node.js Model Simulation

An event-based framework for simulation of models, for example models of economic systems. By building models on events we can allow third-party code to participate and affect the running model. For example running two related models side-by-side can allow a third party to arbitrage between the two models.

The underlying core of simulating a model is the lib/pulse.js (which extends EventEmitter) creates a configurable but steady stream of ticks (or heartbeats). Each tick is an iteration of the model.

The lib/pulse.js emits the following events:

• start -- when the simulation is started
• end -- when the simulation is ended
• tick -- when each iteration is triggered

The file lib/model.js extends lib/pulse.js and encapsulates common model functionality.

Waterflow example

The example.js runs a simple waterflow model attaching callbacks to various interesting events.

The example model models/waterflow.js implements a simple model of a water-container. In each iteration water flows in and water flows out. If the water exceeds the total capacity of the water-container it triggers an overflow event. Similarly if the water-container runs out of water it triggers an underflow event.

The waterflow example uses the following events (in addition to those provided by lib/pulse.js:

• overflow -- when the water-container is overcapacity. This event passes the number of units spilt as an argument.
• underflow -- when the water-container runs dry. This event passes the number of units short as an argument.

Example simulation:

$ node example.js
24 Jul 20:44:14 - Starting model
Starting simulation
Water level: 18/40
Water level: 25/40
Water level: 32/40
Water level: 39/40
Water level: 40/40 [Wasted: 6]
Water level: 40/40 [Wasted: 13]
Water level: 40/40 [Wasted: 20]
Water level: 40/40 [Wasted: 27]
Water level: 40/40 [Wasted: 34]
Water level: 40/40 [Wasted: 41]
24 Jul 20:44:24 - Stopping model
Simulation completed