MinLoc

Specific implementation of ReducerConcept storing the minimum value with an index

Header File: <Kokkos_Core.hpp>

Usage

MinLoc<T,I,S>::value_type result;
parallel_reduce(N,Functor,MinLoc<T,I,S>(result));

Synopsis

template<class Scalar, class Index, class Space>
class MinLoc{
  public:
    typedef MinLoc reducer;
    typedef ValLocScalar<typename std::remove_cv<Scalar>::type,
                         typename std::remove_cv<Index>::type > value_type;
    typedef Kokkos::View<value_type, Space> result_view_type;

    KOKKOS_INLINE_FUNCTION
    void join(value_type& dest, const value_type& src) const;

    KOKKOS_INLINE_FUNCTION
    void init(value_type& val) const;

    KOKKOS_INLINE_FUNCTION
    value_type& reference() const;

    KOKKOS_INLINE_FUNCTION
    result_view_type view() const;

    KOKKOS_INLINE_FUNCTION
    MinLoc(value_type& value_);

    KOKKOS_INLINE_FUNCTION
    MinLoc(const result_view_type& value_);
};

Interface

template<class Scalar, class Index, class Space>
class MinLoc

Public Types

reducer

The self type.

value_type

The reduction scalar type (specialization of ValLocScalar)

result_view_type

A Kokkos::View referencing the reduction result

Constructors

KOKKOS_INLINE_FUNCTION MinLoc(value_type &value_);

Constructs a reducer which references a local variable as its result location.

KOKKOS_INLINE_FUNCTION MinLoc(const result_view_type &value_);

Constructs a reducer which references a specific view as its result location.

Public Member Functions

KOKKOS_INLINE_FUNCTION void join(value_type &dest, const value_type &src) const;

Store minimum with index of src and dest into dest: dest = (src.val < dest.val) ? src :dest;.

KOKKOS_INLINE_FUNCTION void init(value_type &val) const;

Initialize val.val using the Kokkos::reduction_identity<Scalar>::min() method. The default implementation sets val=<TYPE>_MAX. Initialize val.loc using the Kokkos::reduction_identity<Index>::min() method. The default implementation sets val=<TYPE>_MAX.

KOKKOS_INLINE_FUNCTION value_type &reference() const;

Returns a reference to the result provided in class constructor.

KOKKOS_INLINE_FUNCTION result_view_type view() const;

Returns a view of the result place provided in class constructor.

Additional Information

• MinLoc<T,I,S>::value_type is Specialization of ValLocScalar on non-const T and non-const I

• MinLoc<T,I,S>::result_view_type is Kokkos::View<T,S,Kokkos::MemoryTraits<Kokkos::Unmanaged>>. Note that the S (memory space) must be the same as the space where the result resides.

• Requires: Scalar has operator = and operator < defined. Kokkos::reduction_identity<Scalar>::min() is a valid expression.

• Requires: Index has operator = defined. Kokkos::reduction_identity<Index>::min() is a valid expression.

• In order to use MinLoc with a custom type of either Scalar or Index, a template specialization of Kokkos::reduction_identity<CustomType> must be defined. See Built-In Reducers with Custom Scalar Types for details

Example

#include <Kokkos_Core.hpp>
struct Idx3D_t {
  int value[3];
  int& operator[](int i) { return value[i]; }
  const int& operator[](int i) const { return value[i]; }
};
template <>
struct Kokkos::reduction_identity<Idx3D_t> {
  static constexpr Idx3D_t min() { return {0, 0, 0}; }
};
int main(int argc, char* argv[]) {
  Kokkos::initialize(argc, argv);
  {
    Kokkos::View<double***> a("A", 5, 5, 5);
    Kokkos::deep_copy(a, 10);
    a(2, 3, 1)        = 5;
    using MinLoc_t    = Kokkos::MinLoc<double, Idx3D_t>;
    using MinLocVal_t = typename MinLoc_t::value_type;
    MinLocVal_t result;
    Kokkos::parallel_reduce(
        Kokkos::MDRangePolicy<Kokkos::Rank<3>>({0, 0, 0}, {5, 5, 5}),
        KOKKOS_LAMBDA(int i, int j, int k, MinLocVal_t& val) {
          if (a(i, j, k) < val.val) {
            val.val    = a(i, j, k);
            val.loc[0] = i;
            val.loc[1] = j;
            val.loc[2] = k;
          }
        },
        MinLoc_t(result));
    printf("%lf %i %i %i\n", result.val, result.loc[0], result.loc[1],
           result.loc[2]);
  }
  Kokkos::finalize();
}