KokkosBlas::iamax
#################

Defined in header: :code:`KokkosBlas1_iamax.hpp`

.. code:: c++

  template <class execution_space, class XVector>
  typename XVector::size_type iamax(const execution_space& space, const XVector& x);

  template <class XVector>
  typename XVector::size_type iamax(const XVector& x);

  template <class execution_space, class RV, class XMV>
  void iamax(const execution_space& space, const RV& R, const XMV& X);

  template <class RV, class XMV>
  void iamax(const RV& R, const XMV& X);

Finds the index of the entry in each column of ``X`` with the largest magnitude.

1. iterate over the entries in ``X``, identify the lowest-index entry with the largest magnitude, fence the ``space`` instance
2. iterate over the entries in ``X``, identify the lowest-index entry with the largest magnitude, fence the default instance associated with ``typename XVector::execution_space``
3. iterate over the entries in ``X``, store the lowest-index entry with the largest magnitude in each column of ``X`` using the resources of ``space``
4. iterate over the entries in ``X``, store the lowest-index entry with the largest magnitude in each column of ``X`` using the resources of the default instance associated with ``typename XMV::execution_space``

The function will throw a runtime exception if ``X.extent(1) != R.extent(0)``

The result (return value or stored value) from this function is undefined if the vector has no entries.

Parameters
==========

:space: an execution space instance

:R: view holding the indices of entry with the largest magnitude in each column of X

:X: view for which the we identify the index of the entry with the largest magnitude per column

Type Requirements
-----------------

- `execution_space` must be a Kokkos `execution space <https://kokkos.org/kokkos-core-wiki/API/core/execution_spaces.html>`_

- `XVector` must be a Kokkos `View <https://kokkos.org/kokkos-core-wiki/API/core/view/view.html>`_ of rank 1 that satisfies

  - ``Kokkos::SpaceAccessibility<execution_space, typename XVector::memory_space>::accessible == true``

- `RV` must be a Kokkos `View <https://kokkos.org/kokkos-core-wiki/API/core/view/view.html>`_ of rank 0 or 1 that satisfies

  - ``Kokkos::SpaceAccessibility<execution_space, typename RV::memory_space>::accessible == true``
  - ``std::is_same_v<typename RV::value_type, typename RV::non_const_value_type> == true``

- `XMV` must be a Kokkos `View <https://kokkos.org/kokkos-core-wiki/API/core/view/view.html>`_ of rank 1 or 2 that satisfies

  - ``Kokkos::SpaceAccessibility<execution_space, typename XMV::memory_space>::accessible == true``
  - ``RV::rank == XMV::rank - 1``

Example
=======

.. literalinclude:: ../../../../example/wiki/blas/KokkosBlas1_wiki_iamax.cpp
  :language: c++

output:

.. code::

   Iamax of X: 60, Expected: 60