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## dptcon()

subroutine dptcon | ( | integer | n,
|  | double precision, dimension( * ) | d,
|  | double precision, dimension( * ) | e,
|  | double precision | anorm,
|  | double precision | rcond,
|  | double precision, dimension( * ) | work,
|  | integer | info )

DPTCON

Download DPTCON + dependencies [TGZ] [ZIP] [TXT]

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 condition number is computed as
      !>              RCOND = 1 / (ANORM * norm(inv(A))).
      !>

Parameters

  [in]

  N

      !>          N is INTEGER
      !>          The order of the matrix A.  N >= 0.
      !>

  [in]

  D

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

  [in]

  E

      !>          E is 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.
      !>

  [in]

  ANORM

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

  [out]

  WORK

      !>          WORK is DOUBLE PRECISION 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.

Further Details:

      !>
      !>  The method used is described in Nicholas J. Higham, , SIAM J. Sci. Stat. Comput., Vol. 7, No. 1, January 1986.
      !>