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Topics in Graph Automorphisms and Reconstruction - download pdf or read online

By Josef Lauri

ISBN-10: 1316610446

ISBN-13: 9781316610442

This in-depth assurance of vital parts of graph concept continues a spotlight on symmetry homes of graphs. normal subject matters on graph automorphisms are provided early on, whereas in later chapters extra specialized issues are tackled, corresponding to graphical typical representations and pseudosimilarity. the ultimate 4 chapters are dedicated to the reconstruction challenge, and right here exact emphasis is given to these effects that contain the symmetry of graphs, a lot of which aren't to be present in different books. This moment variation expands on numerous of the subjects present in the 1st version and comprises either an enriched bibliography and a large selection of routines. Clearer proofs are supplied, as are new examples of graphs with attention-grabbing symmetry houses. Any scholar who masters the contents of this ebook might be ready for present study in lots of elements of the speculation of graph automorphisms and the reconstruction challenge.

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Get Topics in Graph Automorphisms and Reconstruction PDF

This in-depth assurance of significant parts of graph thought continues a spotlight on symmetry homes of graphs. normal subject matters on graph automorphisms are provided early on, whereas in later chapters extra specialized subject matters are tackled, comparable to graphical standard representations and pseudosimilarity. the ultimate 4 chapters are dedicated to the reconstruction challenge, and right here designated emphasis is given to these effects that contain the symmetry of graphs, a lot of which aren't to be present in different books.

Extra info for Topics in Graph Automorphisms and Reconstruction

Example text

Quite remarkably, for a distance-regular graph the intersection numbers can be defined, and they can be determined from the intersection array. ) is also investigated. Finally, we want to mention one other generalisation of these regularity properties of graphs. This is in the direction of the generalisation from distancetransitivity to distance-regularity, that is, combinatorial regularities that are implied by symmetries of the automorphism group are used as the defining property of the class of graphs in question.

Now, if G is distance-transitive, the numbers |A|, |B|, |C| do not depend on the vertices u, v but only on their distance j. In this case, let these numbers be denoted by |A| = aj , |B| = bj and |C| = cj . If the diameter of G is d, then we can write down these numbers as follows: ⎤ ⎡ ∗ c1 c2 . . cd−1 cd ι(G) = ⎣ a0 a1 a2 . . ad−1 ad ⎦ , b0 b1 b2 . . bd−1 ∗ and ι(G) is then called the intersection array of G. Because a distance-transitive graph is regular, say of degree k, then b0 = k; also, a0 = 0 and c1 = 1.

Let t be an arc of ← → ← → ← → G and let D be the subdigraph of G whose vertex-set is V( G ) and whose arc-set is the orbit of t under the action of H. Then (i) for every edge {a, b} of G, D contains exactly one of the arcs (a, b) or (b, a); (ii) H ≤ Aut(D); (iii) D is vertex-transitive. Proof (i) Let t = (s1 , s2 ). Because G is edge-transitive under the action of H, there is an α ∈ H such that α{s1 , s2 } = {a, b}. Therefore certainly one of (a, b) or (b, a) is an arc of D. Suppose that both are arcs of D.

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Topics in Graph Automorphisms and Reconstruction by Josef Lauri


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