Question: What is the advantage of having a model?

Chapter(s)	System Modeling
Author(s)	Steve Waydo
Date	2003/10/06

The exact question was, "Is the advantage of having a model that you can choose appropriate lengths/constants/gains before spending money and finding out that it doesn't work right? Why not just build it an watch the behavior (trial & error)?"

This is exactly right. We use models to study systems when it is easier, cheaper, safer, or faster than working with a real system. Careful modeling allows us to design and build systems that work well with a minimum of trial and error. Safety is often key here - a test pilot will be much happier getting into a new airplane that has been thoroughly modeled prior to first flight than one that was built just to see if it works! A model can also allow us to study a system that is too large and complicated to build or that cannot be isolated. For example, the predator-prey model discussed in class lets us see the effects of things like a sudden increase in food supply, etc. very clearly, without having to account for the effects of other disturbances that might be present in nature. While we can observe this system in real life, the model may give us more information about specific input-output relationships than we can get from our observations.

It should be noted, however, that modeling is not the correct choice 100% of the time (although it very often is) - occasionally modeling a system may be extremely difficult and time consuming while building the system is relatively easy. In such a case trial and error may be a good alternative. The word of caution here, though, is that modeling often gives us a good understanding of the system in general (i.e. we can see how performance changes as a function of particular parameters), allowing us to make inferences about many systems, while trial & error teaches us only about the systems we actually build.