= PDAF_put_state_prepost =

This page documents the routine `PDAF_put_state_prepost` of PDAF. 

The routine is typically called in `assimilate_pdaf` or directly in the model code.

The routine `PDAF_put_state_prepost` is an alternative to the routines `PDAF_put_state_X` where 'X' is the name of a filter method. 
The routine can be used with the 'flexible' implementation variant of PDAF. The purpose of `PDAF_put_state_prepost` is to collect the ensemble information on the processes usually doing the filter analysis. However, in the case of `PDAF_put_state_prepost`, no filter analysis step is performed when the ensemble integration is complete, but only the user-supplied pre/poststep routine is called to allow the user to analyze the forecast ensemble.

The general aspects of the filter specific routines `PDAF_put_state_*` are described on the page [ModifyModelforEnsembleIntegration Modification of the model code for the ensemble integration] and its sub-page on [InsertAnalysisStep inserting the analysis step]. For the 'fully parallel' implementation variant the alternative routine `PDAF_prepost` is used.

The interface is the following:
{{{
  SUBROUTINE PDAF_put_state_prepost(U_collect_state, U_prepoststep, status_pdaf)
}}}
with the following arguments:
 * `U_collect_state`: The name of the user-supplied routine that initializes a state vector from the array holding the ensemble of model states from the model fields. This is basically the inverse operation to `U_distribute_state` used in [ModifyModelforEnsembleIntegration#PDAF_get_state PDAF_get_state].
 * `U_prepoststep`: The name of the pre/poststep routine as in `PDAF_get_state`
 * `status_pdaf`: The integer status flag. It is zero, if `PDAF_put_state_prepost` is exited without errors.


The user-supplied call-back routines are, for example, described on the page on [ImplementAnalysisestkf implementing the analysis step of the ESKTF algorithm].

It is recommended that the value of `status_pdaf` is checked in the program after `PDAF_put_state_prepoststep` is executed. Only if its value is 0 the initialization was successful.

PDAF also has a [PdafSimplifiedInterface Simplified Interface] providing the routine `PDAF_put_state_prepoststep_si`. In the simplified interface, the name of the user-supplied routines have predefined names and do not appear in the call to `PDAF_put_state_prepoststep_si`.  More information on the pre-defined names is provided, e.g., in the [ImplementAnalysisestkf page on implementing the analysis step of the ESTKF algorithm].