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Introduction to Control
The general goal of control is to get some physical system to respond to a reference input in the way we would like.
In general, there are two different types of control.
Figure 1: Open-Loop Control
Open-Loop control is generally difficult because the disturbances make it difficult to copy the reference exactly.
Figure 2: Closed-Loop Control
Notice how the output signal is subtracted from a reference signal, and we use the difference (a.k.a the error) to determine what input we pass into the plant.