Defined in header <numeric>  

template< class InputIt, class OutputIt, class T > OutputIt exclusive_scan( InputIt first, InputIt last, OutputIt d_first, T init );  (1)  (since C++17) 
template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2, class T > ForwardIt2 exclusive_scan( ExecutionPolicy&& policy, ForwardIt1 first, ForwardIt1 last, ForwardIt2 d_first, T init);  (2)  (since C++17) 
template< class InputIt, class OutputIt, class T, class BinaryOperation > OutputIt exclusive_scan( InputIt first, InputIt last, OutputIt d_first, T init, BinaryOperation binary_op );  (3)  (since C++17) 
template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2, class T, class BinaryOperation > ForwardIt2 exclusive_scan( ExecutionPolicy&& policy, ForwardIt1 first, ForwardIt1 last, ForwardIt2 d_first, T init, BinaryOperation binary_op );  (4)  (since C++17) 
Computes an exclusive prefix sum operation using binary_op
(or std::plus<>()
for overloads (12)) for the range [first, last)
, using init
as the initial value, and writes the results to the range beginning at d_first
. "exclusive" means that the ith input element is not included in the ith sum.
Formally, assigns through each iterator i
in [d_first, d_first + (last  first)) the value of the generalized noncommutative sum of init, *j...
for every j
in [first, first + (i  d_first)) over binary_op
,
where generalized noncommutative sum GNSUM(op, a
1, ..., a
N) is defined as follows:
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) 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.
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 
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 . 
Type requirements  
InputIt must meet the requirements of InputIterator . 

OutputIt must meet the requirements of OutputIterator . 

ForwardIt1, ForwardIt2 must meet the requirements of ForwardIterator . 

T must meet the requirements of MoveConstructible . and binary_op(init, *first) , binary_op(init, init) , and binary_op(*first, *first) must be convertible to T 
Iterator to the element past the last element written.
O(last  first) applications of the binary operation.
The overloads with a template parameter named ExecutionPolicy
report errors as follows:
ExecutionPolicy
is one of the three standard policies, std::terminate
is called. For any other ExecutionPolicy
, the behavior is implementationdefined. std::bad_alloc
is thrown. 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) 

(C++17)  applies a functor, then calculates exclusive scan (function template) 
(C++17)  similar to std::partial_sum , includes the ith input element in the ith sum (function template) 
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