文摘
The atom–bond connectivity (ABC) index is a well-known degree-based molecular structure descriptor with a variety of chemical applications. In 2010 Graovac and Ghorbani introduced a distance-based analog of this index, the Graovac–Ghorbani (class="mathmlsrc">class="formulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0096300316305422&_mathId=si4.gif&_user=111111111&_pii=S0096300316305422&_rdoc=1&_issn=00963003&md5=c0f2ae54e68a4107e9d115a881665e80" title="Click to view the MathML source">GGclass="mathContainer hidden">class="mathCode">) index, which yielded promising results when compared to analogous descriptors. In this paper, we investigate the structure of graphs that maximize and minimize the class="mathmlsrc">class="formulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0096300316305422&_mathId=si4.gif&_user=111111111&_pii=S0096300316305422&_rdoc=1&_issn=00963003&md5=c0f2ae54e68a4107e9d115a881665e80" title="Click to view the MathML source">GGclass="mathContainer hidden">class="mathCode"> index. Specifically, we show that amongst all bipartite graphs, the minimum class="mathmlsrc">class="formulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0096300316305422&_mathId=si4.gif&_user=111111111&_pii=S0096300316305422&_rdoc=1&_issn=00963003&md5=c0f2ae54e68a4107e9d115a881665e80" title="Click to view the MathML source">GGclass="mathContainer hidden">class="mathCode"> index is attained by a complete bipartite graph, while the maximum class="mathmlsrc">class="formulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0096300316305422&_mathId=si4.gif&_user=111111111&_pii=S0096300316305422&_rdoc=1&_issn=00963003&md5=c0f2ae54e68a4107e9d115a881665e80" title="Click to view the MathML source">GGclass="mathContainer hidden">class="mathCode"> index is attained by a path or a cycle-like graph; the structure of the resulting graph depends on the number of vertices. Through the course of the research, we also derive an asymptotic estimate of the class="mathmlsrc">class="formulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0096300316305422&_mathId=si4.gif&_user=111111111&_pii=S0096300316305422&_rdoc=1&_issn=00963003&md5=c0f2ae54e68a4107e9d115a881665e80" title="Click to view the MathML source">GGclass="mathContainer hidden">class="mathCode"> index of paths. In order to obtain our results, we introduce a normalized version of the class="mathmlsrc">class="formulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0096300316305422&_mathId=si4.gif&_user=111111111&_pii=S0096300316305422&_rdoc=1&_issn=00963003&md5=c0f2ae54e68a4107e9d115a881665e80" title="Click to view the MathML source">GGclass="mathContainer hidden">class="mathCode"> index and call it the normalized Graovac–Ghorbani (class="mathmlsrc">class="formulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0096300316305422&_mathId=si5.gif&_user=111111111&_pii=S0096300316305422&_rdoc=1&_issn=00963003&md5=17e8c0e90b0d6aa2743f273153544739" title="Click to view the MathML source">NGGclass="mathContainer hidden">class="mathCode">) index. Finally, we discuss some related open questions as a potential extension of our work.