= PDAFomi_diag_stats = 

This page documents the routine `PDAFomi_diag_stats` of PDAF, which was introduced with PDAF V3.0. This is part of the PDAF-OMI observation diagnostics module. 

The routine returns 
a pointer to an array of a selection of 6 statistics comparing the observations and the observed ensemble mean for each observation type. 

Usually all PDAFomi_diag routines are called in `prepoststep_pdaf` where the observation information can be retrieved and analyzed. These statistics can, for exmaple, be used to plot a Taylor diagram.

The interface is the following: 
{{{
  SUBROUTINE PDAFomi_diag_stats(nobs, obsstats_ptr, verbose)
}}}
with the following arguments:
{{{
    INTEGER, INTENT(inout) :: nobs                     ! Number of observation types
    REAL, POINTER, INTENT(inout) :: obsstats_ptr(:,:)  ! Array of observation statistics
          ! Included statistics are:
          !  (1,:) correlations between observation and observed ensemble mean
          !  (2,:) centered RMSD between observation and observed ensemble mean
          !  (3,:) mean bias for observation minus observed ensemble mean
          !  (4,:) mean absolute difference between observation and observed ensemble mean
          !  (5,:) variance of observations
          !  (6,:) variance of observed ensemble mean
    INTEGER, INTENT(in) :: verbose                     ! Verbosity flag
}}}

**Note:**
 * The computed statistics are for the global model domain. Thus, in case of a parallelized model, all process sub-domains are taken into account and calling `PDAFomi_diag_stats` will return the same value for all processes.
 * In Fortran user code the pointer should be declared in the form[[BR]] `REAL, POINTER :: obsstats_ptr(:)`[[BR]] It does not need to be allocated.. The target array has the size `(6, nobs)`.
 * If the observation diagnostics have not be activated by using [wiki:PDAFomi_set_obs_diag] the pointer array will not be set and `nobs=0` is. One can check this value before assessing the pointer array
 * The routine returns the centered RMSD as displayed in Taylor diagrams. The non-centered RMSD can be computed using [wiki:PDAFomi_diag_obs_rmsd].