2,311 research outputs found
Fitness landscape of the cellular automata majority problem: View from the Olympus
In this paper we study cellular automata (CAs) that perform the computational
Majority task. This task is a good example of what the phenomenon of emergence
in complex systems is. We take an interest in the reasons that make this
particular fitness landscape a difficult one. The first goal is to study the
landscape as such, and thus it is ideally independent from the actual
heuristics used to search the space. However, a second goal is to understand
the features a good search technique for this particular problem space should
possess. We statistically quantify in various ways the degree of difficulty of
searching this landscape. Due to neutrality, investigations based on sampling
techniques on the whole landscape are difficult to conduct. So, we go exploring
the landscape from the top. Although it has been proved that no CA can perform
the task perfectly, several efficient CAs for this task have been found.
Exploiting similarities between these CAs and symmetries in the landscape, we
define the Olympus landscape which is regarded as the ''heavenly home'' of the
best local optima known (blok). Then we measure several properties of this
subspace. Although it is easier to find relevant CAs in this subspace than in
the overall landscape, there are structural reasons that prevent a searcher
from finding overfitted CAs in the Olympus. Finally, we study dynamics and
performance of genetic algorithms on the Olympus in order to confirm our
analysis and to find efficient CAs for the Majority problem with low
computational cost
Evolutionary Approaches to Optimization Problems in Chimera Topologies
Chimera graphs define the topology of one of the first commercially available
quantum computers. A variety of optimization problems have been mapped to this
topology to evaluate the behavior of quantum enhanced optimization heuristics
in relation to other optimizers, being able to efficiently solve problems
classically to use them as benchmarks for quantum machines. In this paper we
investigate for the first time the use of Evolutionary Algorithms (EAs) on
Ising spin glass instances defined on the Chimera topology. Three genetic
algorithms (GAs) and three estimation of distribution algorithms (EDAs) are
evaluated over hard instances of the Ising spin glass constructed from
Sidon sets. We focus on determining whether the information about the topology
of the graph can be used to improve the results of EAs and on identifying the
characteristics of the Ising instances that influence the success rate of GAs
and EDAs.Comment: 8 pages, 5 figures, 3 table
Efficient computational strategies to learn the structure of probabilistic graphical models of cumulative phenomena
Structural learning of Bayesian Networks (BNs) is a NP-hard problem, which is
further complicated by many theoretical issues, such as the I-equivalence among
different structures. In this work, we focus on a specific subclass of BNs,
named Suppes-Bayes Causal Networks (SBCNs), which include specific structural
constraints based on Suppes' probabilistic causation to efficiently model
cumulative phenomena. Here we compare the performance, via extensive
simulations, of various state-of-the-art search strategies, such as local
search techniques and Genetic Algorithms, as well as of distinct regularization
methods. The assessment is performed on a large number of simulated datasets
from topologies with distinct levels of complexity, various sample size and
different rates of errors in the data. Among the main results, we show that the
introduction of Suppes' constraints dramatically improve the inference
accuracy, by reducing the solution space and providing a temporal ordering on
the variables. We also report on trade-offs among different search techniques
that can be efficiently employed in distinct experimental settings. This
manuscript is an extended version of the paper "Structural Learning of
Probabilistic Graphical Models of Cumulative Phenomena" presented at the 2018
International Conference on Computational Science
Generalized charge sensitivity analysis
Charge sensitivity analysis was originally
introduced in the trivial-atom resolution. Here, we extend
this resolution into force-field atoms. The AMBERff99
force-field resolution was employed. The effective elec-
tronegativities and hardnesses were derived for five dif-
ferent population analyses (Mulliken, Hirschfeld, AIM,
NPA and Voronoi charges) by applying evolutionary
algorithms
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Novel integrated computational approach for designing Fe-Ni-based alloys
A novel computational approach for designing high temperature alloys is proposed; the approach incorporates properties prediction and optimisation. As for properties prediction, microstructural parameters, such as the volume fraction and precipitate size after heat treatment (replicating the service conditions of automobile sealing parts) were thermokinetically calculated by adopting phase transformation software. The associated yield stress was then predicted using classical strengthening theories: solid solution, grain boundary and precipitation strengthenings. These calculations were integrated with a genetic algorithm (GA) for searching the optimal chemical compositions considering not only the strength after a long time heat treatment but also cost and producibility constraints. The calculation parameters for the GA, such as population size and mutation ratio, were also considered.
The alloy designed by the computer-aided approach described above was produced and validated. The designed alloy (Fe-opt) whose composition is Fe-33Ni-15.5Cr-1.6Al-0.3Nb-2.8Ti-3.7W-0.9Co-0.01C are proved to have the high strength after a long time high temperature exposure due to finely dispersed precipitates, , although the strength is not as high as expected from the calculation. The microstructure analysis suggests that W in the designed alloy has a negative influence on the mechanical properties of the alloy by forming coarse Laves phases on the grain boundaries. Therefore, the alloy sheet, with the same composition of Fe-opt but without W (Fe-opt2) was prepared and examined. Fe-opt2 has higher strength than Fe-opt and than more expensive Ni-based superalloys, such as Alloy 718Plus.
The integrated approach conducted in this study has successfully provided an efficient and effective alloy design methodology. This approach can be widely adopted for use in many fields beyond high-temperature alloys by adopting suitable thermokinetic databases and strengthening modelling approaches.Nippon stee
Generating Interpretable Fuzzy Controllers using Particle Swarm Optimization and Genetic Programming
Autonomously training interpretable control strategies, called policies,
using pre-existing plant trajectory data is of great interest in industrial
applications. Fuzzy controllers have been used in industry for decades as
interpretable and efficient system controllers. In this study, we introduce a
fuzzy genetic programming (GP) approach called fuzzy GP reinforcement learning
(FGPRL) that can select the relevant state features, determine the size of the
required fuzzy rule set, and automatically adjust all the controller parameters
simultaneously. Each GP individual's fitness is computed using model-based
batch reinforcement learning (RL), which first trains a model using available
system samples and subsequently performs Monte Carlo rollouts to predict each
policy candidate's performance. We compare FGPRL to an extended version of a
related method called fuzzy particle swarm reinforcement learning (FPSRL),
which uses swarm intelligence to tune the fuzzy policy parameters. Experiments
using an industrial benchmark show that FGPRL is able to autonomously learn
interpretable fuzzy policies with high control performance.Comment: Accepted at Genetic and Evolutionary Computation Conference 2018
(GECCO '18
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