Kernkonzepte
Scanwidth is efficiently computed for directed acyclic graphs using decomposition and reduction rules.
Zusammenfassung
The content introduces the concept of scanwidth for directed acyclic graphs (DAGs) as a measure of tree-likeness. It presents algorithms for exact computation and heuristic approximation, focusing on phylogenetic networks. The structure includes an introduction to treewidth, formal definitions of scanwidth, and detailed explanations of reduction rules. The algorithmic approach decomposes DAGs into s-blocks, suppresses vertices with specific characteristics, and computes scanwidth efficiently.
-
Introduction to Scanwidth:
- Scanwidth introduced as a width parameter for DAGs.
- Contrasts with treewidth in preserving arc directions.
-
Phylogenetics Application:
- Phylogenetic networks motivate scanwidth use.
- Parameters like reticulation number and level are key.
-
Algorithmic Approach:
- Decomposition into s-blocks for efficient computation.
- Reduction rule suppresses indegree-1 outdegree-1 vertices.
-
Theoretical Bounds:
- Relation between treewidth, scanwidth, and level discussed.
-
Decomposition Algorithm:
- Algorithm outlined for computing scanwidth efficiently.
-
Complexity Analysis:
- Time complexity analyzed based on graph size and exact algorithm efficiency.
Statistiken
For DAGs with one root and scanwidth k it runs in O(k · nk · m) time.
The heuristic obtains an average practical approximation ratio of 1.5 on synthetic networks.
Zitate
"Scanwidth is not agnostic to the directions of the arcs, making it a more natural parameter for DAGs."
"Algorithms relying on scanwidth are starting to appear in phylogenetics research."