Storyline layouts visualize temporal interactions by drawing each character as an x-monotone curve and enforcing that the participants of every meeting form a contiguous vertical group. We study a drawing extension variant in which a layout of a sub-storyline is fixed and has to be extended by inserting missing characters while preserving all meeting constraints. We minimize the local crossing number χ, i.e., the maximum number of crossings along any single character. We prove that the problem is W[1]-hard parameterized by the number k of inserted characters plus the maximum number σ of active characters, in XP parameterized by σ and in FPT parameterized by σ+χ.
@article{arxiv.2603.08340,
title = {The Complexity of Extending Storylines with Minimum Local Crossing Number},
author = {Alexander Dobler and Siddharth Gupta and Philipp Kindermann and Fabrizio Montecchiani and Martin Nöllenburg},
journal= {arXiv preprint arXiv:2603.08340},
year = {2026}
}