Abstract
Multi-criteria decision making (MCDM) problems have been solved involving various types of fuzzy sets. We know that interval type-2 fuzzy sets (IT2FSs) are the most representative known fuzzy sets since they have the ability to capture both type of linguistic uncertainties associated with a word namely, the intra-personal and inter-personal uncertainties respectively. Here for MCDM problems, we will use the three trapezoidal fuzzy numbers (TT2FNs) which are more effective in capturing the uncertainty than IT2FSs, just like triangular fuzzy numbers has a better representational power than simple interval numbers. Moreover, Entropy method is employed for evaluating the values of unknown attribute weights. The ranking method employed here is the grey correlation projection method (GRPM), obtained by joining grey relational method (GRM) and projection method (PM) respectively. Lastly an example will be given to check the productivity of the suggested method.
Keywords
Introduction
In many complicated problems in the fields of engineering, economics, social and biological sciences, we come across the situations where we have to choose one object from different choices. Neither any analytical (or numerical) nor any statistical approach is often helpful in these situations due to the reason that every person has his/her own choice. Weaver [45] refers to them as the problems of organized complexity. The concept of fuzzy sets (FSs) by Zadeh [54] in 1965 is considered as an evolution for dealing such type of problems, as fuzzy sets do not have precise boundaries like the typical crisp sets. Atanassov and Gargov [2, 3] extended this idea of FSs by introducing the concept of intuitionistic fuzzy set (IFS) and interval valued intutionistic fuzzy set (IVIFS). For solving complex decision making problem, a multiattribute decision making model is presented [5]. Also practical MCDM approach combining hesitant and interval type-2 sets is adopted and put forwarded for permeating the service quality of airline companies [6]. Since then different aggregation operators have been suggested in different applications such as [8, 57], involving group decision making based on IFSs. Many MCDM models involving IFSs are based on optimization theory, where the optimization techniques are used to find the attribute weights in case of partial information or no information on weights. Decision making under such environments have been implemented in many practical applications like [17, 57] involving intuitionistic trapezoidal fuzzy numbers (ITFNS). The problems of organized complexity have been very effectively dealt by modeling attribute values in the form of "type-1 trapezoidal fuzzy numbers (T1TFNs)" and ITFNs. But according to Mendel [24, 25], these types of fuzzy numbers lack the ability of effective modeling of linguistic uncertainties. He proposed that since "words mean different things to different people" therefore only IT2FSs are suitable for modeling linguistic uncertainties. IT2FSs are computationally simple and therefore have widely used by many researchers to cope with uncertain situations. [1, 39] are some examples where different authors have applied IT2FSs for their desired optimal results. Real life decision making problems which cannot be tackled using typical analytical techniques can be handled using different types of fuzzy sets depending upon the situation. Examples are [4, 44]. Here we will make use of three trapezoidal fuzzy numbers (TT2FNs) in a MCDM situation, which are more effective in capturing the uncertainty than IT2FSs, just like triangular fuzzy numbers has a better representational power than simple interval numbers. Moreover, Entropy method is employed for evaluating the values of unknown attribute weights. The ranking method employed here is the grey correlation projection method (GRPM), obtained by joining grey relational method (GRM) and projection method (PM) respectively. Lastly an illustrative example will be provided to check the credibility of the suggested method.
Preliminaries
In the tailing para we will acquaint some fundamental ideas analogous to TT2FNs.
The "Footprint of uncertainty" (FOU) of The principal membership function of For any 0 ≤ α ≤ 1 its α plane is given as:
Here ζ ∈ [0, 1] it shows decision makers optimistic attitude, and is said to be index of optimism. ζ > 0.5 shows decision makers optimistic attitude, ζ < 0.5 shows decision makers pessimistic attitude and ζ = 0.5 if decision maker is moderate.
Uncertainty of a system is measured more effectively using Entropy. As soon as irregularity increases, the value of entropy also rises. Hence there is a direct relationship between Entropy and irregularity. Previously we have discussed in detail the main definitions of FS, FN, T1FNs, T2FNs, IT2FNs and a new type of T2FNs known as TT2FNs. As in this paper the situation is to deal with the case where attribute weights are completely unknown. Various techniques are used to calculate unknown attribute weights. These techniques are Optimization technique, Maximizing deviation method (MDM), Entropy method (EM) and many others. Within that paper EM is utilized to deduce the attribute weights that are not known using Three Trapezoidal Fuzzy numbers.
