Visualization methods have been used to examine the details of resulting probability flows in the phase space.
Current research is directed at higher dimensional systems.
The vibration characteristics of these subsystems are then used to obtain those of the combined system, thus reducing the analysis of a complex system to the problem of investigating some characteristic matrix whose order depends on the number of degrees of freedom taking part in the interaction between subsystems. The Green's operators of the subsystems are used to obtain the characteristic equation of the system, which can be efficiently solved. This research has encompassed both active and passive systems, with current efforts directed at the synthesis of Green's operators for increasingly complex substructures. It sometimes may be desirable to monitor the response of one or more modes of a system to warn of the onset of pathological behavior associated with a single mode, such as flutter. In this context, the efficacy of the concept of modal filtering has been demonstrated, but there remain questions regarding its use for identification of systems having significant uncertainty in their physical, control, and input parameters.