Save last state of each unit separately

[schmoelder]

Currently, the last state (as well as its derivative) is only saved for the entire system.
It would be convenient being able to also save the state for each unit operation separately for re-initialization of systems where individual unit operations might be exchanged.

[Immudzen]

It looks like changes are needed in

CADET/include/common/Driver.hpp

Line 38 in 67648c0

void readDataOutputConfig(ParamProvider_t& pp, StorageConfig_t& cfg, const std::string& dataType)

It looks like a new configuration is needed to control saving the state

and in

CADET/include/common/SolutionRecorderImpl.hpp

Line 385 in 67648c0

virtual void beginUnitOperation(cadet::UnitOpIdx idx, const cadet::IModel& model, const cadet::ISolutionExporter& exporter)

Probably have to read from the model to get the current state for a unit operation using _models and _dofOffset

[Immudzen]

and in SolutionRecordImpl.hpp virtual void beginUnitOperation(cadet::UnitOpIdx idx, const cadet::IModel& model, const cadet::ISolutionExporter& exporter)

It looks like this part is incorrect. It doesn't look like from inside this method there is any access to the state variables.

[sleweke-bayer]

My preferred approach:

1. Add function getModelSlice() to IModelSystem. This function should return start index and length of the model's slice in the global state vector.
2. Implement this function in ModelSystem class.
3. Use this function in Driver to obtain the requested slice of the model.

The SolutionRecorder framework is meant for saving specific parts of a model's state, not necessarily the whole state.