DSPEV(l) ) DSPEV(l)
DSPEV - compute all the eigenvalues and, optionally, eigenvectors of a real symmetric
matrix A in packed storage
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, * )
DSPEV computes all the eigenvalues and, optionally, eigenvectors of a real symmetric
matrix A in packed storage.
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 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 diago-
nal 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 i-th 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 >=
WORK (workspace) DOUBLE PRECISION array, dimension (3*N)
INFO (output) 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.
LAPACK version 3.0 15 June 2000 DSPEV(l)