  A classification of dynamical systems in terms of their variational
properties is reviewed. Within this classification, front propagation is
discussed in a non-gradient relaxational potential flow. The model is motivated
by transient pattern phenomena in nematics. A front propagating into an
unstable homogenous state leaves behind an unstable periodic pattern, which
decays via a second front and a second periodic state. An interface between
unstable periodic states is shown to be a source of propagating fronts in
opposite directions.
