80,803 research outputs found
Empirical Evaluation of the Parallel Distribution Sweeping Framework on Multicore Architectures
In this paper, we perform an empirical evaluation of the Parallel External
Memory (PEM) model in the context of geometric problems. In particular, we
implement the parallel distribution sweeping framework of Ajwani, Sitchinava
and Zeh to solve batched 1-dimensional stabbing max problem. While modern
processors consist of sophisticated memory systems (multiple levels of caches,
set associativity, TLB, prefetching), we empirically show that algorithms
designed in simple models, that focus on minimizing the I/O transfers between
shared memory and single level cache, can lead to efficient software on current
multicore architectures. Our implementation exhibits significantly fewer
accesses to slow DRAM and, therefore, outperforms traditional approaches based
on plane sweep and two-way divide and conquer.Comment: Longer version of ESA'13 pape
OpenACC Based GPU Parallelization of Plane Sweep Algorithm for Geometric Intersection
Line segment intersection is one of the elementary operations in computational geometry. Complex problems in Geographic Information Systems (GIS) like finding map overlays or spatial joins using polygonal data require solving segment intersections. Plane sweep paradigm is used for finding geometric intersection in an efficient manner. However, it is difficult to parallelize due to its in-order processing of spatial events. We present a new fine-grained parallel algorithm for geometric intersection and its CPU and GPU implementation using OpenMP and OpenACC. To the best of our knowledge, this is the first work demonstrating an effective parallelization of plane sweep on GPUs.
We chose compiler directive based approach for implementation because of its simplicity to parallelize sequential code. Using Nvidia Tesla P100 GPU, our implementation achieves around 40X speedup for line segment intersection problem on 40K and 80K data sets compared to sequential CGAL library
History navigation in location-based mobile systems
The aim of this paper is to provide an overview and comparison of concepts that have been proposed to guide users through interaction histories (e.g. for web browsers). The goal is to gain insights into history design that may be used for designing an interaction history for the location-based Tourist Information Provider (TIP) system [8]. The TIP system consists of several services that interact on a mobile device
Space-Efficient DFS and Applications: Simpler, Leaner, Faster
The problem of space-efficient depth-first search (DFS) is reconsidered. A
particularly simple and fast algorithm is presented that, on a directed or
undirected input graph with vertices and edges, carries out a
DFS in time with bits of working memory, where is the
(total) degree of , for each , and . A slightly more complicated variant of the algorithm works in the same
time with at most bits. It is also shown that a DFS can
be carried out in a graph with vertices and edges in
time with bits or in time with either
bits or, for arbitrary integer , bits. These
results among them subsume or improve most earlier results on space-efficient
DFS. Some of the new time and space bounds are shown to extend to applications
of DFS such as the computation of cut vertices, bridges, biconnected components
and 2-edge-connected components in undirected graphs
Optimal randomized incremental construction for guaranteed logarithmic planar point location
Given a planar map of segments in which we wish to efficiently locate
points, we present the first randomized incremental construction of the
well-known trapezoidal-map search-structure that only requires expected preprocessing time while deterministically guaranteeing worst-case
linear storage space and worst-case logarithmic query time. This settles a long
standing open problem; the best previously known construction time of such a
structure, which is based on a directed acyclic graph, so-called the history
DAG, and with the above worst-case space and query-time guarantees, was
expected . The result is based on a deeper understanding of the
structure of the history DAG, its depth in relation to the length of its
longest search path, as well as its correspondence to the trapezoidal search
tree. Our results immediately extend to planar maps induced by finite
collections of pairwise interior disjoint well-behaved curves.Comment: The article significantly extends the theoretical aspects of the work
presented in http://arxiv.org/abs/1205.543
Improved Implementation of Point Location in General Two-Dimensional Subdivisions
We present a major revamp of the point-location data structure for general
two-dimensional subdivisions via randomized incremental construction,
implemented in CGAL, the Computational Geometry Algorithms Library. We can now
guarantee that the constructed directed acyclic graph G is of linear size and
provides logarithmic query time. Via the construction of the Voronoi diagram
for a given point set S of size n, this also enables nearest-neighbor queries
in guaranteed O(log n) time. Another major innovation is the support of general
unbounded subdivisions as well as subdivisions of two-dimensional parametric
surfaces such as spheres, tori, cylinders. The implementation is exact,
complete, and general, i.e., it can also handle non-linear subdivisions. Like
the previous version, the data structure supports modifications of the
subdivision, such as insertions and deletions of edges, after the initial
preprocessing. A major challenge is to retain the expected O(n log n)
preprocessing time while providing the above (deterministic) space and
query-time guarantees. We describe an efficient preprocessing algorithm, which
explicitly verifies the length L of the longest query path in O(n log n) time.
However, instead of using L, our implementation is based on the depth D of G.
Although we prove that the worst case ratio of D and L is Theta(n/log n), we
conjecture, based on our experimental results, that this solution achieves
expected O(n log n) preprocessing time.Comment: 21 page
- …