Mathematical Problems in Engineering
Volume 2016 (2016), Article ID 3080679, 9 pages
http://dx.doi.org/10.1155/2016/3080679

Research Article

Fuzzy Risk Analysis for a Production System Based on the Nagel Point of a Triangle

Handan Akyar

Department of Mathematics, Faculty of Science, Anadolu University, 26470 Eskisehir, Turkey

Received 17 December 2015; Accepted 9 March 2016

Academic Editor: Rosana Rodriguez-Lopez

Copyright © 2016 Handan Akyar. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract.

Ordering and ranking fuzzy numbers and their comparisons play a significant role in decision-making problems such as social and economic systems, forecasting, optimization, and risk analysis problems. In this paper, a new method for ordering triangular fuzzy numbers using the Nagel point of a triangle is presented. With the aid of the proposed method, reasonable properties of ordering fuzzy numbers are verified. Certain comparative examples are given to illustrate the advantages of the new method. Many papers have been devoted to studies on fuzzy ranking methods, but some of these studies have certain shortcomings. The proposed method overcomes the drawbacks of the existing methods in the literature. The suggested method can order triangular fuzzy numbers as well as crisp numbers and fuzzy numbers with the same centroid point. An application to the fuzzy risk analysis problem is given, based on the suggested ordering approach.

1. Introduction

Recently, ordering and ranking fuzzy numbers and their comparisons have become the main research interest in fuzzy decision analysis and real world problems (e.g., see [1–10] and references therein).

Prominent methods for the ordering and ranking of fuzzy numbers have been published since the method for ranking fuzzy numbers was initially proposed by Jain (e.g., see [2, 3, 10–25] and references therein). The most widely used approach for ordering and ranking triangular fuzzy numbers is based on the centroid of a triangle, proposed by Yager (see [12]). Yager’s method considers only the horizontal coordinate of the centroid for the ranking, which lessens its effectiveness. Murakami et al. improved Yager’s method using both coordinates of the centroid (see [10]). To overcome the shortcomings of the aforementioned centroid methods, S.-J. Chen and S.-M. Chen submitted a ranking method that uses the centroid point and the standard deviation of fuzzy numbers (see [3]). In [26], Nazirah and Daud wholly reviewed certain centroid index methods.

In [22], Lee and Chen propose a new method for fuzzy risk analysis based on fuzzy numbers with different shapes and deviations. In [14], Abbasbandy and Asady propose a sign distance method, where its drawbacks are treated in [15] by constructing a revised sign distance method. A new method is proposed by Ezzati et al. [20] that is a modification of Abbasbandy and Hajjari’s method (see [23]) which can also be used for ranking symmetric fuzzy numbers. In [19], Ezzati et al. revise this method to overcome certain shortcomings.

Another approach for the ranking and ordering of fuzzy numbers is given by Akyar et al., based on the incenter of a triangle, which is the center of an inscribed circle (see [2, 18]). However, it will be shown that this method has certain shortcomings, namely, the fact that the result of this method is sometimes inconsistent with human intuition. Düzce suggests a different method using the center of the nine-point circle of a triangle (see [21]). However, Düzce’s method also has certain drawbacks, namely, the fact that this method cannot rank fuzzy numbers with the same centroid.

Recently, an improved method, which considers the areas of the positive side, the areas of the negative side, and the spreads of generalized fuzzy numbers as the ranking factors for ranking fuzzy numbers, has been given by Jiang et al. [24]. Another approach for the ranking of generalized fuzzy numbers with different left and right heights is given by Chutia et al. using integral values [25]. This method considers nonnormal -norm trapezoidal fuzzy numbers as well as -norm generalized fuzzy numbers with different left and right heights.

In this paper, the incenter method will be revised using the Nagel point of a triangle to increase efficiency. The Nagel point is the point of intersection of the line segments from the vertices of the triangle to the points of tangency of the opposite excircles [27]. In order to save most of the information of triangular fuzzy numbers, we associate these fuzzy numbers with triplets instead of real numbers. We will show that, unlike previously mentioned methods, we can efficiently order triangular fuzzy numbers by the proposed method.

The rest of this paper is organized as follows. In Section 2, fuzzy numbers, their fundamental properties, basic definitions, and theorems regarding the Nagel point of a triangle are reviewed. Next, in Section 3, we present a new method for ordering triangular fuzzy numbers based on the Nagel point of a triangle. In Section 4, we investigate reasonable properties of ordering triangular fuzzy numbers by the proposed method. In Section 5, numerical examples are given. We compare the results of the proposed method with other existing methods. An application to the fuzzy risk analysis problem of the proposed method is presented in Section 6. Finally, a conclusion is given in Section 7.

