733,131 research outputs found
Improving local search heuristics for some scheduling problems - I
Local search techniques like simulated annealing and tabu search are based on a neighborhood structure defined on a set of feasible solutions of a discrete optimization problem. For the scheduling problems and we replace a simple neighborhood by a neighborhood on the set of all locally optimal solutions. This allows local search on the set of solutions that are locally optimal
Adaptive Parallel Iterative Deepening Search
Many of the artificial intelligence techniques developed to date rely on
heuristic search through large spaces. Unfortunately, the size of these spaces
and the corresponding computational effort reduce the applicability of
otherwise novel and effective algorithms. A number of parallel and distributed
approaches to search have considerably improved the performance of the search
process. Our goal is to develop an architecture that automatically selects
parallel search strategies for optimal performance on a variety of search
problems. In this paper we describe one such architecture realized in the
Eureka system, which combines the benefits of many different approaches to
parallel heuristic search. Through empirical and theoretical analyses we
observe that features of the problem space directly affect the choice of
optimal parallel search strategy. We then employ machine learning techniques to
select the optimal parallel search strategy for a given problem space. When a
new search task is input to the system, Eureka uses features describing the
search space and the chosen architecture to automatically select the
appropriate search strategy. Eureka has been tested on a MIMD parallel
processor, a distributed network of workstations, and a single workstation
using multithreading. Results generated from fifteen puzzle problems, robot arm
motion problems, artificial search spaces, and planning problems indicate that
Eureka outperforms any of the tested strategies used exclusively for all
problem instances and is able to greatly reduce the search time for these
applications
Development of 2MASS Catalog Server Kit
We develop a software kit called "2MASS Catalog Server Kit" to easily
construct a high-performance database server for the 2MASS Point Source Catalog
(includes 470,992,970 objects) and several all-sky catalogs. Users can perform
fast radial search and rectangular search using provided stored functions in
SQL similar to SDSS SkyServer. Our software kit utilizes open-source RDBMS, and
therefore any astronomers and developers can install our kit on their personal
computers for research, observation, etc. Out kit is tuned for optimal
coordinate search performance. We implement an effective radial search using an
orthogonal coordinate system, which does not need any techniques that depend on
HTM or HEALpix. Applying the xyz coordinate system to the database index, we
can easily implement a system of fast radial search for relatively small (less
than several million rows) catalogs. To enable high-speed search of huge
catalogs on RDBMS, we apply three additional techniques: table partitioning,
composite expression index, and optimization in stored functions. As a result,
we obtain satisfactory performance of radial search for the 2MASS catalog. Our
system can also perform fast rectangular search. It is implemented using
techniques similar to those applied for radial search. Our way of
implementation enables a compact system and will give important hints for a
low-cost development of other huge catalog databases.Comment: 2011 PASP accepte
Batch Informed Trees (BIT*): Sampling-based Optimal Planning via the Heuristically Guided Search of Implicit Random Geometric Graphs
In this paper, we present Batch Informed Trees (BIT*), a planning algorithm
based on unifying graph- and sampling-based planning techniques. By recognizing
that a set of samples describes an implicit random geometric graph (RGG), we
are able to combine the efficient ordered nature of graph-based techniques,
such as A*, with the anytime scalability of sampling-based algorithms, such as
Rapidly-exploring Random Trees (RRT).
BIT* uses a heuristic to efficiently search a series of increasingly dense
implicit RGGs while reusing previous information. It can be viewed as an
extension of incremental graph-search techniques, such as Lifelong Planning A*
(LPA*), to continuous problem domains as well as a generalization of existing
sampling-based optimal planners. It is shown that it is probabilistically
complete and asymptotically optimal.
We demonstrate the utility of BIT* on simulated random worlds in
and and manipulation problems on CMU's HERB, a
14-DOF two-armed robot. On these problems, BIT* finds better solutions faster
than RRT, RRT*, Informed RRT*, and Fast Marching Trees (FMT*) with faster
anytime convergence towards the optimum, especially in high dimensions.Comment: 8 Pages. 6 Figures. Video available at
http://www.youtube.com/watch?v=TQIoCC48gp
Generalized Quantum Search with Parallelism
We generalize Grover's unstructured quantum search algorithm to enable it to
use an arbitrary starting superposition and an arbitrary unitary matrix
simultaneously. We derive an exact formula for the probability of the
generalized Grover's algorithm succeeding after n iterations. We show that the
fully generalized formula reduces to the special cases considered by previous
authors. We then use the generalized formula to determine the optimal strategy
for using the unstructured quantum search algorithm. On average the optimal
strategy is about 12% better than the naive use of Grover's algorithm. The
speedup obtained is not dramatic but it illustrates that a hybrid use of
quantum computing and classical computing techniques can yield a performance
that is better than either alone. We extend the analysis to the case of a
society of k quantum searches acting in parallel. We derive an analytic formula
that connects the degree of parallelism with the optimal strategy for
k-parallel quantum search. We then derive the formula for the expected speed of
k-parallel quantum search.Comment: 14 pages, 2 figure
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