Consider a system represented as in Figure 4.1a. Let the control input be A, the model of the system B, and the output C, as in Figure 4.1b. For other inputs, known or estimated, the fundamental configurations become

In each, something different is known, and it remains to obtain the unknown. Synthesis and investigation are known as inverse configurations. In general,

their results are nonunique, whereas the result of the analysis configuration is generally unique. Nonuniqueness in the synthesis and investigation configurations might be removed through additionally including some optimality measure.