Patrik Schönfeldt

Because NonConvex and Investment are no longer mutually exclusive, we may rethink the structure of Flow, NonConvexFlow and InvestmentFlow, because there is NonConvexInvestmentFlow. For the API, it might be more...

Generally, I see that all the alternatives are possible. (There are more, but more on that later.) Especially, I agree that it should be possible to not explicitly provide `nominal_value`....

For Q1 and Q2, we have the same opinion. For Q3 and Q4, I know that there are people who are setting min=max for single time steps, as you currently...

> Hello @p-snft! Thanks for updating this PR. We checked the lines you've touched for [PEP 8](https://www.python.org/dev/peps/pep-0008) issues, and found: > > * In the file [`src/oemof/solph/flows/_flow.py`](https://github.com/oemof/oemof-solph/blob/ca004d87fb846e40595d2e42fa34b8e941317af1/src/oemof/solph/flows/_flow.py): > > >...

IMHO, the decision is clear by now. Thus I started with the implementation and removed the tags "feedback wanted" and "beginner". I am currently removing code duplications by creating shared...

Before I continue, I'd like to have some feedback on optimised code and duplication. I removed some specialised constraint formulations. This way, one formulation can be used for different kinds...

Almost done. Docs and examples still need to be checked.

> I am wondering, if we introduce the subpackage `flows/_shared`, we should probably shift the code from the module `_options` into the two new modules `investment.py` and `non_convex.py`. ' I...

The style is not 100 % customisable any more, but the order of the documented functions can be customised. I continued with the [doc of InvestNonConvexFlow](https://oemof-solph.readthedocs.io/en/feature-restucture_flow/reference/oemof.solph.flow.html#module-oemof.solph.flows._invest_non_convex_flow_block) as an example.

While refactoring, I found the following description in the documentation. ```Python If `nonconvex.positive_gradient["costs"]` is set by the user: .. math:: \sum_{i, o \in POSITIVE_GRADIENT_FLOWS} \sum_t positive_gradient(i, o, t) \cdot positive\_gradient\_costs(i,...