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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