eu AN ALGORITHM FOR SOLVING ASSIGNMENT PROBLEMS WITH COSTS AS GENERALIZED TRAPEZOIDAL INTUITIONISTIC FUZZY NUMBERS

Assignment problem is a well-known topic and is used very often in solving problems of engineering and management sciences. In this problem cij denotes the cost for assigning the jth job to the ith person. This cost is usually deterministic in nature. In this paper cij has been considered to be generalized trapezoidal intuitionistic fuzzy numbers denoted by c̃ij which are more realistic and general in nature. Here, we present a new algorithm for solving assignment problems whose costs as generalized trapezoidal intuitionistic fuzzy numbers. We developed the algorithm using the fundamental theorem of fuzzy assignment problems. AMS Subject Classification: 03E72, 90C08


Introduction
The Assignment Problem (AP) is one of the well studied optimization problems in engineering and management sciences and has been widely applied in both manufacturing and service systems.In an assignment problem, n jobs are to be performed by n persons depending on their efficiency to do the job.In this problem c ij denotes the cost of assigning the jth job to the ith person.We assume that one person can be assigned exactly one job; also each person can do at most one job.The problem is to find an optimal assignment so that the total cost of performing all jobs is minimum or the total profit is maximum.
To find solutions to assignment problems, various algorithms such as linear programming, Hungarian algorithm, neural network and genetic algorithm have been developed.Over the past 50 years, many variations of the classical assignment problems are proposed, e.g., bottleneck assignment problem, quadratic assignment problem etc. Lin and Wen [5] proposed an efficient algorithm based on the labeling method for solving the linear fractional programming case.Sakawa et al. [10] solved the problems on production and work force assignment in a firm using interactive fuzzy programming for two level linear and linear fractional programming models.Chen [3] projected a fuzzy assignment model that considers all persons to have same skills.Chen Liang-Hsuan and Lu Hai-Wen [4] developed a procedure for solving assignment problems with multiple inadequate inputs and outputs in crisp form for each possible assignment using linear programming model to determine the assignments with maximum efficiency.Linzhong Liu and Xin Goa [6] considered the genetic algorithm for solving the fuzzy weighted equilibrium and multi-job assignment problem.Majumdar and Bhunia [8] developed an exclusive genetic algorithm to solve a generalized assignment problem with imprecise cost(s)/time(s), in which the impreciseness of cost(s)/time(s) are represented by interval valued numbers.Xionghui Ye and Jiuping Xu [17] developed a priority based genetic algorithm to a fuzzy vehicle routing assignment model with connection network.Sathi Mukherjee and Kajla Basu [13] developed a method for solving intuitionistic fuzzy assignment problems by using similarity measures and score function.Pandian and Kavitha [12], Shiny Jose and Sunny Kuriakose [14], Thorani and Ravi Shankar [16], and Nirmala and Anju [11] developed various algorithms for solving assignment problems in the fuzzy context.Here we are considering assignment problems having generalized trapezoidal intuitionistic fuzzy numbers as costs.We apply a ranking method [9] defined on generalized intuitionistic trapezoidal fuzzy numbers to rank the fuzzy costs present in the assignment problem.This paper is organized as follows.In Section 2, we present the basic concepts of generalized trapezoidal intuitionistic fuzzy numbers and described the arithmetic operations of such numbers.In Section 3, a ranking method is given to rank the generalized trapezoidal intuitionistic fuzzy numbers.In Section 4, intuitionistic fuzzy assignment problem, mathematical formulation of intuitionistic fuzzy assignment problem and fundamental theorem of intuitionistic fuzzy assignment problem are reviewed.Section 5 presents an algorithm for solving an assignment problem with costs as generalized trapezoidal intuitionistic fuzzy numbers.In Section 6, numerical example is presented to show the application of the proposed algorithm.Finally, the conclusion is given in Section 7.

Preliminaries on Intuitionistic Fuzzy Sets and Intuitionistic Fuzzy Numbers
In this section we will review the basic concepts of intuitionistic fuzzy sets and intuitionistic fuzzy numbers ).Let X be the universal set.An intuitionistic fuzzy set (IFS) A in X is given by where the functions µ A (x), ν A (x) define respectively, the degree of membership and degree of non-membership of the element x ∈ X to the set A, which is a subset of X, and for every x ∈ X, 0 Obviously, every fuzzy set has the form

For each intuitionistic fuzzy set
is called the hesitancy degree of x to lie in A. If A is a fuzzy set, then π A (x) = 0 for all x ∈ X.

Intuitionistic Fuzzy Numbers
Here we will introduce the intuitionistic fuzzy number (IFN) [7] and generalized trapezoidal intuitionistic fuzzy number (GTIFN) [15] and some properties of them.

Definition 2.2. An IFS
3. An intuitionistic fuzzy number A is said to be a generalized trapezoidal intuitionistic fuzzy number (GTIFN) with parameters and denoted by if its membership and non-membership functions are as follows: and where 0 < ω A ≤ 1, 0 ≤ u A ≤ 1 and 0 < ω A + u A ≤ 1.

