Abstract
The two-dimensional belief function (TDBF = (mA, mB)) uses a pair of ordered basic probability distribution functions to describe and process uncertain information. Among them, mB includes support degree, non-support degree and reliability unmeasured degree of mA. So it is more abundant and reasonable than the traditional discount coefficient and expresses the evaluation value of experts. However, only considering that the expert’s assessment is single and one-sided, we also need to consider the influence between the belief function itself. The difference in belief function can measure the difference between two belief functions, based on which the supporting degree, non-supporting degree and unmeasured degree of reliability of the evidence are calculated. Based on the divergence measure of belief function, this paper proposes an extended two-dimensional belief function, which can solve some evidence conflict problems and is more objective and better solve a class of problems that TDBF cannot handle. Finally, numerical examples illustrate its effectiveness and rationality.
Introduction
Dempster-Shafer evidence theory, also known as D-S evidence theory. The D-S evidence theory of evidence was first proposed by Dempester [1] in 1967, and then further promoted by his student Shafer [2] in 1976. As an extension of probability theory, D-S evidence theory can better describe and deal with uncertain information, so it is widely used. Bappy [3] et al. used D-S evidence theory to combine AHP and HER to evaluate supply chain sustainability; Han [4] et al. used D-S evidence theory for fuzzy reasoning, extending the method of random modeling; Liu [5] et al. used extended D-S evidence theory for multi-attribute data fusion; Fei [6] et al. combined D-S evidence theory with the Elimination and choice translating reality (ELECTRE) method to solve the decision-making problem of supplier selection; others [7–9]. Although D-S evidence theory has many advantages, there are still some problems need to be solved.
Conflict evidence fusion is a research hotspot of D-S evidence theory, and there have been many research results. One type of method is to modify the Dempester’s fusion rule. Yager [10] proposed a method of average support for propositions, and Deng’s method considered evolutionary combination rule [11]. Another method is to modify the idea of the source of evidence. The method D-S under this idea include the arithmetic average method of Murphy [12], and the weighted average method proposed by Deng et al. [13, 14]. Some researchers focus on the D-S evidence theory framework itself [15], such as the D number concept proposed by Deng et al. [16]. The D number theory breaks the limitations of mutual exclusion in the identification framework of traditional evidence theory and requires complete conditions [17–20]. It provides a good reference for the fusion of conflict evidence.
The proposal of Z-number [21] improves the reliability of information and has been studied and improved by many scholars. Kang [22] et al. proposed a method based on OWA weights and maximum entropy to determine Z-number; Qiao [23] et al. constructed a comprehensive weighted cross entropy to compare two discrete Z-numbers; Li [24] et al. proposed a new method to measure the uncertainty of discrete Z-number based on Shannon entropy; Deng [25] et al. discussed the method of measuring the uncertainty of Z-number by considering the influence of fuzzy measure and fuzzy set cardinality, and many more.
The two-dimensional belief function (TDBF) [26] is composed of a pair of ordered basic probability distribution functions (BPA), which is more flexible and more rich than traditional discount coefficients to express the evaluation value of experts, and can also solve part of the conflict of evidence. However, only collecting expert assessments is single and one-sided.
The measurement of the divergence of belief functions is also a research hotspot. S. Kullback proposed Kullback-Leibler divergence [27] in 1997 to measure the difference between two probabilities. Based on Kullback-Leibler divergence, Deng et al. [28, 29] proposed a new method for measuring the divergence of belief functions, considering the influence of multiple subsets. In addition, Deng [30] also proposed a new method of divergence measurement based on Deng entropy. Xiao [31] proposed a new divergence measure called the confidence degree of the Johnson-Shannon divergence.
This paper considers the differences between the belief functions themselves, and incorporates the divergence measure of the belief function into the TDBF, fully considering the subjectivity and objectivity of uncertain information, so that TDBF can better describe and deal with uncertainty. Numerical examples show that the extended TDBF performs well in target recognition, conflict management and special situations.
The rest of this article is arranged as follows. In Section 2, the preliminary knowledge is briefly introduced, including D-S evidence theory, TDBF, divergence of belief function and other theories involved in this article. The proposed model is described in detail in Section 3. In Section 4, numerical examples are given to prove the usefulness of the proposed model. Finally, this article is summarized in Section 5.
Preliminaries
D-S evidence theory
Dempster-Shafer evidence theory, also known as D-S evidence theory. Dempster-Shafer evidence theory is used to describe and process uncertain, incomplete, and inaccurate information.
It meets the following conditions:
Where ϕ is an empty set. B and C are focal elements. K is called the conflict coefficient and is used to indicate the degree of conflict between the two evidences and K < 1.
TDBF, T = (m
A
, m
B
), consisting of two BPAs. Both
The frame of discernment of
Given the TDBF, combinations rule is defined as follows [26]:
Based on Kullback-Leibler divergence, Deng et al. [29] considered the influence of multiple subsets in the belief function and proposed a new method for measuring divergence.
Assume that m1 and m2 are two mass functions, the divergence between m1 and m2 is defined as follows [29]:
It can be seen from the above formula that the belief of each focus element F i is divided by a term (2 F i - 1) representing the number of potential states in F i . Compared with the Kullback-Leibler divergence in probability theory, the elements of D-S evidence theory can be composed of multiple subsets. Deng et al. considered the influence of multiple subsets, so the divergence measure of beliefs is allocated to multiple subsets.
