6. Software aspects

In this section, we propose to illustrate two model reduction techniques in state space, aimed at removing ungovernable or weakly governable states on the one hand, and unobservable or weakly observable states on the other.

The first technique involves eliminating ungovernable or unobservable states from the modal base. This is an exact reduction. From an input-output point of view, the complete system and the reduced system are equivalent.

The second technique illustrates the notion of governability and observability Gramians introduced in section 5