= PDAF_assimilate_lnetf = 

This page documents the routine `PDAF_assimilate_lnetf` of PDAF. 

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

The general aspects of the filter specific routines `PDAF_assimilate_*` 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]. The routine is used in the fully-parallel implementation variant of the data assimilation system. When the 'flexible' implementation variant, the routines `PDAF_put_state_*' are used. 

The interface when using the LNETF algorithm is the following:
{{{
  SUBROUTINE PDAF_assimilate_lnetf(U_collect_state, U_distribute_state, U_init_dim_obs_f, U_obs_op_f, &
                                  U_init_obs_f, U_init_obs_l, U_prepoststep, U_likelihood_l, &
                                  U_init_n_domains, U_init_dim_l, U_init_dim_obs_l, &
                                  U_g2l_state, U_l2g_state, U_g2l_obs, &
                                  U_init_obsvar, U_init_obsvar_l, U_next_observation, 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_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_init_dim_obs_f`: The name of the user-supplied routine that provides the size of the full observation vector
 * `U_obs_op_f`: The name of the user-supplied routine that acts as the full observation operator on some state vector
 * `U_init_obs_f`: The name of the user-supplied routine that initializes the full vector of observations
 * `U_init_obs_l`: The name of the user-supplied routine that initializes the vector of observations for a local analysis domain
 * `U_prepoststep`: The name of the pre/poststep routine as in `PDAF_get_state`
 * `U_likelihood_l`: The name of the user-supplied routine that computes the local likelihood of an ensemble state.
 * `U_init_n_domains`: The name of the routine that provides the number of local analysis domains
 * `U_init_dim_l`: The name of the routine that provides the state dimension for a local analysis domain
 * `U_init_dim_obs_l`: The name of the routine that initializes the size of the observation vector for a local analysis domain
 * `U_g2l_state`: The name of the routine that initializes a local state vector from the global state vector
 * `U_l2g_state`: The name of the routine that initializes the corresponding part of the global state vector from the the provided local state vector
 * `U_g2l_obs`: The name of the routine that initializes a local observation vector from a full observation vector
 * `U_init_obsvar`: The name of the user-supplied routine that provides a global mean observation error variance (This routine will only be executed, if an adaptive forgetting factor is used)
 * `U_init_obsvar_l`: The name of the user-supplied routine that provides a mean observation error variance for the local analysis domain (This routine will only be executed, if a local adaptive forgetting factor is used)
 * `U_next_observation`: The name of a user supplied routine that initializes the variables `nsteps`, `timenow`, and `doexit`. The same routine is also used in `PDAF_get_state`.
 * `status_pdaf`: The integer status flag. It is zero, if `PDAF_assimilate_letkf` is exited without errors.



Note:
 * The order of the routine names does not show the order in which these routines are executed. See the [ImplementAnalysisletkf#Executionorderofuser-suppliedroutines section on the order of the execution] on the page on implementing the analysis step of the LETKF algorithm. 

The user-supplied call-back routines are described on the page on [ImplementAnalysisletkf implementing the analysis step of the LETKF].

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

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