The simplified interface of PDAF

Overview

With version 1.7 of PDAF as simplified (or shortened) interface has been introduced. It can be used as an alternative to the full interface, which remains to exist. In the full interface, the names of all required user-supplied subroutines (e.g. the implementation of the observation operator) need to be specified. This scheme allows the user to choose the names of these routines. In contrast, the simplified interface uses pre-defined routine names and does not require to define the name in the call to PDAF. Thus, the interfaces are shorted. On the other hand, the simplified interface restricts the names of the user-supplied to the pre-defined ones. We leave it to the user to decide, which variant he or she prefers.

The implementation of PDAF with the simplified interface is analogous to the case when the full interface is used. Below, we described the differences in the interfaces. For the general implementation guide, please see the pages describing the implementation with the full interface. (The subroutine names listed there are the pre-defined names required when the simplified interface is used)

Required arguments for PDAF_init_si

The call to PDAF_init_si has the following structure:

CALL PDAF_init_si(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, &
               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
• subtype: An integer defining the sub-type of the filter algorithm (see the example code in testsuite/src/dummymodel_1D for choices)
• 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). 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). The mandatory variable is:
  • The value of the forgetting factor (required to be larger than zero)
• 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. If the model-communicator is named differently in the actual program, the name has to be adapted
• COMM_filter: The communicator variable COMM_filter as initialized by init_parallel_pdaf.
• COMM_couple: The communicator variable COMM_couple as initialized by init_parallel_pdaf.
• task_id: The index of the model tasks as initialized by init_parallel_pdaf.
• n_modeltasks: The number of model tasks as defined before the call to init_parallel_pdaf.
• filterpe: The flag showing if a process belongs to COMM_filter as initialized by init_parallel_pdaf.
• screen: An integer defining whether information output is written to the screen (i.e. standard output). The following choices are available:
  • 0: quite 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.)

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.

The routine PDAF_init call the user-supplied routine init_ens_pdaf. The interface of init_ens_pdaf is described on the page on PDAF_init with full interface.