minmax_element

Header File: Kokkos_StdAlgorithms.hpp

namespace Kokkos{ 
namespace Experimental{

//
// overload set accepting iterators
//
template <class ExecutionSpace, class IteratorType>
auto minmax_element(const ExecutionSpace& exespace,                        (1)
                    IteratorType first, IteratorType last);

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

template <class ExecutionSpace, class IteratorType, class ComparatorType>
auto minmax_element(const ExecutionSpace& exespace,                        (3)
                    IteratorType first, IteratorType last,
                    ComparatorType comp);

template <class ExecutionSpace, class IteratorType, class ComparatorType>
auto minmax_element(const std::string& label,                              (4)
                    const ExecutionSpace& exespace,
                    IteratorType first, IteratorType last,
                    ComparatorType comp);

//
// overload set accepting views
//
template <class ExecutionSpace, class DataType, class... Properties>
auto minmax_element(const ExecutionSpace& exespace,                        (5)
                    const ::Kokkos::View<DataType, Properties...>& view);

template <class ExecutionSpace, class DataType, class... Properties>
auto minmax_element(const std::string& label,                              (6)
                    const ExecutionSpace& exespace,
                    const ::Kokkos::View<DataType, Properties...>& view);

template <class ExecutionSpace, class DataType, class ComparatorType, class... Properties>
auto minmax_element(const ExecutionSpace& exespace,                        (7)
                    const ::Kokkos::View<DataType, Properties...>& view,
                    ComparatorType comp);

template <class ExecutionSpace, class DataType, class ComparatorType, class... Properties>
auto minmax_element(const std::string& label,                              (8)
                    const ExecutionSpace& exespace,
                    const ::Kokkos::View<DataType, Properties...>& view,
                    ComparatorType comp);

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

Description

• (1,2,5,6): Finds the smallest and largest elements in the range [first, last) (1,2) or in view (5,6) using operator< to compare two elements

• (3,4,7,8): Finds the smallest and largest element in the range [first, last) (3,4) or in view (7,8) using the binary functor comp to compare two elements

Parameters and Requirements

• exespace, first, last, view, comp: same as in min_element

• label:

  • used to name the implementation kernels for debugging purposes

  • for 1,3 the default string is: “Kokkos::minmax_element_iterator_api_default”

  • for 5,7 the default string is: “Kokkos::minmax_element_view_api_default”

Return

A Kokkos pair of iterators to the smallest and largest elements in that order. The following special cases apply:

• if the range [first, last) is empty it returns Kokkos::pair(first, first).

• if view is empty, it returns Kokkos::pair(Kokkos::Experimental::begin(view), Kokkos::Experimental::begin(view)).

• if several elements are equivalent to the smallest element, the iterator to the first such element is returned.

• if several elements are equivalent to the largest element, the iterator to the last such element is returned.

Example

namespace KE = Kokkos::Experimental;
Kokkos::View<double*> a("a", 11);

auto itPair = KE::minmax_element(Kokkos::DefaultExecutionSpace(), KE::begin(a), KE::end(a));

// passing the view directly
auto itPair = KE::minmax_element(Kokkos::DefaultExecutionSpace(), a);


// using a custom comparator
template <class ValueType1, class ValueType2 = ValueType1>
struct CustomLessThanComparator {
  KOKKOS_INLINE_FUNCTION
  bool operator()(const ValueType1& a,
                  const ValueType2& b) const {
    // here we use < but one can put any custom logic to return true if a is less than b
    return a < b;
  }

  KOKKOS_INLINE_FUNCTION
  CustomLessThanComparator() {}
};

// passing the view directly
auto res = KE::minmax_element(Kokkos::DefaultExecutionSpace(), a, CustomLessThanComparator<double>());