---
name: "dsytrf_aa.f"
section: "3"
platform: "linux"
package: "lapack-doc"
version: "3.12.1-2"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/dsytrf_aa.f"
---

# dsytrf\_aa.f(3)

## NAME

SRC/dsytrf\_aa.f

## SYNOPSIS

### Functions/Subroutines

subroutine **dsytrf\_aa** (uplo, n, a, lda, ipiv, work, lwork, info)\
 **DSYTRF\_AA**

## Function/Subroutine Documentation

### subroutine dsytrf\_aa (character uplo, integer n, double precision, dimension( lda, \* ) a, integer lda, integer, dimension( \* ) ipiv, double precision, dimension( \* ) work, integer lwork, integer info)

**DSYTRF\_AA**

**Purpose:**

```
!>
!> DSYTRF_AA computes the factorization of a real symmetric matrix A
!> using the Aasen's algorithm.  The form of the factorization is
!>
!>    A = U**T*T*U  or  A = L*T*L**T
!>
!> where U (or L) is a product of permutation and unit upper (lower)
!> triangular matrices, and T is a symmetric tridiagonal matrix.
!>
!> This is the blocked version of the algorithm, calling Level 3 BLAS.
!>
```

**Parameters**

*UPLO*

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

*N*

```
!>          N is INTEGER
!>          The order of the matrix A.  N >= 0.
!>
```

*A*

```
!>          A is DOUBLE PRECISION array, dimension (LDA,N)
!>          On entry, the symmetric matrix A.  If UPLO = 'U', the leading
!>          N-by-N upper triangular part of A contains the upper
!>          triangular part of the matrix A, and the strictly lower
!>          triangular part of A is not referenced.  If UPLO = 'L', the
!>          leading N-by-N lower triangular part of A contains the lower
!>          triangular part of the matrix A, and the strictly upper
!>          triangular part of A is not referenced.
!>
!>          On exit, the tridiagonal matrix is stored in the diagonals
!>          and the subdiagonals of A just below (or above) the diagonals,
!>          and L is stored below (or above) the subdiagonals, when UPLO
!>          is 'L' (or 'U').
!>
```

*LDA*

```
!>          LDA is INTEGER
!>          The leading dimension of the array A.  LDA >= max(1,N).
!>
```

*IPIV*

```
!>          IPIV is INTEGER array, dimension (N)
!>          On exit, it contains the details of the interchanges, i.e.,
!>          the row and column k of A were interchanged with the
!>          row and column IPIV(k).
!>
```

*WORK*

```
!>          WORK is DOUBLE PRECISION array, dimension (MAX(1,LWORK))
!>          On exit, if INFO = 0, WORK(1) returns the optimal LWORK.
!>
```

*LWORK*

```
!>          LWORK is INTEGER
!>          The length of WORK.
!>          LWORK >= 1, if N <= 1, and LWORK >= 2*N, otherwise.
!>          For optimum performance LWORK >= N*(1+NB), where NB is
!>          the optimal blocksize, returned by ILAENV.
!>
!>          If LWORK = -1, then a workspace query is assumed; the routine
!>          only calculates the optimal size of the WORK array, returns
!>          this value as the first entry of the WORK array, and no error
!>          message related to LWORK is issued by XERBLA.
!>
```

*INFO*

```
!>          INFO is INTEGER
!>          = 0:  successful exit
!>          < 0:  if INFO = -i, the i-th argument had an illegal value.
!>
```

**Author**

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Definition at line **133** of file **dsytrf\_aa.f**.

## Author

Generated automatically by Doxygen for LAPACK from the source code.