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A homomorphism from a graph $G$ to a graph $H$ is an edge-preserving mapping from $V(G)$ to $V(H)$. For a fixed graph $H$, in the list homomorphism problem, denoted by LHom($H$), we are given a graph $G$, whose every vertex $v$ is equipped…

Computational Complexity · Computer Science 2022-02-04 Karolina Okrasa , Paweł Rzążewski

A homomorphism from a graph $G$ to a graph $H$ is an edge-preserving mapping from $V(G)$ to $V(H)$. Let $H$ be a fixed graph with possible loops. In the list homomorphism problem, denoted by LHom($H$), we are given a graph $G$, whose every…

Computational Complexity · Computer Science 2020-09-23 Karolina Okrasa , Marta Piecyk , Paweł Rzążewski

A locally surjective homomorphism from a graph $G$ to a graph $H$ is an edge-preserving mapping from $V(G)$ to $V(H)$ that is surjective in the neighborhood of each vertex in $G$. In the list locally surjective homomorphism problem, denoted…

Data Structures and Algorithms · Computer Science 2024-01-11 Pavel Dvořák , Monika Krawczyk , Tomáš Masařík , Jana Novotná , Paweł Rzążewski , Aneta Żuk

We consider the complexity of finding weighted homomorphisms from intersection graphs of curves (string graphs) with $n$ vertices to a fixed graph $H$. We provide a complete dichotomy for the problem: if $H$ has no two vertices sharing two…

Computational Complexity · Computer Science 2019-06-24 Karolina Okrasa , Paweł Rzążewski

The goal of this work is to give precise bounds on the counting complexity of a family of generalized coloring problems (list homomorphisms) on bounded-treewidth graphs. Given graphs $G$, $H$, and lists $L(v)\subseteq V(H)$ for every $v\in…

Computational Complexity · Computer Science 2021-11-01 Jacob Focke , Dániel Marx , Paweł Rzążewski

For graphs $G$ and $H$, a \emph{homomorphism} from $G$ to $H$ is an edge-preserving mapping from the vertex set of $G$ to the vertex set of $H$. For a fixed graph $H$, by \textsc{Hom($H$)} we denote the computational problem which asks…

Computational Complexity · Computer Science 2020-02-20 Karolina Okrasa , Paweł Rzążewski

The graph homomorphism problem (HOM) asks whether the vertices of a given $n$-vertex graph $G$ can be mapped to the vertices of a given $h$-vertex graph $H$ such that each edge of $G$ is mapped to an edge of $H$. The problem generalizes the…

Data Structures and Algorithms · Computer Science 2015-02-20 Fedor V. Fomin , Alexander Golovnev , Alexander S. Kulikov , Ivan Mihajlin

For graphs $G,H$, a homomorphism from $G$ to $H$ is an edge-preserving mapping from $V(G)$ to $V(H)$. In the list homomorphism problem, denoted by \textsc{LHom}($H$), we are given a graph $G$ and lists $L: V(G) \to 2^{V(H)}$, and we ask for…

Computational Complexity · Computer Science 2020-09-25 Marta Piecyk , Paweł Rzążewski

We consider a generalization of finding a homomorphism from an input digraph $G$ to a fixed digraph $H$, HOM($H$). In this setting, we are given an input digraph $G$ together with a list function from $G$ to $2^H$. The goal is to find a…

Data Structures and Algorithms · Computer Science 2020-11-13 Jeff Kinne , Ashwin Murali , Arash Rafiey

A homomorphism from a graph G to a graph H is a vertex mapping f from the vertex set of G to the vertex set of H such that there is an edge between vertices f(u) and f(v) of H whenever there is an edge between vertices u and v of G. The…

Computational Complexity · Computer Science 2017-03-28 Petr Golovach , Matthew Johnson. Barnaby Martin , Daniel Paulusma , Anthony Stewart

Let $H$ be an undirected graph. In the List $H$-Homomorphism Problem, given an undirected graph $G$ with a list constraint $L(v) \subseteq V(H)$ for each variable $v \in V(G)$, the objective is to find a list $H$-homomorphism $f:V(G) \to…

Data Structures and Algorithms · Computer Science 2011-06-17 Yuichi Yoshida

A homomorphism from a graph $G$ to a graph $H$ is an edge-preserving mapping from $V(G)$ to $V(H)$. In the graph homomorphism problem, denoted by $Hom(H)$, the graph $H$ is fixed and we need to determine if there exists a homomorphism from…

Discrete Mathematics · Computer Science 2023-12-08 Carla Groenland , Isja Mannens , Jesper Nederlof , Marta Piecyk , Paweł Rzążewski

For a fixed graph $H$ and for arbitrarily large host graphs $G$, the number of homomorphisms from $H$ to $G$ and the number of subgraphs isomorphic to $H$ contained in $G$ have been extensively studied in extremal graph theory and graph…

Combinatorics · Mathematics 2021-07-05 Chun-Hung Liu

We consider the following problem for a fixed graph H: given a graph G and two H-colorings of G, i.e. homomorphisms from G to H, can one be transformed (reconfigured) into the other by changing one color at a time, maintaining an H-coloring…

Computational Complexity · Computer Science 2017-03-28 Marcin Wrochna

Correspondence homomorphisms are both a generalization of standard homomorphisms and a generalization of correspondence colourings. For a fixed target graph $H$, the problem is to decide whether an input graph $G$, with each edge labeled by…

Discrete Mathematics · Computer Science 2018-03-30 Tomas Feder , Pavol Hell

The Surjective Homomorphism problem is to test whether a given graph G called the guest graph allows a vertex-surjective homomorphism to some other given graph H called the host graph. The bijective and injective homomorphism problems can…

Discrete Mathematics · Computer Science 2016-12-16 Petr A. Golovach , Bernard Lidický , Barnaby Martin , Daniël Paulusma

In the deletion version of the list homomorphism problem, we are given graphs G and H, a list L(v) that is a subset of V(H) for each vertex v of G, and an integer k. The task is to decide whether there exists a subset W of V(G) of size at…

Data Structures and Algorithms · Computer Science 2013-08-06 Rajesh Chitnis , Laszlo Egri , Daniel Marx

We study the \textsc{Max Partial $H$-Coloring} problem: given a graph $G$, find the largest induced subgraph of $G$ that admits a homomorphism into $H$, where $H$ is a fixed pattern graph without loops. Note that when $H$ is a complete…

Data Structures and Algorithms · Computer Science 2020-04-22 Maria Chudnovsky , Jason King , Michał Pilipczuk , Paweł Rzążewski , Sophie Spirkl

The generic homomorphism problem, which asks whether an input graph $G$ admits a homomorphism into a fixed target graph $H$, has been widely studied in the literature. In this article, we provide a fine-grained complexity classification of…

Computational Complexity · Computer Science 2022-10-14 Robert Ganian , Thekla Hamm , Viktoriia Korchemna , Karolina Okrasa , Kirill Simonov

We consider homomorphisms of signed graphs from a computational perspective. In particular, we study the list homomorphism problem seeking a homomorphism of an input signed graph $(G,\sigma)$, equipped with lists $L(v) \subseteq V(H), v \in…

Combinatorics · Mathematics 2023-05-30 Jan Bok , Richard Brewster , Tomás Feder , Pavol Hell , Nikola Jedličková
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