We investigate the problem of constructing planar drawings with few bends for two related problems, the partially embedded graph problem---to extend a straight-line planar drawing of a subgraph to a planar drawing of the whole graph---and the simultaneous planarity problem---to find planar drawings of two graphs that coincide on shared vertices and edges. In both cases we show that if the required planar drawings exist, then there are planar drawings with a linear number of bends per edge and, in the case of simultaneous planarity, a constant number of crossings between every pair of edges. Our proofs provide efficient algorithms if the combinatorial embedding of the drawing is given. Our result on partially embedded graph drawing generalizes a classic result by Pach and Wenger which shows that any planar graph can be drawn with a linear number of bends per edge if the location of each vertex is fixed.
Concerning PEG, Pach and Wenger @cite_12 proved the following result: given an @math -vertex planar graph @math with fixed vertex locations, a planar drawing of @math in which each edge has at most @math bends can be constructed in @math time. They also proved that such a bound is asymptotically tight in the worst case. Regarding the constant, @cite_3 improved the bound to @math bends per edge. Biedl and Floderus @cite_18 considered the more general problem of drawing an @math -vertex planar graph on fixed vertex locations where the drawing is constrained to lie inside a @math -vertex polygon. They show that there is a drawing with @math bends per edge.
@cite_18 @cite_3 @cite_12
98352059 2063120809
In this paper, we study the problem of drawing a given planar graph such that vertices are at pre-specified points and the entire drawing is inside a given polygon. We give a method that shows that for an n-vertex graph and a k-sided polygon, Θ(kn2) bends are always sufficient. We also give an example of a graph where Θ(kn2) bends are necessary for such a drawing. Let G be a planar graph with n vertices and with a partition of the vertex set into subsets V"0,...,V"k"-"1 for some positive integer [email protected][email protected]?n. Let S be a set of n distinct points in the plane with a partition into subsets S"0,...,S"k"-"1 with |V"i|=|S"i| ([email protected][email protected]?k-1). This paper studies the problem of computing a planar polyline drawing of G, such that each vertex of V"i is mapped to a distinct point of S"i. Lower and upper bounds on the number of bends per edge are proved for any [email protected][email protected]?n. In the special case k=n, we improve the upper and lower bounds presented in a paper by Pach and Wenger [J. Pach, R. Wenger, Embedding planar graphs at fixed vertex locations, Graphs and Combinatorics 17 (2001) 717-728]. The upper bound is based on an algorithm for computing a topological book embedding of a planar graph, such that the vertices follow a given left-to-right order and the number of crossings between every edge and the spine is asymptotically optimal, which can be regarded as a result of independent interest.