.. SPDX-FileCopyrightText: 2019-2020 Intel Corporation .. .. SPDX-License-Identifier: CC-BY-4.0 .. _onemkl_lapack_hetrf: hetrf ===== Computes the Bunch-Kaufman factorization of a complex Hermitian matrix. .. container:: section .. rubric:: Description ``hetrf`` supports the following precisions. .. list-table:: :header-rows: 1 * - T * - ``std::complex`` * - ``std::complex`` The routine computes the factorization of a complex Hermitian matrix :math:`A` using the Bunch-Kaufman diagonal pivoting method. The form of the factorization is: - if ``upper_lower=uplo::upper``, :math:`A` = :math:`UDU^{H}` - if ``upper_lower=uplo::lower``, :math:`A` = :math:`LDL^{H}` where :math:`A` is the input matrix, :math:`U` and :math:`L` are products of permutation and triangular matrices with unit diagonal (upper triangular for :math:`U` and lower triangular for :math:`L`), and :math:`D` is a Hermitian block-diagonal matrix with :math:`1 \times 1` and :math:`2 \times 2` diagonal blocks. :math:`U` and :math:`L` have :math:`2 \times 2` unit diagonal blocks corresponding to the :math:`2 \times 2` blocks of :math:`D`. hetrf (Buffer Version) ---------------------- .. container:: section .. rubric:: Syntax .. code-block:: cpp namespace oneapi::mkl::lapack { void hetrf(sycl::queue &queue, oneapi::mkl::uplo upper_lower, std::int64_t n, sycl::buffer &a, std::int64_t lda, sycl::buffer &ipiv, sycl::buffer &scratchpad, std::int64_t scratchpad_size) } .. container:: section .. rubric:: Input Parameters queue The queue where the routine should be executed. upper_lower Indicates whether the upper or lower triangular part of :math:`A` is stored and how :math:`A` is factored: If ``upper_lower=uplo::upper``, the buffer ``a`` stores the upper triangular part of the matrix :math:`A`, and :math:`A` is factored as :math:`UDU^H`. If ``upper_lower=uplo::lower``, the buffer ``a`` stores the lower triangular part of the matrix :math:`A`, and :math:`A` is factored as :math:`LDL^H`. n The order of matrix :math:`A` (:math:`0 \le n`). a The buffer ``a``, size :math:`\max(1,\text{lda} \cdot n)`. The buffer ``a`` contains either the upper or the lower triangular part of the matrix :math:`A` (see ``upper_lower``). The second dimension of ``a`` must be at least :math:`\max(1, n)`. lda The leading dimension of ``a``. scratchpad Buffer holding scratchpad memory to be used by the routine for storing intermediate results. scratchpad_size Size of scratchpad memory as a number of floating point elements of type ``T``. Size should not be less than the value returned by :ref:`onemkl_lapack_hetrf_scratchpad_size` function. .. container:: section .. rubric:: Output Parameters a The upper or lower triangular part of a is overwritten by details of the block-diagonal matrix :math:`D` and the multipliers used to obtain the factor :math:`U` (or :math:`L`). ipiv Buffer, size at least :math:`\max(1, n)`. Contains details of the interchanges and the block structure of :math:`D`. If :math:`\text{ipiv}(i)=k>0`, then :math:`d_{ii}` is a :math:`1 \times 1` block, and the :math:`i`-th row and column of :math:`A` was interchanged with the :math:`k`-th row and column. If ``upper_lower=oneapi::mkl::uplo::upper`` and :math:`\text{ipiv}(i)=\text{ipiv}(i-1)=-m<0`, then :math:`D` has a :math:`2 \times 2` block in rows/columns :math:`i` and :math:`i`-1, and (:math:`i-1`)-th row and column of :math:`A` was interchanged with the :math:`m`-th row and column. If ``upper_lower=oneapi::mkl::uplo::lower`` and :math:`\text{ipiv}(i)=\text{ipiv}(i+1)=-m<0`, then :math:`D` has a :math:`2 \times 2` block in rows/columns :math:`i` and :math:`i+1`, and (:math:`i+1`)-th row and column of :math:`A` was interchanged with the :math:`m`-th row and column. hetrf (USM Version) ---------------------- .. container:: section .. rubric:: Syntax .. code-block:: cpp namespace oneapi::mkl::lapack { sycl::event hetrf(sycl::queue &queue, oneapi::mkl::uplo upper_lower, std::int64_t n, T *a, std::int64_t lda, int_64 *ipiv, T *scratchpad, std::int64_t scratchpad_size, const std::vector &events = {}) } .. container:: section .. rubric:: Input Parameters queue The queue where the routine should be executed. upper_lower Indicates whether the upper or lower triangular part of :math:`A` is stored and how :math:`A` is factored: If ``upper_lower=uplo::upper``, the array ``a`` stores the upper triangular part of the matrix :math:`A`, and :math:`A` is factored as :math:`UDU^H`. If ``upper_lower=uplo::lower``, the array ``a`` stores the lower triangular part of the matrix :math:`A`, and :math:`A` is factored as :math:`LDL^H`. n The order of matrix :math:`A` (:math:`0 \le n`). a The pointer to :math:`A`, size :math:`\max(1,\text{lda} \cdot n)`, containing either the upper or the lower triangular part of the matrix :math:`A` (see ``upper_lower``). The second dimension of ``a`` must be at least :math:`\max(1, n)`. lda The leading dimension of ``a``. scratchpad Pointer to scratchpad memory to be used by the routine for storing intermediate results. scratchpad_size Size of scratchpad memory as a number of floating point elements of type ``T``. Size should not be less than the value returned by :ref:`onemkl_lapack_hetrf_scratchpad_size` function. events List of events to wait for before starting computation. Defaults to empty list. .. container:: section .. rubric:: Output Parameters a The upper or lower triangular part of a is overwritten by details of the block-diagonal matrix :math:`D` and the multipliers used to obtain the factor :math:`U` (or :math:`L`). ipiv Pointer to array of size at least :math:`\max(1, n)`. Contains details of the interchanges and the block structure of :math:`D`. If :math:`\text{ipiv}(i)=k>0`, then :math:`d_{ii}` is a :math:`1 \times 1` block, and the :math:`i`-th row and column of :math:`A` was interchanged with the :math:`k`-th row and column. If ``upper_lower=oneapi::mkl::uplo::upper`` and :math:`\text{ipiv}(i)=\text{ipiv}(i-1)=-m<0`, then :math:`D` has a :math:`2 \times 2` block in rows/columns :math:`i` and :math:`i-1`, and (:math:`i-1`)-th row and column of :math:`A` was interchanged with the :math:`m`-th row and column. If ``upper_lower=oneapi::mkl::uplo::lower`` and :math:`\text{ipiv}(i)=\text{ipiv}(i+1)=-m<0`, then :math:`D` has a :math:`2 \times 2` block in rows/columns :math:`i` and :math:`i+1`, and (:math:`i+1`)-th row and column of :math:`A` was interchanged with the :math:`m`-th row and column. .. container:: section .. rubric:: Return Values Output event to wait on to ensure computation is complete. **Parent topic:** :ref:`onemkl_lapack-linear-equation-routines`