Provided by: liblapack-doc_3.3.1-1_all #### NAME

```       LAPACK-3  -  computes  all  eigenvalues  and, optionally, eigenvectors of a real symmetric
tridiagonal matrix A

```

#### SYNOPSIS

```       SUBROUTINE DSTEV( JOBZ, N, D, E, Z, LDZ, WORK, INFO )

CHARACTER     JOBZ

INTEGER       INFO, LDZ, N

DOUBLE        PRECISION D( * ), E( * ), WORK( * ), Z( LDZ, * )

```

#### PURPOSE

```       DSTEV  computes  all  eigenvalues  and,  optionally,  eigenvectors  of  a  real  symmetric
tridiagonal matrix A.

```

#### ARGUMENTS

```        JOBZ    (input) CHARACTER*1
= 'N':  Compute eigenvalues only;
= 'V':  Compute eigenvalues and eigenvectors.

N       (input) INTEGER
The order of the matrix.  N >= 0.

D       (input/output) DOUBLE PRECISION array, dimension (N)
On entry, the n diagonal elements of the tridiagonal matrix
A.
On exit, if INFO = 0, the eigenvalues in ascending order.

E       (input/output) DOUBLE PRECISION array, dimension (N-1)
On entry, the (n-1) subdiagonal elements of the tridiagonal
matrix A, stored in elements 1 to N-1 of E.
On exit, the contents of E are destroyed.

Z       (output) DOUBLE PRECISION array, dimension (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 D(i).
If JOBZ = 'N', then Z is not referenced.

LDZ     (input) INTEGER
The leading dimension of the array Z.  LDZ >= 1, and if
JOBZ = 'V', LDZ >= max(1,N).

WORK    (workspace) DOUBLE PRECISION array, dimension (max(1,2*N-2))
If JOBZ = 'N', WORK is not referenced.

INFO    (output) INTEGER
= 0:  successful exit
< 0:  if INFO = -i, the i-th argument had an illegal value
> 0:  if INFO = i, the algorithm failed to converge; i
off-diagonal elements of E did not converge to zero.

LAPACK driver routine (version 3.2)        April 2011                             DSTEV(3lapack)
```