1. A method of creating a physically based crank-resolved simplified computer implementable engine model, the method comprising: obtaining a complete crank-resolved computer implementable engine model, wherein the complete crank-resolved computer implementable engine model is operable to simulate engine operation of the entire engine, including simulating wave-action effects throughout the engine, and produce outputs based on parametric inputs to the engine; selecting, from the complete crank-resolved computer implementable engine model, one or more elements defining start and end points of the physically based crank-resolved simplified computer implementable engine model which is to be created; obtaining from a library of rules, at least one computer implementable model creation rule corresponding to the one or more selected elements; creating, using a computer, the physically based crank-resolved simplified computer implementable engine model using the at least one computer implementable model creation rule, wherein the physically based crank-resolved simplified computer implementable engine model is also operable to simulate engine operation, including simulating wave-action effects throughout the simplified engine model, and produce outputs in real time based on the parametric inputs to the engine; wherein said simplified computer implementable engine model employs an approximation for a mathematical function employed by the complete crank-resolved engine model, comprising: identifying an operation which the complete crank-resolved engine model employs, for which a corresponding mathematical function requires a complex numerical algorithm; obtaining an approximation to the mathematical function which requires a simplified algorithm; and generating a control rule under which, when a simplified engine model implementing the operation is created from the complete crank-resolved engine model, the approximation will be employed instead of the mathematical function, and wherein said generated control rule is stored in a module which is operable to create a simplified engine model from the complete crank-resolved engine model; and simulating engine operation, including simulating wave-action effects throughout the simplified engine model, using the computer and the physically based crank-resolved simplified computer implementable engine model.