Equation (12) is a symmetric divergence proposed in consideration of symmetry [29]. Where F i is the focal element of m, |F i | is the cardinality of F i .
Based on the divergence measurement of the belief function, we propose an extended two-dimensional belief function (ETDBF). The proposed method is as follows:
Step 1. Calculate the divergence between belief functions based on formulas (11) (12) to obtain the divergence matrix DMM.
Where D ij represents the divergence measurement between m i and m j .
Step 2. Calculate the support degree Y1 of m
i
based on the divergence matrix.
The larger the value of Y1, the higher the support for m i from other evidences, and the smaller the conflict with other evidences.
Step 3. Calculate the unsupported degree N1 of m
i
based on the divergence matrix.
Where D i is divergence of m i based on the divergence matrix.
Step 4. Calculate the reliability of the unmeasured degree Θ1 of m
i
based on the divergence matrix.
Step 5. Fusion of evaluation value of expert team and reliability of evidence based on belief function divergence measurement.
T = (mA, mB), where the three monomers in mB are respectively Y, N and Θ, and the expert ’s evaluation value is respectively Y2, N2 and Θ2.
Where α is the binding coefficient, and α = 0.5 is used for calculations unless otherwise stated in this paper.
Step 6. Using Equation (10) to combine mA and mB of T = (mA, mB) and standardize.
Step 7. If there are n pieces of evidence, we can use the classical Dempster’s rule to combine the new masses n –1 times.
Examples 1 and 2 in this paper use several examples from Deng’s [26] article to prove the rationality and effectiveness of the proposed model.
m
A
of T = (m
A
, m
B
) in Example 1
m A of T = (m A , m B ) in Example 1
m B of T = (m A , m B ) in Example 1
Calculate the divergence matrix DMM based on formulas (11) and (12).
Calculate the support degree, non-support degree and reliability unmeasured degree based on the divergence of belief function based on formula (14) (15) and (16). The results are shown in Table 3.
Y1, N1, Θ1 in Example 1
The support degree, non-support degree and reliability unmeasured degree based on divergence measurement are combined with the evaluation value of experts using formula (17). The results are shown in Table 4.
Y, N, Θ in Example 1
Based on formula (10), the given TDBF is combined and standardized. The results are shown in Tables 5 and 6.
The data is combined with the rules of TDBF
Table 5 standardized data
By combining these three mass functions twice using the classic Dempster combining rule, the following results can be obtained.
If only the evaluation value of experts is considered using traditional TDBF, the results are as follows:
It can be clearly seen that the results obtained by the two methods are the same, the target is x1. Evidence 2 has a low degree of support for the target x1, because Evidence 2 has a large divergence from other evidences, so it has a low degree of support and has no effect on the results. The ETDBF can effectively solve the target recognition problem.
m A of T = (m A , m B ) in Example 2
m B of T = (m A , m B ) in Example 2
Calculate the divergence matrix DMM based on formulas (11) and (12).
By combining these three mass functions twice using the classic Dempster’s combining rule, the results are as follows:
The ETDBF takes into consideration the evidence support degree, non-support degree and the unmeasured degree of reliability based on the divergence measurement and the evaluation value directly from the experts, which is more objective. It can be seen from the Table 11 that the results obtained using the ETDBF are consistent with the calculation results of Murphy ’s average combination rule, Deng et al ’s weighted average combination rule, and TDBF ’s combination. It can be explained that the method we proposed can partially solve the conflict of evidence.
Y, N, Θ in Example 2
The data is combined with the rules of TDBF and standardization
The results of combination by different rules
m A of T = (m A , m B ) in Example 3
m B of T = (m A , m B ) in Example 3
Using traditional TDBF for data fusion can get the following results:
It can be seen from the results that the support levels of x1 and x2 are very close, and it is difficult to determine the final result or even wrong judgment.
The calculation using the ETDBF is as follows:
When α = 1 / 3using the ETDBF fusion data, the results are as follows:
After using the ETDBF, we can see from the results that the support of the three targets is relatively close, but the target can still be identified as x2. Change the combination coefficient, the result does not change with it, the target is still x2. When the target cannot be determined using TDBF, the ETDBF based on divergence measurement proposed in this paper can better solve such problems.
The divergence of the belief function can measure the difference between the two belief functions and has a strong objectivity. TDBF can better solve the problems in uncertain environment due to its flexibility and richness in describing and handling uncertain information. But only considering the evaluation value from experts is very subjective and one-sided. In this paper, the divergence of the belief function is used to measure the support degree, non-support degree and reliability unmeasured degree, and the combination coefficient is combined with the evaluation value of experts. Numerical examples prove that the proposed ETDBF can effectively deal with uncertain information, and can also partially solve the problem of evidence conflict, and even better solve the problem that TDBF cannot handle.
Since Deng proposed TDBF, no one has studied its practical application. In future research, TDBF and ETDBF can be applied to actual problems in uncertain environments, such as supplier selection, FMEA, fault diagnosis, and risk assessment. Take advantage of their greater value in describing and processing uncertain information.
Footnotes
Acknowledgments
This work was supported in part by the Fund for Shanxi “1331 Project” Key Innovative Research Team 2017, and in part by “The Discipline Group Construction Plan for Serving Industries Innovation”, Shanxi, China: The Discipline Group Program of Intelligent Logistics Management for Serving Industries Innovation 2018.
