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Discrete Simulation
From SystemsWiki
Discrete simulation is a technique where the simulation is advanced from event time to event time rather than using a continuously advancing time clock as in Continuous Simulation.
Suppose we consider the example of the interaction of the principle and interest associated with a savings account. This can be represented as a Causal Loop Diagram in Fig. 1.
This diagram indicates that deposits increase the principal and withdrawals decrease the principal. Also, the principal interacts with the interest rate, on some periodic basis, to create interest. The interest then serves to increase the principal. The structure created in Fig. 1 represents a Reinforcing Loop.
If we then turn this into a 10 year simulation with the assumptions that the principal is initially $100, there are no deposits or withdrawals, and an interest rate of 5% is paid once a year it might look like Fig. 2 in ExtendSim.
In Fig. 2 Yearly Events block schedules events, which in this particular example just happen to be yearly. When an event happens, Interest is computed based on the Principal and the Interest Rate and the result is added to the Principal. The event then exits the system.
The above graph shows the result of running the model for 10 years. Note that the Interest is computed and added to the Principal at the end of each year and the discrete nature of the simulation is very evident.
[edit] References
- Continuous Simulation
- ExtendSim used for Stock & Flow Diagram and Simulation
- Vensim PLE used for Causal Loop Diagram
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