The model solution programs accept user supplied runtime modifications to the elastic links and immersed boundary point locations, and specify sources and sinks of fluid.
To specify the motion of active links or immersed boundary points, the user is required to provide a FORTRAN subroutine called actmov. To specify a fluid source or sink, the user is required to provide a FORTRAN subroutine called getsrc. Default programs (with no active motion or link modification, and no sources or sinks) are provided in the IBIS software. These defaults can be found in the file Fcode/udefine.f.
The file Fcode/udefine.f must be present and contain actmov and getsrc for IBIS to successfully execute.