.. _4Csimulation:

|FOURC| Simulation
====================

The basic command to execute 4C is (relative to the build directory)

.. code-block:: bash

    ./4C <input_file> <output_basename>

The input file is commonly a file with the suffix ``.dat``, and it is commonly created by a preprocessing step,
which is explained in detail in :ref:`preprocessing`.

The ``<output_basename>`` should not have any suffix.
Output generated by |FOURC| consists at least of one file named ``<output_basename>.control``.
If further output has been requested, a number of further files are created.
The file names are all given in the \*.control file.

These results in the output files are by default stored in a proprietary format.
However, output data can also be stored in a format that is readable by other programs.
For further information, see :ref:`Postprocessing`.

All available options when starting |FOURC| from the command line are shown by an output of ``./4C --help``:

.. literalinclude:: /4C-help.txt


Running examples
----------------

In ``tests/input_files`` a huge number of test examples are available. For example,

.. code-block:: bash

   ./4C tests/input_files/f2_drivencavity20x20_drt.dat xxx

runs the 2d fluid driven cavity example and writes the output to files beginning with ``xxx``.
You can also run the code in parallel with the ``mpirun`` command like this:

.. code-block:: bash

   mpirun -np 1 ./4C tests/input_files/f2_drivencavity20x20_drt.dat xxx


Restarting an analysis
-----------------------

For restarting an analysis one has to provide restart information in the first simulation by including the parameter
``RESTARTEVERY  <numsteps>`` in the ``STRUCTURAL DYNAMICS`` section,
so that the information is written every *numsteps* step.

In the second simulation, no additional parameters have be included. The information that it is a restart, is
given on the command line:

::

   ./4C <restart_input_file> <output_basename> [restartfrom=<restart_filename>] restart=<step>

Here, one has to provide the step, at which the restart is started from the previous simulation.
If the parameter ``restartfrom`` is given, the initial configuration is read from this file,
otherwise it is read from ``<output_basename>``. In the latter case the filename of the new output is the same with an appended number, e.g., ``outfile-1``.
Note that the value for ``step`` must be given in the file ``<output_basename>.control`` in one of the step lines: ``step = <step>``.

.. note::

   - The parameters RESTART and RESTARTTIME in the PROBLEM TYPE section
     are not needed anymore, and will probably vanish soon.
   - The parameter MAXTIME indicates the maximum time of all simulations,
     it is NOT a step time, so be aware that MAXTIME in the subsequent simulation
     must be larger than in the first one.
   - The parameter TIMEINIT can be 0 also in the subsequent simulation, it is not used,
     since the initial time is defined by the restart.