dgtcon()

subroutine dgtcon	(	character	norm,
		integer	n,
		double precision, dimension( * )	dl,
		double precision, dimension( * )	d,
		double precision, dimension( * )	du,
		double precision, dimension( * )	du2,
		integer, dimension( * )	ipiv,
		double precision	anorm,
		double precision	rcond,
		double precision, dimension( * )	work,
		integer, dimension( * )	iwork,
		integer	info )

DGTCON

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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))).
!> 

Parameters

[in]	NORM	!> NORM is 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. !>
[in]	N	!> N is INTEGER !> The order of the matrix A. N >= 0. !>
[in]	DL	!> DL is 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. !>
[in]	D	!> D is DOUBLE PRECISION array, dimension (N) !> The n diagonal elements of the upper triangular matrix U from !> the LU factorization of A. !>
[in]	DU	!> DU is DOUBLE PRECISION array, dimension (N-1) !> The (n-1) elements of the first superdiagonal of U. !>
[in]	DU2	!> DU2 is DOUBLE PRECISION array, dimension (N-2) !> The (n-2) elements of the second superdiagonal of U. !>
[in]	IPIV	!> IPIV is 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. !>
[in]	ANORM	!> ANORM is 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. !>
[out]	RCOND	!> RCOND is 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. !>
[out]	WORK	!> WORK is DOUBLE PRECISION array, dimension (2*N) !>
[out]	IWORK	!> IWORK is INTEGER array, dimension (N) !>
[out]	INFO	!> INFO is INTEGER !> = 0: successful exit !> < 0: if INFO = -i, the i-th argument had an illegal value !>

Author

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.