Developer Reference

  • 2020.2
  • 07/15/2020
  • Public Content
Contents

?lasyf_aa

Factorizes a panel of a real or complex symmetric matrix using Aasen's algorithm.
call slasyf_aa
(
uplo
,
j1
,
m
,
nb
,
a
,
lda
,
ipiv
,
h
,
ldh
,
work
)
call dlasyf_aa
(
uplo
,
j1
,
m
,
nb
,
a
,
lda
,
ipiv
,
h
,
ldh
,
work
)
call clasyf_aa
(
uplo
,
j1
,
m
,
nb
,
a
,
lda
,
ipiv
,
h
,
ldh
,
work
)
call zlasyf_aa
(
uplo
,
j1
,
m
,
nb
,
a
,
lda
,
ipiv
,
h
,
ldh
,
work
)
Description
?lasyf_aa
factorizes a panel of a real or complex symmetric matrix
A
using 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, 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)-st row, or column, of
A
(without the unit diagonals), while the diagonal and subdiagonal of
A
are overwritten by those of
T
.
Input Parameters
uplo
CHARACTER*1
.
If
uplo
= 'U': Upper triangular of
A
is stored.
If
uplo
= 'L': Lower triangular of
A
is stored..
j1
INTEGER
.
The location of the first row, or column, of the panel within the submatrix of
A
, passed to this routine: when called by
?sytrf_aa
, for the first panel,
j1
is 1, while for the remaining panels,
j1
is 2.
m
INTEGER
.
The size of the submatrix.
m
0.
nb
INTEGER
.
The size of the panel to be factorized.
a
REAL
for
slasyf_aa
DOUBLE PRECISION
for
dlasyf_aa
REAL
for
clasyf_aa
COMPLEX*16
for
zlasyf_aa
Array of size
(
lda
,
m
)
for the first panel, and size
(
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, when only the panel is passed.
lda
INTEGER
.
The leading dimension of the array
a
.
lda
max(1,
n
).
h
REAL
for
slasyf_aa
DOUBLE PRECISION
for
dlasyf_aa
REAL
for
clasyf_aa
COMPLEX*16
for
zlasyf_aa
Workspace array of size
(
ldh
,
nb
)
.