Why should we introduce dynamic and functional nodes in bond graphs?

In many applications, cautious use of non-elementary nodes defined by dynamic systems (dynamic nodes) and by functional operators (functional nodes) would bring much power and simplicity to bond graph modelling. The authors present here a survey of the application fields which suggest the need to study these nodes: generalised memristors, higher order nodes, continuous delays, functional operators. To be acceptable in bond graphs, dynamic and functional nodes must have clear energetic properties (conservation of energy, losslessness, passivity...). The authors´ conclusion section briefly addresses this problem