Convexity, distance invariants and longest paths in graphs

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Networks are useful models for transportation, communication and computer networks. In this proposal we are interested in the problem of connecting a set S of nodes in a network by some optimal subnetwork. This could be (i) a shortest connected subnetwork containing S ,i.e., with the smallest number of nodes or (ii) a connected subnetwork containing S that is minimal in the sense that if any node not in S is deleted from the subnetwork, then this disconnects S. The interval for S with respect to either of these two optimal ways of connecting S consist of all nodes that belong to some shortest subnetwork connecting S (or some minimal subnetwork containing S). A set T of nodes is convex or closed if it contains the interval for every subset S of T having a fixed size. We propose to study structures of networks for which these closed sets have certain properties.