DGTCON(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 1norm condition number or the
infinitynorm condition number is required:
= '1' or 'O': 1norm;
= 'I': Infinitynorm.
 N (input) INTEGER

The order of the matrix A. N >= 0.
 DL (input) DOUBLE PRECISION array, dimension (N1)

The (n1) 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 (N1)

The (n1) elements of the first superdiagonal of U.
 DU2 (input) DOUBLE PRECISION array, dimension (N2)

The (n2) 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 1norm of the original matrix A.
If NORM = 'I', the infinitynorm 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 1norm 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 ith argument had an illegal value