Tag Archives: Cayley graphs

Normal

Posted on 14/11/2018 by

There are various overused terms in mathematics. “Normal” is one of them. Perhaps the four commonest uses are the following: A complex square matrix is normal if it commutes with its conjugate transpose. Normal matrices are precisely the ones which … Continue reading →

Posted in exposition | Tagged , , , , , | 3 Comments

A Cayley graph challenge

Posted on 08/01/2014 by

Greg Cherlin showed that Henson’s graphs are Cayley graphs, so perhaps it is time to look again at the question: Is Covington’s graph a Cayley graph? Here, to start things off, is a simple fact: Covington’s graph G is not … Continue reading →

Posted in open problems | Tagged , | Leave a comment

The sound of problems falling

Posted on 23/12/2013 by

This month brought news that two problems I posed have been solved. A conjecture of mine was proved by Martin Bridson and Henry Wilton, and another question (which I didn’t feel brave enough to connjecture) has been answered by Greg … Continue reading →

Posted in exposition, open problems | Tagged , , , , , , | 6 Comments

London Combinatorics Colloquia, 2

Posted on 20/05/2013 by

It’s that time of year again, and while I miss the buttercups in Reading, we had as usual a feast of interesting mathematics and a large and enthusiastic audience. It was a bit more tightly focussed than I would have … Continue reading →

Posted in events, exposition | Tagged , , , , , , , , | Leave a comment