

The irregularity of a graph is the sum of the absolute values of the differences of degrees of pairs of adjacent vertices. The extremal graph with minimal irregularity among trees of order n with maximum degree ∆ and the second maximum degree ∆1 are determined, as well as unicyclic graphs of order n with girth g and maximum degree ∆. Lower and upper bounds are established on irregularity. Furthermore, the inverse problem for the irregularity of maximally irregular graphs is solved. © 2023 University of Kragujevac, Faculty of Science. All rights reserved.
Horoldagva, B.; Department of Mathematics, Mongolian National University of Education, Baga toiruu-14, Ulaanbaatar, Mongolia;
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