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Motivation The Model Two-Sided Matching Matroids Uniqueness of Nash Equilibria for TSM Matroids Uniqueness of Nash Equilibria in Atomic Splittable Congestion Games Veerle Timmermans Tobias Harks Maastricht University Dagstuhl 2015 Veerle


  1. Motivation The Model Two-Sided Matching Matroids Uniqueness of Nash Equilibria for TSM Matroids Uniqueness of Nash Equilibria in Atomic Splittable Congestion Games Veerle Timmermans Tobias Harks Maastricht University Dagstuhl 2015 Veerle Timmermans , Tobias Harks Uniqueness of Nash Equilibria in Matroid Congestion Games

  2. Motivation The Model Two-Sided Matching Matroids Uniqueness of Nash Equilibria for TSM Matroids Motivation and related work ”In general, a game may have several equilibria. Yet uniqueness is crucial . . . . Nash equilibrium makes sense only if each player knows which strategies the others are playing; if the equilibrium recommended by the theory is not unique, the players will not have this knowledge.” - Robert J. Aumann (foreword to Harsanyi & Seltens book) Veerle Timmermans , Tobias Harks Uniqueness of Nash Equilibria in Matroid Congestion Games

  3. Motivation The Model Two-Sided Matching Matroids Uniqueness of Nash Equilibria for TSM Matroids Motivation and related work ”In general, a game may have several equilibria. Yet uniqueness is crucial . . . . Nash equilibrium makes sense only if each player knows which strategies the others are playing; if the equilibrium recommended by the theory is not unique, the players will not have this knowledge.” - Robert J. Aumann (foreword to Harsanyi & Seltens book) ◮ Non-atomic players: unique NE [Milchtaich, 2000] Veerle Timmermans , Tobias Harks Uniqueness of Nash Equilibria in Matroid Congestion Games

  4. Motivation The Model Two-Sided Matching Matroids Uniqueness of Nash Equilibria for TSM Matroids Motivation and related work ”In general, a game may have several equilibria. Yet uniqueness is crucial . . . . Nash equilibrium makes sense only if each player knows which strategies the others are playing; if the equilibrium recommended by the theory is not unique, the players will not have this knowledge.” - Robert J. Aumann (foreword to Harsanyi & Seltens book) ◮ Non-atomic players: unique NE [Milchtaich, 2000] ◮ Standard game with atomic players: often multiple equilibria Veerle Timmermans , Tobias Harks Uniqueness of Nash Equilibria in Matroid Congestion Games

  5. Motivation The Model Two-Sided Matching Matroids Uniqueness of Nash Equilibria for TSM Matroids Motivation and related work ”In general, a game may have several equilibria. Yet uniqueness is crucial . . . . Nash equilibrium makes sense only if each player knows which strategies the others are playing; if the equilibrium recommended by the theory is not unique, the players will not have this knowledge.” - Robert J. Aumann (foreword to Harsanyi & Seltens book) ◮ Non-atomic players: unique NE [Milchtaich, 2000] ◮ Standard game with atomic players: often multiple equilibria ◮ Atomic splittable games → ? Veerle Timmermans , Tobias Harks Uniqueness of Nash Equilibria in Matroid Congestion Games

  6. Motivation The Model Two-Sided Matching Matroids Uniqueness of Nash Equilibria for TSM Matroids Definition (Congestion Model) M = ( N , R , S , ( d i ) i ∈ N , ( c i , r ) r ∈ R ; i ∈ N ), ◮ N = { 1 , . . . , n } players with demands d i > 0 ◮ R = { 1 , . . . , m } resources ◮ Strategies S = ×S i , with S i ⊆ 2 R ◮ Strategy distribution ( x S ) S ∈S i satisfying � S ∈S i x S = d i . ◮ c i , r : R + → R + , increasing and convex Veerle Timmermans , Tobias Harks Uniqueness of Nash Equilibria in Matroid Congestion Games

  7. Motivation The Model Two-Sided Matching Matroids Uniqueness of Nash Equilibria for TSM Matroids Definition (Congestion Model) M = ( N , R , S , ( d i ) i ∈ N , ( c i , r ) r ∈ R ; i ∈ N ), ◮ N = { 1 , . . . , n } players with demands d i > 0 ◮ R = { 1 , . . . , m } resources ◮ Strategies S = ×S i , with S i ⊆ 2 R ◮ Strategy distribution ( x S ) S ∈S i satisfying � S ∈S i x S = d i . ◮ c i , r : R + → R + , increasing and convex ◮ Complete strategy profile x = (( x S ) S ∈S i ) i ∈ N ◮ Load on resource r : x r = � S ∈S ; r ∈ S x S ◮ Load of a player i : x i , r = � S ∈S i ; r ∈ S x S Veerle Timmermans , Tobias Harks Uniqueness of Nash Equilibria in Matroid Congestion Games

  8. Motivation The Model Two-Sided Matching Matroids Uniqueness of Nash Equilibria for TSM Matroids Example 1 5 3 s t 2 4 6 Veerle Timmermans , Tobias Harks Uniqueness of Nash Equilibria in Matroid Congestion Games

