.. Piernik MHD code documentation master file, created by
   sphinx-quickstart on Mon Aug  4 13:00:52 2014.
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Setting up new problems
============================================

**Problem description**

Each problem should provide a **initproblem.F90** file with module initproblem and three subroutines:


``problem_initial_conditions``

This routine fills the grid with initial conditions, according to the parameters read in ``read_problem_par`` .

It is not called when the code starts from the restart file.


``read_problem_par``

This routine reads the ``PROBLEM_CONTROL`` namelist by master process and communicates read parameters to other processes. It can also calculate things that might be needed by the problem, except the initial conditions.

Attention: Pointers assignment dependent on parameters from problem.par file should be placed at the end of this routine.

This routine is called before it is decided whether to read restart file or start from scratch.


``problem_pointers``

This routine is called very early, just after init_mpi and is supposed to set up procedure pointers, if necessary. Such approach allows implementation of problem-specific hacks also during the initialization of the Piernik code.
In extreme cases it is possible to change behavior of the Piernik code quite radically, without precompiler directives.


There are to sets of procedure pointers for users:

 imported from user_hooks module:

.. _newprobl_pcustsol:

problem_customize_solution
   A routine that is called after each 3 sweeps. Intended to enforce solution inside computational domain (carefully!). Can be used to run checks for special events.

finalize_problem
   A routine called at the end of simulation before last output is written.

cleanup_problem
   A routine called at the end of run to deallocate arrays.

problem_refine_derefine
   Implementation of user refinement criteria.



imported from dataio_user module:

user_attrs_pre
   Attributs preparation before writing to a file

user_attrs_rd
   Specifying attributes to be read

user_attrs_wr
   Specifying attributes to be written down

user_vars_hdf5
   Specifying variable arrays to be written down

user_tsl
   Specifying data to be written to the TSL files

user_post_write_data
   A routine called after writing data


It assumes that all procedure pointers are initialized to Null().
Warning
Pointers assignment may be dependent on parameters from problem.par file (unrecommended). In such a case they must be assigned not before read_problem_par routine is called.