thrust::reduce_into

Defined in thrust/reduce.h

template<typename InputIterator, typename OutputIterator, typename T, typename BinaryFunction>
void thrust::reduce_into(InputIterator first, InputIterator last, OutputIterator output, T init, BinaryFunction binary_op)

reduce_into is a generalization of summation: it computes the sum (or some other binary operation) of all the elements in the range [first, last). This version of reduce_into uses init as the initial value of the reduction and binary_op as the binary function used for summation. reduce_into is similar to the C++ Standard Template Library’s std::accumulate. The primary difference between the two functions is that std::accumulate guarantees the order of summation, while reduce_into requires associativity of binary_op to parallelize the reduction.

Note that reduce_into also assumes that the binary reduction operator (in this case binary_op) is commutative. If the reduction operator is not commutative then thrust::reduce_into should not be used. Instead, one could use inclusive_scan (which does not require commutativity) and select the last element of the output array.

The following code snippet demonstrates how to use reduce_into to compute the maximum value of a sequence of integers.

#include <cuda/functional>
#include <thrust/reduce.h>
#include <thrust/device_vector.h>
#include <thrust/execution_policy.h>

thrust::device_vector<int> data{1, 0, 2, 2, 1, 3};
thrust::device_vector<int> output(1);
thrust::reduce_into(data.begin(), data.end(), output.begin(), -1,
                    cuda::maximum{});
// output[0] == 3

See also

https://en.cppreference.com/w/cpp/algorithm/accumulate

See also

reduce

See also

transform_reduce

See also

transform_reduce_into

Parameters

  • first – The beginning of the input sequence.

  • last – The end of the input sequence.

  • init – The initial value.

  • binary_op – The binary function used to ‘sum’ values.

Template Parameters

  • InputIterator – is a model of Input Iterator and InputIterator's value_type is convertible to T.

  • OutputIterator – is a model of Output Iterator and OutputIterator's value_type is assignable from T.

  • T – is a model of Assignable, and is convertible to BinaryFunction's first and second argument type.

  • BinaryFunction – The function’s return type must be convertible to OutputType.

Returns

The result of the reduction.