SRC/claed0.f(3)

NAME
SRC/claed0.f

SYNOPSIS

  Functions/Subroutines
subroutine claed0 (qsiz, n, d, e, q, ldq, qstore, ldqs, rwork, iwork, info)
CLAED0 used by CSTEDC. Computes all eigenvalues and corresponding eigenvectors of an unreduced symmetric tridiagonal matrix using the divide and conquer method.

Function/Subroutine Documentation

  subroutine claed0 (integer qsiz, integer n, real, dimension( * ) d, real, dimension( * ) e, complex, dimension( ldq, * ) q, integer ldq, complex, dimension( ldqs, * ) qstore, integer ldqs, real, dimension( * ) rwork, integer, dimension( * ) iwork, integer info)

CLAED0 used by CSTEDC. Computes all eigenvalues and corresponding eigenvectors of an unreduced symmetric tridiagonal matrix using the divide and conquer method.

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 eigenvectors of the dense or band matrix.

Parameters
    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).

Author
    Univ. of Tennessee

    Univ. of California Berkeley

    Univ. of Colorado Denver

    NAG Ltd.

Definition at line 143 of file claed0.f.

Author

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