This is a big topic, and some points can be selected for research. For example, in biological taxonomy, we can study whether an organism belongs to a known species by selecting some feature points. These feature points can be used as variables, and these feature points can have different weights, so that something similar to a matrix or an array can be formed. Then you can define an eigenvalue of it. When this eigenvalue is within a certain range, it can belong to the same category and can also be compared. When it is divided into several different categories, the corresponding eigenvalues can be calculated, and then a judgment standard can be set to make appropriate classification.