dptcon.f(3)

NAME
dptcon.f -

SYNOPSIS

  Functions/Subroutines
subroutine dptcon (N, D, E, ANORM, RCOND, WORK, INFO)
DPTCON

Function/Subroutine Documentation

  subroutine dptcon (integerN, double precision, dimension( * )D, double precision, dimension( * )E, double precisionANORM, double precisionRCOND, double precision, dimension( * )WORK, integerINFO)

DPTCON

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:
    N

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

    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.

    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.

    ANORM

              ANORM is DOUBLE PRECISION
              The 1-norm of the original matrix A.

    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.

    WORK

              WORK is DOUBLE PRECISION array, dimension (N)

    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.

Date:
    September 2012

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.

Definition at line 119 of file dptcon.f.

Author

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