DSPEV(3)
computes all the eigenvalues and, optionally, eigenvectors of a real symmetric matrix A in packed storage
SYNOPSIS
 SUBROUTINE DSPEV(

JOBZ, UPLO, N, AP, W, Z, LDZ, WORK, INFO )

CHARACTER
JOBZ, UPLO

INTEGER
INFO, LDZ, N

DOUBLE
PRECISION AP( * ), W( * ), WORK( * ), Z( LDZ, * )
PURPOSE
DSPEV computes all the eigenvalues and, optionally, eigenvectors of a
real symmetric matrix A in packed storage.
ARGUMENTS
 JOBZ (input) CHARACTER*1

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

= 'U': Upper triangle of A is stored;
= 'L': Lower triangle of A is stored.
 N (input) INTEGER

The order of the matrix A. N >= 0.
 AP (input/output) DOUBLE PRECISION 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 jth column of A
is stored in the array AP as follows:
if UPLO = 'U', AP(i + (j1)*j/2) = A(i,j) for 1<=i<=j;
if UPLO = 'L', AP(i + (j1)*(2*nj)/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 (output) DOUBLE PRECISION array, dimension (N)

If INFO = 0, the eigenvalues in ascending order.
 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 ith column of Z
holding the eigenvector associated with W(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 (3*N)

 INFO (output) INTEGER

= 0: successful exit.
< 0: if INFO = i, the ith argument had an illegal value.
> 0: if INFO = i, the algorithm failed to converge; i
offdiagonal elements of an intermediate tridiagonal
form did not converge to zero.