max_element

Header File: Kokkos_StdAlgorithms.hpp

namespace Kokkos{
namespace Experimental{

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

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

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

template <class ExecutionSpace, class IteratorType, class ComparatorType>
auto max_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 max_element(const ExecutionSpace& exespace,                        (5)
                 const ::Kokkos::View<DataType, Properties...>& view);

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

template <class ExecutionSpace, class DataType, class ComparatorType, class... Properties>
auto max_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 largest element in the range [first, last) or in view using operator< to compare two elements

• (3,4,7,8): Finds the largest element in the range [first, last) or in view 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::max_element_iterator_api_default”

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

Return

Iterator to the largest element. The following special cases apply:

• if several elements are equivalent to the largest element, returns the iterator to the first such element.

• if the range [first, last) is empty it returns last.

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

Example

namespace KE = Kokkos::Experimental;
Kokkos::View<double*> a("a", 13);
// fill a somehow

auto res = KE::max_element(Kokkos::DefaultExecutionSpace(), KE::begin(a), KE::end(a));

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