The TOPSIS method follows a basic principle, that is, the better the alternative, the farther the alternative is to the pessimistic ideal solution, and the closer the alternative is to the optimistic ideal solution. However, in the decision-making process, there may be some alternatives whose ranking cannot be directly judged from this perspective. Therefore, researchers have proposed some sorting formulas, which can accomplish the overall sorting of alternatives. But, these formulas can only be used to deal with the sorting of alternatives. To expand the application scope and decision prospect of the TOPSIS method, we introduce decision-theoretic rough fuzzy sets, and design a novel TOPSIS method that simultaneously deals with the sorting and classification of alternatives. Using the basic principle of the TOPSIS method to acquire the optimistic and pessimistic ideal distances, we regard these two distances as two fuzzy concepts, here their features are opposite, and utilize the newly defined decision-theoretic rough fuzzy set models to obtain the corresponding decision areas. Then, according to these two distances, we analyze connection between the ordering of alternatives and the total loss of alternatives and summarize the sorting rules when alternatives are classified into the same decision area and the sorting rules when alternatives are classified into different decision areas. Further, the concept of joint decision area is defined. Meanwhile, we summarize the sorting rules when alternatives are classified into the same joint decision area and the sorting rules when alternatives are classified into different joint decision areas. Using these rules, we introduce the detailed process of the novel TOPSIS method and analyze the rationality of the method. Subsequently, we test the feasibility of our method with project investment decision example and illustrate its superiority and stability through comparative analysis and parameter test. Besides, we conduct simulation experiment to further verify the similarities and differences of the sorting function of the traditional TOPSIS method and our method.
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