Such software are used for detailed analysis of individual components of a system. However, it is often necessary to simulate a whole engineering system or a subsystem. The concept of the virtual prototype, in which physical prototypes are replaced by mathematical computer models, makes simulation of this type vital. In this case, it is normal to reduce any partial differential equations to ordinary differential equations. Many general and specialized simulation software packages are available for solving such systems of equations.
Models arising from engineering systems vary greatly in their character.
A large variety of numerical integration methods can be employed to solve such problems. Typically the user of simulation software is presented with a menu of seven methods from which he must choose. Selection of the wrong method may lead to failure or unnecessary long run times. Even specialist numerical mathematicians find such a choice very difficult. The situation is made worse because the characteristics of the equations may change during the simulation.