In the mathematical field of graph theory, the Nauru graph is a symmetric, bipartite, cubic graph with 24 vertices and 36 edges. It was named by David Eppstein after the twelve-pointed star in the flag of Nauru.
It has chromatic number 2, chromatic index 3, diameter 4, radius 4 and girth 6. It is also a 3-vertex-connected and 3-edge-connected graph. It has book thickness 3 and queue number 2.
The Nauru graph requires at least eight crossings in any drawing of it in the plane. It is one of three non-isomorphic graphs tied for being the smallest cubic graph that requires eight crossings. Another of these three graphs is the McGee graph, also known as the (3-7)-cage.
The Nauru graph is Hamiltonian and can be described by the LCF notation : [5, −9, 7, −7, 9, −5]4.
The Nauru graph can also be constructed as the generalized Petersen graph G(12, 5) which is formed by the vertices of a dodecagon connected to the vertices of a twelve-point star in which each point of the star is connected to the points five steps away from it.
There is also a combinatorial construction of the Nauru graph. Take three distinguishable objects and place them in four distinguishable boxes, no more than one object per box. There are 24 ways to so distribute the objects, corresponding to the 24 vertices of the graph. If it is possible to go from one state to another state by moving exactly one object from its present location to an empty box, then the vertices corresponding to the two states are joined by an edge. The resulting state-transition graph is the Nauru graph.
The automorphism group of the Nauru graph is a group of order 144. It is isomorphic to the direct product of the symmetric groups S4 and S3 and acts transitively on the vertices, on the edges and on the arcs of the graph. Therefore, the Nauru graph is a symmetric graph (though not distance transitive). It has automorphisms that take any vertex to any other vertex and any edge to any other edge. According to the Foster census, the Nauru graph is the only cubic symmetric graph on 24 vertices.
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In the mathematical field of graph theory, the Desargues graph is a distance-transitive, cubic graph with 20 vertices and 30 edges. It is named after Girard Desargues, arises from several different combinatorial constructions, has a high level of symmetry, is the only known non-planar cubic partial cube, and has been applied in chemical databases. The name "Desargues graph" has also been used to refer to a ten-vertex graph, the complement of the Petersen graph, which can also be formed as the bipartite half of the 20-vertex Desargues graph.
In graph theory, the crossing number cr(G) of a graph G is the lowest number of edge crossings of a plane drawing of the graph G. For instance, a graph is planar if and only if its crossing number is zero. Determining the crossing number continues to be of great importance in graph drawing, as user studies have shown that drawing graphs with few crossings makes it easier for people to understand the drawing.
In the mathematical field of graph theory, a toroidal graph is a graph that can be embedded on a torus. In other words, the graph's vertices can be placed on a torus such that no edges cross. Any graph that can be embedded in a plane can also be embedded in a torus. A toroidal graph of genus 1 can be embedded in a torus but not in a plane. The Heawood graph, the complete graph K7 (and hence K5 and K6), the Petersen graph (and hence the complete bipartite graph K3,3, since the Petersen graph contains a subdivision of it), one of the Blanuša snarks, and all Möbius ladders are toroidal.
Determining the size of a maximum independent set of a graph G, denoted by alpha(G), is an NP-hard problem. Therefore many attempts are made to find upper and lower bounds, or exact values of alpha(G) for special classes of graphs. This paper is aimed towa ...