A351413 - OEIS

OFFSET

1,2

COMMENTS

In the Latin Stable Marriage Problem of order n, the sum of a man and woman's rankings of each other is n+1. This implies that the men's and women's ranking tables are Latin squares. As a subproblem of the Stable Marriage Problem, Latin instances provide lower bounds for the maximum number of stable matchings in the general problem, such as A005154 and A065982. For sizes 1 to 4, Latin instances provide exact bounds; they are conjectured to provide exact bounds for sizes a power of 2; they provide the best lower bounds known for sizes 6, 10, 12, and 24, of 48, 1000, 6472, and 126112960, respectively.

The next term, a(8), is conjectured to be 268, consistent with A005154. The minimum number of stable matchings for Latin instances of order n is n, and is realized for the cyclic group of order n. The average number of stable matchings is 7 for n=4 (cf. A351430 showing an average of about 1.5 for the general problem), and benefits from avoidance of mutual first choices and more generally the lack of overlap between the men's and women's preferred matchings. The Latin squares of A005154 and A065982 can be interpreted as multiplication tables of groups, n-th powers of the cyclic group C2 and n-th dihedral groups, respectively.

The sequence decreases from a(4)=10 to a(5)=9, in contrast to the corresponding sequence for the general problem, which Thurber showed to be strictly increasing. This has motivated the study of less restrictive subproblems, such as pseudo-Latin squares (A069124, A069156), Latin x Latin instances (A344664, A344665, A343697), instances where participants have different first choices (A343475, A343694, A343695), or instances with unspecified/tied/template rankings (A284458 with only first choices specified).

The sequence is empirically derived, originally based on reduced Latin squares (A000315). There are fewer instances to try using RC-equivalent Latin squares (A123234) instead of reduced Latin squares.

REFERENCES

C. Converse, Lower bounds for the maximum number of stable pairings for the general marriage problem based on the latin marriage problem, Ph. D. Thesis, Claremont Graduate School, Claremont, CA (1992) [Examples are from 69-70].

LINKS

Table of n, a(n) for n=1..7.

A. T. Benjamin, C. Converse, and H. A. Krieger, Note. How do I marry thee? Let me count the ways, Discrete Appl. Math. 59 (1995) 285-292.

Matvey Borodin, Eric Chen, Aidan Duncan, Tanya Khovanova, Boyan Litchev, Jiahe Liu, Veronika Moroz, Matthew Qian, Rohith Raghavan, Garima Rastogi, and Michael Voigt, Sequences of the Stable Matching Problem, arXiv:2201.00645 [math.HO], 2021 [Sections 3.7 and 4.2].

J. S. Hwang, Complete stable marriages and systems of I-M preferences, In: McAvaney K.L. (eds) Combinatorial Mathematics VIII. Lecture Notes in Mathematics, vol 884. Springer, Berlin, Heidelberg (1981) 49-63.

E. G. Thurber, Concerning the maximum number of stable matchings in the stable marriage problem, Discrete Math., 248 (2002), 195-219.

EXAMPLE

Maximal instance of order 2 with 2 stable matchings:

12

21

Maximal instance of order 3 with 3 stable matchings:

123

231

312

Maximal instance of order 4 with 10 stable matchings (group C2xC2):

1234

2143

3412

4321

Maximal instance of order 5 with 9 stable matchings:

12345

21453

34512

45231

53124

Maximal instance of order 6 with 48 stable matchings (Dihedral group):

123456

214365

365214

456123

541632

632541

Maximal instance of order 7 with 61 stable matchings:

1234567

2316745

3125476

4657312

5743621

6471253

7562134

CROSSREFS

Cf. A005154 (powers of 2), A065982 (multiples of 2), A069156 (not necessarily Latin), A000315 (reduced Latin squares), A123234 (RC-equivalent Latin squares).

Sequence in context: A193729 A303115 A074068 * A283436 A225558 A362089

Adjacent sequences: A351410 A351411 A351412 * A351414 A351415 A351416

KEYWORD

nonn,hard,more

AUTHOR

Dan Eilers, Feb 10 2022

STATUS

approved