Implement a Process​#

A process names the biological or physical phenomenon being simulated; a model supplies one set of equations for it. PlantBiophysics already defines light interception, energy balance, photosynthesis, and stomatal conductance. Reuse those processes when adding an alternative equation, as in Implement a model.

Declare a new process when you introduce a different phenomenon, such as plant growth. The declaration gives its models a shared identity; it does not choose their equations or create a simulation.

Declare the process​#

PlantSimEngine provides the @process macro. The first argument is the process name and the optional second argument documents its meaning:

using PlantSimEngine

@process "growth" "Models that calculate plant growth." verbose=false
AbstractGrowthModel

This creates AbstractGrowthModel, the parent type for implementations of growth. verbose=false suppresses the macro's interactive guidance; omit it when you want that help in a Julia REPL.

Give a model that identity​#

A model inherits from the generated type. For example if we implement a growth model named GrowthExample, we would declare it as:

struct GrowthExample <: AbstractGrowthModel end
process(GrowthExample())

The process function made a process name as an abstract type, here AbstractGrowthModel. It is used to group models that implement the same process using model <: AbstractProcessModel.

Before this can run, choose and document the scientific equation, its parameters, and the meaning and units of its variables. Then add:

• inputs_ for values read from the simulated object;

• outputs_ for values calculated by the model;

• environment_inputs_ if it reads weather or other shared conditions;

• run! for the calculation over one timestep.

The model implementation tutorial walks through these steps with a working stomatal-conductance model. For a growth model, also make clear whether an output is a growth rate, a biomass increment over the timestep, or a cumulative biomass state. Those quantities require different equations and cannot be exchanged just because they share a variable name.

Once complete, use the model in a PlantSimEngine CompositeModel, selecting the plant or organ on which it acts. Process declarations do not determine that selection, and a growth model need not act on a leaf. See Whole-plant simulation for assembling models on different organs.