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man pages->IRIX man pages -> complib/sstev (3)
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### Contents

```
SSTEV(3F)							     SSTEV(3F)

```

### NAME[Toc][Back]

```     SSTEV - compute all eigenvalues and, optionally, eigenvectors of a	real
symmetric tridiagonal matrix A
```

### SYNOPSIS[Toc][Back]

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

CHARACTER     JOBZ

INTEGER       INFO, LDZ, N

REAL	       D( * ), E( * ), WORK( * ), Z( LDZ, * )
```

### PURPOSE[Toc][Back]

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

```

### ARGUMENTS[Toc][Back]

```     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) REAL 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) REAL array,	dimension (N)
On	entry, the (n-1) subdiagonal elements of the tridiagonal
matrix A, stored in elements 1 to N-1 of E; E(N) need not be set,
but is used by the	routine.  On exit, the contents	of E are
destroyed.

Z	     (output) REAL 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) REAL 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

Page 1

SSTEV(3F)							     SSTEV(3F)

> 0:  if INFO = i,	the algorithm failed to	converge; i offdiagonal
elements of E did	not converge to	zero.
SSTEV(3F)							     SSTEV(3F)

```

### NAME[Toc][Back]

```     SSTEV - compute all eigenvalues and, optionally, eigenvectors of a	real
symmetric tridiagonal matrix A
```

### SYNOPSIS[Toc][Back]

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

CHARACTER     JOBZ

INTEGER       INFO, LDZ, N

REAL	       D( * ), E( * ), WORK( * ), Z( LDZ, * )
```

### PURPOSE[Toc][Back]

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

```

### ARGUMENTS[Toc][Back]

```     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) REAL 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) REAL array,	dimension (N)
On	entry, the (n-1) subdiagonal elements of the tridiagonal
matrix A, stored in elements 1 to N-1 of E; E(N) need not be set,
but is used by the	routine.  On exit, the contents	of E are
destroyed.

Z	     (output) REAL 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) REAL 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

Page 1

SSTEV(3F)							     SSTEV(3F)

> 0:  if INFO = i,	the algorithm failed to	converge; i offdiagonal
elements of E did	not converge to	zero.

PPPPaaaaggggeeee 2222```
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