ssyev.f −

**Functions/Subroutines**

subroutine **ssyev** (JOBZ, UPLO, N, A, LDA, W, WORK, LWORK, INFO)

SSYEV computes the eigenvalues and, optionally, the left and/or right eigenvectors for SY matrices

**subroutine ssyev (characterJOBZ, characterUPLO, integerN, real, dimension( lda, * )A, integerLDA, real, dimension( * )W, real, dimension( * )WORK, integerLWORK, integerINFO)
SSYEV computes the eigenvalues and, optionally, the left and/or right eigenvectors for SY matrices**

**Purpose:**

SSYEV computes all eigenvalues and, optionally, eigenvectors of a

real symmetric matrix A.

**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.

*A*

A is REAL array, dimension (LDA, N)

On entry, the symmetric matrix A. If UPLO = ’U’, the

leading N-by-N upper triangular part of A contains the

upper triangular part of the matrix A. If UPLO = ’L’,

the leading N-by-N lower triangular part of A contains

the lower triangular part of the matrix A.

On exit, if JOBZ = ’V’, then if INFO = 0, A contains the

orthonormal eigenvectors of the matrix A.

If JOBZ = ’N’, then on exit the lower triangle (if UPLO=’L’)

or the upper triangle (if UPLO=’U’) of A, including the

diagonal, is destroyed.

*LDA*

LDA is INTEGER

The leading dimension of the array A. LDA >= max(1,N).

*W*

W is REAL array, dimension (N)

If INFO = 0, the eigenvalues in ascending order.

*WORK*

WORK is REAL array, dimension (MAX(1,LWORK))

On exit, if INFO = 0, WORK(1) returns the optimal LWORK.

*LWORK*

LWORK is INTEGER

The length of the array WORK. LWORK >= max(1,3*N-1).

For optimal efficiency, LWORK >= (NB+2)*N,

where NB is the blocksize for SSYTRD returned by ILAENV.

If LWORK = -1, then a workspace query is assumed; the routine

only calculates the optimal size of the WORK array, returns

this value as the first entry of the WORK array, and no error

message related to LWORK is issued by XERBLA.

*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 133 of file ssyev.f.

Generated automatically by Doxygen for LAPACK from the source code.