## Developer Reference

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

# p?syev

Computes selected eigenvalues and eigenvectors of a symmetric matrix.

## Syntax

Include Files
Description
The
p?syev
routine
computes all eigenvalues and, optionally, eigenvectors of a real symmetric matrix
A
by calling the recommended sequence of ScaLAPACK
routines
.
In its present form, the
routine
assumes a homogeneous system and makes no checks for consistency of the eigenvalues or eigenvectors across the different processes. Because of this, it is possible that a heterogeneous system may return incorrect results without any error messages.
Input Parameters
np
= the number of rows local to a given process.
nq
= the number of columns local to a given process.
jobz
(global)
CHARACTER
.
Must be
'N'
or
'V'
. Specifies if it is necessary to compute the eigenvectors:
If
jobz
=
'N'
, then only eigenvalues are computed.
If
jobz
=
'V'
, then eigenvalues and eigenvectors are computed.
uplo
(global)
CHARACTER
.
Must be
'U'
or
'L'
. Specifies whether the upper or lower triangular part of the symmetric matrix
A
is stored:
If
uplo
=
'U'
,
a
stores the upper triangular part of
A
.
If
uplo
=
'L'
,
a
stores the lower triangular part of
A
.
n
(global)
INTEGER
.
The number of rows and columns of the matrix
A
(
n
0)
.
a
(local)
REAL
for
pssyev
.
DOUBLE PRECISION
for
pdsyev
.
Block cyclic array of global size
(
n
,
n
)
and local size
(
lld_a
,
LOC
c
(
ja
+
n
-1))
. On entry, the symmetric matrix
A
.
If
uplo
=
'U'
, only the upper triangular part of
A
is used to define the elements of the symmetric matrix.
If
uplo
=
'L'
, only the lower triangular part of
A
is used to define the elements of the symmetric matrix.
ia
,
ja
(global)
INTEGER
.
The row and column indices in the global matrix
A
indicating the first row and the first column of the submatrix
A
, respectively.
desca
(global and local)
INTEGER
array of size
dlen_
. The array descriptor for the distributed matrix
A
.
iz
,
jz
(global)
INTEGER
.
The row and column indices in the global matrix
Z
indicating the first row and the first column of the submatrix
Z
, respectively.
descz
(global and local)
INTEGER
array of size
dlen_
. The array descriptor for the distributed matrix
Z
.