63,549 research outputs found
An Algorithmic Framework for Labeling Road Maps
Given an unlabeled road map, we consider, from an algorithmic perspective,
the cartographic problem to place non-overlapping road labels embedded in their
roads. We first decompose the road network into logically coherent road
sections, e.g., parts of roads between two junctions. Based on this
decomposition, we present and implement a new and versatile framework for
placing labels in road maps such that the number of labeled road sections is
maximized. In an experimental evaluation with road maps of 11 major cities we
show that our proposed labeling algorithm is both fast in practice and that it
reaches near-optimal solution quality, where optimal solutions are obtained by
mixed-integer linear programming. In comparison to the standard OpenStreetMap
renderer Mapnik, our algorithm labels 31% more road sections in average.Comment: extended version of a paper to appear at GIScience 201
Label Placement in Road Maps
A road map can be interpreted as a graph embedded in the plane, in which each
vertex corresponds to a road junction and each edge to a particular road
section. We consider the cartographic problem to place non-overlapping road
labels along the edges so that as many road sections as possible are identified
by their name, i.e., covered by a label. We show that this is NP-hard in
general, but the problem can be solved in polynomial time if the road map is an
embedded tree.Comment: extended version of a CIAC 2015 pape
Placing Arrows in Directed Graph Drawings
We consider the problem of placing arrow heads in directed graph drawings
without them overlapping other drawn objects. This gives drawings where edge
directions can be deduced unambiguously. We show hardness of the problem,
present exact and heuristic algorithms, and report on a practical study.Comment: Appears in the Proceedings of the 24th International Symposium on
Graph Drawing and Network Visualization (GD 2016
Polynomial-Time Fence Insertion for Structured Programs
To enhance performance, common processors feature relaxed memory models that reorder instructions. However, the correctness of concurrent programs is often dependent on the preservation of the program order of certain instructions. Thus, the instruction set architectures offer memory fences. Using fences is a subtle task with performance and correctness implications: using too few can compromise correctness and using too many can hinder performance. Thus, fence insertion algorithms that given the required program orders can automatically find the optimum fencing can enhance the ease of programming, reliability, and performance of concurrent programs. In this paper, we consider the class of programs with structured branch and loop statements and present a greedy and polynomial-time optimum fence insertion algorithm. The algorithm incrementally reduces fence insertion for a control-flow graph to fence insertion for a set of paths. In addition, we show that the minimum fence insertion problem with multiple types of fence instructions is NP-hard even for straight-line programs
Distribution System Outage Detection using Consumer Load and Line Flow Measurements
An outage detection framework for power distribution networks is proposed.
Given the tree structure of the distribution system, a method is developed
combining the use of real-time power flow measurements on edges of the tree
with load forecasts at the nodes of the tree. A maximum a posteriori detector
{\color{black} (MAP)} is formulated for arbitrary number and location of
outages on trees which is shown to have an efficient detector. A framework
relying on the maximum missed detection probability is used for optimal sensor
placement and is solved for tree networks. Finally, a set of case studies is
considered using feeder data from the Pacific Northwest National Laboratories.
We show that a 10\% loss in mean detection reliability network wide reduces the
required sensor density by 60 \% for a typical feeder if efficient use of
measurements is performed.Comment: Complete rework of result
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