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

NAME

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

SYNOPSIS

       SUBROUTINE SSTEDC( COMPZ, N, D, E, Z, LDZ, WORK, LWORK, IWORK, LIWORK, INFO )

           CHARACTER      COMPZ

           INTEGER        INFO, LDZ, LIWORK, LWORK, N

           INTEGER        IWORK( * )

           REAL           D( * ), E( * ), WORK( * ), Z( LDZ, * )

PURPOSE

       SSTEDC computes all eigenvalues and, optionally, eigenvectors of a  symmetric  tridiagonal
       matrix using the divide and conquer method.
        The eigenvectors of a full or band real symmetric matrix can also be
        found if SSYTRD or SSPTRD or SSBTRD has been used to reduce this
        matrix to tridiagonal form.
        This code 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.  See SLAED3 for details.

ARGUMENTS

        COMPZ   (input) CHARACTER*1
                = 'N':  Compute eigenvalues only.
                = 'I':  Compute eigenvectors of tridiagonal matrix also.
                = 'V':  Compute eigenvectors of original dense symmetric
                matrix also.  On entry, Z contains the orthogonal
                matrix used to reduce the original matrix to
                tridiagonal form.

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

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

        E       (input/output) REAL array, dimension (N-1)
                On entry, the subdiagonal elements of the tridiagonal matrix.
                On exit, E has been destroyed.

        Z       (input/output) REAL array, dimension (LDZ,N)
                On entry, if COMPZ = 'V', then Z contains the orthogonal
                matrix used in the reduction to tridiagonal form.
                On exit, if INFO = 0, then if COMPZ = 'V', Z contains the
                orthonormal eigenvectors of the original symmetric matrix,
                and if COMPZ = 'I', Z contains the orthonormal eigenvectors
                of the symmetric tridiagonal matrix.
                If  COMPZ = 'N', then Z is not referenced.

        LDZ     (input) INTEGER
                The leading dimension of the array Z.  LDZ >= 1.
                If eigenvectors are desired, then LDZ >= max(1,N).

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

        LWORK   (input) INTEGER
                The dimension of the array WORK.
                If COMPZ = 'N' or N <= 1 then LWORK must be at least 1.
                If COMPZ = 'V' and N > 1 then LWORK must be at least
                ( 1 + 3*N + 2*N*lg N + 3*N**2 ),
                where lg( N ) = smallest integer k such
                that 2**k >= N.
                If COMPZ = 'I' and N > 1 then LWORK must be at least
                ( 1 + 4*N + N**2 ).
                Note that for COMPZ = 'I' or 'V', then if N is less than or
                equal to the minimum divide size, usually 25, then LWORK need
                only be max(1,2*(N-1)).
                If LWORK = -1, then a workspace query is assumed; the routine
                only calculates the optimal size of the WORK array, returns
                this value as the first entry of the WORK array, and no error
                message related to LWORK 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 COMPZ = 'N' or N <= 1 then LIWORK must be at least 1.
                If COMPZ = 'V' and N > 1 then LIWORK must be at least
                ( 6 + 6*N + 5*N*lg N ).
                If COMPZ = 'I' and N > 1 then LIWORK must be at least
                ( 3 + 5*N ).
                Note that for COMPZ = 'I' or 'V', then if N is less than or
                equal to the minimum divide size, usually 25, then LIWORK
                need only be 1.
                If LIWORK = -1, then a workspace query is assumed; the
                routine only calculates the optimal size of the IWORK array,
                returns this value as the first entry of the IWORK array, and
                no error message related to LIWORK is issued by XERBLA.

        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
        Modified by Francoise Tisseur, University of Tennessee.

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