# Covering Vectors by Spaces in Perturbed Graphic Matroids and Their Duals

## TL;DR

This paper investigates the parameterized complexity of the Space Cover problem on perturbed graphic and cographic matroids, establishing fixed-parameter tractability results for fixed perturbation rank and hardness results when parameters grow.

## Contribution

It introduces the Space Cover problem for perturbed graphic matroids, proves fixed-parameter tractability for fixed rank, and shows W[1]-hardness and NP-completeness in other parameter regimes.

## Key findings

- Space Cover is FPT for fixed r on graphic matroids.
- W[1]-hard when parameterized by r+k+|T|.
- NP-complete for r ≤ 2 and |T| ≤ 2.

## Abstract

Perturbed graphic matroids are binary matroids that can be obtained from a graphic matroid by adding a noise of small rank. More precisely, r-rank perturbed graphic matroid M is a binary matroid that can be represented in the form I +P, where I is the incidence matrix of some graph and P is a binary matrix of rank at most r. Such matroids naturally appear in a number of theoretical and applied settings. The main motivation behind our work is an attempt to understand which parameterized algorithms for various problems on graphs could be lifted to perturbed graphic matroids. We study the parameterized complexity of a natural generalization (for matroids) of the following fundamental problems on graphs: Steiner Tree and Multiway Cut. In this generalization, called the Space Cover problem, we are given a binary matroid M with a ground set E, a set of terminals T\subseteq E, and a non-negative integer k. The task is to decide whether T can be spanned by a subset of E\setminus T of size at most k. We prove that on graphic matroid perturbations, for every fixed r, Space Cover is fixed-parameter tractable parameterized by k. On the other hand, the problem becomes W[1]-hard when parameterized by r+k+|T| and it is NP-complete for r\leq 2 and |T|\leq 2. On cographic matroids, that are the duals of graphic matroids, Space Cover generalizes another fundamental and well-studied problem, namely Multiway Cut. We show that on the duals of perturbed graphic matroids the Space Cover problem is fixed-parameter tractable parameterized by r+k.