SRC/dlaed0.f(3)

NAME
SRC/dlaed0.f

SYNOPSIS

  Functions/Subroutines
subroutine dlaed0 (icompq, qsiz, n, d, e, q, ldq, qstore, ldqs, work, iwork, info)
DLAED0 used by DSTEDC. Computes all eigenvalues and corresponding eigenvectors of an unreduced symmetric tridiagonal matrix using the divide and conquer method.

Function/Subroutine Documentation

  subroutine dlaed0 (integer icompq, integer qsiz, integer n, double precision, dimension( * ) d, double precision, dimension( * ) e, double precision, dimension( ldq, * ) q, integer ldq, double precision, dimension( ldqs, * ) qstore, integer ldqs, double precision, dimension( * ) work, integer, dimension( * ) iwork, integer info)

DLAED0 used by DSTEDC. Computes all eigenvalues and corresponding eigenvectors of an unreduced symmetric tridiagonal matrix using the divide and conquer method.

Purpose:

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

Parameters
    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).

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

Definition at line 170 of file dlaed0.f.

Author

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