0
$\begingroup$

Short and informal version: Does the stable marriage problem have a solution if there are $\kappa$ men and $\kappa$ women for any cardinal $\kappa \geq \aleph_0$?

Long and formal version: Let $\kappa$ be an infinite cardinal. For any set $X$ we set $\text{Bij}(X)$ to be the set of bijections from $X$ to itself.

We are given two "preference functions" $$P_M, P_W: \kappa \to \text{Bij}(\kappa).$$ Let $\mu:M\to W$ be a bijection (also called "marriage"). We say that $(m_0, w_0)\in \kappa\times \kappa$ is a blocking pair for the marriage $\mu$ if

  1. $\mu(m_0) \neq w_0$, and
  2. $\big(P_M(m_0)\big)(w_0) < \mu(m_0)$ and vice versa, $\big(P_W(w_0)\big)(m_0) < \mu^{-1}(w_0)$.

A marriage is said to be stable if there are no blocking pairs.

Given $\kappa, P_M, P_W$ as above, is there always a stable marriage?

[This looks so ugly that I'm not even sure it's the correct formalisation, feel free to correct & downvote if I got it wrong.]

$\endgroup$

1 Answer 1

4
$\begingroup$

Your formal version does not look correct. For each boy $b$, there should be a total order $\leq_b$ on the set of girls $G$ (this is the preference order for $b$) and for each girl $g$, there should be a total order $\leq^g$ on the set of boys (this is the preference order for $g$). In the special case that $G$ and $B$ are both countably infinite and each $\leq_b$ and $\leq^g$ has order type $\omega$ (this is a natural generalization of the finite case), there is indeed a Stable Marriage Theorem. See Theorem 2.1 of this paper of Cenzer and Remmel. The proof of correctness is to simply extend the Gale-Shapley algorithm to the infinite case. Theorem 2.5 of the same paper shows that as long as the preference orderings $\leq_b$ and $\leq^g$ are all well-orderings, then there is a stable matching.

$\endgroup$
1
  • $\begingroup$ Thanks for your answer. I thought since the preference functions are functions to a well-ordered set ($\kappa$), it might work. But your pointer to the paper of Cenzer & Remmel is very helpful, thanks a lot! $\endgroup$ Apr 5, 2016 at 6:33

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.