2. Preliminaries

2.1. Fuzzy Numbers

Here, certain essential concepts of fuzzy numbers and their basic properties will be given. For further information see [28, 29].

A fuzzy set on a set is a function . Commonly, the symbol is used for the function , and it is said that the fuzzy set is characterized by its membership function which associates each with a real number . The degree to which belongs to is interpreted by the value of .

Let be a fuzzy set on . The support of is given as

and the height of is defined as

The fuzzy set is called a normal fuzzy set if .

Let be a fuzzy set on and . The -cut (-level set) of the fuzzy set is given by

where denotes the closure of sets.

A fuzzy set on is called a convex fuzzy set if its -cuts are convex sets for all .

If is a fuzzy set in , then is called a fuzzy number if

(1) is convex,(2) is normal,(3) is upper semicontinuous,(4)the support of is bounded.

Hereafter, lower case lettering such as will be used to denote fuzzy numbers.

Generally, certain special types of fuzzy numbers, such as triangular, trapezoidal, and -fuzzy numbers, are used for real life applications (e.g., see [1–10] and references therein).

Let be two continuous and increasing functions satisfying , . Let be real numbers. The fuzzy number is an -fuzzy number if

In particular, we get trapezoidal fuzzy numbers when the functions and are linear. Furthermore, if and

then the fuzzy number is called a triangular fuzzy number. Then we can denote a triangular fuzzy number by a triplet and we can write .

Let and be fuzzy numbers. Then the sum of fuzzy numbers and is defined as

In particular, if and are triangular fuzzy numbers, then one can verify that

The multiplication of fuzzy numbers and is also defined as

Although and are triangular fuzzy numbers, their multiplication is not a triangular fuzzy number. For convenience, we can express it as a triangular fuzzy number using two end points and one peak point. Therefore, for triangular fuzzy numbers and we define . Similarly, we define .

The set of all triangular fuzzy numbers will be denoted by . In this paper, we will only consider triangular fuzzy numbers.

2.2. Nagel Point of a Triangle

The Nagel point of a triangle is defined as the point of intersection of the cevians , , and , where , , and are points where the excircles touch the sides (Figure 1). The existence of the Nagel point was proved in 1836, by German mathematician C. H. Nagel.

Figure 1: The Nagel point of a triangle .

Theorem 1 (Nagel Point Theorem [30]). The cevians joining the vertices of a triangle to the points of tangency of the opposite sides with the corresponding excircles are concurrent.

Note that, in Figure 1, . Hence, point is halfway-around the perimeter of the triangle from vertex . Similarly, points and are also halfway-around vertices and , respectively. Therefore, the Nagel Point Theorem is also named the Halfway-Around Theorem.

Given a triangle , the trilinear coordinates of a point , with respect to triangle , are an ordered triple of numbers, each of which is proportional to the directed distance from to one of the side lines. Trilinear coordinates are usually denoted by (see Figure 2). Trilinear coordinates of the Nagel point are given as

or its equivalent:

where , , and (see [31]).

Figure 2: Trilinear coordinates of point .

If point has trilinear coordinates , then the Cartesian coordinates of are calculated as follows:

Here, , , and .

Proposition 2. Let be a Nagel point of triangle . If then .

Proof. Let have the trilinear coordinates . If , then by the definition of trilinear coordinates and . Using (11) we achieve the desired result.

3. A New Method for Ordering Triangular Fuzzy Numbers

Let be a triangular fuzzy number. Then this corresponds to the triangle with Cartesian coordinates , , and in the Euclidean plane. Then we find

Using (9) and (12), we find trilinear coordinates of Nagel point of triangle as follows:

Therefore, for all by means of the given method one can always get a point in the Euclidean plane.

Using (11) the Cartesian coordinates of for can be calculated as follows:

Different triangular fuzzy numbers may have the same Nagel point. Indeed let , , and ; then using (9) and (11) we get the same Nagel point

Therefore, the correspondence between triangular fuzzy numbers and their Nagel points is not one to one.

Let and be two different triangular fuzzy numbers, such that . If then it is obvious that . Hence, the correspondence

is one to one. Here, and .

Using lexicographical order, we can now order triangular fuzzy numbers by the function defined by (16); that is, for triangular fuzzy numbers and

where the symbol denotes the lexicographical order, and it is defined as follows:

Obviously, if and only if or ( and ) or ( and and ).

In view of Proposition 2, we get the following result.

