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In this paper, we study the notion of mending: given a partial solution to a graph problem, how much effort is needed to take one step towards a proper solution? For example, if we have a partial coloring of a graph, how hard is it to properly color one more node? In prior work (SIROCCO 2022), this question was formalized and studied from the perspective of mending radius: if there is a hole that we need to patch, how far do we need to modify the solution? In this work, we investigate a complementary notion of mending volume: how many nodes need to be modified to patch a hole? We focus on the case of locally checkable labeling problems (LCLs) in trees, and show that already in this setting there are two infinite hierarchies of problems: for infinitely many values 0 < α ≤ 1, there is an LCL problem with mending volume Θ(n^α), and for infinitely many values k ≥ 1, there is an LCL problem with mending volume Θ(log^k n). Hence the mendability of LCL problems on trees is a much more fine-grained question than what one would expect based on the mending radius alone.
@InProceedings{melnyk_et_al:LIPIcs.OPODIS.2022.21,
author = {Melnyk, Darya and Suomela, Jukka and Villani, Neven},
title = {{Mending Partial Solutions with Few Changes}},
booktitle = {26th International Conference on Principles of Distributed Systems (OPODIS 2022)},
pages = {21:1--21:17},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-265-5},
ISSN = {1868-8969},
year = {2023},
volume = {253},
editor = {Hillel, Eshcar and Palmieri, Roberto and Rivi\`{e}re, Etienne},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2022.21},
URN = {urn:nbn:de:0030-drops-176413},
doi = {10.4230/LIPIcs.OPODIS.2022.21},
annote = {Keywords: mending, LCL problems, volume model}
}