I have the following apllication software setup:
A numerical simulation "engine" = OpenModelica (which in open source, released under GPL v.3), used to simulate e.g. hydraulic systems;
A proprietary GUI (e.g. an Excel sheet with VBA macros, a Python script, a Windows .NET application, ...) that interacts with OpenModelica via its APIs to: load a model, set parameters, run the simulation, get the results. The GUI provides a dedicated user interface to set parameters and visualize the results.
The OpenModelica source code has not been modified in any way.
Is this combination an "aggregate" according to GPL v.3, thus allowing me to distribute in a "bundle":
OpenModelica as FLOSS, according to GPL v.3;
the GUI as a proprietary copyrighted software,
or would the combination be a "larger program", forcing me to distribute everything under GPL v.3 conditions?