PDAF_diag_rmsd

This page documents the routine PDAF_diag_rmsd of PDAF, which was introduced with PDAF V3.0.

This routine computes root mean square difference (RMSD) beween two input vectors. These could be the ensemble mean state and a reference state.

The routine can be called in the pre/poststep routine of PDAF both before and after the analysis step to compute the ensemble statistics.

This variant computes the RMSD for the state vectors stateA and stateB over the full decomposed domain of a parallel model. The variant without parallelization is PDAF_diag_rmsd_nompi.

The interface is:

SUBROUTINE PDAF_diag_rmsd(dim_p, stateA_p, stateB_p, &
     rmsd_p, COMM_filter, status)

  INTEGER, INTENT(in) :: dim_p                 !< state dimension
  REAL, INTENT(in)    :: stateA_p(dim_p)       !< State vector A
  REAL, INTENT(in)    :: stateB_p(dim_p)       !< State vector B
  REAL, INTENT(out)   :: rmsd_p                !< RSMD
  INTEGER, INTENT(in) :: COMM_filter           !< Filter communicator
  INTEGER, INTENT(out) :: status               !< Status flag (0=success)

Note:

• * The routine is used to compute the RMSD between two state vectors. To compute the ensemble-sampled standard deviation, i.e. the estimated RMSD from the data assimilation, there are the routines PDAF_diag_stddev_nompi and PDAF_diag_stddev.
• The routine performs MPI operations to obtain the global result. These operations are done within the communicator COMM_filter which is specified as an argument. This allows to also use the routine if PDAF was not initialized by calling PDAF_init.