= PDAF_init = 

This page documents the routine PDAF_init of PDAF.
In `init_pdaf` the variables for the call to `PDAF_init` are set. 

The call to `PDAF_init` has the following structure:
{{{
CALL PDAF_init(filtertype, subtype, step_null, &
               filter_param_i, length_filter_param_i, &
               filter_param_r, length_filter_param_r, &
               COMM_model, COMM_filter, COMM_couple, &
               task_id, n_modeltasks, filterpe, &
               U_init_ens, screen, status_pdaf)
}}}

The required variables are the following:

 * `filtertype`: An integer defining the type of filter algorithm. Available are
  * 0: SEEK 
  * 1: SEIK 
  * 2: EnKF 
  * 3: LSEIK 
  * 4: ETKF 
  * 5: LETKF 
  * 6: ESTKF
  * 7: LESTKF
 * `subtype`: An integer defining the sub-type of the filter algorithm (see the example code in `testsuite/src/dummymodel_1D` for choices). If `PDAF_init` is called with `subtype=-1` the available options are shown for the selected filter algorithm.
 * `step_null`: An integer defining the initial time step. For some cases it can use useful to set `step_null` larger to 0. 
 * `filter_param_i`: Integer array collecting several variables for PDAF. The first two variables are mandatory and equal for all filters. Further variables are optional (see example code or use `subtype=-1` to display available options.). The mandatory variables are in the following order:
  * The size of the local state vector for the current process.
  * The ensemble size for all ensemble-based filters (or the rank of the state covariance matrix for mode-based filters like SEEK)
 * `length_filter_param_i`: An Integer defining the length of the array `filter_param_i`. The entries in the array are parsed up to this index.
 * `filter_param_r`: Array of reals collecting floating point variables for PDAF. The first variable is mandatory and equal for all filters.  Further variables are optional (see example code in `testsuite/src/dummymodel_1D` or use `subtype=-1` to display available options.). The mandatory variable is:
  * The value of the forgetting factor controlling covariance inflation (required to be larger than zero; common are values between 0.9 and 1.0. For 1.0 the ensemble is not inflated.)
 * `length_filter_param_r`: An Integer defining the length of the array `filter_param_r`. The entries in the array are parsed up to this index.
 * `COMM_model`: The communicator variable `COMM_model` as initialized by `init_parallel_pdaf`. (Usually stored in the module `mod_assimilation`)
 * `COMM_filter`: The communicator variable `COMM_filter` as initialized by `init_parallel_pdaf`. (Usually stored in the module `mod_assimilation`)
 * `COMM_couple`: The communicator variable `COMM_couple` as initialized by `init_parallel_pdaf`. (Usually stored in the module `mod_assimilation`)
 * `task_id`: The index of the model tasks  as initialized by `init_parallel_pdaf`. (Usually stored in the module `mod_assimilation`)
 * `n_modeltasks`: The number of model tasks as defined before the call to `init_parallel_pdaf`. (Usually stored in the module `mod_assimilation`)
 * `filterpe`: A logical flag showing whether a process belongs to `COMM_filter` as initialized by `init_parallel_pdaf`. (Usually stored in the module `mod_assimilation`)
 * `U_init_ens`: The name of the user-supplied routine that is called by `PDAF_init` to initialize the ensemble of model states. (See '[InsertAnalysisStep#User-suppliedroutineU_init_ensinit_ens_pdaf.F90 User-supplied routine U_init_ens]'
 * `screen`: An integer defining whether information output is written to the screen (i.e. standard output). The following choices are available:
  * 0: quiet mode - no information is displayed. 
  * 1: Display standard information (recommended)
  * 2: as 1 plus display of timing information during the assimilation process
  * 3: Display detailed information for debugging
 * `status_pdaf`: An integer used as status flag of PDAF. If `status_pdaf` is zero upon exit from `PDAF_init` the initialization was successful. An error occurred for non-zero values. (The error codes are documented in the routine `PDAF_init`.) 

An overview of available options for each filter an be found on the [wiki:AvailableOptionsforInitPDAF overview page on options].

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

PDAF also has a [PdafSimplifiedInterface Simplified Interface] providing the routine `PDAF_init_si`. In the simplified interface, the name of the user-supplied routine `U_init_ens` is predefined to `init_ens_pdaf` such that it does not appear in the call to `PDAF_init_si`.  More information on the pre-defined names is provided in the [PdafSimplifiedInterface documentation of PDAF's simplified interface].