Arithmetic Operations on Generalized Trapezoidal Intuitionistic Fuzzy Numbers
be two GTIFNs and λ be a real number.Then where ω = min{ω A , ω B } and u = max{u A , u B }.

Ranking of Generalized Trapezoidal Intuitionistic Fuzzy Numbers
The ranking order relation between two GTIFNs is a difficult problem.However, GTIFNs must be ranked before the action is taken by the decision maker.We use the following method for ranking generalized trapezoidal intuitionistic fuzzy numbers. where 11 + 7u A 18 .

Intuitionistic Fuzzy Assignment Problems
Suppose there are n jobs to be performed and n persons are available for doing the jobs.Assume that each person can do each job at a time, depending on their efficiency to do the job.Let cij be the intuitionistic fuzzy cost if the ith person is assigned the jth job.The objective is to minimize the total intuitionistic fuzzy cost of assigning all the jobs to the available persons (one job to one person).
The intuitionistic fuzzy assignment problem can be stated in the form of an n × n cost matrix [c ij ] of intuitionistic fuzzy numbers as given in the following where x ij = 1, if the ith person is assigned the jth job 0, otherwise is the decision variable denoting the assignment of the person i to job j. cij is the cost of assigning the jth job to the ith person.The special algorithm to solve the assignment problem is based on the following theorem.
Proof.We have Since n i=1 ũi and n j=1 ṽj are independent of x ij , if [x * ij ] make z′ minimum, they would also make z minimum.This theorem enables us to add or subtract an intuitionistic fuzzy constant from any row or column of [c ij ] without affecting the optimal solution.Thus in an intuitionistic fuzzy assignment problem with cost matrix x * ij = 0 is also an optimal solution for the problem.

An Algorithm for Solving Assignment Problems with Costs as
Generalized Trapezoidal Intuitionistic Fuzzy Numbers Step 1: First test whether the given fuzzy cost matrix is a balanced one or not.If it is a balanced one (i.e., the number of persons are equal to the number of works), then go to step 2. If it is not balanced (i.e., the number of persons are not equal to the number of works), then introduce dummy rows (or columns) with zero intuitionistic fuzzy costs so as to form a balanced one.Then go to step 2.
Step 2: Find the rank of each cell cij of the chosen fuzzy cost matrix by using the given ranking procedure and determine the element with least rank from each row.Subtract this element of each row in the cost matrix from every element in that row.
Step 3: Find the rank of each cell cij of the reduced fuzzy cost matrix obtained in step 2 and determine the element with least rank from each column.Subtract this element of each column in the cost matrix from every element in that column.
Step 4: Find the rank of each cell cij of the first modified fuzzy cost matrix obtained in step 3. Thus, the first modified matrix of ranks [R (c ij )] is obtained, and some of its entries are zeros.
Step 5: Draw the least number of lines through columns and rows which will cover all zeros of the matrix [R (c ij )].Let this number be p.Obviously p cannot be greater than n, the order of the matrix [R (c ij )].If p = n, the desired solution exists; if p < n, it does not exist and then goes to step 6.
Step 6: Determine the minimum element in the matrix [R (c ij )] which is not covered by the p lines and its corresponding fuzzy element.Subtract this fuzzy element from all fuzzy elements corresponding to the elements which are uncovered by the p lines and add the same fuzzy element to the fuzzy elements corresponding to the elements which are placed at the intersection of the horizontal and vertical lines.Thus, the second modified fuzzy cost matrix is obtained.
Step 7: Find the rank of each cell cij of the second modified fuzzy cost matrix obtained in step 6.Thus, the second modified matrix of ranks [R (c ij )] is obtained.Repeat steps 5 and 6 until we get p = n.
Step 8: Examine the rows of [R (c ij )] successively until a row with exactly one zero is found, make an assignment there.Then cross over all zeroes lying in the corresponding column, showing that they cannot be considered for future assignment.Continue in this manner until all the rows have been examined.Repeat the same procedure for columns also.If there is more than one zero in any row column, then mark one of the zeros arbitrarily and cross all zeros in the respective row or column and repeat the above process.Thus we get one marked zero in each row and each column of [R (c ij )].
Step 9: Add the intuitionistic fuzzy numbers corresponding to the cells having a marked zero to get the total optimal fuzzy cost.

Remarks
(i) If the problem is of maximization type then find the rank of each element of the chosen fuzzy cost matrix [c ij ] by using the given ranking procedure and determine the element with the highest rank.Subtract each element of the cost matrix from this element.Then the problem with the modified matrix is a minimization problem.
(ii) Sometimes technical, legal or other restrictions do not permit the assignment of a particular facility to a particular job.In such cases also we use algorithm by assigning a very high intuitionistic fuzzy cost to the cells which do not permit the assignment so that the activity will be automatically excluded from the optimal solution.

Numerical Example
To illustrate the proposed algorithm, let us consider an intuitionistic fuzzy assignment problem with rows representing 4 persons A,B,C,D and columns representing the 4 jobs namely, Job1, Job2, Job3 and Job4.The cost matrix [c ij ] is given whose elements are generalized trapezoidal intuitionistic fuzzy numbers.The problem is to find the optimal assignment so that the total cost of job assignment becomes minimum.