Construction Techniques for Linear Realizations of Multisets with Small Support

Abstract

A Hamiltonian path in the complete graph $K_v$ whose vertices are labeled with the integers $0,1,\ldots,v-1$ is a linear realization for the multiset $L$ of the linear edge-lengths (given by $|x-y|$ for the edge between vertices $x$ and $y$) of the edges in the path. A linear realization is standard if an end-vertex is 0 and perfect if the end-vertices are 0 and $v-1$. Linear realizations are useful in the study of the Buratti-Horak-Rosa (BHR) Conjecture on the existence of cyclic realizations (where cyclic edge-lengths are given by distance modulo $v$) for given multisets. In this paper, we focus on multisets of the form $\{1^a, (y-k)^b, y^c\}$. Using core perfect linear realizations for supports of size 2 (which have the forms $\{x^{y-1},y^{x+1}\}$ whenever $\gcd(x,y)=1$), we construct standard linear realizations (with $a=k-1$, $b=j(y-k)$, $c=jy$) when $k\mid y$ or $k \leq 4$. When $k=2$, these allow us to show that there is a linear realization whenever $a \geq y$. This is in line with the known results for the case of $k=1$. We also supplement these results for $k=1$ by constructing linear realizations whenever $b+c < y$ and $a \geq y - \min(b,c)$, from which the coprime version of the BHR Conjecture (requiring that $v$ is coprime with each element of the multiset) follows for $k=1$ when $y \leq 16$. Our methods show promise for constructing linear realizations for arbitrary $k$, in the direction of a resolution of the BHR Conjecture for supports of size 3.