Counting Complexity for Reasoning in Abstract Argumentation
This work addresses computational complexity challenges in formal argumentation, which is incremental as it builds on existing methods for reasoning in abstract argumentation.
The paper tackles the problem of counting and projected model counting of extensions in abstract argumentation under various semantics, establishing classical and parameterized complexity results based on treewidth, with algorithms running in double or triple exponential time in treewidth and lower bounds under the exponential time hypothesis.
In this paper, we consider counting and projected model counting of extensions in abstract argumentation for various semantics. When asking for projected counts we are interested in counting the number of extensions of a given argumentation framework while multiple extensions that are identical when restricted to the projected arguments count as only one projected extension. We establish classical complexity results and parameterized complexity results when the problems are parameterized by treewidth of the undirected argumentation graph. To obtain upper bounds for counting projected extensions, we introduce novel algorithms that exploit small treewidth of the undirected argumentation graph of the input instance by dynamic programming (DP). Our algorithms run in time double or triple exponential in the treewidth depending on the considered semantics. Finally, we take the exponential time hypothesis (ETH) into account and establish lower bounds of bounded treewidth algorithms for counting extensions and projected extension.