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

.. _onemkl_lapack_hegvd_scratchpad_size:

hegvd_scratchpad_size
=====================

Computes size of scratchpad memory required for :ref:`onemkl_lapack_hegvd` function.

.. container:: section

  .. rubric:: Description

``hegvd_scratchpad_size`` supports the following precisions.

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

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

Computes the number of elements of type ``T`` the scratchpad memory to be passed to :ref:`onemkl_lapack_hegvd` function should be able to hold.
Calls to this routine must specify the template parameter
explicitly.

hegvd_scratchpad_size
---------------------

.. container:: section

  .. rubric:: Syntax
         
.. code-block:: cpp

    namespace oneapi::mkl::lapack {
      template <typename T>
      std::int64_t hegvd_scratchpad_size(sycl::queue &queue, std::int64_t itype, oneapi::mkl::job jobz, oneapi::mkl::uplo upper_lower, std::int64_t n, std::int64_t lda, std::int64_t ldb) 
    }

.. container:: section

  .. rubric:: Input Parameters
         
queue
   Device queue where calculations by :ref:`onemkl_lapack_hegvd` function will be performed.

itype
   Must be 1 or 2 or 3. Specifies the problem type to be solved:

   if :math:`\text{itype} = 1`, the problem type is :math:`Ax = \lambda Bx`;

   if :math:`\text{itype} = 2`, the problem type is :math:`ABx = \lambda x`;

   if :math:`\text{itype} = 3`, the problem type is :math:`BAx = \lambda x`.

jobz
   Must be ``job::novec`` or ``job::vec``.

   If ``jobz = job::novec``, then only eigenvalues are computed.

   If ``jobz = job::vec``, then eigenvalues and eigenvectors are
   computed.

upper_lower
   Must be ``uplo::upper`` or ``uplo::lower``.

   If ``upper_lower = uplo::upper``, ``a`` and ``b`` store the upper
   triangular part of :math:`A` and :math:`B`.

   If ``upper_lower = uplo::lower``, ``a`` and ``b`` store the lower
   triangular part of :math:`A` and :math:`B`.

n
   The order of the matrices :math:`A` and :math:`B` (:math:`0 \le n`).

lda
   The leading dimension of ``a``. Currently ``lda`` is not referenced in
   this function.

ldb
   The leading dimension of ``b``. Currently ``ldb`` is not referenced in
   this function.

.. container:: section

  .. rubric:: Return Value

The number of elements of type ``T`` the scratchpad memory to be passed to :ref:`onemkl_lapack_hegvd` function should be able to hold.

**Parent topic:** :ref:`onemkl_lapack-singular-value-eigenvalue-routines`