1. A method executed in a computer system for producing a model of a combined physical system having physical quantities by representing physical quantities of the combined system in terms of partial differential equations, said method comprising: representing each of a plurality of systems as an application mode modeling in up to three space dimensions said physical quantities of each system, wherein said application modes are configured to model said physical quantities of at least one of a structural system, a fluids system, and an electromagnetic system; determining, using a processor, a representation of a partial differential equation for each application mode corresponding to one of said plurality of systems using at least one non-local coupling, said at least one non-local coupling determining a value in at least one portion of a domain depending on a value from at least one other portion of a domain, parameters of said partial differential equations being physical quantities of corresponding ones of said plurality of systems; determining, using said processor or another processor, a solution to said model of said combined physical system using said partial differential equations corresponding to said plurality of systems, said model representing a mathematical expression of said physical quantities of said combined physical system; and storing in a computer readable memory or in a computer readable data storage system said solution to said model.