MCDM on basis of three trapezoidal fuzzy numbers
In a few MADM issues, consider there are p alternatives A = {L1, L2, L3, . . . . , L
p
}, n decision criteria C = {C1, C2, C3, . . . . , C
q
}, and W = {w1, w2, w3, . . . . , w
q
}, is weight vector of attributes, wherew
y
∈ [0, 1],
To avoid the consequence from various physical measurements to decision outcomes, at first the normalization of matrix for decision making is done. Let us consider that R = (s
xy
) p×q denotes the decision matrix where
For cost type of criteria
As in this paper we are dealing with TT2FNs to determine the unknown attribute weights. So, these three trapezoidal fuzzy numbers are translated into crisp form through use of the formula of expected value. As three trapezoidal fuzzy numbers contains upper membership values, principal membership values and lower membership values respectively. The formula of expected value to be used is shown as under:
Attribute weights are calculated by various ways; like maximizing deviation method (MDM) [36], information entropy method (IEM) [26, 27] and a multitude of optimizing methods here we employ “Information Entropy method" (IEM) to findout the weights of attribute. Shannon [26, 27] for the very first time gave concept of entropy which is one of the notion of thermodynamics. It is also related to communication theory. Entropy is assumed to be comparable to uncertainty. Many researches has been made in other branches using the concept of entropy, like administrative sciences [15, 52] and engineering automation [29, 31]. In these areas of development entropy is used to quantify the disorderly and uneven distribution and measure of chaos within the system. The quality of adequate information is measured by entropy which is perfect, solution of uncertainty from the concept of entropy the entropy would be greater if the degree system chaos is higher which is understandable by the concept of entropy.
Uncertainty of a system is measure more effectively using Entropy. As soon as irregularity increases, the value of entropy also rises. Hence there is a direct relationship between Entropy and irregularity. We will explain idea of entropy with the help of an example. It is observed that entropy of earth is increasing day by day, as a result earth is loosing its order tremendously from very first day of its formation. Entropy is usually related with information. Hence as irregularity increases probability decreases as a result the information will decrease.
Entropy value should be larger if for all alternatives terms of attribute should have less difference under one attribute, and hence least information is provided for ranking alternatives and it plays only a minor part in preference system. If difference is large for all alternatives in between their attribute values, then the entropy value of such attribute is less, and hence plays vital role in finding the best alternative. Thus small weight would be given if entropy value of an attribute is large and large weight would be assigned if entropy value is small. While working on three trapezoidal fuzzy number classical entropy method fails but is usually appropriate for attribute values that takes shape of crisp entries.
Calculation of entropy value of attribute
The entropy value of an attribute is calculate using:
Deng [10] put forth the grey theory, its adequate mathematical way to pledge the system scrutiny portrayed by inadequate information. In grey system the relational analysis is a form of perceptible scrutiny for interpreting alternatives. Precarious relations like relation among things among elements and and behaviors etc are referred by the grey relation. Grey theory is broadly connected in fields for example frameworks examination, information handling, demonstrating and expectation, as well as control and basic leadership. GRA is a significant piece of grey relational analysis, that is reasonable for taking care of issues with arduous relationships between various components and factors. GRA has been effectively connection clarifying the variety of MADM issues, example hiring election, employing choice the reclamations making arrangements for power appropriation organizations, recognition of silicon disk cutting imperfections and so on.
MADM problems can be solved by GRA by joining the complete territory of attribute terms actually supposed for every alternative into individual term. Thus initial complication will be reduced into single attribute decision making problem, so after GRA process alternatives with various attributes can be correlated easily. Thus approach enroute in SAW and TOPSIS is somewhat analogous to the procedure of joining attribute terms into an individual term. The attribute values of all alternatives are translated into comparability sequence by discarding the outcome from different physical dimensions. The grey relational coefficient is calculated between all the comparability sequence and reference sequence. Lastly based on grey relational coefficient(GRC), GRG is calculated between reference sequence and every comparability sequence.
