Provided by: liblapack-doc_3.3.1-1_all bug

NAME

       LAPACK-3  -  computes  all  eigenvalues  and  corresponding  eigenvectors  of  a symmetric
       tridiagonal matrix using the divide and conquer method

SYNOPSIS

       SUBROUTINE DLAED0( ICOMPQ, QSIZ, N, D, E, Q, LDQ, QSTORE, LDQS, WORK, IWORK, INFO )

           INTEGER        ICOMPQ, INFO, LDQ, LDQS, N, QSIZ

           INTEGER        IWORK( * )

           DOUBLE         PRECISION D( * ), E( * ), Q( LDQ, * ), QSTORE( LDQS, * ), WORK( * )

PURPOSE

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

ARGUMENTS

        ICOMPQ  (input) 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   (input) INTEGER
               The dimension of the orthogonal matrix used to reduce
               the full matrix to tridiagonal form.  QSIZ >= N if ICOMPQ = 1.

        N      (input) INTEGER
               The dimension of the symmetric tridiagonal matrix.  N >= 0.

        D      (input/output) DOUBLE PRECISION array, dimension (N)
               On entry, the main diagonal of the tridiagonal matrix.
               On exit, its eigenvalues.

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

        Q      (input/output) 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    (input) INTEGER
               The leading dimension of the array Q.  If eigenvectors are
               desired, then  LDQ >= max(1,N).  In any case,  LDQ >= 1.
               QSTORE (workspace) 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   (input) INTEGER
               The leading dimension of the array QSTORE.  If ICOMPQ = 1,
               then  LDQS >= max(1,N).  In any case,  LDQS >= 1.

        WORK   (workspace) DOUBLE PRECISION array,
               If ICOMPQ = 0 or 1, the dimension of WORK must be at least
               1 + 3*N + 2*N*lg N + 2*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  (workspace) 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   (output) 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).

FURTHER DETAILS

        Based on contributions by
           Jeff Rutter, Computer Science Division, University of California
           at Berkeley, USA

 LAPACK routine (version 3.2)               April 2011                            DLAED0(3lapack)