Incremental passivity
In circuit design, informally, passive components refer to ones that are not capable of power gain. Under this definition, passive components include capacitors, inductors, resistors, diodes, and transformers. They exclude devices like transistors, vacuum tubes, relays, glow tubes, energy sources like current- or voltage sources, and similar devices. Formally, for a memoryless two-terminal element, this means that the current?voltage characteristic is monotonically increasing. For this reason, control systems and circuit network theorists refer to these devices as locally passive, incrementally passive, increasing, monotone increasing, or monotonic. It is not clear how this definition would be formalized to multiport devices with memory ? as a practical matter, circuit designers use this term informally, so it may not be necessary to formalize it.[nb 1]