NAME

       slaed0.f -

SYNOPSIS

   Functions/Subroutines
       subroutine slaed0 (ICOMPQ, QSIZ, N, D, E, Q, LDQ, QSTORE, LDQS, WORK, IWORK, INFO)
           SLAED0 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 slaed0 (integerICOMPQ, integerQSIZ, integerN, real, dimension( * )D, real,
       dimension( * )E, real, dimension( ldq, * )Q, integerLDQ, real, dimension( ldqs, * )QSTORE,
       integerLDQS, real, dimension( * )WORK, integer, dimension( * )IWORK, integerINFO)
       SLAED0 used by sstedc. Computes all eigenvalues and corresponding eigenvectors of an
       unreduced symmetric tridiagonal matrix using the divide and conquer method.

       Purpose:

            SLAED0 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 REAL array, dimension (N)
                    On entry, the main diagonal of the tridiagonal matrix.
                    On exit, its eigenvalues.

           E

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

           Q

                     Q is REAL 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 REAL 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 REAL 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.

       Date:
           September 2012

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

       Definition at line 172 of file slaed0.f.

Author

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