Control theory is an interdisciplinary branch of engineering and mathematics. It deals with the behavior of systems. The desired output of a system is called the reference. In that context, a system can be influenced by certain input values. Depending on the input values, the system may change its state or its behavior. Common questions control theory asks:
One of the first modern people to talk about control theory was James Clerk Maxwell. In his work On Governors, of 1868, he looked at the dynamic properties of centrifugal governors, as they were used by steam engines.[1] Such governors were already used to regulate the speed of windmills.