Modeling is to build a model, which is an abstraction to understand things and a clear written description of things. The process of building a system model is also called modeling. Modeling is an important means and premise to study the system. Any process in which a model is used to describe the causality or interrelation of a system belongs to modeling.

Because of the different relationships described, there are various means and methods to realize this process. Through the analysis of the motion law of the system itself, the model can be established according to the mechanism of things; It can also be modeled by processing the experimental or statistical data of the system and based on the existing knowledge and experience about the system. You can also use several methods at the same time

① Analyze and design the actual system. For example, when analyzing and designing a new system, engineering usually carries out mathematical simulation and physical simulation experiments first, and then carries out physical experiments on the spot. Mathematical simulation is simpler than physical simulation. When analyzing and designing an actual system with mathematical simulation, there must be a model that describes the characteristics of the system. Modeling is usually the most critical and difficult task for many complex industrial control processes. Qualitative or quantitative research on social and economic systems also begins with modeling. For example, in population cybernetics, we can analyze the influence of population policy on population development by establishing various types of population models and changing some parameters in the models.

② Predicting or forecasting the future development trend of some states of the actual system. Prediction or prediction is based on the consistency of the development process of things. For example, according to the previous measurement data, a mathematical model of meteorological change is established to predict the future weather.

③ Optimal control of the system. The key or premise of designing controller or optimal control law by using control theory is to have a mathematical model that can represent the characteristics of the system. On the basis of modeling, various controllers or control laws are designed according to the maximum principle, dynamic programming, feedback, decoupling, pole assignment, self-organization, adaptive and intelligent control. System modeling is mainly used in three aspects. For the same actual system, people can build different models according to different purposes and uses. But any established model is only a simplification of the prototype of the actual system, because it is impossible and unnecessary to list all the details of the actual system. If some essential features of the system prototype can be retained in the simplified model, then it can be considered that the model is similar to the system prototype and can be used to describe the original system. Therefore, in the actual modeling, it is often a principle to make a proper compromise between the simplification of the model and the accuracy of the analysis results.