sspevd()

subroutine sspevd	(	character	jobz,
		character	uplo,
		integer	n,
		real, dimension( * )	ap,
		real, dimension( * )	w,
		real, dimension( ldz, * )	z,
		integer	ldz,
		real, dimension( * )	work,
		integer	lwork,
		integer, dimension( * )	iwork,
		integer	liwork,
		integer	info )

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

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Purpose:

!>
!> SSPEVD computes all the eigenvalues and, optionally, eigenvectors
!> of a real symmetric matrix A in packed storage. If eigenvectors are
!> desired, it uses a divide and conquer algorithm.
!>
!> 

Parameters

[in]	JOBZ	!> JOBZ is CHARACTER*1 !> = 'N': Compute eigenvalues only; !> = 'V': Compute eigenvalues and eigenvectors. !>
[in]	UPLO	!> UPLO is CHARACTER*1 !> = 'U': Upper triangle of A is stored; !> = 'L': Lower triangle of A is stored. !>
[in]	N	!> N is INTEGER !> The order of the matrix A. N >= 0. !>
[in,out]	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. !>
[out]	W	!> W is REAL array, dimension (N) !> If INFO = 0, the eigenvalues in ascending order. !>
[out]	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. !>
[in]	LDZ	!> LDZ is INTEGER !> The leading dimension of the array Z. LDZ >= 1, and if !> JOBZ = 'V', LDZ >= max(1,N). !>
[out]	WORK	!> WORK is REAL array, dimension (MAX(1,LWORK)) !> On exit, if INFO = 0, WORK(1) returns the required LWORK. !>
[in]	LWORK	!> LWORK is INTEGER !> The dimension of the array WORK. !> If N <= 1, LWORK must be at least 1. !> If JOBZ = 'N' and N > 1, LWORK must be at least 2*N. !> If JOBZ = 'V' and N > 1, LWORK must be at least !> 1 + 6*N + N**2. !> !> If LWORK = -1, then a workspace query is assumed; the routine !> only calculates the required sizes of the WORK and IWORK !> arrays, returns these values as the first entries of the WORK !> and IWORK arrays, and no error message related to LWORK or !> LIWORK is issued by XERBLA. !>
[out]	IWORK	!> IWORK is INTEGER array, dimension (MAX(1,LIWORK)) !> On exit, if INFO = 0, IWORK(1) returns the required LIWORK. !>
[in]	LIWORK	!> LIWORK is INTEGER !> The dimension of the array IWORK. !> If JOBZ = 'N' or N <= 1, LIWORK must be at least 1. !> If JOBZ = 'V' and N > 1, LIWORK must be at least 3 + 5*N. !> !> If LIWORK = -1, then a workspace query is assumed; the !> routine only calculates the required sizes of the WORK and !> IWORK arrays, returns these values as the first entries of !> the WORK and IWORK arrays, and no error message related to !> LWORK or LIWORK is issued by XERBLA. !>
[out]	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.