• Non-commercial use:
  
  The full software package 4A/OP is available as a freeware product only for academic use and to those wishing to use the code for scientific research. Click here to access the conditions of a non-commercial use of the software.
  If you accept the terms of these conditions, please complete the Licence Agreement by way of the on-line registration form.

• Commercial use:
  
  For a purpose other than a research or academic use, please click here to access the conditions of a commercial use of the software.
  If you accept the terms of these conditions, please complete the Licence Agreement by way of the on-line registration form.

4A/OP may be obtained for implementation under Unix (Sun and Linux) operating system. The source code is the same for all, but the method of building the executable program varies. 4A/OP has been compiled and tested on Sun (Sparc Solaris, with the Forte 6.2 Fortran 90 compiler) and Linux PC environments (tested compilers: pgf90, f90-sun, ifort, g95/gfortran, gcc compiler (GNU compiler) and cc (SUN compiler)).

The 4A/OP Graphical User Interface (GUI) needs that Tcl/Tk (at least version 8.4) is installed on the system. See http://www.tcl.tk for more information on Tcl/Tk.
The visualization part of the 4A/OP GUI needs Gnuplot software in order to plot graphs. The GUI has been tested with the following version of Gnuplot: Unix version 3.7 patchlevel 0. See http://www.gnuplot.info for more information on Gnuplot.

The 4A/OP installation occupies about 25 MB on disk.

In addition, the Atlas files can require up to 6.5 GB of disk space (this volume depends on the simulation needs).