A connected bipartite graph is called Hamilton-laceable, a term apparently introduced in Simmons (1978),
if it has a Hamiltonian path for all pairs of vertices
and
,
where
belongs to one set of the bipartition, and
to the other.
A bipartite graph whose detour matrix elements are maximal for all
and
corresponding to different elements of the vertex bipartition
is therefore Hamilton-laceable.
Including the singleton graph (which is generally considered both traceable and bipartite), the numbers of Hamilton-laceable graphs
on ,
2, ... vertices are 1, 1, 0, 1, 0, 2, 0, 12, 0, 226, 0, ... (OEIS A236219),
the first few of which are illustrated above.
Since a Hamiltonian path from one vertex in one set of the bipartition to a vertex in the other set must contain an odd number of edges (i.e., edge endpoints alternate
between bipartition components), the number of vertices in a Hamilton-laceable graph
must be even (with the exception of the degenerate case ). With the exception of
, Hamilton-laceable graphs are also Hamiltonian
since one can always find two vertices
and
from different components that contain an edge
, the definition of Hamilton-laceable requires that a Hamiltonian
path exists starting at
and ending at
, and
connects the ends of this path into a Hamiltonian
cycle.
Not all even-vertex count, bipartite, Hamiltonian graphs are Hamilton-laceable. For example, the domino
graph
has 6 vertices and is Hamiltonian and bipartite but contains no Hamiltonian path
connecting the vertices of the middle rung (which lie in separate components of the
bipartition). The numbers of such graphs on
, 4, ... nodes are 0, 0, 2, 12, 253, ....
Dupuis and Wagon (2014) conjectured that all bipartite Hamiltonian vertex-transitive
graphs are Hamilton-laceable except for even cycle
graphs
with
.
A slightly more general and precise statement of this conjecture can be made in terms
of H-*-connected graphs.
Assuming ,
the grid graph
is Hamilton-laceable iff
or at least one of
is even and
. A grid graph in three
or more dimensions is hamilton-laceable iff it has at least
one even index (Simmons 1978).
All hypercube graphs are Hamilton-laceable, a result that follows from results of Chen and Quimpo (1981).
The knight graph is Hamilton-laceable iff
,
,
and at least one of
,
is even (Dupuis and Wagon 2014).
Pensaert (2002) conjectured that for with
, the generalized
Petersen graph
is Hamilton-laceable if
is even and
is odd, and Hamilton-connected otherwise.
A collection of common graphs can be checked precomputed values in the Wolfram Language using GraphData[g, "HamiltonLaceable"].