 Open Access
 Total Downloads : 134
 Authors : T. Ramachandran , D. Udayakumar , T. Selvakumar
 Paper ID : IJERTV4IS010338
 Volume & Issue : Volume 04, Issue 01 (January 2015)
 Published (First Online): 23012015
 ISSN (Online) : 22780181
 Publisher Name : IJERT
 License: This work is licensed under a Creative Commons Attribution 4.0 International License
Variants of N – Factor Satisfactory Roommates Problem
T. Ramachandran 1
1 Department of Mathematics, M.V.Muthiah Government Arts College for Women
Dindigul 624001, Tamilnadu, India.

Udayakumar 2
2 Department of Mathematics,
Government Arts College, Karur639005, Tamilnadu, India.
T. Selvakumar 3
3 Department of Mathematics, Chettinad College of Engineering & Technology,
Karur639114, Tamilnadu, India.
Abstract In this paper we discussed the variants of NFactor satisfactory roommates problem with suitable examples that gives some interesting result in the case of satisfactory roommates problem.
Keywords NFactors, Preference Value, Satisfactory value matrix, Satisfactory Level, Roommates problem.

INTRODUCTION
The Stable Roommates problem(SRP) is a classical combinatorial problem that has received much attention in the literature [1,2,5,9,10,11].Gale and Shapley were the first two study SRP and they defined an instance I comprises n members pi (i = 1,2,3..n) ,where n is even, each of whom ranks the others in strict order of preference. A matching (M) in I is a set of n/2 disjoint pairs of members
{pi,pj}each of whom prefers the other his partner in the matching M . A Matching M is stable if it admits no blocking pair .A pair (pi,pj)will form a blocking pair in M iff pi and pj are not assigned to each other in M and they either prefer each other to their respective assigned partner in M or are unmatched in M.Gale and Shapley [1] showed that an SRP instance need not admit a stable matching. Irving [9] solved a problem posed by Knuth [10] when he described an O (n2) algorithm that finds a stable matching or reports that none exists, for a given instance of SRP.
The classical satisfactory roommates problem (SFRP) is closely related to the stable roommates problem. In the satisfactory roommates problem each person in the set of even cardinality n ranks the n1 others in the order of preference. The objective is to find satisfactory matching of roommates problem. This is the partition of the set into n/2 pairs of roommates based on the individual satisfactory level. It is known that some of the instances of the satisfactory roommates problem are unsolvable.

NFACTOR SATISFACTORY ROOMMATES PROBLEM WITH TIES
As mentioned earlier, classical Satisfactory Roommates problem (SFRP) in which complete preference lists will be given for each member of the group. A natural generalization of Satisfactory Roommates problem (SFRP) is called Satisfactory Roommates problem with ties lists (SFRPT) and which is closely related to Stable roommates problem with ties (SRT) [2, 3, 4]. The case arises when each person need not rank all members of his group in strict order. Some of those might be indifferent among certain members of the group, so that preference lists may involve ties. We use SFRPT to stand for the variant of SFRP in which preference lists may include ties. (Henceforth we assume that a tie is of length at least two.) By breaking the ties arbitrarily, an instance of SFRPT becomes an instance of SFRP [13].
In this paper, the NFactor SFRP [6] extended into N Factor SFRPT. For the related terminologies such as satisfactory value matrix, satisfactory level, satisfactory matching, assignment model and SMAR algorithm refer [7, 8].
Example 2.1 Here the problem is discussed with 5 different parameters, Consider the problem instance of size 4 based on order of preference.
1
3
2
4
2
(4
3)
1
3
2
4
1
4
1
(2
3)
Preference list based on Parameter A
The Satisfactory value Matrix is Preference list based on Parameter D
1
1
3
SVM = 2 3
3 4
3
4 4
2 3 4
3 4 4
3 3 3
11 4
6 3
11 7
6 6
4 7
1
3
(2
4)
2
4
1
3
3
1
4
2
4
1
(3
2)
The Satisfactory value Matrix is
3 3 6
1 2 3 4
Preference list based on Parameter B 1 2 4 3
2 4 (3 1)
3 (1 2) 4
4 3 1 2
The Satisfactory value Matrix is
1
SVM = 2
3
4
7 6 3
6 3 2
7 2 3
6 3 2
6 2 7
3 3 6
3 3 7
2 2 6
1
SVM = 2
3
4
1 2 3 4
3 7 4
2 6 3
3 4 4
2 3 3
7 4 4
6 3 3
4 4 4
3 3 3
Preference list based on Parameter E 1 2 (4 3)
2 3 4 1
3 1 2 4
4 (1 3) 2
The Satisfactory value Matrix is
Preference list based on Parameter C
1
(4
2)
3
2
1
3
4
3
2
1
4
4
(3
2)
1
The Satisfactory value Matrix is
2
3
4
11
3
7
6
3
6
1
1
SVM = 2
3
4
1 2 3 4
4 3 4
3 2 3
4 5 3
3 3 3
3 5 7
2 3 6
4 3 7
3 3 6
1
SVM = 2
3
4
11 5 7
6 3 6
3 5 7
3 3 6
7 7 7
6 6 6
The sum of all Satisfactory value Matrix is
The Satisfactory value Matrix is
1
SVM = 2
3
4
Result:
1 2 3 4
41 42 40
6 6 6
41 43 38
6 6 6
42 43 36
6 6 6
40 38 36
6 6 6
1
SVM = 2
3
4
1 2 3 4
3 6 3
3 3 3
3 6
3 3
6 4
3 3
3 6 4
3 3 3
The resultant matching for the above instance is (1,
4) and (2, 3).This matching is obtained by using the above five mentioned parameters. The above result shows that the average satisfactory level of matching (1, 4) is 66.6% and for (2, 3) is 71.6 %.

