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Hamil­tonic­ity for con­vex shape De­lau­nay and Gabriel graphs
Pilar Cano
Car­leton Uni­ver­sity

We study Hamil­tonic­ity for some of the most gen­eral vari­ants of De­lau­nay and Gabriel graphs. In­stead of defin­ing these prox­im­ity graphs using cir­cles, we use an ar­bi­trary con­vex shape C. Let S be a point set in the plane. The k-order De­lau­nay graph of S, de­noted k-DGC(S), has ver­tex set S and edge pq pro­vided that there ex­ists some ho­mo­thet of C with p and q on its bound­ary and con­tain­ing at most k points of S dif­fer­ent from p and q. The k-order Gabriel graph k-GGC(S) is de­fined anal­o­gously, ex­cept for the fact that the ho­mo­thets con­sid­ered are re­stricted to be small­est ho­mo­thets of C with p and q on its bound­ary.

We pro­vide upper bounds on the min­i­mum value of k for which k-GGC(S) is Hamil­ton­ian. Since k-GGC(S)\subseteq k-DGC(S), all re­sults carry over to k-DGC(S). In par­tic­u­lar, we give upper bounds of 24 for every C and 15 for every point-sym­met­ric C. We also im­prove the bound to 7 for squares, 11 for reg­u­lar hexa­gons, 12 for reg­u­lar oc­tagons, and 11 for even-sided reg­u­lar t-gons (for t\geq 10). These con­sti­tute the first gen­eral re­sults on Hamil­tonic­ity for con­vex shape De­lau­nay and Gabriel graphs.