive_scan( InputIt first, InputIt last, OutputIt d_first, (5) (since C++17)
BinaryOperation binary_op, T init );
template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2,
class BinaryOperation, class T >
ForwardIt2 inclusive_scan( ExecutionPolicy&& policy, (6) (since C++17)
ForwardIt1 first, ForwardIt1 last, ForwardIt2 d_first,
BinaryOperation binary_op, T init );


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, and the behavior is nondeterministic if binary_op is not associative.
Overloads (2,4,6) are executed according to policy. This overload only participates in overload resolution if std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is true.
binary_op shall not invalidate iterators (including the end iterators) or subranges, nor modify elements in the ranges [first, last) or [d_first, d_first + (last - first)). Otherwise, the behavior is undefined.

Parameters


first, last - the range of elements to sum
d_first - the beginning of the destination range; may be equal to first
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 LegacyInputIterator.
-
OutputIt must meet the requirements of LegacyOutputIterator.
-
ForwardIt1 must meet the requirements of LegacyForwardIterator. and, if init is not provided, ForwardIt1's value_type must be MoveConstructible and binary_op(*first, *first) must be convertible to ForwardIt1's value type
-
ForwardIt2 must meet the requirements of LegacyForwardIterator.
-
T (if init is provided) must meet the requirements of MoveConstructible. All of binary_op(init, *first), binary_op(init, init), and binary_op(*first, *first) must be convertible to T

Return value


Iterator to the element past the last element written.

Complexity


O(last - first) applications of the binary operation

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 and ExecutionPolicy is one of the standard_policies, std::terminate is called. For any other ExecutionPolicy, the behavior is implementation-defined.
* If the algorithm fails to allocate memory, std::bad_alloc is thrown.

Example


// Run this code


  #include <functional>
  #include <iostream>
  #include <iterator>
  #include <numeric>
  #include <vector>


  int main()
  {
    std::vector data {3, 1, 4, 1, 5, 9, 2, 6};


    std::cout << "exclusive sum: ";
    std::exclusive_scan(data.begin(), data.end(),
   std::ostream_iterator<int>(std::cout, " "),

   0);

    std::cout << "\ninclusive sum: ";
    std::inclusive_scan(data.begin(), data.end(),
   std::ostream_iterator<int>(std::cout, " "));


    std::cout << "\n\nexclusive product: ";
    std::exclusive_scan(data.begin(), data.end(),
   std::ostream_iterator<int>(std::cout, " "),

   1, std::multiplies<>{});


  std::cout << "\ninclusive product: ";
  std::inclusive_scan(data.begin(), data.end(),
std::ostream_iterator<int>(std::cout, " "),

std::multiplies<>{});


}

Output:


  exclusive sum: 0 3 4 8 9 14 23 25
  inclusive sum: 3 4 8 9 14 23 25 31


  exclusive product: 1 3 3 12 12 60 540 1080
  inclusive product: 3 3 12 12 60 540 1080 6480

See also


                         computes the differences between adjacent elements in a range
adjacent_difference (function template)
                         sums up a range of elements
accumulate (function template)
                         computes the partial sum of a range of elements
partial_sum (function template)


transform_inclusive_scan applies a functor, then calculates inclusive scan
                         (function template)
(C++17)


exclusive_scan similar to std::partial_sum, excludes the ith input element from the ith sum
                         (function template)
(C++17)