Explanation: A model determined by a completely positive functional relationship (causality). The model includes the mathematical model described by differential equation, which can be solved by analytical solution, numerical solution and electric simulation method. When the water balance elements are not treated as random variables, the model described by the water balance equation is also deterministic.

A deterministic model refers to a model that does not contain any random components. For the deterministic model, as long as the relationship between input and input is set, its output is also deterministic, regardless of the number of experiments. The deterministic model is actually a simplified stochastic model.

The mathematical model describes the changing law of nature.

The mathematical model provides us with a quantitative and qualitative analysis method.

The mathematical model can be solved in the following ways:

Analysis: solve by hand.

Numerically, it is solved by computer.

Mathematical models usually consist of mathematical objects and equations.

Mathematical objects are divided into variables and parameters:

Variable: it will change with the phenomenon.

Discrete variable: smooth (such as time TT TT).

Continuous variable: continuous (e.g. quantity N NN).

Parameter: will not change with the phenomenon.

The most commonly used variable in mathematical model: TT TT time.