slaed0()

subroutine slaed0	(	integer	icompq,
		integer	qsiz,
		integer	n,
		real, dimension( * )	d,
		real, dimension( * )	e,
		real, dimension( ldq, * )	q,
		integer	ldq,
		real, dimension( ldqs, * )	qstore,
		integer	ldqs,
		real, dimension( * )	work,
		integer, dimension( * )	iwork,
		integer	info )

SLAED0 used by SSTEDC. Computes all eigenvalues and corresponding eigenvectors of an unreduced symmetric tridiagonal matrix using the divide and conquer method.

Download SLAED0 + dependencies [TGZ] [ZIP] [TXT]

Purpose:

!>
!> SLAED0 computes all eigenvalues and corresponding eigenvectors of a
!> symmetric tridiagonal matrix using the divide and conquer method.
!> 

Parameters

[in]	ICOMPQ	!> ICOMPQ is INTEGER !> = 0: Compute eigenvalues only. !> = 1: Compute eigenvectors of original dense symmetric matrix !> also. On entry, Q contains the orthogonal matrix used !> to reduce the original matrix to tridiagonal form. !> = 2: Compute eigenvalues and eigenvectors of tridiagonal !> matrix. !>
[in]	QSIZ	!> QSIZ is INTEGER !> The dimension of the orthogonal matrix used to reduce !> the full matrix to tridiagonal form. QSIZ >= N if ICOMPQ = 1. !>
[in]	N	!> N is INTEGER !> The dimension of the symmetric tridiagonal matrix. N >= 0. !>
[in,out]	D	!> D is REAL array, dimension (N) !> On entry, the main diagonal of the tridiagonal matrix. !> On exit, its eigenvalues. !>
[in]	E	!> E is REAL array, dimension (N-1) !> The off-diagonal elements of the tridiagonal matrix. !> On exit, E has been destroyed. !>
[in,out]	Q	!> Q is REAL array, dimension (LDQ, N) !> On entry, Q must contain an N-by-N orthogonal matrix. !> If ICOMPQ = 0 Q is not referenced. !> If ICOMPQ = 1 On entry, Q is a subset of the columns of the !> orthogonal matrix used to reduce the full !> matrix to tridiagonal form corresponding to !> the subset of the full matrix which is being !> decomposed at this time. !> If ICOMPQ = 2 On entry, Q will be the identity matrix. !> On exit, Q contains the eigenvectors of the !> tridiagonal matrix. !>
[in]	LDQ	!> LDQ is INTEGER !> The leading dimension of the array Q. If eigenvectors are !> desired, then LDQ >= max(1,N). In any case, LDQ >= 1. !>
[out]	QSTORE	!> QSTORE is REAL array, dimension (LDQS, N) !> Referenced only when ICOMPQ = 1. Used to store parts of !> the eigenvector matrix when the updating matrix multiplies !> take place. !>
[in]	LDQS	!> LDQS is INTEGER !> The leading dimension of the array QSTORE. If ICOMPQ = 1, !> then LDQS >= max(1,N). In any case, LDQS >= 1. !>
[out]	WORK	!> WORK is REAL array, !> If ICOMPQ = 0 or 1, the dimension of WORK must be at least !> 1 + 3*N + 2*N*lg N + 3*N**2 !> ( lg( N ) = smallest integer k !> such that 2^k >= N ) !> If ICOMPQ = 2, the dimension of WORK must be at least !> 4*N + N**2. !>
[out]	IWORK	!> IWORK is INTEGER array, !> If ICOMPQ = 0 or 1, the dimension of IWORK must be at least !> 6 + 6*N + 5*N*lg N. !> ( lg( N ) = smallest integer k !> such that 2^k >= N ) !> If ICOMPQ = 2, the dimension of IWORK must be at least !> 3 + 5*N. !>
[out]	INFO	!> INFO is INTEGER !> = 0: successful exit. !> < 0: if INFO = -i, the i-th argument had an illegal value. !> > 0: The algorithm failed to compute an eigenvalue while !> working on the submatrix lying in rows and columns !> INFO/(N+1) through mod(INFO,N+1). !>

Author

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Contributors:

Jeff Rutter, Computer Science Division, University of California at Berkeley, USA