## Developer Reference

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

# p?syevd

Computes all eigenvalues and eigenvectors of a real symmetric matrix by using a divide and conquer algorithm.

## Syntax

Include Files
Description
The
p?syevd
routine
computes all eigenvalues and eigenvectors of a real symmetric matrix
A
by using a divide and conquer algorithm.
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*1
.
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*1
.
Must be
'U'
or
'L'
.
Specifies whether the upper or lower triangular part of the Hermitian 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
pssyevd
DOUBLE PRECISION
for
pdsyevd
.
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
. If
desca
(
ctxt_
)
is incorrect,
p?syevd
cannot guarantee correct error reporting.
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
.
descz
(
ctxt_
)
must equal
desca
(
ctxt_
)
.
work
(local).
REAL
for
pssyevd
DOUBLE PRECISION
for
pdsyevd
.
Array of size
lwork
.
lwork
(local)
INTEGER
.
The size of the array
work
.
If eigenvalues are requested:
lwork
max( 1+6*
n
+ 2*
np
*
nq
,