1. An apparatus for producing a model of a combined system having physical quantities by representing physical quantities of the combined system in terms of partial differential equations, the apparatus comprising: means for selecting an application mode modeling in up to three space dimensions the physical quantities for one or more of a plurality of systems, wherein the plurality of systems comprise at least one of a structural system, a fluids system, and an electromagnetic system; means for receiving an input of one or more physical properties for each of the application modes; means for determining a representation of a set of one or more partial differential equations for each application mode corresponding to one of the plurality of systems using at least one non-local coupling and the one or more input physical properties, the at least one non-local coupling defining a value from a first portion of a first domain to another portion of a second domain; and means for producing the model of the combined system by forming a combined set of one or more partial differential equations using the determined sets of partial differential equations associated with the plurality of systems, whereby the model represents a mathematical expression of the physical quantities of the combined physical system.