CLAED0(l) ) CLAED0(l)NAME
CLAED0 - the divide and conquer method, CLAED0 computes all eigenvalues
of a symmetric tridiagonal matrix which is one diagonal block of those
from reducing a dense or band Hermitian matrix and corresponding eigen‐
vectors of the dense or band matrix
SYNOPSIS
SUBROUTINE CLAED0( QSIZ, N, D, E, Q, LDQ, QSTORE, LDQS, RWORK, IWORK,
INFO )
INTEGER INFO, LDQ, LDQS, N, QSIZ
INTEGER IWORK( * )
REAL D( * ), E( * ), RWORK( * )
COMPLEX Q( LDQ, * ), QSTORE( LDQS, * )
PURPOSE
Using the divide and conquer method, CLAED0 computes all eigenvalues of
a symmetric tridiagonal matrix which is one diagonal block of those
from reducing a dense or band Hermitian matrix and corresponding eigen‐
vectors of the dense or band matrix.
ARGUMENTS
QSIZ (input) INTEGER
The dimension of the unitary matrix used to reduce the full
matrix to tridiagonal form. QSIZ >= N if ICOMPQ = 1.
N (input) INTEGER
The dimension of the symmetric tridiagonal matrix. N >= 0.
D (input/output) REAL array, dimension (N)
On entry, the diagonal elements of the tridiagonal matrix. On
exit, the eigenvalues in ascending order.
E (input/output) REAL array, dimension (N-1)
On entry, the off-diagonal elements of the tridiagonal matrix.
On exit, E has been destroyed.
Q (input/output) COMPLEX array, dimension (LDQ,N)
On entry, Q must contain an QSIZ x N matrix whose columns uni‐
tarily orthonormal. It is a part of the unitary matrix that
reduces the full dense Hermitian matrix to a (reducible) symmet‐
ric tridiagonal matrix.
LDQ (input) INTEGER
The leading dimension of the array Q. LDQ >= max(1,N).
IWORK (workspace) INTEGER array,
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 )
RWORK (workspace) REAL array,
dimension (1 + 3*N + 2*N*lg N + 3*N**2) ( lg( N ) = smallest
integer k such that 2^k >= N )
QSTORE (workspace) COMPLEX array, dimension (LDQS, N) Used to
store parts of the eigenvector matrix when the updating matrix
multiplies take place.
LDQS (input) INTEGER
The leading dimension of the array QSTORE. LDQS >= max(1,N).
INFO (output) 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 work‐
ing on the submatrix lying in rows and columns INFO/(N+1)
through mod(INFO,N+1).
LAPACK version 3.0 15 June 2000 CLAED0(l)
