On Proper-Path Colorings in Graphs

Eric Andrews1, Chira Lumduanhom2, Elliot Laforge3, Ping Zhang3
1Department of Mathematics and Statistics University of Alaska Anchorage Anchorage, Alaska 99508, USA
2Department of Mathematics Srinakharinwirot University, Sukhumvit Soi 23, Bangkok 10110, Thailand
3Department of Mathematics Western Michigan University Kalamazoo, MI 49008, USA

Abstract

Let \( G \) be an edge-colored connected graph. A path \( P \) is a proper path in \( G \) if no two adjacent edges of \( P \) are colored the same. If \( P \) is a proper \( u \) — \( v \) path of length \( d(u,v) \), then \( P \) is a proper \( u \) — \( v \) geodesic. An edge coloring \( c \) is a proper-path coloring of a connected graph \( G \) if every pair \( u,v \) of distinct vertices of \( G \) are connected by a proper \( u \) — \( v \) path in \( G \) and \( c \) is a strong proper coloring if every two vertices \( u \) and \( v \) are connected by a proper \( u \) — \( v \) geodesic in \( G \). The minimum number of colors used in a proper-path coloring and strong proper coloring of \( G \) are called the proper connection number \( \text{pc}(G) \) and strong proper connection number \( \text{spc}(G) \) of \( G \), respectively. These concepts are inspired by the concepts of rainbow coloring, rainbow connection number \( \text{rc}(G) \), strong rainbow coloring, and strong connection number \( \text