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

NAME

       LAPACK-3 - estimates the reciprocal of the condition number of a real tridiagonal matrix A
       using the LU factorization as computed by DGTTRF

SYNOPSIS

       SUBROUTINE DGTCON( NORM, N, DL, D, DU, DU2, IPIV, ANORM, RCOND, WORK, IWORK, INFO )

           CHARACTER      NORM

           INTEGER        INFO, N

           DOUBLE         PRECISION ANORM, RCOND

           INTEGER        IPIV( * ), IWORK( * )

           DOUBLE         PRECISION D( * ), DL( * ), DU( * ), DU2( * ), WORK( * )

PURPOSE

       DGTCON estimates the reciprocal of the condition number of a  real  tridiagonal  matrix  A
       using the LU factorization as computed by DGTTRF.
        An estimate is obtained for norm(inv(A)), and the reciprocal of the
        condition number is computed as RCOND = 1 / (ANORM * norm(inv(A))).

ARGUMENTS

        NORM    (input) CHARACTER*1
                Specifies whether the 1-norm condition number or the
                infinity-norm condition number is required:
                = '1' or 'O':  1-norm;
                = 'I':         Infinity-norm.

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

        DL      (input) DOUBLE PRECISION array, dimension (N-1)
                The (n-1) multipliers that define the matrix L from the
                LU factorization of A as computed by DGTTRF.

        D       (input) DOUBLE PRECISION array, dimension (N)
                The n diagonal elements of the upper triangular matrix U from
                the LU factorization of A.

        DU      (input) DOUBLE PRECISION array, dimension (N-1)
                The (n-1) elements of the first superdiagonal of U.

        DU2     (input) DOUBLE PRECISION array, dimension (N-2)
                The (n-2) elements of the second superdiagonal of U.

        IPIV    (input) INTEGER array, dimension (N)
                The pivot indices; for 1 <= i <= n, row i of the matrix was
                interchanged with row IPIV(i).  IPIV(i) will always be either
                i or i+1; IPIV(i) = i indicates a row interchange was not
                required.

        ANORM   (input) DOUBLE PRECISION
                If NORM = '1' or 'O', the 1-norm of the original matrix A.
                If NORM = 'I', the infinity-norm of the original matrix A.

        RCOND   (output) DOUBLE PRECISION
                The reciprocal of the condition number of the matrix A,
                computed as RCOND = 1/(ANORM * AINVNM), where AINVNM is an
                estimate of the 1-norm of inv(A) computed in this routine.

        WORK    (workspace) DOUBLE PRECISION array, dimension (2*N)

        IWORK   (workspace) INTEGER array, dimension (N)

        INFO    (output) INTEGER
                = 0:  successful exit
                < 0:  if INFO = -i, the i-th argument had an illegal value

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