156 research outputs found
Size of the Largest Induced Forest in Subcubic Graphs of Girth at least Four and Five
In this paper, we address the maximum number of vertices of induced forests
in subcubic graphs with girth at least four or five. We provide a unified
approach to prove that every 2-connected subcubic graph on vertices and
edges with girth at least four or five, respectively, has an induced forest on
at least or vertices, respectively, except
for finitely many exceptional graphs. Our results improve a result of Liu and
Zhao and are tight in the sense that the bounds are attained by infinitely many
2-connected graphs. Equivalently, we prove that such graphs admit feedback
vertex sets with size at most or , respectively.
Those exceptional graphs will be explicitly constructed, and our result can be
easily modified to drop the 2-connectivity requirement
On cycle packings and feedback vertex sets
For a graph , let and denote the minimum size of a feedback vertex set in and the maximum size of a cycle packing in , respectively. Kloks, Lee, and Liu conjectured that if is planar. They proved a weaker inequality, replacing by . We improve this, replacing by , and verifying the resulting inequality for graphs embedded in surfaces of nonnegative Euler characteristic. We also generalize to arbitrary surfaces. We show that, if a graph embeds in a surface of Euler characteristic , then . Lastly, we consider what the best possible bound on might be, and give some open problems
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