
Median graphs are connected graphs in which for all three vertices there is a unique vertex that belongs to shortest paths between each pair of these three vertices. In this paper we provide several novel characterizations of planar median graphs. More specifically, we characterize when a planar graph $G$ is a median graph in terms of forbidden subgraphs and the structure of isometric cycles in $G$, and also in terms of subgraphs of $G$ that are contained inside and outside of 4-cycles with respect to an arbitrary planar embedding of $G$. These results lead us to a new characterization of planar median graphs in terms of cubesquare-graphs that is, graphs that can be obtained by starting with cubes and square graphs, and iteratively replacing 4-cycle boundaries (relative to some embedding) by cubes or square-graphs. As a corollary we also show that a graph is planar median if and only if it can be obtained from cubes and square-graphs by a sequence of ``square-boundary'' amalgamations. These considerations also lead to an $\mathcal{O}(n\log n)$-time recognition algorithm to compute a decomposition of a planar median graph with $n$ vertices into cubes and square-graphs.
FOS: Computer and information sciences, Artificial intelligence, Discrete Mathematics (cs.DM), 101004 Biomathematics, Graph, Planar graphs; geometric and topological aspects of graph theory, 101004 Biomathematik, Clique-sum, Graph algorithms (graph-theoretic aspects), characterization, Connectivity, Planar median graph, Mesh Generation Algorithms, 102004 Bioinformatik, Indifference graph, Discrete mathematics, QS-graph, Computer Graphics and Computer-Aided Design, 004, recognition algorithm, Computational Theory and Mathematics, Pancyclic graph, planar median graph, Physical Sciences, Combinatorics (math.CO), 1-planar graph, Graph Theory and Algorithms, Embedding, Planar Graph Embedding, Computer Networks and Communications, Characterization, Cograph, Pathwidth, Metric dimension, hybercube, Planar graph, Chordal graph, Polyhedral graph, FOS: Mathematics, Hybercube, Mathematics - Combinatorics, 102004 Bioinformatics, Distance in graphs, Square-graph, Line graph, Computer science, Book embedding, square-graph, Networks on Chip in System-on-Chip Design, Recognition algorithm, Combinatorics, Outerplanar graph, Computer Science, Paths and cycles, Mathematics, Computer Science - Discrete Mathematics
FOS: Computer and information sciences, Artificial intelligence, Discrete Mathematics (cs.DM), 101004 Biomathematics, Graph, Planar graphs; geometric and topological aspects of graph theory, 101004 Biomathematik, Clique-sum, Graph algorithms (graph-theoretic aspects), characterization, Connectivity, Planar median graph, Mesh Generation Algorithms, 102004 Bioinformatik, Indifference graph, Discrete mathematics, QS-graph, Computer Graphics and Computer-Aided Design, 004, recognition algorithm, Computational Theory and Mathematics, Pancyclic graph, planar median graph, Physical Sciences, Combinatorics (math.CO), 1-planar graph, Graph Theory and Algorithms, Embedding, Planar Graph Embedding, Computer Networks and Communications, Characterization, Cograph, Pathwidth, Metric dimension, hybercube, Planar graph, Chordal graph, Polyhedral graph, FOS: Mathematics, Hybercube, Mathematics - Combinatorics, 102004 Bioinformatics, Distance in graphs, Square-graph, Line graph, Computer science, Book embedding, square-graph, Networks on Chip in System-on-Chip Design, Recognition algorithm, Combinatorics, Outerplanar graph, Computer Science, Paths and cycles, Mathematics, Computer Science - Discrete Mathematics
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