.. SPDX-FileCopyrightText: 2019-2020 Intel Corporation
..
.. SPDX-License-Identifier: CC-BY-4.0

.. _onemkl_sparse_gemv:

gemv
====


Computes a sparse matrix-dense vector product.

.. rubric:: Description and Assumptions

Refer to :ref:`onemkl_sparse_supported_types` for a
list of supported ``<fp>`` and ``<intType>``. 
The oneapi::mkl::sparse::gemv routine computes a sparse matrix-dense vector
product defined as

.. math::

      y \leftarrow \alpha \text{op}(A) x + \beta y

where :math:`\alpha` and :math:`\beta` are scalars, :math:`x` and :math:`y` are dense vectors, ``A`` is a sparse matrix.


.. _onemkl_sparse_gemv_buffer:

gemv (Buffer version)
---------------------

.. rubric:: Syntax

.. code-block:: cpp

   namespace oneapi::mkl::sparse {

      void gemv (sycl::queue                          &queue, 
                 oneapi::mkl::transpose               transpose_val, 
                 const fp                             alpha, 
                 oneapi::mkl::sparse::matrix_handle_t A_handle, 
                 sycl::buffer<fp, 1>                  &x, 
                 const fp                             beta, 
                 sycl::buffer<fp, 1>                  &y); 

   }


.. container:: section

    .. rubric:: Input Parameters

    queue
         Specifies the SYCL command queue which will be used for SYCL
         kernels execution.


    transpose_val
         Specifies operation ``op()`` on input matrix. The possible options
         are described in :ref:`onemkl_enum_transpose` enum class.


    alpha
       Specifies the scalar :math:`\alpha`.


    A_handle
       Handle to object containing sparse matrix, :math:`A`. Created using the
       oneapi::mkl::sparse::set_csr_data routine.


    x
       SYCL memory object containing an array of size at least
       equal to the number of columns of matrix :math:`\text{op}(A)`.


    beta
       Specifies the scalar :math:`\beta`.


    y
       SYCL memory object containing an array of size at least
       equal to the number of rows of matrix :math:`\text{op}(A)`.

.. container:: section

    .. rubric:: Output Parameters
         :class: sectiontitle

    y
       Overwritten by the updated vector ``y``.


.. container:: section

    .. rubric:: Throws
       :class: sectiontitle

    This routine shall throw the following exceptions if the associated condition is detected.
    An implementation may throw additional implementation-specific exception(s)
    in case of error conditions not covered here.

    | :ref:`oneapi::mkl::computation_error<onemkl_exception_computation_error>`
    | :ref:`oneapi::mkl::device_bad_alloc<onemkl_exception_device_bad_alloc>`
    | :ref:`oneapi::mkl::host_bad_alloc<onemkl_exception_host_bad_alloc>`
    | :ref:`oneapi::mkl::invalid_argument<onemkl_exception_invalid_argument>`
    | :ref:`oneapi::mkl::unimplemented<onemkl_exception_unimplemented>`
    | :ref:`oneapi::mkl::uninitialized<onemkl_exception_uninitialized>`
    | :ref:`oneapi::mkl::unsupported_device<onemkl_exception_unsupported_device>`

.. _onemkl_sparse_gemv_usm:

gemv (USM version)
------------------

.. rubric:: Syntax


.. code-block:: cpp

   namespace oneapi::mkl::sparse {

      sycl::event gemv (sycl::queue                           &queue, 
                        oneapi::mkl::transpose                transpose_val, 
                        const fp                              alpha, 
                        oneapi::mkl::sparse::matrix_handle_t  A_handle, 
                        const fp                              *x, 
                        const fp                              beta, 
                        const fp                              *y, 
                        const std::vector<sycl::event>        &dependencies = {});

   }


.. container:: section

    .. rubric:: Input Parameters

    queue
         Specifies the SYCL command queue which will be used for SYCL
         kernels execution.


    transpose_val
         Specifies operation ``op()`` on input matrix. The possible options
         are described in :ref:`onemkl_enum_transpose` enum class.


    alpha
       Specifies the scalar :math:`\alpha`.


    A_handle
       Handle to object containing sparse matrix, :math:`A`. Created using the
       oneapi::mkl::sparse::set_csr_data routine.


    x
       Device-accessible USM object containing an array of size at least
       equal to the number of columns of matrix :math:`\text{op}(A)`. 


    beta
       Specifies the scalar :math:`\beta`.


    y
       Device-accessible USM object containing an array of size at least
       equal to the number of rows of matrix :math:`\text{op}(A)`.


    dependencies
       List of events that oneapi::mkl::sparse::gemv routine depends on.
       If omitted, defaults to no dependencies.

.. container:: section

    .. rubric:: Output Parameters
         :class: sectiontitle

    y
       Overwritten by the updated vector ``y``.

.. container:: section

    .. rubric:: Throws
         :class: sectiontitle

    This routine shall throw the following exceptions if the associated condition is detected.
    An implementation may throw additional implementation-specific exception(s)
    in case of error conditions not covered here.

    | :ref:`oneapi::mkl::computation_error<onemkl_exception_computation_error>`
    | :ref:`oneapi::mkl::device_bad_alloc<onemkl_exception_device_bad_alloc>`
    | :ref:`oneapi::mkl::host_bad_alloc<onemkl_exception_host_bad_alloc>`
    | :ref:`oneapi::mkl::invalid_argument<onemkl_exception_invalid_argument>`
    | :ref:`oneapi::mkl::unimplemented<onemkl_exception_unimplemented>`
    | :ref:`oneapi::mkl::uninitialized<onemkl_exception_uninitialized>`
    | :ref:`oneapi::mkl::unsupported_device<onemkl_exception_unsupported_device>`

.. container:: section

    .. rubric:: Return Values
       :class: sectiontitle

    Output event that can be waited upon or added as a
    dependency for the completion of gemv routine.


.. container:: familylinks


   .. container:: parentlink


      **Parent topic:** :ref:`onemkl_spblas`