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

NAME

       LAPACK-3  -  computes  all  eigenvalues  and, optionally, eigenvectors of a real symmetric
       tridiagonal matrix

SYNOPSIS

       SUBROUTINE DSTEVD( JOBZ, N, D, E, Z, LDZ, WORK, LWORK, IWORK, LIWORK, INFO )

           CHARACTER      JOBZ

           INTEGER        INFO, LDZ, LIWORK, LWORK, N

           INTEGER        IWORK( * )

           DOUBLE         PRECISION D( * ), E( * ), WORK( * ), Z( LDZ, * )

PURPOSE

       DSTEVD computes  all  eigenvalues  and,  optionally,  eigenvectors  of  a  real  symmetric
       tridiagonal matrix. If eigenvectors are desired, it
        uses a divide and conquer algorithm.
        The divide and conquer algorithm makes very mild assumptions about
        floating point arithmetic. It will work on machines with a guard
        digit in add/subtract, or on those binary machines without guard
        digits which subtract like the Cray X-MP, Cray Y-MP, Cray C-90, or
        Cray-2. It could conceivably fail on hexadecimal or decimal machines
        without guard digits, but we know of none.

ARGUMENTS

        JOBZ    (input) CHARACTER*1
                = 'N':  Compute eigenvalues only;
                = 'V':  Compute eigenvalues and eigenvectors.

        N       (input) INTEGER
                The order of the matrix.  N >= 0.

        D       (input/output) DOUBLE PRECISION array, dimension (N)
                On entry, the n diagonal elements of the tridiagonal matrix
                A.
                On exit, if INFO = 0, the eigenvalues in ascending order.

        E       (input/output) DOUBLE PRECISION array, dimension (N-1)
                On entry, the (n-1) subdiagonal elements of the tridiagonal
                matrix A, stored in elements 1 to N-1 of E.
                On exit, the contents of E are destroyed.

        Z       (output) DOUBLE PRECISION array, dimension (LDZ, N)
                If JOBZ = 'V', then if INFO = 0, Z contains the orthonormal
                eigenvectors of the matrix A, with the i-th column of Z
                holding the eigenvector associated with D(i).
                If JOBZ = 'N', then Z is not referenced.

        LDZ     (input) INTEGER
                The leading dimension of the array Z.  LDZ >= 1, and if
                JOBZ = 'V', LDZ >= max(1,N).

        WORK    (workspace/output) DOUBLE PRECISION array,
                dimension (LWORK)
                On exit, if INFO = 0, WORK(1) returns the optimal LWORK.

        LWORK   (input) INTEGER
                The dimension of the array WORK.
                If JOBZ  = 'N' or N <= 1 then LWORK must be at least 1.
                If JOBZ  = 'V' and N > 1 then LWORK must be at least
                ( 1 + 4*N + N**2 ).
                If LWORK = -1, then a workspace query is assumed; the routine
                only calculates the optimal sizes of the WORK and IWORK
                arrays, returns these values as the first entries of the WORK
                and IWORK arrays, and no error message related to LWORK or
                LIWORK is issued by XERBLA.

        IWORK   (workspace/output) INTEGER array, dimension (MAX(1,LIWORK))
                On exit, if INFO = 0, IWORK(1) returns the optimal LIWORK.

        LIWORK  (input) INTEGER
                The dimension of the array IWORK.
                If JOBZ  = 'N' or N <= 1 then LIWORK must be at least 1.
                If JOBZ  = 'V' and N > 1 then LIWORK must be at least 3+5*N.
                If LIWORK = -1, then a workspace query is assumed; the
                routine only calculates the optimal sizes of the WORK and
                IWORK arrays, returns these values as the first entries of
                the WORK and IWORK arrays, and no error message related to
                LWORK or LIWORK is issued by XERBLA.

        INFO    (output) INTEGER
                = 0:  successful exit
                < 0:  if INFO = -i, the i-th argument had an illegal value
                > 0:  if INFO = i, the algorithm failed to converge; i
                off-diagonal elements of E did not converge to zero.

 LAPACK driver routine (version 3.2)        April 2011                            DSTEVD(3lapack)