Francisco Javier Zaragoza Martínez*+
Rafael López Bracho†*

*Dirección para correspondencia

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Abstract

Given a connected mixed graph with costs on its edges and arcs, the mixed postman problem consists of finding a minimum cost closed tour of the mixed graph traversing all of its edges and arcs. It is well-known that this problem is NPhard. However, under certain conditions, the problem can be solved in polynomial time using linear programming, in other words, the corresponding polyhedra are integral. Some of these conditions are: the mixed graph is series-parallel or the mixed graph is even. Also, we show that if we add the constraint that each edge is traversed exactly once then the problem can be solved in polynomial time if the set of arcs forms a forest.

Keywords: Mixed graph, postman problem, linear programming.

Resumen

Dada una gráfica mixta y conexa con costos en sus aristas y arcos, el problema del cartero mixto consiste en encontrar un circuito cerrado de la gráfica mixta que recorra sus aristas y arcos a costo mínimo. Se sabe que este problema es NP-duro. Sin embargo, bajo ciertas condiciones adicionales, el problema se puede resolver en tiempo polinomial usando programación lineal, en otras palabras, los poliedros correspondientes son enteros. Algunas de estas condiciones son: la gráfica mixta es serie paralelo o la gráfica mixta tiene grado total par en todos sus vértices. Además, mostramos que si agregamos la restricción adicional de que cada arista se recorra exactamente una vez entonces el problema se puede resolver en tiempo polinomial si el conjunto de arcos forma un bosque.

Palabras clave: Gráfica mixta, problema de cartero, programación lineal.

Mathematics Subject Classification: 05C45, 90C35.

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*Correspondencia a: Francisco Javier Zaragoza Martínez. Universidad Autónoma Metropolitana Unidad Azcapotzalco, Departamento de Sistemas. Av. San Pablo 180, México, D.F., México 02200. E-mail franz@correo.azc.uam.mx

Rafael López Bracho. Universidad Autónoma Metropolitana Unidad Azcapotzalco, Departamento de Sistemas. Av. San Pablo 180, México, D.F., México 02200. E-mail rlb@correo.azc.uam.mx

*Universidad Autónoma Metropolitana Unidad Azcapotzalco, Departamento de Sistemas. Av. San Pablo 180, México, D.F., México 02200. E-mail franz@correo.azc.uam.mx
†Universidad Autónoma Metropolitana Unidad Azcapotzalco, Departamento de Sistemas. Av. San Pablo 180, México, D.F., México 02200. E-mail rlb@correo.azc.uam.mx