The domain of computer-aided design and optimization for circuits and filters alone is very broad, especially since the design objectives are usually multiple. Physical design deals with concrete geometrical parameters while electrical design deals with the electrical performances of the physical object. Strictly speaking, both design aspects are inseparable since any physical design is a realization of a particular electrical design. The performance of a particular circuit can be measured in many ways according to application and design goals. In essence, each performance measure is an indication of the circuit output which the designer is interested in for a particular operating condition. The circuit functionally depends on the input–output relationships and thus circuit specifications and test specifications are made on the basis of the input–output relations. A given input–output pair is said to have a memoryless relationship if it can be described statically without the use of any ordinary or partial differential equation.