Proposition 3. Let , be arbitrarily small positive real numbers and let be a triangular fuzzy number. Then

Therefore, if a triangular fuzzy number is a crisp number, that is, , then we can assume that . Hence, using the proposed method, we can also order crisp numbers. Furthermore, since the function defined by (16) is one to one, the proposed method is discriminative.

Example 4. Let , , and be triangular fuzzy numbers and let be a crisp number (see Figure 3). Then using (14) and Proposition 3 we get

Since , , , and , we have

and we find

as expected.

Figure 3: Triangular fuzzy numbers with their Nagel points in Example 4.

4. Reasonable Ordering Properties

In [32, 33], Wang and Kerre propose certain axioms as reasonable properties to determine the rationality of an order method. In this section, it will be shown that the proposed method satisfies Wang and Kerre’s reasonable properties.

Let . If or , then we write . It is clear that when the proposed method is applied on the set of all triangular fuzzy numbers , one of the following is true for : .

Now, we investigate the following axioms defined as reasonable properties of ordering triangular fuzzy numbers for the proposed method.

(1)It is clear that, for an arbitrary finite subset of and by the proposed method on .(2)Since lexicographical order is a total order relation, for an arbitrary finite subset of and and by the proposed method on , we have by the proposed method on .(3)Similarly, since lexicographical order is a total order relation, for an arbitrary finite subset of and , and by the proposed method on , we have by the proposed method on .(4)For an arbitrary finite subset of and ,

 we have by the proposed method on , where denotes the support of triangular fuzzy number defined by (1). Indeed, if and then and . By the definition of a Nagel point, we get , where and are horizontal coordinates of the Nagel points of and , respectively. This axiom means that if two triangular fuzzy numbers have separate supports, then the fuzzy number with support on the right is at least as good as the one with support on the left.(5)Let and be arbitrary sets of triangular fuzzy numbers and let and be in . Then it is clear that by the proposed method on if and only if by the proposed method on .(6)Let , , and be elements of . Then by the definition of the sum of fuzzy numbers and . If by the proposed method on , then by the proposed method on except for the case in which and are isosceles triangles with the same peak point. Indeed, if , , and then it is easy to find that and . Hence, we get . However, since and we obtain .(7)Let , , and be triangular fuzzy numbers, such that and , , and are nonnegative real numbers. Then by the proposed method on implies that by the proposed method on except for the case in which and are isosceles triangles with the same peak point.

5. Numerical Examples

In this section, we initially give a simple example to show that the proposed method overcomes the shortcomings of the method of Akyar et al. (see [18]).

Example 5. Consider two triangular fuzzy numbers and (see Figure 4). According to the method of Akyar et al. [18], the coordinates of the incenters of triangles corresponding to triangular fuzzy numbers and are and , respectively. Hence, in view of this method, we get , but this is not consistent with human intuition.
However, using the proposed method we get from (14)

Therefore, we have and . Since

we find which is reasonable and similar to the results of the aforementioned methods (see [15, 19, 21, 24, 25]).
Thus, the proposed method overcomes the shortcoming of the method of Akyar et al. in this example.

Figure 4: Triangular fuzzy numbers with their Nagel points in Example 5.

Now, to compare the proposed method with certain existing methods, we use seven sets of triangular fuzzy numbers. Four of these are adopted from [3, 22]. Note that we set in the method of Chutia et al. [25]. The sets are shown in Figure 5, and a comparison of the results for different methods is shown in Table 1.

Table 1: A comparison of methods.

Method
Ordering results

Set 1
Set 2
Set 3
Set 4
Set 5
Set 6
Set 7

S.-J. Chen and S.-M. Chen [3]

Lee and Chen [22]

Akyar et al. [18]

Abbasbandy et al. [15]

Chutia et al. [25]

Düzce [21]

Ezzati et al. [19]

Jiang et al. [24]

Proposed

Figure 5: Sets of triangular fuzzy numbers.

From Table 1, we can see the drawbacks of the existing methods, described as follows:

(1)In Set 1, Set 4, and Set 6 of Figure 5, all the listed methods achieve the same order as well as the proposed method.(2)In Set 2 of Figure 5, the method of Düzce and Chutia et al. is not discriminative. For the revised sign distance method of Abbasbandy et al. is not discriminative and for as it achieves a counterintuitive order. However the methods of Lee and Chen, S.-J. Chen and S.-M. Chen, Akyar et al., and Ezzati et al. and the proposed method obtain the same order.(3)In Set 3 of Figure 5, all listed methods achieve the same order except for the method of Ezzati et al.(4)In Set 5 of Figure 5, the method of S.-J. Chen and S.-M. Chen achieves a counterintuitive order, while the proposed method and the other listed methods obtain the same order.(5)In Set 7 of Figure 5, the methods of S.-J. Chen and S. M. Chen, Abbasbandy et al., and Akyar et al. achieve a counterintuitive order. However, by the proposed method we have overcome this shortcoming and obtain the same order as the other listed methods.

