Ashim Garg

On the Computational Complexity of Upward and Rectilinear Planarity Testing

A directed graph is upward planar if it can be drawn in the plane such that every edge is a monotonically increasing curve in the vertical direction and no two edges cross. An undirected graph is rectilinear planar if it can be drawn in the plane such that every edge is a horizontal or vertical segment and no two edges cross. Testing upward planarity and rectilinear planarity are fundamental problems in the effective visualization of various graph and network structures. For example, upward planarity is useful for the display of order diagrams and subroutine-call graphs, while rectilinear planarity is useful for the display of circuit schematics and entity-relationship diagrams. We show that upward planarity testing and rectilinear planarity testing are NP-complete problems. We also show that it is NP-hard to approximate the minimum number of bends in a planar orthogonal drawing of an n-vertex graph with an

An experimental comparison of four graph drawing algorithms

O(n^{1-\epsilon})

Compact Encodings of Planar Graphs via Canonical Orderings and Multiple Parentheses

error for any

A New Minimum Cost Flow Algorithm with Applications to Graph Drawing

\epsilon > 0

On the Compuational Complexity of Upward and Rectilinear Planarity Testing

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Planar drawings and angular resolution: Algorithms and bounds

Abstract In this paper we present an extensive experimental study comparing four general-purpose graph drawing algorithms. The four algorithms take as input general graphs (with no restrictions whatsoever on connectivity, planarity, etc.) and construct orthogonal grid drawings, which are widely used in software and database visualization applications. The test data (available by anonymous ftp) are 11,582 graphs, ranging from 10 to 100 vertices, which have been generated from a core set of 112 graphs used in “real-life” software engineering and database applications. The experiments provide a detailed quantitative evaluation of the performance of the four algorithms, and show that they exhibit trade-offs between “aesthetic” properties (e.g., crossings, bends, edge length) and running time.

Upward planarity testing

We consider the problem of coding planar graphs by binary strings. Depending on whether O(1)-time queries for adjacency and degree are supported, we present three sets of coding schemes which all take linear time for encoding and decoding. The encoding lengths are significantly shorter than the previously known results in each case.

Area-efficient upward tree drawings

Let N be a single-source single-sink flow network with n nodes, m arcs, and positive arc costs. We present a pseudo-polynomial algorithm that computes a maximum flow of minimum cost for N in time O(χ3/4m√log n), where χ is the cost of the flow. This improves upon previously known methods for networks where the minimum cost of the flow is small. We also show an application of our flow algorithm to a well-known graph drawing problem. Namely, we show how to compute a planar orthogonal drawing with the minimum number of bends for an n- vertex embedded planar graph in time O(n7/4√log n). This is the first subquadratic algorithm for bend minimization. The previous best bound for this problem was O(n2 log n) [19].

An experimental comparison of three graph drawing algorithms (extended abstract)

A directed graph is upward planar if it can be drawn in the plane such that every edge is a monotonically increasing curve in the vertical direction, and no two edges cross. An undirected graph is rectilinear planar if it can be drawn in the plane such that every edge is a horizontal or vertical segment, and no two edges cross. Testing upward planarity and rectilinear planarity are fundamental problems in the effective visualization of various graph and network structures. In this paper we show that upward planarity testing and rectilinear planarity testing are NP-complete problems. We also show that it is NP-hard to approximate the minimum number of bends in a planar orthogonal drawing of an n-vertex graph with an O(n1−∈) error, for any ∈>0.

InteractiveGiotto: An Algorithm for Interactive Orthogonal Graph Drawing

We investigate the problem of constructing planar straightline drawings of graphs with large angles between the edges. Namely, we study the angular resolution of planar straight-line drawings, defined as the smallest angle formed by two incident edges. We prove the first nontrivial upper bound on the angular resolution of planar straight-line drawings, and show a continuous trade-off between the area and the angular resolution. We also give linear-time algorithms for constructing planar straight-line drawings with high angular resolution for various classes of graphs, such as series-parallel graphs, outerplanar graphs, and triangulations generated by nested triangles. Our results are obtained by new techniques that make extensive use of geometric constructions.