.. _onemkl_blas_iamax:

iamax
=====

Finds the index of the element with the largest absolute value in a vector.

.. _onemkl_blas_iamax_description:

.. rubric:: Description

The ``iamax`` routines return an index ``i`` such that ``x[i]``
has the maximum absolute value of all elements in vector ``x`` (real
variants), or such that (\|Re(``x[i]``)\| + \|Im(``x[i]``)\|) is maximal
(complex variants).

If either ``n`` or ``incx`` are not positive, the routine returns
``0``.

If more than one vector element is found with the same largest
absolute value, the index of the first one encountered is returned.

If the vector contains ``NaN`` values, then the routine returns the
index of the first ``NaN``.

``iamax`` supports the following precisions.

   .. list-table:: 
      :header-rows: 1

      * -  T 
      * -  ``float`` 
      * -  ``double`` 
      * -  ``std::complex<float>`` 
      * -  ``std:complex<double>`` 

.. container:: Note

   .. rubric:: Note
      :class: NoteTipHead

   The index is zero-based.

.. _onemkl_blas_iamax_buffer:

iamax (Buffer Version)
----------------------

.. rubric:: Syntax

.. code-block:: cpp

   namespace oneapi::mkl::blas::column_major {
       void iamax(sycl::queue &queue,
                  std::int64_t n,
                  sycl::buffer<T,
                  1> &x,
                  std::int64_t incx,
                  sycl::buffer<std::int64_t,
                  1> &result)
   }
.. code-block:: cpp

   namespace oneapi::mkl::blas::row_major {
       void iamax(sycl::queue &queue,
                  std::int64_t n,
                  sycl::buffer<T,
                  1> &x,
                  std::int64_t incx,
                  sycl::buffer<std::int64_t,
                  1> &result)
   }

.. container:: section

   .. rubric:: Input Parameters

   queue
      The queue where the routine should be executed.

   n
      The number of elements in vector ``x``.

   x
      The buffer that holds the input vector ``x``. The buffer must be
      of size at least (1 + (``n`` - 1)*abs(``incx``)). See :ref:`matrix-storage`
      for more details.

   incx
      The stride of vector ``x``.

.. container:: section

   .. rubric:: Output Parameters

   result
      The buffer where the zero-based index ``i`` of the maximal element
      is stored.


.. _onemkl_blas_iamax_usm:

iamax (USM Version)
-------------------

.. rubric:: Syntax

.. code-block:: cpp

   namespace oneapi::mkl::blas::column_major {
       sycl::event iamax(sycl::queue &queue,
                         std::int64_t n,
                         const T *x,
                         std::int64_t incx,
                         T_res *result,
                         const std::vector<sycl::event> &dependencies = {})
   }
.. code-block:: cpp

   namespace oneapi::mkl::blas::row_major {
       sycl::event iamax(sycl::queue &queue,
                         std::int64_t n,
                         const T *x,
                         std::int64_t incx,
                         T_res *result,
                         const std::vector<sycl::event> &dependencies = {})
   }

.. container:: section

   .. rubric:: Input Parameters

   queue
      The queue where the routine should be executed.

   n
      The number of elements in vector ``x``.

   x
      The pointer to the input vector ``x``. The array holding the
      input vector ``x`` must be of size at least (1 + (``n`` -
      1)*abs(``incx``)). See :ref:`matrix-storage` for
      more details.

   incx
      The stride of vector ``x``.

   dependencies
      List of events to wait for before starting computation, if any.
      If omitted, defaults to no dependencies.

.. container:: section

   .. rubric:: Output Parameters

   result
      The pointer to where the zero-based index ``i`` of the maximal
      element is stored.

.. container:: section

   .. rubric:: Return Values

   Output event to wait on to ensure computation is complete.


   **Parent topic:** :ref:`blas-level-1-routines`