PDAF_diag_rsmd_nompi

This page documents the routine PDAF_diag_rmsd_nompi 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 only computes the standard deviation for the provided state vectors stateA and stateB without considering parallelization. Thus, with a domain-decomposed parallel model, the value of the RMSD does not consider the full domain. The variant taking into account parallelization is PDAF_diag_rmsd.

The interface is:

SUBROUTINE PDAF_diag_rmsd_nompi(dim_p, stateA_p, stateB_p, &
     rmsd_p, 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(out) :: status               !< Status flag (0=success)

Note:

• The routine is used to compute the RMSD with regard to some reference state. 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.
• We recommend to use this routine only in cases where the MPI parallelization is not initialized, e.g. in separate post-analysis programs. In assimilation programs, where the parallelization is initialized for PDAF, we recommend to use the routine PDAF_diag_rmsd for better overall compatibility.
• The routine does not perform any MPI operations and can also be used if PDAF was not initialized by calling PDAF_init.