ges nor to discuss their strengths and shortcomings. In what follows, mathematics will be the main language of choice. 2.1.5 Modeling and analysis: model creation, transformation and interpretation Models are almost never given to us in a manner that directly suits our needs. In the very beginning, there might even be no model available at all. There are only our observations or a vague idea that we have in mind. Therefore, we need techniques to create and manipulate models. This is where modeling and analysis come into play. Definition (Modeling and Analysis): Modeling and analysis concern the acts of cre- ating, manipulating and interpreting models. Hereby, the aim of modeling is to create a model, i.e. models are considered a result of the operation. In carrying out analysis, 2.1 MODELS, MODELING AND ANALYSIS models are just a means to gain the information necessary to make design decisions. Analysis involves interpreting models. The main difference between both concepts comes down to whether models are con- sidered a result of the act or a means to obtain results. Looked upon in this manner, analysis always involves modeling steps followed by the interpretation of the resulting models and the consequences they imply towards design. One of the hardest parts of the modeling process is the creation of a starting point. We need to construct an initial specification or implementation model. This requires a formalized description of ideas or observations. There is often nothing to guide us but our past experience and our capability to detect similarities between different systems and problems. Here, again, a hierarchical classification of systems and their behavior can be of great help (see chapter 1). Once an initial model is created, we can proceed by transforming one model into an- other. A circuit netlist, for example, can be transformed into a small-signal model. Symbolic modeling techniques [Fern98, Gie91, Gie94, Lin91, Wamb98b] in turn trans- form this small-signal model into a set of transfer functions. The