  9. Motivation The Model Two-Sided Matching Matroids Uniqueness of Nash Equilibria for TSM Matroids Example 1 5 3 s t 2 4 6 ◮ Player cost π i ( x ) = � r ∈ R x i , r c i , r ( x r ) Veerle Timmermans , Tobias Harks Uniqueness of Nash Equilibria in Matroid Congestion Games

  10. Motivation The Model Two-Sided Matching Matroids Uniqueness of Nash Equilibria for TSM Matroids Example 1 5 3 s t 2 4 6 ◮ Player cost π i ( x ) = � r ∈ R x i , r c i , r ( x r ) ◮ Marginal cost resource: µ i , r ( x ) = c i , r ( x r ) + x i , r c ′ 1 ( x r ) Veerle Timmermans , Tobias Harks Uniqueness of Nash Equilibria in Matroid Congestion Games

  11. Motivation The Model Two-Sided Matching Matroids Uniqueness of Nash Equilibria for TSM Matroids Example 1 5 3 s t 2 4 6 ◮ Player cost π i ( x ) = � r ∈ R x i , r c i , r ( x r ) ◮ Marginal cost resource: µ i , r ( x ) = c i , r ( x r ) + x i , r c ′ 1 ( x r ) ◮ Marginal cost strategy: µ i , S ( x ) = � r ∈ S µ i , r ( x ) Veerle Timmermans , Tobias Harks Uniqueness of Nash Equilibria in Matroid Congestion Games

  12. Motivation The Model Two-Sided Matching Matroids Uniqueness of Nash Equilibria for TSM Matroids Example 1 5 3 s t 2 4 6 ◮ Player cost π i ( x ) = � r ∈ R x i , r c i , r ( x r ) ◮ Marginal cost resource: µ i , r ( x ) = c i , r ( x r ) + x i , r c ′ 1 ( x r ) ◮ Marginal cost strategy: µ i , S ( x ) = � r ∈ S µ i , r ( x ) ◮ Equilibrium condition: If x i , S > 0, then µ i , S ( x ) ≤ µ i , S ′ ( x ) Veerle Timmermans , Tobias Harks Uniqueness of Nash Equilibria in Matroid Congestion Games

  13. Motivation The Model Two-Sided Matching Matroids Uniqueness of Nash Equilibria for TSM Matroids Related work atomic splittable games On cost function: ◮ When players experience congestion the same: Polynomials with degree at most 3 [Altman et al., 2002] On strategy space in network congestion games: ◮ If players are of the same type [Orda et al., 1993] Using a potential function [Cominetti, Correa and Stier-Moses, 2009] ◮ If the network is a two-terminal nearly-parallel graph [Richman and Shimkin, 2007] ◮ If the network is a ring graph, with some properties on the order-destination pairs [Meunier and Pradeau, 2014] ◮ When players experience congestion the same, full characterization by [Bhaskar et al., 2015] Veerle Timmermans , Tobias Harks Uniqueness of Nash Equilibria in Matroid Congestion Games

  14. Motivation The Model Two-Sided Matching Matroids Uniqueness of Nash Equilibria for TSM Matroids Can we find a sufficient condition that guarantees us a unique Nash equilibrium, no matter how strategy spaces are interweaved? Veerle Timmermans , Tobias Harks Uniqueness of Nash Equilibria in Matroid Congestion Games

  15. Motivation The Model Two-Sided Matching Matroids Uniqueness of Nash Equilibria for TSM Matroids Can we find a sufficient condition that guarantees us a unique Nash equilibrium, no matter how strategy spaces are interweaved? → Two-sided matching matroids are sufficient. Veerle Timmermans , Tobias Harks Uniqueness of Nash Equilibria in Matroid Congestion Games

  16. Motivation The Model Two-Sided Matching Matroids Uniqueness of Nash Equilibria for TSM Matroids Can we find a sufficient condition that guarantees us a unique Nash equilibrium, no matter how strategy spaces are interweaved? → Two-sided matching matroids are sufficient. → Currently working on the generalization to polymatroids Veerle Timmermans , Tobias Harks Uniqueness of Nash Equilibria in Matroid Congestion Games

  17. Motivation The Model Two-Sided Matching Matroids Uniqueness of Nash Equilibria for TSM Matroids Definition Matroid A matroid is a pair M = ( S , I ) where S is a set of resources, and I is a family of subsets of S such that: ◮ I � = ∅ ◮ If I ⊂ J and J ∈ I , then I ∈ I ◮ Let I , J ∈ I and | I | < | J | , then there exists an x ∈ S such that I + s ∈ I Veerle Timmermans , Tobias Harks Uniqueness of Nash Equilibria in Matroid Congestion Games

  18. Motivation The Model Two-Sided Matching Matroids Uniqueness of Nash Equilibria for TSM Matroids Definition Matroid A matroid is a pair M = ( S , I ) where S is a set of resources, and I is a family of subsets of S such that: ◮ I � = ∅ ◮ If I ⊂ J and J ∈ I , then I ∈ I ◮ Let I , J ∈ I and | I | < | J | , then there exists an x ∈ S such that I + s ∈ I Bases are sets in I of maximal cardinality, denoted by B Veerle Timmermans , Tobias Harks Uniqueness of Nash Equilibria in Matroid Congestion Games

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