NFACTOR SATISFACTORY ROOMMATES PROBLEM WITH INCOMPLETE LIST
A classical Satisfactory Roommates problem (SFRP) in which complete preference lists will be given for each member of the group. Suppose that a person may declare one or more of the members of the opposite side to be an unacceptable partner, so that the preference list of such a person contains a proper subset of the
Preference list based on Parameter B
1
2
3 4
2
3
1
3
4
2 1
4
3
1
The Satisfactory value Matrix is
2
3
4
5
3
/td> 3
3
3
3
1
member of the opposite side. Then a person can be matched only if they are acceptable to each other [5]. We have already discussed about Satisfactory Roommates problem with incomplete preference list and it is denoted as SFRPI. That is for some member in the group of n members the preference list consists of less than n1 members. The satisfactory matching for this type of SFRPI problem can be obtained by using SMAR algorithm described in [7].In SFRPI the participant p is acceptable to participant q if p appears on the preference list of q, and unacceptable otherwise. Here the NFactor SFRP [6] extended into NFactor SFRPI.
1
SVM = 2
3
4
5 5
3 3
3 5 6
3 3 3
3 6
3 3
EXAMPLE: 3.1 Here the problem is discussed with 5 different parameters, Consider the problem instance of size 4 based on order of preference.
Preference list based on Parameter A 1 3 4 2
2 4 1
3 1 4
4 2 3 1
Preference list based on Parameter C 1 4 3 2
2 1 4
3 4 1
4 3 2 1
The Satisfactory value Matrix is The Satisfactory value Matrix is
1
SVM = 2
3
4
1 2 3 4
4 4 4
3 3 3
4 4
3 3
4 6
3 3
4 4 6
3 3 3
1
SVM = 2
3
4
1 2 3 4
5 5 4
3 3 3
5 4 4
3 3 3
5 4
3 3
4 4
3 3
Preference list based on Parameter D 1 4 3
The sum of all Satisfactory value Matrix is
2
3
4
17
22
19
3
3
3
1
2 3 4
3 2 1 4
4 3 1 2
The Satisfactory value Matrix is
1
SVM = 2
3
17
3
22 15
3 3
15 17
3 3
20
3
1 2 3 4
1 4 5
3 3
4
Result:
19 17 20
3 3 3
SVM = 2
3
4
6 3
3 3
4 6 4
3 3 3
5 3 4
3 3 3
The resultant matching for the above instance is (1, 3) and (2, 4).This matching is obtained by using the above five mentioned parameters. The above result shows that the average satisfactory level of matching (1, 3) is 73.2% and for (2, 4) is 56.6 %.

