# Graph Minors for Preserving Terminal Distances Approximately - Lower and Upper Bounds

Cheung, Yun Kuen; Goranci, Gramoz; Henzinger, Monika
Given a graph where vertices are partitioned into {\\$}k{\\$} terminals and non-terminals, the goal is to compress the graph (i.e., reduce the number of non-terminals) using minor operations while preserving terminal distances approximately.The distortion of a compressed graph is the maximum multiplicative blow-up of distances between all pairs of terminals. We study the trade-off between the number of non-terminals and the distortion. This problem generalizes the Steiner Point Removal (SPR) problem, in which all non-terminals must be removed. We introduce a novel black-box reduction to convert any lower bound on distortion for the SPR problem into a super-linear lower bound on the number of non-terminals, with the same distortion, for our problem. This allows us to show that there exist graphs such that every minor with distortion less than {\\$}2{\~{}}/{\~{}}2.5{\~{}}/{\~{}}3{\\$} must have {\\$}\backslashOmega(k{\^{}}2){\~{}}/{\~{}}\backslashOmega(k{\^{}}{\{}5/4{\}}){\~{}}/{\~{}}\backslashOmega(k{\^{}}{\{}6/5{\}}){\\$} non-terminals, plus more trade-offs in between. The black-box reduction has an interesting consequence: if the tight lower bound on distortion for the SPR problem is super-constant, then allowing any {\\$}O(k){\\$} non-terminals will not help improving the lower bound to a constant. We also build on the existing results on spanners, distance oracles and connected 0-extensions to show a number of upper bounds for general graphs, planar graphs, graphs that exclude a fixed minor and bounded treewidth graphs. Among others, we show that any graph admits a minor with {\\$}O(\backslashlog k){\\$} distortion and {\\$}O(k{\^{}}{\{}2{\}}){\\$} non-terminals, and any planar graph admits a minor with {\\$}1+\backslashvarepsilon{\\$} distortion and {\\$}\backslashwidetilde{\{}O{\}}((k/\backslashvarepsilon){\^{}}{\{}2{\}}){\\$} non-terminals.
Research areas:
Year:
2016
Type of Publication:
In Proceedings
Keywords:
graph compression; graph minor; metric embedding; minor
Book title:
ICALP 2016
Pages:
131
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