Classifying K-Geodetic Graphs Via Combinatorial Designs and Distance-regularity

Abstract

The classification of K-geodetic graphs is a fundamental problem in graph theory concerning the number of shortest paths connecting pairs of vertices. A graph is called K-geodetic if every pair of distinct vertices is joined by at most K geodesics, where a geodesic is a shortest path between two vertices. The cases K=1,2,3 correspond, respectively, to geodetic, bigeodetic, and trigeodetic graphs. Despite substantial progress in the study of their structural properties, a comprehensive classification of these graph families remains elusive. This paper develops a research framework for investigating the classification problems by combining metric graph theory, distance-regular graphs, algebraic graph theory, and combinatorial design theory. Particular attention is given to distance-regular graphs, for which the number of geodesics between vertices at a fixed distance is determined by the intersection numbers of the graph. This property converts the K-geodetic condition into a finite collection of arithmetic inequalities. We establish the resulting necessary conditions for K=1,2,3, discuss representative examples, and distinguish these conditions from the stronger requirements needed to prove the existence and classification of graphs with a given intersection array. The paper also investigates the potential role of balanced incomplete block designs (BIBDs) in constructing and organizing families of K-geodetic graphs. Finally, it proposes a computational research methodology based on constraint satisfaction, graph-isomorphism testing, exhaustive enumeration, and machine-assisted conjecture generation.