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 implicit QL or QR method

SYNOPSIS

       SUBROUTINE DSTEQR( COMPZ, N, D, E, Z, LDZ, WORK, INFO )

           CHARACTER      COMPZ

           INTEGER        INFO, LDZ, N

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

PURPOSE

       DSTEQR computes all eigenvalues and, optionally, eigenvectors of a  symmetric  tridiagonal
       matrix using the implicit QL or QR method.
        The eigenvectors of a full or band symmetric matrix can also be found
        if DSYTRD or DSPTRD or DSBTRD has been used to reduce this matrix to
        tridiagonal form.

ARGUMENTS

        COMPZ   (input) CHARACTER*1
                = 'N':  Compute eigenvalues only.
                = 'V':  Compute eigenvalues and eigenvectors of the original
                symmetric matrix.  On entry, Z must contain the
                orthogonal matrix used to reduce the original matrix
                to tridiagonal form.
                = 'I':  Compute eigenvalues and eigenvectors of the
                tridiagonal matrix.  Z is initialized to the identity
                matrix.

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

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

        Z       (input/output) DOUBLE PRECISION 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, and if
                eigenvectors are desired, then  LDZ >= max(1,N).

        WORK    (workspace) DOUBLE PRECISION array, dimension (max(1,2*N-2))
                If COMPZ = 'N', then WORK is not referenced.

        INFO    (output) INTEGER
                = 0:  successful exit
                < 0:  if INFO = -i, the i-th argument had an illegal value
                > 0:  the algorithm has failed to find all the eigenvalues in
                a total of 30*N iterations; if INFO = i, then i
                elements of E have not converged to zero; on exit, D
                and E contain the elements of a symmetric tridiagonal
                matrix which is orthogonally similar to the original
                matrix.

 LAPACK routine (version 3.3.1)             April 2011                            DSTEQR(3lapack)