Field port-Lagrangian systems with degenerate Lagrangian and external forces

The relation between a port-representation and an infinite-dimensional Euler-Lagrange equation has previously been studied before by the authors. The formal form is called a field port-Lagrangian system. However, this system was considered under the condition that the Lagrangian was regular and the case of a degenerate Lagrangian was not explicitly shown. This paper presents a more general framework for the field port-Lagrangian system from the viewpoint of the treatment of degenerate Lagrangian and external forces.