System composition clarity

[GJHSimmons]

A dynamic complex system model is described by:

• The differential equations
• The functions
• The parameters

Differential equations and functions are described by VariablePortedObject and FunctionalPortedObject classes, respectively. The core component of FunctionalPortedObject classes are ParameterAssignment classes, which store the correspondence between a SymbolContainer and sympy.Expression object.

The class ParameterAssignment is also used to store:

• Assignments produced by CompositePortedObject classes
• Default parameter assignments produced by InputPort classes

It is proposed to subclass ParameterAssignment to differentiate between those assignments coming from FunctionalPortedObject classes, and the other assignments listed above. This will aid clarity in being able to provide the model description described above.

Further subclassing is proposed to differentiate between different parameter assignments, differentiating between those produced by CompositePortedObject classes, and moreover the default parameter assignments produced by InputPort classes of:

• children objects with default values: 'exposable' parameters which are coded into a model, but can be made available to a user
• the compiled object with default values: 'optional' parameters which are naturally changeable to alter the behaviour of the system
• the compiled object with no default value: 'required' parameters which must be specified before a system can be simulated, but which on inspection represent the dependence of a compiled object on external sources