NAME

       claed0.f -

SYNOPSIS

   Functions/Subroutines
       subroutine claed0 (QSIZ, N, D, E, Q, LDQ, QSTORE, LDQS, RWORK, IWORK, INFO)
           CLAED0 used by sstedc. 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 sstedc. 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.

       Date:
           September 2012

Author

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