Results 1 
7 of
7
Finding shortest nontrivial cycles in directed graphs on surfaces
 In These Proceedings
, 2010
"... Let D be a weighted directed graph cellularly embedded in a surface of genus g, orientable or not, possibly with boundary. We describe algorithms to compute a shortest noncontractible and a shortest surface nonseparating cycle in D. This generalizes previous results that only dealt with undirected ..."
Abstract

Cited by 13 (3 self)
 Add to MetaCart
(Show Context)
Let D be a weighted directed graph cellularly embedded in a surface of genus g, orientable or not, possibly with boundary. We describe algorithms to compute a shortest noncontractible and a shortest surface nonseparating cycle in D. This generalizes previous results that only dealt with undirected graphs. Our first algorithm computes such cycles in O(n 2 log n) time, where n is the total number of vertices and edges of D, thus matching the complexity of the best known algorithm in the undirected case. It revisits and extends Thomassen’s 3path condition; the technique applies to other families of cycles as well. We also give an algorithm with subquadratic complexity in the complexity of the input graph, if g is fixed. Specifically, we can solve the problem in O ( √ g n 3/2 log n) time, using a divideandconquer technique that simplifies the graph while preserving the topological properties of its cycles. A variant runs in O(ng log g + nlog 2 n) for graphs of bounded treewidth.
Multiplesource shortest paths in embedded graphs
, 2012
"... Let G be a directed graph with n vertices and nonnegative weights in its directed edges, embedded on a surface of genus g, and let f be an arbitrary face of G. We describe an algorithm to preprocess the graph in O(gn log n) time, so that the shortestpath distance from any vertex on the boundary of ..."
Abstract

Cited by 10 (6 self)
 Add to MetaCart
Let G be a directed graph with n vertices and nonnegative weights in its directed edges, embedded on a surface of genus g, and let f be an arbitrary face of G. We describe an algorithm to preprocess the graph in O(gn log n) time, so that the shortestpath distance from any vertex on the boundary of f to any other vertex in G can be retrieved in O(log n) time. Our result directly generalizes the O(n log n)time algorithm of Klein [Multiplesource shortest paths in planar graphs. In Proc. 16th Ann. ACMSIAM Symp. Discrete Algorithms, 2005] for multiplesource shortest paths in planar graphs. Intuitively, our preprocessing algorithm maintains a shortestpath tree as its source point moves continuously around the boundary of f. As an application of our algorithm, we describe algorithms to compute a shortest noncontractible or nonseparating cycle in embedded, undirected graphs in O(g² n log n) time.
Finding cycles with topological properties in embedded graphs
, 2010
"... Let G be a graph cellularly embedded on a surface. We consider the problem of determining whether G contains a cycle (i.e. a closed walk without repeated vertices) of a certain topological type. We show that the problem can be answered in linear time when the topological type is one of the following ..."
Abstract

Cited by 8 (1 self)
 Add to MetaCart
(Show Context)
Let G be a graph cellularly embedded on a surface. We consider the problem of determining whether G contains a cycle (i.e. a closed walk without repeated vertices) of a certain topological type. We show that the problem can be answered in linear time when the topological type is one of the following: contractible, noncontractible, or nonseparating. In either case we obtain the same time complexity if we require the cycle to contain a given vertex. On the other hand, we prove that the problem is NPcomplete when considering separating or splitting cycles. We also show that deciding the existence of a separating or a splitting cycle of length at most k is fixedparameter tractable with respect tok plus the genus of the surface.
Combinatorial Optimization of Cycles and Bases
 PROCEEDINGS OF SYMPOSIA IN APPLIED MATHEMATICS
"... We survey algorithms and hardness results for two important classes of topology optimization problems: computing minimumweight cycles in a given homotopy or homology class, and computing minimumweight cycle bases for the fundamental group or various homology groups. ..."
Abstract

Cited by 3 (0 self)
 Add to MetaCart
We survey algorithms and hardness results for two important classes of topology optimization problems: computing minimumweight cycles in a given homotopy or homology class, and computing minimumweight cycle bases for the fundamental group or various homology groups.
Multicuts in Planar and BoundedGenus Graphs with Bounded Number of Terminals
, 2015
"... Given an undirected, edgeweighted graph G together with pairs of vertices, called pairs of terminals, the minimum multicut problem asks for a minimumweight set of edges such that, after deleting these edges, the two terminals of each pair belong to different connected components of the graph. Rely ..."
Abstract
 Add to MetaCart
Given an undirected, edgeweighted graph G together with pairs of vertices, called pairs of terminals, the minimum multicut problem asks for a minimumweight set of edges such that, after deleting these edges, the two terminals of each pair belong to different connected components of the graph. Relying on topological techniques, we provide a polynomialtime algorithm for this problem in the case where G is embedded on a fixed surface of genus g (e.g., when G is planar) and has a fixed number t of terminals. The running time is a polynomial
unknown title
"... Computational topology is an exciting new area which is emerging at the intersection of theoretical computer science and mathematics. Algorithmic techniques in topology are far from new, but the increasing use of computational geometry in many disciplines has led to an explosion of new results in bo ..."
Abstract
 Add to MetaCart
(Show Context)
Computational topology is an exciting new area which is emerging at the intersection of theoretical computer science and mathematics. Algorithmic techniques in topology are far from new, but the increasing use of computational geometry in many disciplines has led to an explosion of new results in both computer science and mathematics. There is currently great demand for algorithms which can make topological guarantees, as well as great opportunity to apply algorithmic proofs in topology. Problems in computational topology are motivated by a wide variety of areas; applications abound in areas such as shape modeling in graphics, pathfinding in motion planning, geometric and topological modeling for protein docking prediction, encoding low dimensional spans for high dimensional data in statistical analysis, and modeling networks using cell complexes and meshes. Many topological questions are provably hard or even unsolvable in the most general settings, making it necessary to examine specific instances. My research focuses on several instances in this larger setting of computational topology. In each instance, the goal is to find an interesting topological feature, usually a cycle or path with certain desired properties. Combinatorial Surfaces
Irreducible Triangulations of Surfaces with Boundary
, 2011
"... A triangulation of a surface is irreducible if no edge can be contracted to produce a triangulation of the same surface. In this paper, we investigate irreducible triangulations of surfaces with boundary. We prove that the number of vertices of an irreducible triangulation of a (possibly nonorientab ..."
Abstract
 Add to MetaCart
A triangulation of a surface is irreducible if no edge can be contracted to produce a triangulation of the same surface. In this paper, we investigate irreducible triangulations of surfaces with boundary. We prove that the number of vertices of an irreducible triangulation of a (possibly nonorientable) surface of genus g ≥ 0 with b ≥ 0 boundaries is O(g +b). So far, the result was known only for surfaces without boundary (b = 0). While our technique yields a worse constant in the O(.) notation, the present proof is elementary, and simpler than the previous ones in the case of surfaces without boundary.