thrust::inclusive_scan
Defined in thrust/scan.h
-
template<typename DerivedPolicy, typename InputIterator, typename OutputIterator, typename AssociativeOperator>
OutputIterator thrust::inclusive_scan(const thrust::detail::execution_policy_base<DerivedPolicy> &exec, InputIterator first, InputIterator last, OutputIterator result, AssociativeOperator binary_op) inclusive_scan
computes an inclusive prefix sum operation. The term ‘inclusive’ means that each result includes the corresponding input operand in the partial sum. When the input and output sequences are the same, the scan is performed in-place.inclusive_scan
is similar tostd::partial_sum
in the STL. The primary difference between the two functions is thatstd::partial_sum
guarantees a serial summation order, whileinclusive_scan
requires associativity of the binary operation to parallelize the prefix sum.Results are not deterministic for pseudo-associative operators (e.g., addition of floating-point types). Results for pseudo-associative operators may vary from run to run.
The algorithm’s execution is parallelized as determined by
exec
.The following code snippet demonstrates how to use
inclusive_scan
to compute an in-place prefix sum using thethrust::host
execution policy for parallelization:int data[10] = {-5, 0, 2, -3, 2, 4, 0, -1, 2, 8}; thrust::maximum<int> binary_op; thrust::inclusive_scan(thrust::host, data, data + 10, data, binary_op); // in-place scan // data is now {-5, 0, 2, 2, 2, 4, 4, 4, 4, 8}
- Parameters
exec – The execution policy to use for parallelization.
first – The beginning of the input sequence.
last – The end of the input sequence.
result – The beginning of the output sequence.
binary_op – The associatve operator used to ‘sum’ values.
- Template Parameters
DerivedPolicy – The name of the derived execution policy.
InputIterator – is a model of Input Iterator and
InputIterator's
value_type
is convertible toOutputIterator's
value_type
.OutputIterator – is a model of Output Iterator and
OutputIterator's
value_type
is convertible to bothAssociativeOperator's
first_argument_type
andsecond_argument_type
.AssociativeOperator – is a model of Binary Function and
AssociativeOperator's
result_type
is convertible toOutputIterator's
value_type
.
- Returns
The end of the output sequence.
- Pre
first
may equalresult
but the range[first, last)
and the range[result, result + (last - first))
shall not overlap otherwise.