reduce

Header File: Kokkos_StdAlgorithms.hpp

namespace Kokkos{
namespace Experimental{

//
// overload set A
//
template <class ExecutionSpace, class IteratorType>
typename IteratorType::value_type reduce(const ExecutionSpace& exespace,        (1)
                                         IteratorType first,
                                         IteratorType last);

template <class ExecutionSpace, class IteratorType>
typename IteratorType::value_type reduce(const std::string& label,              (2)
                                         const ExecutionSpace& exespace,
                                         IteratorType first,
                                         IteratorType last);

template <class ExecutionSpace, class DataType, class... Properties>
auto reduce(const ExecutionSpace& exespace,                                     (3)
            const ::Kokkos::View<DataType, Properties...>& view);

template <class ExecutionSpace, class DataType, class... Properties>
auto reduce(const std::string& label, const ExecutionSpace& exespace,           (4)
            const ::Kokkos::View<DataType, Properties...>& view);

//
// overload set B
//
template <class ExecutionSpace, class IteratorType, class ValueType>
ValueType reduce(const ExecutionSpace& exespace,                                (5)
                 IteratorType first, IteratorType last,
                 ValueType init_reduction_value);

template <class ExecutionSpace, class IteratorType, class ValueType>
ValueType reduce(const std::string& label, const ExecutionSpace& exespace,      (6)
                 IteratorType first, IteratorType last,
                 ValueType init_reduction_value);

template <class ExecutionSpace, class DataType, class... Properties, class ValueType>
ValueType reduce(const ExecutionSpace& exespace,                                (7)
                 const ::Kokkos::View<DataType, Properties...>& view,
                 ValueType init_reduction_value);

template <class ExecutionSpace, class DataType, class... Properties, class ValueType>
ValueType reduce(const std::string& label,                                      (8)
                 const ExecutionSpace& exespace,
                 const ::Kokkos::View<DataType, Properties...>& view,
                 ValueType init_reduction_value);

//
// overload set C
//
template <
  class ExecutionSpace, class IteratorType, class ValueType,
  class BinaryOp>
ValueType reduce(const ExecutionSpace& exespace,                                (9)
                 IteratorType first, IteratorType last,
                 ValueType init_reduction_value,
                 BinaryOp joiner);

template <
  class ExecutionSpace, class IteratorType, class ValueType,
  class BinaryOp>
ValueType reduce(const std::string& label, const ExecutionSpace& exespace,      (10)
                 IteratorType first, IteratorType last,
                 ValueType init_reduction_value,
                 BinaryOp joiner);

template <
  class ExecutionSpace, class DataType, class... Properties,
  class ValueType, class BinaryOp>
ValueType reduce(const ExecutionSpace& exespace,                                (11)
                 const ::Kokkos::View<DataType, Properties...>& view,
                 ValueType init_reduction_value,
                 BinaryOp joiner);

template <
  class ExecutionSpace, class DataType, class... Properties,
  class ValueType, class BinaryOp>
ValueType reduce(const std::string& label, const ExecutionSpace& exespace,      (12)
                 const ::Kokkos::View<DataType, Properties...>& view,
                 ValueType init_reduction_value,
                 BinaryOp joiner);

} //end namespace Experimental
} //end namespace Kokkos

Description

• Overload set A (1,2,3,4): performs a reduction of the elements in the range [first, last) (1,2) or in view (3,4).

• Overload set B (5,6,7,8): performs a reduction of the elements in the range [first, last) (5,6) or in view (7,8) accounting for the initial value init_reduction_value.

• Overload set C (9,10,11,12): performs a reduction of the elements in the range [first, last) (9,10) or in view (11,12) accounting for the initial value init_reduction_value using the functor joiner to join operands during the reduction operation.

Parameters and Requirements

• exespace:

  • execution space instance

• label:

  • used to name the implementation kernels for debugging purposes

  • for 1,5,9 the default string is: “Kokkos::reduce_iterator_api_default”

  • for 3,7,11 the default string is: “Kokkos::reduce_view_api_default”

• first, last:

  • range of elements to reduce over

  • must be random access iterators

  • must represent a valid range, i.e., last >= first (checked in debug mode)

  • must be accessible from exespace

• view:

  • view to reduce

  • must be rank-1, and have LayoutLeft, LayoutRight, or LayoutStride

  • must be accessible from exespace

• init_reduction_value:

  • initial reduction value to use

• joiner:

  • binary functor performing the desired operation to join two elements. Must be valid to be called from the execution space passed, and callable with two arguments a,b of type (possible const) ValueType, and must not modify a,b.

  • Must conform to:

  struct JoinFunctor {
    KOKKOS_FUNCTION
    constexpr ValueType operator()(const ValueType& a, const ValueType& b) const {
      return /* ... */
    }
  };
  

  • The behavior is non-deterministic if the joiner operation is not associative or not commutative.

Return

The reduction result.