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I'm working on a model in NetLogo and I'm having some difficulty wrapping my head around what one time step actually means. What I'm working on is similar to the wolf-sheep predation model. What would one time step in that model represent? Since each agent has an opportunity to reproduce at each time step, I would have thought that this would be about one year. But agents only move one step (one patch to another) at each time step, so this seems like it would be far less than a year. I want my model to best represent reality, so would like to work out exactly what each time step is.

Sorry if this is an obvious question, but it's something I've been thinking about for a while.

Thanks, Damien

91dpo
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  • I have no idea what you're asking. – erip Sep 04 '15 at 01:19
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    ticks are not a representation of real world time, it's just a unit of time and the meaning is determined by the developer. Check out this with better explainations: http://stackoverflow.com/questions/3571485/netlogo-1-tick-how-many-seconds – drstein Sep 04 '15 at 07:31

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It sound like you need to change your idea of a "model". A model should be exactly as representative of the reality as is strictly neccesary to produce meaningfull results. No more, no less. Most models are supposed to be more like 'thought experiments', not simulators.

A realistic model of fluid dynamics needs 30^10 molecules. but a model of 5^10 might do the trick just fine. A realistic neural network simulator would need to implement all kinds of physics, ions, cell mechanics etc. But most models just consist of some mathematical formulas, and still produce a very good approximation of reality.

The wolf-sheep example is not trying to be realistic. If it would, it would also need to implement landscapes, other animals that wolves eat, diseases, and 100 other things. It is just trying to make a point: the wolves/sheep ratio fluctuates. No sheep --> no wolves. no wolves --> too many sheep --> no grass --> no sheep.

In short, most models will try to tell you that "eventually" X will happen. whether that's 10 seconds or 10 years is just not the point.

Jumboman
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