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Discrete Mathematics & Theoretical Computer Science |
Andrew Goodall ; Criel Merino ; Anna de Mier ; Marc Noy - On the evaluation of the Tutte polynomial at the points (1,-1) and (2,-1)
dmtcs:2921 - Discrete Mathematics & Theoretical Computer Science, January 1, 2011, DMTCS Proceedings vol. AO, 23rd International Conference on Formal Power Series and Algebraic Combinatorics (FPSAC 2011) - https://doi.org/10.46298/dmtcs.2921
1; Criel Merino 2; Anna de Mier 3,4; Marc Noy 3,4
- 1 Department of Applied Mathematics and Institute of Theoretical Computer Science
- 2 Instituto de Matematicas
- 3 Universitat Politècnica de Catalunya [Barcelona]
- 4 Universitat Politècnica de Catalunya = Université polytechnique de Catalogne [Barcelona] [UPC]
[en]
C. Merino [Electron. J. Combin. 15 (2008)] showed that the Tutte polynomial of a complete graph satisfies $t(K_{n+2};2,-1)=t(K_n;1,-1)$. We first give a bijective proof of this identity based on the relationship between the Tutte polynomial and the inversion polynomial for trees. Next we move to our main result, a sufficient condition for a graph G to have two vertices u and v such that $t(G;2,-1)=t(G-\{u,v\};1,-1)$; the condition is satisfied in particular by the class of threshold graphs. Finally, we give a formula for the evaluation of $t(K_{n,m};2,-1)$ involving up-down permutations.
[fr]
C. Merino [Electron. J. Combin. 15 (2008)] a montré que le polynôme de Tutte du graphe complet satisfait $t(K_{n+2};2,-1)=t(K_n;1,-1)$. Le rapport entre le polynôme de Tutte et le polynôme d'inversions d'un arbre nous permet de donner une preuve bijective de cette identité. Le résultat principal du travail est une condition suffisante pour qu'un graphe ait deux sommets u et v tels que $t(G;2,-1)=t(G-\{u,v\};1,-1)$; en particulier, les graphes ``threshold'' satisfont cette condition. Finalement, nous donnons une formule pour $t(K_{n,m};2,-1)$ qui fait intervenir les permutations alternées.