  The structural analysis, i.e., the investigation of the
differential-algebraic nature, of circuits containing simple elements, i.e.,
resistances, inductances and capacitances is well established. However,
nowadays circuits contain all sorts of elements, e.g. behavioral models or
partial differential equations stemming from refined device modelling. This
paper proposes the definition of generalized circuit elements which may for
example contain additional internal degrees of freedom, such that those
elements still behave structurally like resistances, inductances and
capacitances. Several complex examples demonstrate the relevance of those
definitions.
