Hysteresis loop

Hysteresis can be defined as the time-based dependence of a system's output on present and past inputs. The dependence arises because the history affects the value of an internal state. To predict its future outputs, either its internal state or its history must be known.
The mathematical and graphical explanation shown in fig. (a), is a typical and simple case showing the relationship between y = f (x), with the time t as a parameter. As in the case of (b), the digital electronic circuit often uses hysteresis for discretely changing signal processing, and it is also used for motor control. The quadrilateral shape shows that the process is irreversible. That is, the outbound route and the return route are different. The form of change in these figures is called a hysteresis loop.