Contents

# ?stev

Computes all eigenvalues and, optionally, eigenvectors of a real symmetric tridiagonal matrix.

## Syntax

Include Files
• mkl.h
Description
The routine computes all eigenvalues and, optionally, eigenvectors of a real symmetric tridiagonal matrix
A
.
Input Parameters
matrix_layout
Specifies whether matrix storage layout is row major (
LAPACK_ROW_MAJOR
) or column major (
LAPACK_COL_MAJOR
).
jobz
Must be
'N'
or
'V'
.
If
jobz
=
'N'
, then only eigenvalues are computed.
If
jobz
=
'V'
, then eigenvalues and eigenvectors are computed.
n
The order of the matrix
A
(
n
0
).
d
,
e
Arrays:
Array
d
contains the
n
diagonal elements of the tridiagonal matrix
A
.
The size of
d
must be at least max(1,
n
).
Array
e
contains the
n
-1 subdiagonal elements of the tridiagonal matrix
A
.
The size of
e
must be at least max(1,
n
). The
n
-th element of this array is used as workspace.
ldz
The leading dimension of the output array
z
;
ldz
1
. If
jobz
=
'V'
then
ldz
max
(1,
n
).
Output Parameters
d
On exit, if
info
= 0
, contains the eigenvalues of the matrix
A
in ascending order.
z
Array, size
(size max(1,
ldz
*
n
))
.
If
jobz
=
'V'
, then if
info
= 0
,
z
contains the orthonormal eigenvectors of the matrix
A
, with the
i
-th column of
z
holding the eigenvector associated with the eigenvalue returned in
d
[
i
- 1]
.
If
job
=
'N'
, then
z
is not referenced.
e
On exit, this array is overwritten with intermediate results.
Return Values
This function returns a value
info
.
If
info
=0
, the execution is successful.
If
info
=
-i
, the
i
-th parameter had an illegal value.
If
info
=
i
, then the algorithm failed to converge;
i
elements of
e
did not converge to zero.

#### Product and Performance Information

1

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