Physical model and simulation model. ① physical model: the original system based on the similarity theory and scaled down (you can also zoom in or with the original system size) of the kind, such as the aircraft model in wind tunnel experiments, the experimental model of the hydraulic system, building models, ship model . ② model of analogy: in the different areas of physics (mechanics, electrical, thermal, fluid dynamics, etc.) systems, the respective variables are sometimes subject to the same law, the physical meaning of the common law system is completely different analogy and analogy model. Such as the pressure response of a pneumatic system under certain conditions by the throttle valve and gas capacity, consisting of a resistor and capacitor circuit output voltage characteristics have similar laws, so you can use the circuit is relatively easy to conduct experiments to simulate the pneumatic system .
Mathematical language to describe a class of model. The mathematical model can be one or a set of algebraic equations, differential equations, differential equations, integral equations or statistical equation, it can be them some appropriate combination, these equations quantitatively or qualitatively describe the system variables the relationship between cause and effect relationship. In addition to describe the mathematical model using the equation, as well as other mathematical tools, such as algebra, geometry, topology, mathematical logic description model. Should be noted that the mathematical model describes the behavior and characteristics of the system rather than the actual structure of the system.
The structural model reflects the system's structural characteristics and causal relationship model. The structural model of an important class of model is a graph model. In addition, the compartment model commonly used in the analysis of biological systems (see compartment model), also belong to the structural model. The structural model is an effective means of studying complex systems.