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NETLOGO SYSTEM DYNAMICS HOW TO
System Dynamics -> Exponential Growth HOW TO CITE Interesting to compare with the standard ABM model. This model uses the System Dynamics Modeler. Or diffusion of innovations (i.e., BASS Model of Diffusion). This would be a model useful for all sorts of problems, like infection rates on the INFLOW side and recovery rates on the OUTFLOW.
Try having the level of one stock influence the growth rate of the other. EXTENDING THE MODELĬreate a new stock that grows linearly. Use the System Dynamics Modeler to add an outflow. View the plot to observe the growth of STOCK over time. View the STOCK monitor to see the current value of STOCK. Note that the simulation length can be set by the user but increased during a model run if needed. The "Step 1 Year" button repeats the GO command 1000 times because "dt" in the System Dynamics model is set to 0.001. Press the SETUP button, then press the GO button to run the model. We usually think of deaths in terms of life span of an individual, so the death rate, d, becomes 1/life-span. But r = b - d, so if we split up the rate in and rate out, we have bN(K-N/K) on the birth side and dN(K-N/K) on the death side (as the OUTFLOW for the system). So the rate equation for logistic growth is rN(K-N/K). However, in a logistic model, the rate of change is reduced by (K - N)/K, where N is the population size and K is an upper limit - i.e., the carrying capacity. The growth rate for an exponential model of population growth is the BirthRate. The value of INFLOW is always the previous value of STOCK times a specified growth rate. This is a change from the original model as a build-up for converting the logistic from a population model into a form for studies of chaos.Īt each step, the value of INFLOW is added to STOCK. So if the Life Span is 10 years, the death rate is 0.1 with 1/Years as the units. This is a model of logistic growth using the System Dynamics Modeler. Do you have questions or comments about this model?
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