!>
!> DLAED0 computes all eigenvalues and corresponding eigenvectors of a
!> symmetric tridiagonal matrix using the divide and conquer method.
!> 

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.
!> 

QSIZ

!>          QSIZ is INTEGER
!>         The dimension of the orthogonal 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 DOUBLE PRECISION array, dimension (N)
!>         On entry, the main diagonal of the tridiagonal matrix.
!>         On exit, its eigenvalues.
!> 

E

!>          E is DOUBLE PRECISION array, dimension (N-1)
!>         The off-diagonal elements of the tridiagonal matrix.
!>         On exit, E has been destroyed.
!> 

Q

!>          Q is DOUBLE PRECISION 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.
!> 

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.
!> 

QSTORE

!>          QSTORE is DOUBLE PRECISION array, dimension (LDQS, N)
!>         Referenced only when ICOMPQ = 1.  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.  If ICOMPQ = 1,
!>         then  LDQS >= max(1,N).  In any case,  LDQS >= 1.
!> 

WORK

!>          WORK is DOUBLE PRECISION 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.
!> 

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.
!> 

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.

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