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DSPEV(1) LAPACK driver routine (version 3.2) DSPEV(1)

NAME

DSPEV - computes all the eigenvalues and, optionally, eigenvectors of a real symmetric matrix A in packed storage

SYNOPSIS

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

= 'N': Compute eigenvalues only;
= 'V': Compute eigenvalues and eigenvectors.

= 'U': Upper triangle of A is stored;
= 'L': Lower triangle of A is stored.
The order of the matrix A. N >= 0.
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.
If INFO = 0, the eigenvalues in ascending order.
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.
The leading dimension of the array Z. LDZ >= 1, and if JOBZ = 'V', LDZ >= max(1,N).
= 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.
November 2008 LAPACK driver routine (version 3.2)