Model reduction is an ubiquitous tool in analysis and simulation of
dynamical systems, control design, circuit simulation, structural
dynamics, CFD, etc. In the past decades many approaches have been
developed for reducing the order of a given model. Often these
methods have been derived in parallel in different disciplines
with particular applications in mind. We will discuss some of the
most prominent methods used for linear systems, compare their
properties and highlight similarities. In particular, we will
emphasize the role of recent developments in numerical linear algebra
in the different approaches. Efficiently using these new techniques,
the range of applicability of some of the methods has considerably widened.