SEMINAR: Groups and Combinatorics Seminar: Cheryl Praeger, 4pm May 17 in Weatherburn LT


Groups and Combinatorics Seminar: Cheryl Praeger, 4pm May 17 in Weatherburn LT 
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Speaker: Cheryl E Praeger (University of Western Australia)
Title: Limited geodesic transitivity for finite regular graphs
Time and place: 4pm Friday 17 May 2019, Weatherburn LT
Abstract: Joint work with Wei Jin.
For vertex transitive graphs, transitivity on tarcs, tgeodesics, or distance t vertex pairs, for t leq s, all give symmetry measures of the graph in balls of radius s about a vertex. If the graph has girth g, and s leq g/2, then the sets of tarcs and tgeodesics are the same for each t leq s, and so the conditions of sarc transitivity and sgeodesic transitivity are equivalent. The next cases where s= (g+1)/2 and s=(g+2)/2 are interesting. There are sgeodesic transitive examples that are not sarc transitive. Those which have s=2 and g=3 are collinearity graphs of pointline incidence geometries. However there is no nice general description for the cases where s= 3 and g is 4 or 5. Our approach has required us to classify, as a bye product, all 2arc transitive strongly regular graphs, and to examine their normal covers. We have lots to describe, as well as open problems to pose.
Contact 
Stephen Glasby
<[email protected]>

Start 
Fri, 17 May 2019 16:00

End 
Fri, 17 May 2019 17:00

Submitted by 
Stephen Glasby <[email protected]>

Last Updated 
Wed, 15 May 2019 09:32

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