sytrf#

Computes the Bunch-Kaufman factorization of a symmetric matrix.

Description

sytrf supports the following precisions.

T

float

double

std::complex<float>

std::complex<double>

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

The routine computes the factorization of a real/complex symmetric matrix \(A\) using the Bunch-Kaufman diagonal pivoting method. The form of the factorization is:

if upper_lower=uplo::upper, \(A\) = \(UDU^{T}\)
if upper_lower=uplo::lower, \(A\) = \(LDL^{T}\)

where \(A\) is the input matrix, \(U\) and \(L\) are products of permutation and triangular matrices with unit diagonal (upper triangular for \(U\) and lower triangular for \(L\)), and \(D\) is a symmetric block-diagonal matrix with \(1 \times 1\) and \(2 \times 2\) diagonal blocks. \(U\) and \(L\) have \(2 \times 2\) unit diagonal blocks corresponding to the \(2 \times 2\) blocks of \(D\).

sytrf (Buffer Version)#

Syntax

namespace oneapi::math::lapack {
  void sytrf(cl::sycl::queue &queue, oneapi::math::uplo upper_lower, std::int64_t n, cl::sycl::buffer<T,1> &a, std::int64_t lda, cl::sycl::buffer<int_64,1> &ipiv, cl::sycl::buffer<T,1> &scratchpad, std::int64_t scratchpad_size)
}

Input Parameters

queue: The queue where the routine should be executed.
upper_lower: Indicates whether the upper or lower triangular part of \(A\) is stored and how \(A\) is factored:

If upper_lower=uplo::upper, the buffer a stores the upper triangular part of the matrix \(A\), and \(A\) is factored as \(UDU^T\).

If upper_lower=uplo::lower, the buffer a stores the lower triangular part of the matrix \(A\), and \(A\) is factored as \(LDL^T\).
n: The order of matrix \(A\) (\(0 \le n\)).
a: The buffer a, size \(\max(1,lda \cdot n)\). The buffer a contains either the upper or the lower triangular part of the matrix \(A\) (see upper_lower). The second dimension of a must be at least \(\max(1, n)\).
lda: The leading dimension of a.
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 sytrf_scratchpad_size function.

Output Parameters

a: The upper or lower triangular part of a is overwritten by details of the block-diagonal matrix \(D\) and the multipliers used to obtain the factor \(U\) (or \(L\)).
ipiv: Buffer, size at least \(\max(1, n)\). Contains details of the interchanges and the block structure of \(D\). If \(\text{ipiv}(i)=k>0\), then \(d_{ii}\) is a \(1 \times 1\) block, and the \(i\)-th row and column of \(A\) was interchanged with the \(k\)-th row and column.

If upper_lower=oneapi::math::uplo::upper and \(\text{ipiv}(i)=\text{ipiv}(i-1)=-m<0\), then \(D\) has a \(2 \times 2\) block in rows/columns \(i\) and \(i\)-1, and (\(i-1\))-th row and column of \(A\) was interchanged with the \(m\)-th row and column.

If upper_lower=oneapi::math::uplo::lower and \(\text{ipiv}(i)=\text{ipiv}(i+1)=-m<0\), then \(D\) has a \(2 \times 2\) block in rows/columns \(i\) and \(i+1\), and (\(i+1\))-th row and column of \(A\) was interchanged with the \(m\)-th row and column.
scratchpad: Buffer holding scratchpad memory to be used by routine for storing intermediate results.

Throws

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.

oneapi::math::host_bad_alloc

oneapi::math::device_bad_alloc

oneapi::math::unimplemented

oneapi::math::unsupported_device

oneapi::math::lapack::invalid_argument

oneapi::math::lapack::computation_error

Exception is thrown in case of problems during calculations. The info code of the problem can be obtained by info() method of exception object:

If \(\text{info}=-i\), the \(i\)-th parameter had an illegal value.

If \(\text{info}=i\), \(d_{ii}\) is 0. The factorization has been completed, but \(D\) is exactly singular. Division by 0 will occur if you use \(D\) for solving a system of linear equations.

If info equals to value passed as scratchpad size, and detail() returns non zero, then passed scratchpad is of insufficient size, and required size should not be less than value return by detail() method of exception object.

sytrf (USM Version)#