NFACTOR SATISFACTORY ROOMMATES PROBLEM WITH TIES AND INCOMPLETE LIST

Preference list based on Parameter E
1 
3 
2 4 
2 
1 
4 3 
3 
2 
1 
4 
1 
2 
Similarly the other natural generalization of Satisfactory Roommates problem (SFRP) is called Satisfactory Roommates problem with ties and incomplete lists (SFRPTI).This is also closely related to Stable Roommates with Ties and Incomplete lists (SRTI)[4,12].The variant of the Satisfactory Roommates problem which incorporates both extensions described above is denoted SFRPTI[13]. Thus an instance I of SFRPTI comprises preference lists, each of which may involve ties and/or unacceptable partners. As observed above, all satisfactory matching for a given instance of SFRPI are of the same size, and all satisfactory matching for a given instance of SFRPT are complete (and therefore of the same size). However, for a given instance of SFRPTI, it is no longer the case that all satisfactory matching need be of the same size. Furthermore, each of the problems of finding a satisfactory matching of maximum or minimum size, given an SFRPTI instance, is NP hard. With this idea we are extending the SFRPTI into NFactor Satisfactory Roommates problem with Ties and Incomplete list.
Example 4.1 Here the problem is discussed with 5 different parameters, Consider the problem instance of size 4 based on order of preference.
Preference list based on Parameter A
1 
3 
4 

2 
4 
3 

3 
2 
(4 
1) 
4 
(3 
1) 
2 
The Satisfactory value Matrix is
2 
3 
4 

9 
10 
8 

6 
6 
6 
1
1
9
8
SVM = 2 6 6
3 10 9
6 6
4 8 8 9
6 6 6
The Satisfactory value Matrix is
Preference list based on Parameter D
1
1
SVM = 2
3 9
9 
8 
8 

6 
6 
6 
6
4
2 3 4
9 9
6 6
10 8
6 6
10 8
6 6
1 4 (2 3)
2 3 1
3 1 (4 2)
4 1 3
The Satisfactory value Matrix is
Preference list based on Parameter B 1 2 4
2 (3 4) 1
3 4 2
4 (2 1) 3
1
SVM = 2
3
4
1 2
9
6
9
6
4 9
6 6
11
6
3 4
4 11
6 6
9
6
7
6
7
6
The Satisfactory value Matrix is
Preference list based on Parameter E
1
SVM = 2
3
4
1 2
8
6
8
6
9
6
9 10
3 4
9
6
9 10
6 6
8
6
8
1 2 3
2 (3 4) 1
3 1 4 2
4 (2 3)
The Satisfactory value Matrix is
6 6 6
1 2 3 4
1 8 10
Preference list based on Parameter C
6
1 
3 
2 
4 
SVM = 

2 
(4 
1) 
3 

3 
4 
1 
4 

4 
1 
(3 
2) 
2 8
6
10 7
6 6
10
6
6
7 10
6 6
9
6
9
6
The sum of all Satisfactory value Matrix is V.CONCLUSION
1
SVM = 2
3
4
1 2 3 4
34 33 37
6 6 6
34 35 36
6 6 6
33 30 41
6 6 6
37 36 41
3 6 6
Many researchers described Roommates problem considering only one factor and solved by using their methods so far, in this paper we presented an NFactor roommates problem and solved it by using SMAR algorithm. The concept is analyzed by solving RP with ties, incomplete list, ties and incomplete list. After examining the results we find that, this algorithm results a matching in which each pair attains maximum satisfactory level. So SMAR results NFactor Satisfactory matching of roommates problem with all other extended cases.
Result: The resultant matching for the above instance is (1, 2) and (3, 4).This matching is obtained by using the above five mentioned parameters. The above result shows
that the average satisfactory level of matching (1, 2) is 68.3% and for (3, 4).is 56.6 %.
REFERENCES

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Tamas Fleiner, Robert W.Irving and David F.Manlove. Efficient algorithms for generalized Stable Marriage and Roommates problems. Theoretical Computer Science 381 (2007) 162176.

Sandy Scott, A Study Of Stable Marriage Problems With Ties – Ph.D Thesis, University of Glasgow2005.

D. Gusfield and R.W. Irving. The Stable Marriage Problem: Structure and Algorithms. MIT Press, 1989.

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