Journal of Combinatorial Optimization

, Volume 30, Issue 1, pp 34–41

# L($$d$$,1)-labelings of the edge-path-replacement by factorization of graphs

• Nathaniel Karst
• Jessica Oehrlein
• Denise Sakai Troxell
• Junjie Zhu
Article

## Abstract

For an integer $$d \ge 2$$, an $$L(d$$,1)-labeling of a graph $$G$$ is a function $$f$$ from its vertex set to the non-negative integers such that $${\vert }f(x) - f(y){\vert } \ge d$$ if vertices $$x$$ and $$y$$ are adjacent, and $${\vert }f(x) - f(y){\vert } \ge$$ 1 if $$x$$ and $$y$$ are at distance two. The minimum span over all the L($$d$$,1)-labelings of $$G$$ is denoted by $$\lambda _{d}(G)$$. For a given integer $$k \ge 2$$, the edge-path-replacement of $$G$$ or $$G(P_{k})$$ is the graph obtained from $$G$$ by replacing each edge with a path $$P_{k}$$ on $$k$$ vertices. We show that the edges of $$G$$ can be colored with $$\lceil \varDelta (G)/2\rceil$$ colors so that each monochromatic subgraph has maximum degree at most 2 and use this fact to establish general upper bounds on $$\lambda _{d}(G(P_{k}))$$ for $$k \ge 4$$. As a corollary, we settle the following conjecture by Lü (J Comb Optim, 2012): for any graph $$G$$ with $$\varDelta (G) \ge$$ 2, $$\lambda _{2}(G(P_{4})) \le \varDelta (G)$$ + 2. Moreover, $$\lambda _{2}(G(P_{4})) = \varDelta (G) + 1$$ when $$\varDelta (G)$$ is even and different from 2. We also show that the class of graphs $$G(P_{k})$$ with $$k \ge$$ 4 satisfies a conjecture by Havet and Yu (2008 Discrete Math 308:498–513) in the related area of ($$d,1$$)-total labeling of graphs.

## Keywords

L(2$$,$$1)-labeling L($$d,$$1)-labeling ($$d,$$1)-Total labeling Edge-path-replacement Factorization of graphs

## Notes

### Acknowledgments

The authors would like to thank Sarah Spence Adams for participating in the initial brainstorming sessions and Paul Booth for contributing to an earlier version of this work. The authors would also like to thank the referees for their helpful comments and suggestions.

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© Springer Science+Business Media New York 2013

## Authors and Affiliations

• Nathaniel Karst
• 1
• Jessica Oehrlein
• 2
• Denise Sakai Troxell
• 1
• Junjie Zhu
• 2
1. 1.Mathematics and Sciences DivisionBabson CollegeBabson ParkUSA
2. 2.Franklin W. Olin College of EngineeringNeedhamUSA