System Dynamics Java-Framework

Introduction

This Framework allows you to create your own System Dynamics model of complex systems and to simulate its dynamic behavior.

Usage

Best practise sample

1. Create the model

Model model = new Model(0, 10, 0.1, new EulerCauchyIntegration());

2. Create all system elements

// create a stock
Stock populationPrey = (Stock) model.createModelEntity(ModelEntityType.STOCK, POPULATION_PREY_KEY);
// set initial value
populationPrey.setInitialValue(100);

// create a variable
Variable expansionRatePrey = (Variable) model.createModelEntity(ModelEntityType.VARIABLE, BIRTH_RATE_PREY_KEY);
// set initial value
expansionRatePrey.setInitialValue(0.1);

// create another variable
Variable meetings = (Variable) model.createModelEntity(ModelEntityType.VARIABLE, MEETINGS_KEY);

3. Create the flows

// create some flows
Flow birthsPrey = (Flow) model.createModelEntity(ModelEntityType.FLOW, BIRTHS_PREY_KEY);
Flow deathsPrey = (Flow) model.createModelEntity(ModelEntityType.FLOW, DEATHS_PREY_KEY);
  
// add them to a stock
populationPrey.addInputFlows(birthsPrey);
populationPrey.addOutputFlows(deathsPrey);

// set calculation function
populationPrey.setChangeRateFunction(
	() -> birthsPrey.getCurrentValue() – deathsPrey.getCurrentValue()
);

4. Define the converters

// define a converter
Converter deathsPreyConverter = model.createConverter(deathsPrey, meetings, lossRatePrey);

// set function
deathsPreyConverter.setFunction(
	() -> meetings.getCurrentValue() * lossRatePrey.getCurrentValue()
);

5. Create the simulation

Simulation simulation = new Simulation(model);

6. Add result handler

// add a CSVExport
simulation.addSimulationEventListener(
	new CSVExporter("output.csv", ";")
);

// Add a ChartViewer
simulation.addSimulationEventListener(
	new ChartViewer()
);

7. Run the simulation

simulation.run();