Model coupling for modelers

This section uses notions from the previous section. If you are not familiar with the concepts of model coupling in PlantSimEngine, please read the previous section first: Model coupling for users.

Hard coupling

A model that calls explicitly another process is called a hard-coupled model. It is implemented by calling the process function directly.

Let's go through the example processes and models from a script provided by the package here examples/dummy.jl

In this script, we declare seven processes and seven models, one for each process. The processes are simply called "process1", "process2"..., and the model implementations are called Process1Model, Process2Model...

Process2Model calls Process1Model explicitly, which defines Process1Model as a hard-dependency of Process2Model. The is as follows:

function PlantSimEngine.run!(::Process2Model, models, status, meteo, constants, extra)
    # computing var3 using process1:
    run!(models.process1, models, status, meteo, constants)
    # computing var4 and var5:
    status.var4 = status.var3 * 2.0
    status.var5 = status.var4 + 1.0 * meteo.T + 2.0 * meteo.Wind + 3.0 * meteo.Rh
end

We see that coupling a model (Process2Model) to another process (process1) is done by calling the run! function again. The run! function is called with the same arguments as the run! function of the model that calls it, except that we pass the process we want to simulate as the first argument.

A hard-dependency must always be declared to PlantSimEngine. This is done by adding a method to the dep function. For example, the hard-dependency to process1 into Process2Model is declared as follows:

PlantSimEngine.dep(::Process2Model) = (process1=AbstractProcess1Model,)

This way PlantSimEngine knows that Process2Model needs a model for the simulation of the process1 process. Note that we don't add any constraint to the type of model we have to use (we use AbstractProcess1Model), because we want any model implementation to work with the coupling, as we only are interested in the value of a variable, not the way it is computed.

Even if it is discouraged, you may have a valid reason to force the coupling with a particular model, or a kind of models though. For example, if we want to use only Process1Model for the simulation of process1, we would declare the dependency as follows:

PlantSimEngine.dep(::Process2Model) = (process1=Process1Model,)

Soft coupling

A model that takes outputs of another model as inputs is called a soft-coupled model. There is nothing to do on the modeler side to declare a soft-dependency. The detection is done automatically by PlantSimEngine using the inputs and outputs of the models.