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))).

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

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

December 2016

  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.