sstev.f −

**Functions/Subroutines**

subroutine **sstev** (JOBZ, N, D, E, Z, LDZ, WORK, INFO)

SSTEV computes the eigenvalues and, optionally, the left and/or right eigenvectors for OTHER matrices

**subroutine sstev (characterJOBZ, integerN, real, dimension( * )D, real, dimension( * )E, real, dimension( ldz, * )Z, integerLDZ, real, dimension( * )WORK, integerINFO)
SSTEV computes the eigenvalues and, optionally, the left and/or right eigenvectors for OTHER matrices**

**Purpose:**

SSTEV computes all eigenvalues and, optionally, eigenvectors of a

real symmetric tridiagonal matrix A.

**Parameters:**

*JOBZ*

JOBZ is CHARACTER*1

= ’N’: Compute eigenvalues only;

= ’V’: Compute eigenvalues and eigenvectors.

*N*

N is INTEGER

The order of the matrix. N >= 0.

*D*

D is 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*

E is REAL 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*

Z is 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*

LDZ is INTEGER

The leading dimension of the array Z. LDZ >= 1, and if

JOBZ = ’V’, LDZ >= max(1,N).

*WORK*

WORK is REAL array, dimension (max(1,2*N-2))

If JOBZ = ’N’, WORK is not referenced.

*INFO*

INFO is 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.

**Author:**

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

**Date:**

November 2011

Definition at line 117 of file sstev.f.

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