With this background about semi-continuous variables, consider an example using them. Assume that you are managing a power plant of several generators. Each of the generators may be on or off (producing or not producing power). When a generator is on, it produces power between its minimum and maximum level, and each generator has its own minimum and maximum levels. The cost for producing a unit of output differs for each generator as well. The aim of the problem is to satisfy demand for power while minimizing cost in the best way possible.