redhat man page for dptcon

DPTCON(l)								 )								 DPTCON(l)

NAME
       DPTCON  - compute the reciprocal of the condition number (in the 1-norm) of a real symmetric positive definite tridiagonal matrix using the
       factorization A = L*D*L**T or A = U**T*D*U computed by DPTTRF

SYNOPSIS
       SUBROUTINE DPTCON( N, D, E, ANORM, RCOND, WORK, INFO )

	   INTEGER	  INFO, N

	   DOUBLE	  PRECISION ANORM, RCOND

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

PURPOSE
       DPTCON computes the reciprocal of the condition number (in the 1-norm) of a real symmetric positive definite tridiagonal matrix	using  the
       factorization A = L*D*L**T or A = U**T*D*U computed by DPTTRF.  Norm(inv(A)) is computed by a direct method, and the reciprocal of the con-
       dition number is computed as
		    RCOND = 1 / (ANORM * norm(inv(A))).

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

       D       (input) DOUBLE PRECISION array, dimension (N)
	       The n diagonal elements of the diagonal matrix D from the factorization of A, as computed by DPTTRF.

       E       (input) DOUBLE PRECISION array, dimension (N-1)
	       The (n-1) off-diagonal elements of the unit bidiagonal factor U or L from the factorization of A,  as computed by DPTTRF.

       ANORM   (input) DOUBLE PRECISION
	       The 1-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  the	1-norm	of
	       inv(A) computed in this routine.

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

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

FURTHER DETAILS
       The method used is described in Nicholas J. Higham, "Efficient Algorithms for Computing the Condition Number of a Tridiagonal Matrix", SIAM
       J. Sci. Stat. Comput., Vol. 7, No. 1, January 1986.

LAPACK version 3.0						   15 June 2000 							 DPTCON(l)