The Schrijver system of the flow cone in series-parallel graphs

Barbato, M;Grappe, R;Lacroix, M;Lancini, E;Wolfler Calvo, R

2022-01-01

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Abstract

We represent a flow of a graph G = (V, E) as a couple (C, e) with C a circuit of G and e an edge of C, and its incidence vector is the 0/ +/- 1 vector chi C\e - chi e. The flow cone of G is the cone generated by the flows of G and the unit vectors. When G has no K5-minor, this cone can be described by the system x(M) >= 0 for all multicuts M of G. We prove that this system is box-totally dual integral if and only if G is series-parallel. Then, we refine this result to provide the Schrijver system describing the flow cone in series-parallel graphs. This answers a question raised by Chervet et al., (2018). (c) 2020 Elsevier B.V. All rights reserved.