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 eigenvectors of the dense or band matrix.

QSIZ

          QSIZ is INTEGER


         The dimension of the unitary matrix used to reduce


         the full matrix to tridiagonal form.  QSIZ >= N if ICOMPQ = 1.

N

          N is INTEGER


         The dimension of the symmetric tridiagonal matrix.  N >= 0.

D

          D is REAL array, dimension (N)


         On entry, the diagonal elements of the tridiagonal matrix.


         On exit, the eigenvalues in ascending order.

E

          E is REAL array, dimension (N-1)


         On entry, the off-diagonal elements of the tridiagonal matrix.


         On exit, E has been destroyed.

Q

          Q is COMPLEX array, dimension (LDQ,N)


         On entry, Q must contain an QSIZ x N matrix whose columns


         unitarily orthonormal. It is a part of the unitary matrix


         that reduces the full dense Hermitian matrix to a


         (reducible) symmetric tridiagonal matrix.

LDQ

          LDQ is INTEGER


         The leading dimension of the array Q.  LDQ >= max(1,N).

IWORK

          IWORK is 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

          RWORK is REAL array,


                               dimension (1 + 3*N + 2*N*lg N + 3*N**2)


                        ( lg( N ) = smallest integer k


                                    such that 2^k >= N )

QSTORE

          QSTORE is COMPLEX array, dimension (LDQS, N)


         Used to store parts of


         the eigenvector matrix when the updating matrix multiplies


         take place.

LDQS

          LDQS is INTEGER


         The leading dimension of the array QSTORE.


         LDQS >= max(1,N).

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).

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

September 2012