LAPACK 3.11.0
LAPACK: Linear Algebra PACKage

◆ cptcon()

subroutine cptcon ( integer  N,
real, dimension( * )  D,
complex, dimension( * )  E,
real  ANORM,
real  RCOND,
real, dimension( * )  RWORK,
integer  INFO 
)

CPTCON

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

Purpose:
 CPTCON computes the reciprocal of the condition number (in the
 1-norm) of a complex Hermitian positive definite tridiagonal matrix
 using the factorization A = L*D*L**H or A = U**H*D*U computed by
 CPTTRF.

 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 REAL array, dimension (N)
          The n diagonal elements of the diagonal matrix D from the
          factorization of A, as computed by CPTTRF.
[in]E
          E is COMPLEX 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 CPTTRF.
[in]ANORM
          ANORM is REAL
          The 1-norm of the original matrix A.
[out]RCOND
          RCOND is REAL
          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]RWORK
          RWORK is REAL 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, "Efficient
  Algorithms for Computing the Condition Number of a Tridiagonal
  Matrix", SIAM J. Sci. Stat. Comput., Vol. 7, No. 1, January 1986.