7,896 research outputs found
Automatic Deduction in Dynamic Geometry using Sage
We present a symbolic tool that provides robust algebraic methods to handle
automatic deduction tasks for a dynamic geometry construction. The main
prototype has been developed as two different worksheets for the open source
computer algebra system Sage, corresponding to two different ways of coding a
geometric construction. In one worksheet, diagrams constructed with the open
source dynamic geometry system GeoGebra are accepted. In this worksheet,
Groebner bases are used to either compute the equation of a geometric locus in
the case of a locus construction or to determine the truth of a general
geometric statement included in the GeoGebra construction as a boolean
variable. In the second worksheet, locus constructions coded using the common
file format for dynamic geometry developed by the Intergeo project are accepted
for computation. The prototype and several examples are provided for testing.
Moreover, a third Sage worksheet is presented in which a novel algorithm to
eliminate extraneous parts in symbolically computed loci has been implemented.
The algorithm, based on a recent work on the Groebner cover of parametric
systems, identifies degenerate components and extraneous adherence points in
loci, both natural byproducts of general polynomial algebraic methods. Detailed
examples are discussed.Comment: In Proceedings THedu'11, arXiv:1202.453
A Unified Approach for Representing Structurally-Complex Models in SBML Level 3
The aim of this document is to explore a unified approach to handling several of the proposed extensions to the SBML Level 3 Core specification. The approach is illustrated with reference to Simile, a modelling environment which appears to have most of the capabilities of the various SBML Level 3 package proposals which deal with model structure. Simile (http://www.simulistics.com) is a visual modelling environment for continuous systems modelling which includes the ability to handle complex disaggregation of model structure, by allowing the modeller to specify classes of object and the relationships between them.

The note is organised around the 6 packages listed on the SBML Level 3 Proposals web page (http://sbml.org/Community/Wiki/SBML_Level_3_Proposals) which deal with model structure, namely comp, arrays, spatial, geom, dyn and multi. For each one, I consider how the requirements which motivated the package can be handled using Simile's unified approach. Although Simile has a declarative model-representation language (in both Prolog and XML syntax), I use Simile diagrams and equation syntax throughout, since this is more compact and readable than large chunks of XML.

The conclusion is that Simile can indeed meet most of the requirements of these various packages, using a generic set of constructs - basically, the multiple-instance submodel, the concept of a relationship (association) between submodels, and array variables. This suggests the possibility of having a single SBML Level 3 extension package similar to the Simile data model, rather than a series of separate packages. Such an approach has a number of potential advantages and disadvantages compared with having the current set of discrete packages: these are discussed in this paper
Sequential importance sampling for multiway tables
We describe an algorithm for the sequential sampling of entries in multiway
contingency tables with given constraints. The algorithm can be used for
computations in exact conditional inference. To justify the algorithm, a theory
relates sampling values at each step to properties of the associated toric
ideal using computational commutative algebra. In particular, the property of
interval cell counts at each step is related to exponents on lead
indeterminates of a lexicographic Gr\"{o}bner basis. Also, the approximation of
integer programming by linear programming for sampling is related to initial
terms of a toric ideal. We apply the algorithm to examples of contingency
tables which appear in the social and medical sciences. The numerical results
demonstrate that the theory is applicable and that the algorithm performs well.Comment: Published at http://dx.doi.org/10.1214/009053605000000822 in the
Annals of Statistics (http://www.imstat.org/aos/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Relative fixed-width stopping rules for Markov chain Monte Carlo simulations
Markov chain Monte Carlo (MCMC) simulations are commonly employed for
estimating features of a target distribution, particularly for Bayesian
inference. A fundamental challenge is determining when these simulations should
stop. We consider a sequential stopping rule that terminates the simulation
when the width of a confidence interval is sufficiently small relative to the
size of the target parameter. Specifically, we propose relative magnitude and
relative standard deviation stopping rules in the context of MCMC. In each
setting, we develop sufficient conditions for asymptotic validity, that is
conditions to ensure the simulation will terminate with probability one and the
resulting confidence intervals will have the proper coverage probability. Our
results are applicable in a wide variety of MCMC estimation settings, such as
expectation, quantile, or simultaneous multivariate estimation. Finally, we
investigate the finite sample properties through a variety of examples and
provide some recommendations to practitioners.Comment: 24 page
Multirobot heterogeneous control considering secondary objectives
Cooperative robotics has considered tasks that are executed frequently, maintaining the
shape and orientation of robotic systems when they fulfill a common objective, without taking
advantage of the redundancy that the robotic group could present. This paper presents a proposal
for controlling a group of terrestrial robots with heterogeneous characteristics, considering primary
and secondary tasks thus that the group complies with the following of a path while modifying its
shape and orientation at any time. The development of the proposal is achieved through the use
of controllers based on linear algebra, propounding a low computational cost and high scalability
algorithm. Likewise, the stability of the controller is analyzed to know the required features that have
to be met by the control constants, that is, the correct values. Finally, experimental results are shown
with di erent configurations and heterogeneous robots, where the graphics corroborate the expected
operation of the proposalThis research was funded by Corporación Ecuatoriana para el Desarrollo de la Investigación
y Academia–CEDI
An efficient multi-core implementation of a novel HSS-structured multifrontal solver using randomized sampling
We present a sparse linear system solver that is based on a multifrontal
variant of Gaussian elimination, and exploits low-rank approximation of the
resulting dense frontal matrices. We use hierarchically semiseparable (HSS)
matrices, which have low-rank off-diagonal blocks, to approximate the frontal
matrices. For HSS matrix construction, a randomized sampling algorithm is used
together with interpolative decompositions. The combination of the randomized
compression with a fast ULV HSS factorization leads to a solver with lower
computational complexity than the standard multifrontal method for many
applications, resulting in speedups up to 7 fold for problems in our test
suite. The implementation targets many-core systems by using task parallelism
with dynamic runtime scheduling. Numerical experiments show performance
improvements over state-of-the-art sparse direct solvers. The implementation
achieves high performance and good scalability on a range of modern shared
memory parallel systems, including the Intel Xeon Phi (MIC). The code is part
of a software package called STRUMPACK -- STRUctured Matrices PACKage, which
also has a distributed memory component for dense rank-structured matrices
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