Conclusion and outlook
Representations of a linear system. Extension to uncertain systems

In this article, we have discussed the notion of LTI systems (linear invariant systems) and different types of representation, with particular emphasis on state representation. Whether for simulation or, much more importantly, for control (analysis or synthesis), it is this representation that is now most widely used, thanks in large part to the development of efficient and easy-to-use software tools. In a second part of the article, we also showed that this state representation could be easily generalized, via the LFT formalism, to the case of uncertain linear systems. Direct extensions of this formalism, not dealt with in this article, can also cover a wider class of systems including time-varying parameters and even non-linearities.