文摘
A graph is said to admit a system of collective additive tree -spanners if there is a system of at most spanning trees of such that for any two vertices of a spanning tree exists such that the distance in between and is at most plus their distance in . In this paper, we examine the problem of finding ¡°small?systems of collective additive tree -spanners for small values of on circle graphs and on polygonal graphs. Among other results, we show that every -vertex circle graph admits a system of at most collective additive tree 2-spanners and every -vertex -polygonal graph admits a system of at most collective additive tree 2-spanners. Moreover, we show that every -vertex -polygonal graph admits an additive -spanner with at most edges and every -vertex 3-polygonal graph admits a system of at most three collective additive tree 2-spanners and an additive tree 6-spanner. All our collective tree spanners as well as all sparse spanners are constructible in polynomial time.