21,504 research outputs found
An Exponential Lower Bound for the Runtime of the cGA on Jump Functions
In the first runtime analysis of an estimation-of-distribution algorithm
(EDA) on the multi-modal jump function class, Hasen\"ohrl and Sutton (GECCO
2018) proved that the runtime of the compact genetic algorithm with suitable
parameter choice on jump functions with high probability is at most polynomial
(in the dimension) if the jump size is at most logarithmic (in the dimension),
and is at most exponential in the jump size if the jump size is
super-logarithmic. The exponential runtime guarantee was achieved with a
hypothetical population size that is also exponential in the jump size.
Consequently, this setting cannot lead to a better runtime.
In this work, we show that any choice of the hypothetical population size
leads to a runtime that, with high probability, is at least exponential in the
jump size. This result might be the first non-trivial exponential lower bound
for EDAs that holds for arbitrary parameter settings.Comment: To appear in the Proceedings of FOGA 2019. arXiv admin note: text
overlap with arXiv:1903.1098
Meta-Modeling by Symbolic Regression and Pareto Simulated Annealing
The subject of this paper is a new approach to Symbolic Regression.Other publications on Symbolic Regression use Genetic Programming.This paper describes an alternative method based on Pareto Simulated Annealing.Our method is based on linear regression for the estimation of constants.Interval arithmetic is applied to ensure the consistency of a model.In order to prevent over-fitting, we merit a model not only on predictions in the data points, but also on the complexity of a model.For the complexity we introduce a new measure.We compare our new method with the Kriging meta-model and against a Symbolic Regression meta-model based on Genetic Programming.We conclude that Pareto Simulated Annealing based Symbolic Regression is very competitive compared to the other meta-model approachesapproximation;meta-modeling;pareto simulated annealing;symbolic regression
Comparison of Weighted Sum Fitness Functions for PSO Optimization of Wideband Medium-gain Antennas
In recent years PSO (Particle Swarm Optimization) has been successfully applied in antenna design. It is well-known that the cost function has to be carefully chosen in accordance with the requirements in order to reach an optimal result. In this paper, two different wideband medium-gain arrays are chosen as benchmark structures to test the performance of four PSO fitness functions that can be considered in such a design. The first one is a planar 3 element, the second one a linear 4 element antenna. A MoM (Method of Moments) solver is used in the design. The results clearly show that the fitness functions achieve a similar global best candidate structure. The fitness function based on realized gain however converges slightly faster than the others
Accelerating Asymptotically Exact MCMC for Computationally Intensive Models via Local Approximations
We construct a new framework for accelerating Markov chain Monte Carlo in
posterior sampling problems where standard methods are limited by the
computational cost of the likelihood, or of numerical models embedded therein.
Our approach introduces local approximations of these models into the
Metropolis-Hastings kernel, borrowing ideas from deterministic approximation
theory, optimization, and experimental design. Previous efforts at integrating
approximate models into inference typically sacrifice either the sampler's
exactness or efficiency; our work seeks to address these limitations by
exploiting useful convergence characteristics of local approximations. We prove
the ergodicity of our approximate Markov chain, showing that it samples
asymptotically from the \emph{exact} posterior distribution of interest. We
describe variations of the algorithm that employ either local polynomial
approximations or local Gaussian process regressors. Our theoretical results
reinforce the key observation underlying this paper: when the likelihood has
some \emph{local} regularity, the number of model evaluations per MCMC step can
be greatly reduced without biasing the Monte Carlo average. Numerical
experiments demonstrate multiple order-of-magnitude reductions in the number of
forward model evaluations used in representative ODE and PDE inference
problems, with both synthetic and real data.Comment: A major update of the theory and example
Properties of Interstellar Turbulence from Gradients of Linear Radio Polarization Maps
Faraday rotation of linearly polarized radio signals provides a very
sensitive probe of fluctuations in the interstellar magnetic field and ionized
gas density resulting from magnetohydrodynamic (MHD) turbulence. We used a set
of statistical tools to analyze images of the spatial gradient of linearly
polarized radio emission () from the ISM for both
observational data from a test image of the Southern Galactic Plane Survey
(SGPS) and isothermal simulations of MHD turbulence. We compared the
observational data with results of synthetic observations obtained with the
simulations of 3D turbulence. Visually, in both data sets, a complex network of
filamentary structures is seen. Our analysis shows that the filaments in the
gradient can be produced by shocks as well as random fluctuations
characterizing the non-differentiable field of MHD turbulence. The latter
dominates for subsonic turbulence, while the former dominates for supersonic
turbulence. In order to quantitatively characterize these differences we use
the topology tool known as a genus curve as well as the moments of the image
distribution. We find that higher values for the moments correspond to cases of
with larger Mach numbers, but the strength of the
dependency is connected to the telescope angular resolution. In regards to the
topology, the supersonic filaments observed in have a
positive genus shift, which indicates a "swisscheese" like topology, while the
subsonic cases show a negative genus, indicating a "clump" like topology. In
the case of the genus, the dependency on the telescope resolution is not as
strong. The SGPS test region data has a distribution and morphology that
matches subsonic to transsonic type turbulence, which independently confirms
what is now expected for the WIM.Comment: Submitted to Ap
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