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NAME
     dgtcon - estimate 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( *
               )



     #include <sunperf.h>

     void dgtcon(char norm, int n, double *dl, double *d,  double
               *du,  double *du2, int *ipivot, double anorm, dou-
               ble *drcond, int *info) ;

PURPOSE
     DGTCON estimates the reciprocal of the condition number of a
     real tridiagonal matrix A using the LU factorization as com-
     puted 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  indi-
               cates 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 ille-
               gal value

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