Thus, other listed methods have certain drawbacks, such as the result order being inconsistent with human intuition; the method is not discriminative, or it cannot order fuzzy numbers with the same centroid. However, the proposed method avoids these problems for ordering triangular fuzzy numbers. The limitations of each method are presented in Table 2.

Table 2: The limitations of each method (✕: does not satisfy the property; ✓: satisfies the property).

Method
Discriminative
Rank correctly FNs with the same centroid point
Rank crisp numbers

S.-J. Chen and S.-M. Chen [3]
✕
✓
✓

Lee and Chen [22]
✓
✓
✓

Akyar et al. [18]
✓
✓
✓

Abbasbandy et al. [15]
✕
✕
✓

Chutia et al. [25]
✕
✕
✓

Düzce [21]
✕
✕
✓

Ezzati et al. [19]
✓
✓
✓

Jiang et al. [24]
✓
✓
✓

Proposed
✓
✓
✓

6. Fuzzy Risk Analysis Based on the Proposed Method

Here, we present an application of the proposed method to a fuzzy risk analysis problem.

Let us assume that we have manufactories and manufactory produces the component which is composed of different subcomponents .

If denotes the probability of failure and denotes the severity of loss of the subcomponent ( and ) then one can obtain the probability of failure of the manufactory . The basic structure used to analyze the probability of failure of component made by manufactory is shown in Figure 6 (see [34]).

Figure 6: The structure for fuzzy risk analysis.

We propose a fuzzy risk analysis method similar to that of Chen and Sanguansat (see [17]) as follows.

Step 1. Using the fuzzy weighted method for every component made by manufactory calculates the probability of failure

() by means of and of subcomponent .

Step 2. Transform each triangular fuzzy number into standardized triangular fuzzy number

where , , and denotes the smallest integer greater than the absolute value of the real number .

Step 3. For all order triangular fuzzy numbers by the proposed method. The larger triangular fuzzy number represents the higher probability of failure of component made by the manufactory .

Here, we present an example to illustrate the fuzzy risk analysis algorithm inspired by [16].

Example 6. Let us assume that , , and are the same product manufactured by different manufactories , , and , respectively. Furthermore, for all the component is composed of three subcomponents , , and .
Using , the severity of loss of subcomponent , and , which is the probability of failure of subcomponent , we can find the probability of failure of component made by manufactory .
We use a seven-member linguistic term set shown in Table 3, suggested by S.-J. Chen and S. M. Chen, to represent the linguistic terms and their corresponding triangular fuzzy numbers (see [9]).
The linguistic values of and of subcomponent made by manufactory are shown in Table 4.

Table 3: Linguistic terms and their corresponding triangular fuzzy numbers.

Linguistic term
Triangular fuzzy numbers

Very low

Low

Fairly low

Medium

Fairly high

High

Very high

Table 4: Linguistic values of the evaluating items of the subcomponents made by manufactories.

Manufactory
Subcomponents
Linguistic values

The severity of loss
The probability of failure

= low
= fairly low

= fairly high
= medium

= very low
= fairly high

= low
= very high

= fairly high
= fairly high

= very low
= medium

= low
= fairly low

= fairly high
= high

= very low
= fairly high

Step 1. From (26) and the given data we get

Step 2. Since for all and , it is not necessary to transform triangular fuzzy numbers into standardized form. Therefore we get

Step 3. It follows from (16) that

Since then . This means that component , made by manufactory , has the highest probability of failure, followed by and , respectively.

7. Conclusion

In this paper, we present a new method for ordering triangular fuzzy numbers. The Nagel point of a triangle and the peak point for ordering triangular fuzzy numbers are used. We show that the proposed method can overcome the drawbacks of certain well-known ordering and ranking methods. The advantages of the proposed method are presented with comparative examples. We also give an application of the proposed fuzzy ordering method to the fuzzy risk analysis problem, where the evaluating values are represented by triangular numbers. Consequently, the proposed ordering process is simple and efficient for calculation and comparison purposes, which makes its application more effective.

Competing Interests

The author declares that she has no competing interests.

Acknowledgments

This study was supported by the Anadolu University Scientific Research Projects Commission under Grant no. 1403F077.

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