Developer Reference

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

p?latrd

Reduces the first
nb
rows and columns of a symmetric/Hermitian matrix
A
to real tridiagonal form by an orthogonal/unitary similarity transformation.

Syntax

call pslatrd
(
uplo
,
n
,
nb
,
a
,
ia
,
ja
,
desca
,
d
,
e
,
tau
,
w
,
iw
,
jw
,
descw
,
work
)
call pdlatrd
(
uplo
,
n
,
nb
,
a
,
ia
,
ja
,
desca
,
d
,
e
,
tau
,
w
,
iw
,
jw
,
descw
,
work
)
call pclatrd
(
uplo
,
n
,
nb
,
a
,
ia
,
ja
,
desca
,
d
,
e
,
tau
,
w
,
iw
,
jw
,
descw
,
work
)
call pzlatrd
(
uplo
,
n
,
nb
,
a
,
ia
,
ja
,
desca
,
d
,
e
,
tau
,
w
,
iw
,
jw
,
descw
,
work
)
Description
The
p?latrd
routine
reduces
nb
rows and columns of a real symmetric or complex Hermitian matrix sub(
A
)=
A
(
ia
:
ia
+
n
-1
,
ja
:
ja
+
n
-1)
to symmetric/complex tridiagonal form by an orthogonal/unitary similarity transformation
Q'
*sub(
A
)*
Q
, and returns the matrices
V
and
W
, which are needed to apply the transformation to the unreduced part of sub(
A
).
If
uplo
=
U
,
p?latrd
reduces the last
nb
rows and columns of a matrix, of which the upper triangle is supplied;
if
uplo
=
L
,
p?latrd
reduces the first
nb
rows and columns of a matrix, of which the lower triangle is supplied.
This is an auxiliary
routine
called by
p?sytrd
/
p?hetrd
.
Input Parameters
uplo
(global)
CHARACTER
.
Specifies whether the upper or lower triangular part of the symmetric/Hermitian matrix sub(
A
) is stored:
=
'U'
: Upper triangular
=
L
: Lower triangular.
n
(global)
INTEGER
.
The number of rows and columns to be operated on, that is, the order of the distributed matrix sub(
A
).
n
0
.
nb
(global)
INTEGER
.