= PDAF_get_state =

This page documents the routine `PDAF_get_state` of PDAF.

The routine `PDAF_get_state` has to be called once at the end of the initialization of PDAF. Usually, the call will be added to the routine `init_pdaf` that was discussed on the [InitPdaf page on initializing PDAF]. 

The routine `PDAF_get_state` has the purpose to initialize the model fields to be propagates from the array holding the ensemble states. In addition, the routine can initialized the information, whether further model integrations have to be computed and how many time steps have to be performed. For the fully-parallel implementation variant, the number of time steps is used inside PDAF, while the flag on further model integrations is not used.

The interface of `PDAF_get_state` is the following:
{{{
  SUBROUTINE PDAF_get_state(nsteps, timenow, doexit, U_next_observation, U_distribute_state, &
                            U_prepoststep, status)
}}}
with the following arguments:
 * `nsteps`: An integer specifying upon exit the number of time steps to be performed
 * `timenow`: A real specifying upon exit the current model time. (This value is usually not used in the fully-parallel implemenation variant)
 * `doexit`: An integer variable defining whether the assimilation process is completed. For compatibility 1 should be used for exit, 0 for continuing. (This value is not used in the fully-parallel implemenation variant)
 * `U_next_observation`: The name of a user supplied routine that initializes the variables `nsteps`, `timenow`, and `doexit`
 * `U_distribute_state`: The name of a user supplied routine that initializes the model fields from the array holding the ensemble of model state vectors
 * `U_prepoststep`: The name of a user supplied routine that is called before and after the analysis step. Here the user has the possibility to access the state ensemble and can e.g. compute estimated variances or can write the ensemble states the state estimate into files.
 * `status`: The integer status flag. It is zero, if `PDAF_get_state` is exited without errors.

The specifications of the user-supplied routines (`U_next_observation`, `U_distribute_state`, `U_prepoststep`) are documented on the page on [InsertAnalysisStep inserting the analysis step].

PDAF also has a [PdafSimplifiedInterface Simplified Interface] providing the routine '[wiki:PDAF_get_state_si]'. In the simplified interface, the names of all user-supplied call back routines are predefined such that they not appear in the call to `PDAF_get_state_si`. More information on the pre-defined names is provided in the [PdafSimplifiedInterface documentation of PDAF's simplified interface].