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LAPACK version 3.0
dptcon(3)

PURPOSE
  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

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

      INTEGER	     INFO, N

      DOUBLE	     PRECISION ANORM, RCOND

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

DESCRIPTION
  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 condition 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.