= U_init_obsvars =

The page documents the user-supplied call-back routine `U_init_obsvars`, which was introduced with PDAF V3.0.

The routine `U_init_obsvars` is a call-back routine that has to be provided by the user.  The typical name in user code is `init_obsvars_pdaf`, but the user can choose the name.
The routine is used only with the ENSRF/EAKF. 

The routine is called by PDAF during the analysis step and has to provide the filter with a vector of observation error variances.

The interface is:
{{{
SUBROUTINE U_init_obsvars(step, dim_obs_f, var_f)

  INTEGER, INTENT(in) :: step           ! Current time step
  INTEGER, INTENT(in) :: dim_obs_f      ! Dimension of full observation vector
  REAL, INTENT(out) :: var_f(dim_obs_f) ! vector of observation error variances
}}}

The variance vector `var_f` is for the full observation vector.