sspev.f −

**Functions/Subroutines**

subroutine **sspev** (JOBZ, UPLO, N, AP, W, Z, LDZ, WORK, INFO)

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

**subroutine sspev (characterJOBZ, characterUPLO, integerN, real, dimension( * )AP, real, dimension( * )W, real, dimension( ldz, * )Z, integerLDZ, real, dimension( * )WORK, integerINFO)
SSPEV computes the eigenvalues and, optionally, the left and/or right eigenvectors for OTHER matrices**

**Purpose:**

SSPEV computes all the eigenvalues and, optionally, eigenvectors of a

real symmetric matrix A in packed storage.

**Parameters:**

*JOBZ*

JOBZ is CHARACTER*1

= ’N’: Compute eigenvalues only;

= ’V’: Compute eigenvalues and eigenvectors.

*UPLO*

UPLO is CHARACTER*1

= ’U’: Upper triangle of A is stored;

= ’L’: Lower triangle of A is stored.

*N*

N is INTEGER

The order of the matrix A. N >= 0.

*AP*

AP is REAL array, dimension (N*(N+1)/2)

On entry, the upper or lower triangle of the symmetric matrix

A, packed columnwise in a linear array. The j-th column of A

is stored in the array AP as follows:

if UPLO = ’U’, AP(i + (j-1)*j/2) = A(i,j) for 1<=i<=j;

if UPLO = ’L’, AP(i + (j-1)*(2*n-j)/2) = A(i,j) for j<=i<=n.

On exit, AP is overwritten by values generated during the

reduction to tridiagonal form. If UPLO = ’U’, the diagonal

and first superdiagonal of the tridiagonal matrix T overwrite

the corresponding elements of A, and if UPLO = ’L’, the

diagonal and first subdiagonal of T overwrite the

corresponding elements of A.

*W*

W is REAL array, dimension (N)

If INFO = 0, the eigenvalues in ascending order.

*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 W(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 (3*N)

*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 an intermediate tridiagonal

form 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 131 of file sspev.f.

Generated automatically by Doxygen for LAPACK from the source code.