Contents

# ?sytrf_aa

Computes the factorization of a symmetric matrix using Aasen's algorithm.
Description
?sytrf_aa
computes the factorization of a symmetric matrix A using Aasen's algorithm. The form of the factorization is A = U*T*U
T
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 complex symmetric tridiagonal matrix.
This is the blocked version of the algorithm, calling Level 3 BLAS.
Input Parameters
matrix_layout
Specifies whether matrix storage layout is row major (
LAPACK_ROW_MAJOR
) or column major (
LAPACK_COL_MAJOR
).
uplo
• =
'U'
: The upper triangle of A is stored.
• =
'L'
: The lower triangle of A is stored.
n
The order of the matrix A.
n
≥ 0.
A
Array of size max(1,
lda
*
n
). The array
A
contains either the upper or the lower triangular part of the matrix A (see
uplo
).
lda
The leading dimension of the array
A
.
Output Parameters
A
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'
).
ipiv
Array of size
n
.
On exit, it contains the details of the interchanges; that is, the row and column
k
of A were interchanged with the row and column
ipiv
(
k
)
.
Return Values
This function returns a value
info
.
= 0: Successful exit.
< 0: If
info
=
-i
, the
i
th
> 0: If
info
=
i
, D(
i
,
i
) is exactly zero. The factorization has been completed, but the block diagonal matrix D is exactly singular, and division by zero will occur if it is used to solve a system of equations.

#### Product and Performance Information

1

Performance varies by use, configuration and other factors. Learn more at www.Intel.com/PerformanceIndex.