The fuzzy positive ideal solution (FPIS) and negative ideal solution (FNIS)
Trapezoidal FPIS for a standardized trapezoidal fuzzy decision matrix is as follows:
Also the trapezoidal FNIS can be evaluated using:
Using the FPIS, GRC of each alternative is calculated. The from FPIS the GRC of each alternative is defined as:
From FPIS the GRG is evaluated by the formula given below:
The idea of GRA method is that the optimal alternatives ought to have the "grey relation’s highest degree from the FPIS and "gray relation’s least degree from the FNIS.
Projection Method
Direction and norm are two major parts by which a vector is composed. The cosine of angle that is cos(β, γ) determines whether their directions are accordant, but cannot ponder upon magnitude of norm. The similarity between two vectors can only be quantified through the projection method if we want to consider the cosine of angle and norm magnitude together. Projection method can be defined as under:
In trend curve the change in the data is evaluated by GRA method, and actually it is the degree of closeness to shape of curve. The role courting in statistics curve between every alternative and ideal solution is asserted by projection method. Grey correlation and projection method collectively form GCP method. Both methods are characterized by their own. For each alternative and positive ideal solution Grey correlation coefficient matrix (GCCM) is given as:
Weighed grey correlation matrix (WGCM)
Suppose that their is a (WGCM) Y which can be obtained by GCCM (matrix) and weight vector denoted by w, then:
Defining the linguistics terms and assigning TT2FNs to each of them
Estimation of GCP of all the alternatives onto FPIS or alternatives are ranked by projection to FNIS. If the value of similarity measure of an alternative onto FPIS is higher then such alternative with higher value will be closer to FPIS, hence is said to be the best alternative. If the value of projection of an alternative onto FNIS is smaller it would be more far to FNIS and hence is said to be the best alternative. So to consider predominantly both projections on FPIS and FNIS, we consider the relative closeness of each alternative to FPIS, which is given as:
Assume that there are five different locations for constructing a bridge for defence purpose, set of alternatives is denoted as A = {L1, L2, L3, L4, L5}. These locations and bridge conditions are to be evaluated under four criteria that are bearing capacity, length of place, wall piers, and topography and set of these four attributes is denoted by C = {C1, C2, C3, C4}. Since weight vector in this case is completely unknown, (which is given by decision maker). For conveying the estimation information in linguistics form, a DM makes use of linguistic term set.
Evaluation values given by decision maker
Evaluation values given by decision maker
Evaluation values given by decision maker
Eq. 12 is employed to calculate the expected values of each entry of the above matrix as under: I
xy
=
H
y
=
W
y
=
and FNIS relative to each attribute by using 19, as:
By using eqs. 20, we will evaluate the values of GRC of each alternative from FPIS as:
Evaluation values given by decision maker
Evaluation values given by decision maker
Evaluation values given by decision maker
Evaluation values given by decision maker
Evaluation values given by decision maker
Evaluation values given by decision maker
Evaluation values given by decision maker
Evaluation values given by decision maker
Lastly, 30 is employed to calculate the relative closeness of each alternative to FPIS as: CC1 = 0.47187, CC2 = 0.57266, CC3 = 0.54591, CC4 = 0.59969, CC5 = 0.54637 The ranking order of alternatives is obtained in accordance to the relative closeness to FPIS and ranking order thus obtained is:
For MCDM problems, though computationally more demanding but a more representative TT2FN has been used involving three TITFNs. It is therefore more effective in capturing the uncertainty than IT2FSs, just like triangular fuzzy numbers has a better representational power than simple interval numbers. We have considered the environment where there is no information on attribute weights. Therefore, Entropy method has been employed for evaluating the values of attribute weights for which the attribute values were changed into crisp numbers by using the expected value of a TT2FN. Grey correlation projection method (GRPM) has been employed to rank the alternatives. An illustrative example elaborates the practicality of the method by considering various locations for a bridge to be constructed for security purposes. Work is in progress to extend the proposed technique for other decision making problems. In future we expect that TT2FN can be employed for solving models where we want to capture the inter-personal uncertainties involved in them.
