Irregularity and Modular Irregularity Strength of Wheels

Abstract

It is easily observed that the vertices of a simple graph cannot have pairwise distinct degrees. This means that no simple graph of the order of at least two is, in this way, irregular. However, a multigraph can be irregular. Chartrand et al., in 1988, posed the following problem: in a loopless multigraph, how can one determine the fewest parallel edges required to ensure that all vertices have distinct degrees? This problem is known as the graph labeling problem and, for its solution, Chartrand et al. introduced irregular assignments. The irregularity strength of a graph G is known as the maximal edge label used in an irregular assignment, minimized over all irregular assignments. Thus, the irregularity strength of a simple graph G is equal to the smallest maximum multiplicity of an edge of G in order to create an irregular multigraph from G. In the present paper, we show the existence of a required irregular labeling scheme that proves the exact value of the irregularity strength of wheels. Then, we modify this irregular mapping in six cases and obtain labelings that determine the exact value of the modular irregularity strength of wheels as a natural modification of the irregularity strength.

Modular irregularity strength on some flower graphs

“…In 2021, Bača et al [4] characterized the modular irregularity strength of fan graphs F n for n ≥ 2. In the same year, Bača et al in [3] found the modular irregularity strength of wheels W n . Sugeng et al in [14] provided the results for the modular irregularity strength of double-stars S k,k and friendship graphs f n .…”

Two types irregular labelling on dodecahedral modified generalization graph

“…The modular irregularity strength for some graphs have known, such as path, star, tree, cycle, gear graph [4] , fan graph [3] , and wheel graph [1] . Recently, Sugeng, et al have determined the modular irregularity strength of double stars and friendship graphs [12] .…”

The Modular Irregularity Strength of C_n⊙mK_1

“…Considering Theorem 1, the interesting topic is the conditions for a graph 𝐺 such that 𝑠(𝐺) = 𝑚𝑠(𝐺) and 𝑠(𝐺) < 𝑚𝑠(𝐺). Bača et al in [29] compared the irregularity strength and modular irregularity strength of wheels. If 𝑛 = 5 or 𝑛 ≡ 1 (𝑚𝑜𝑑 4), then 𝑠(𝑊 𝑛 ) < 𝑚𝑠(𝑊 𝑛 ), otherwise 𝑠(𝑊 𝑛 ) = 𝑚𝑠(𝑊 𝑛 ).…”