U_cvt_adj_ens

The page document the user-supplied call-back routine U_cvt_adj_ens.

The routine U_cvt_adj_ens is a call-back routine that has to be provided by the user. In the simplified interface the predefined name of the routine is cvt_adj_ens_pdaf, but in the full interface, the user can choose the name of the routine.

The routine is used with the parameterized 3D-Var and the hybrid 3D-Var methods.

The routine is called during the iterative optimization. It has to perform the adjoint of the control vector transform (preconditioning) which is usually a multiplication with the transponse square-root of the background covariance matrix B. The routine is provided with a state vector and has to return a vector in control space. The routine allows a user to implement the control vector transform in form of covariance operators.

The interface for this routine is:

SUBROUTINE U_cvt_adj_ens(iter, dim_p, dim_ens, dim_cv_ens_p, ens_p, Vcv_p, cv_p)

  INTEGER, INTENT(in) :: iter                ! Iteration of optimization
  INTEGER, INTENT(in) :: dim_p               ! PE-local observation dimension
  INTEGER, INTENT(in) :: dim_ens             ! Ensemble size
  INTEGER, INTENT(in) :: dim_cv_ens_p        ! PE-local dimension of control vector
  REAL, INTENT(in) :: ens_p(dim_p, dim_ens)  ! PE-local ensemble
  REAL, INTENT(in)    :: Vcv_p(dim_p)        ! PE-local input vector
  REAL, INTENT(inout) :: cv_p(dim_cv_ens_p)  ! PE-local result vector

Hints:

• If the state vector is decomposed in case of parallelization one needs to take care that the application of the trasformation is complete. This usually requries a communication with MPI_Allreduce to obtain a global sun.