A Hamiltonian cycle system of the complete graph minus a 1–factor $K_{2v} − I$ (briefly, an HCS(2v)) is 2-pyramidal if it admits an automorphism group of order 2v − 2 fixing two vertices. In spite of the fact that the very first example of an HCS(2v) is very old and 2-pyramidal, a thorough investigation of this class of HCSs is lacking. We give first evidence that there is a strong relationship between 2-pyramidal HCS(2v) and 1-rotational Hamiltonian cycle systems of the complete graph $K_{2v−1}$. Then, as main result, we determine the full automorphism group of every 2-pyramidal HCS(2v). This allows us to obtain an exponential lower bound on the number of non-isomorphic 2-pyramidal HCS(2v).
On 2-pyramidal Hamiltonian cycle systems / Bailey, Rosemary; Buratti, Marco; Rinaldi, Gloria; Traetta, Tommaso. - In: BULLETIN OF THE BELGIAN MATHEMATICAL SOCIETY SIMON STEVIN. - ISSN 1370-1444. - 21:4(2014), pp. 747-758.
On 2-pyramidal Hamiltonian cycle systems
BURATTI, Marco;
2014
Abstract
A Hamiltonian cycle system of the complete graph minus a 1–factor $K_{2v} − I$ (briefly, an HCS(2v)) is 2-pyramidal if it admits an automorphism group of order 2v − 2 fixing two vertices. In spite of the fact that the very first example of an HCS(2v) is very old and 2-pyramidal, a thorough investigation of this class of HCSs is lacking. We give first evidence that there is a strong relationship between 2-pyramidal HCS(2v) and 1-rotational Hamiltonian cycle systems of the complete graph $K_{2v−1}$. Then, as main result, we determine the full automorphism group of every 2-pyramidal HCS(2v). This allows us to obtain an exponential lower bound on the number of non-isomorphic 2-pyramidal HCS(2v).I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
