The answer is related to your last post. There are three kind of Flow classes at the moment:
- Flow (normal flow)
- InvestmentFlow
- NonConvexFlow
These are three different classes and you have to decide which class you want to use for your object. I think it is not difficult to create a NonConvexInvestmentFlow based on the idea of both flows, because all equations are already there. Basically you need to replace the nominal_value with an investment variable.
If you need help you can contact me or you can join the developing meeting. One aim of the meeting is to help new developers to do their first contributions. There will be an Open Space at the meeting to write your own code with people around that can help you with your problems.