a system is a model used to describe the behaviour of something in the real world that takes inputs and produces outputs. for example, a car is a system in that the driver chooses how hard to press on the gas pedal (the input) and the car drives along the road at a certain speed (the output). in the case of a car, the input to the gas pedal does not fully determine the speed of the car. the weight in the car, the incline of the road, the traction of the tires, the current speed of the car, and other factors can all change the output received for a particular input. control theory attempts to determine what inputs will result in a desired output, or reference. this is accomplished using differential equations, linear algebra, and other branches of math. control theory relies heavily on computational models and software.