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    David Hartvigsen

    A simple 2-matching in an edge-weighted graph is a subgraph all of whose vertices have degree 1 or 2. We consider the problem of finding a maximum weight simple 2-matching that contains no triangles, which is closely related to a class of... more
    A simple 2-matching in an edge-weighted graph is a subgraph all of whose vertices have degree 1 or 2. We consider the problem of finding a maximum weight simple 2-matching that contains no triangles, which is closely related to a class of relaxations of the TSP. Our main results are, for graphs with maximum degree 3, a complete description of
    ABSTRACT A simple 2-matching in a graph is a subgraph whose connected components are nontrivial paths and cycles. A simple 2-matching is called 1-restricted if each connected component has two or more edges. In this paper we consider the... more
    ABSTRACT A simple 2-matching in a graph is a subgraph whose connected components are nontrivial paths and cycles. A simple 2-matching is called 1-restricted if each connected component has two or more edges. In this paper we consider the problem of finding maximum weight 1-restricted simple 2-matchings (which is a relaxation of the traveling salesman problem). We present an integer programming formulation for this problem, characterize the extreme points of the linear programming relaxation, and characterize the graphs for which the linear programming relaxation has all integral extreme points. We show how to recognize these graphs in polynomial time. We also introduce a new class of blossom-type inequalities that tighten the general linear programming relaxation. A complete description of the convex hull of 1-restricted simple 2-matchings is unknown.
    ABSTRACT The all-pairs min cut (APMC) problem on a normegative weighted graph is the problem of finding, for every pair of nodes, the min cut separating the pair. It is shown that on planar graphs, the APMC problem is equivalent to... more
    ABSTRACT The all-pairs min cut (APMC) problem on a normegative weighted graph is the problem of finding, for every pair of nodes, the min cut separating the pair. It is shown that on planar graphs, the APMC problem is equivalent to another problem, the minimum cycle basis (MCB) problem, on the dual graph. This is shown by characterizing the structure of MCBs on planar graphs in several ways. This leads to a new algorithm for solving both of these problems on planar graphs. The complexity of this algorithm equals that of the best algorithm for either problem, but is simpler.
    ... 7, Number 1 OPERATIONS RESEARCH LETFERS February 1988 RECOGNIZING MAXFLOW MINCUT PATH MATRICES * David B HARTVIGSEN Kellogg Graduate ... If an instance of (D) is a maximumflow prob lem on a matroid satisfying Seymour's characteri... more
    ... 7, Number 1 OPERATIONS RESEARCH LETFERS February 1988 RECOGNIZING MAXFLOW MINCUT PATH MATRICES * David B HARTVIGSEN Kellogg Graduate ... If an instance of (D) is a maximumflow prob lem on a matroid satisfying Seymour's characteri zation and if a ...
    ABSTRACT Gomory and Hu proved the following classical result: For any graph with nonnegative edge weights, there exists a collection of noncrossing cuts that contains a minimum cut for every pair of nodes. In this paper, we show how this... more
    ABSTRACT Gomory and Hu proved the following classical result: For any graph with nonnegative edge weights, there exists a collection of noncrossing cuts that contains a minimum cut for every pair of nodes. In this paper, we show how this result generalizes for a natural multiterminal cut problem. We also show that our result is “best possible,” for k = 3, by using a computer to find feasible solutions to several large systems of linear inequalities. © 1999 John Wiley & Sons, Inc. Networks 34: 215–220, 1999