# slasyf_aa.f - Man Page

SRC/slasyf_aa.f

## Synopsis

### Functions/Subroutines

subroutine **slasyf_aa** (uplo, j1, m, nb, a, lda, ipiv, h, ldh, work)**SLASYF_AA**

## Function/Subroutine Documentation

### subroutine slasyf_aa (character uplo, integer j1, integer m, integer nb, real, dimension( lda, * ) a, integer lda, integer, dimension( * ) ipiv, real, dimension( ldh, * ) h, integer ldh, real, dimension( * ) work)

**SLASYF_AA**

**Purpose:**

DLATRF_AA factorizes a panel of a real symmetric matrix A using the Aasen's algorithm. The panel consists of a set of NB rows of A when UPLO is U, or a set of NB columns when UPLO is L. In order to factorize the panel, the Aasen's algorithm requires the last row, or column, of the previous panel. The first row, or column, of A is set to be the first row, or column, of an identity matrix, which is used to factorize the first panel. The resulting J-th row of U, or J-th column of L, is stored in the (J-1)-th row, or column, of A (without the unit diagonals), while the diagonal and subdiagonal of A are overwritten by those of T.

**Parameters***UPLO*UPLO is CHARACTER*1 = 'U': Upper triangle of A is stored; = 'L': Lower triangle of A is stored.

*J1*J1 is INTEGER The location of the first row, or column, of the panel within the submatrix of A, passed to this routine, e.g., when called by SSYTRF_AA, for the first panel, J1 is 1, while for the remaining panels, J1 is 2.

*M*M is INTEGER The dimension of the submatrix. M >= 0.

*NB*NB is INTEGER The dimension of the panel to be facotorized.

*A*A is REAL array, dimension (LDA,M) for the first panel, while dimension (LDA,M+1) for the remaining panels. On entry, A contains the last row, or column, of the previous panel, and the trailing submatrix of A to be factorized, except for the first panel, only the panel is passed. On exit, the leading panel is factorized.

*LDA*LDA is INTEGER The leading dimension of the array A. LDA >= max(1,M).

*IPIV*IPIV is INTEGER array, dimension (M) Details of the row and column interchanges, the row and column k were interchanged with the row and column IPIV(k).

*H*H is REAL workspace, dimension (LDH,NB).

*LDH*LDH is INTEGER The leading dimension of the workspace H. LDH >= max(1,M).

*WORK*WORK is REAL workspace, dimension (M).

**Author**Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Definition at line **142** of file **slasyf_aa.f**.

## Author

Generated automatically by Doxygen for LAPACK from the source code.

## Referenced By

The man page slasyf_aa(3) is an alias of slasyf_aa.f(3).

Tue Nov 28 2023 12:08:42 Version 3.12.0 LAPACK