97,115 research outputs found
A Feature-Based Analysis on the Impact of Set of Constraints for e-Constrained Differential Evolution
Different types of evolutionary algorithms have been developed for
constrained continuous optimization. We carry out a feature-based analysis of
evolved constrained continuous optimization instances to understand the
characteristics of constraints that make problems hard for evolutionary
algorithm. In our study, we examine how various sets of constraints can
influence the behaviour of e-Constrained Differential Evolution. Investigating
the evolved instances, we obtain knowledge of what type of constraints and
their features make a problem difficult for the examined algorithm.Comment: 17 Page
A Feature-Based Comparison of Evolutionary Computing Techniques for Constrained Continuous Optimisation
Evolutionary algorithms have been frequently applied to constrained
continuous optimisation problems. We carry out feature based comparisons of
different types of evolutionary algorithms such as evolution strategies,
differential evolution and particle swarm optimisation for constrained
continuous optimisation. In our study, we examine how sets of constraints
influence the difficulty of obtaining close to optimal solutions. Using a
multi-objective approach, we evolve constrained continuous problems having a
set of linear and/or quadratic constraints where the different evolutionary
approaches show a significant difference in performance. Afterwards, we discuss
the features of the constraints that exhibit a difference in performance of the
different evolutionary approaches under consideration.Comment: 16 Pagesm 2 Figure
Solving the G-problems in less than 500 iterations: Improved efficient constrained optimization by surrogate modeling and adaptive parameter control
Constrained optimization of high-dimensional numerical problems plays an
important role in many scientific and industrial applications. Function
evaluations in many industrial applications are severely limited and no
analytical information about objective function and constraint functions is
available. For such expensive black-box optimization tasks, the constraint
optimization algorithm COBRA was proposed, making use of RBF surrogate modeling
for both the objective and the constraint functions. COBRA has shown remarkable
success in solving reliably complex benchmark problems in less than 500
function evaluations. Unfortunately, COBRA requires careful adjustment of
parameters in order to do so.
In this work we present a new self-adjusting algorithm SACOBRA, which is
based on COBRA and capable to achieve high-quality results with very few
function evaluations and no parameter tuning. It is shown with the help of
performance profiles on a set of benchmark problems (G-problems, MOPTA08) that
SACOBRA consistently outperforms any COBRA algorithm with fixed parameter
setting. We analyze the importance of the several new elements in SACOBRA and
find that each element of SACOBRA plays a role to boost up the overall
optimization performance. We discuss the reasons behind and get in this way a
better understanding of high-quality RBF surrogate modeling
Statistical constraints on the IR galaxy number counts and cosmic IR background from the Spitzer GOODS survey
We perform fluctuation analyses on the data from the Spitzer GOODS survey
(epoch one) in the Hubble Deep Field North (HDF-N). We fit a parameterised
power-law number count model of the form dN/dS = N_o S^{-\delta} to data from
each of the four Spitzer IRAC bands, using Markov Chain Monte Carlo (MCMC)
sampling to explore the posterior probability distribution in each case. We
obtain best-fit reduced chi-squared values of (3.43 0.86 1.14 1.13) in the four
IRAC bands. From this analysis we determine the likely differential faint
source counts down to , over two orders of magnitude in flux
fainter than has been previously determined.
From these constrained number count models, we estimate a lower bound on the
contribution to the Infra-Red (IR) background light arising from faint
galaxies. We estimate the total integrated background IR light in the Spitzer
GOODS HDF-N field due to faint sources. By adding the estimates of integrated
light given by Fazio et al (2004), we calculate the total integrated background
light in the four IRAC bands. We compare our 3.6 micron results with previous
background estimates in similar bands and conclude that, subject to our
assumptions about the noise characteristics, our analyses are able to account
for the vast majority of the 3.6 micron background. Our analyses are sensitive
to a number of potential systematic effects; we discuss our assumptions with
regards to noise characteristics, flux calibration and flat-fielding artifacts.Comment: 10 pages; 29 figures (Figure added); correction made to flux scale of
Fazio points in Figure
The velocity function in the local environment from LCDM and LWDM constrained simulations
Using constrained simulations of the local Universe for generic cold dark
matter and for 1keV warm dark matter, we investigate the difference in the
abundance of dark matter halos in the local environment. We find that the mass
function within 20 Mpc/h of the Local Group is ~2 times larger than the
universal mass function in the 10^9-10^13 M_odot/h mass range. Imposing the
field of view of the on-going HI blind survey ALFALFA in our simulations, we
predict that the velocity function in the Virgo-direction region exceeds the
universal velocity function by a factor of 3. Furthermore, employing a scheme
to translate the halo velocity function into a galaxy velocity function, we
compare the simulation results with a sample of galaxies from the early catalog
release of ALFALFA. We find that our simulations are able to reproduce the
velocity function in the 80-300 km/s velocity range, having a value ~10 times
larger than the universal velocity function in the Virgo-direction region. In
the low velocity regime, 35-80 km/s, the warm dark matter simulation reproduces
the observed flattening of the velocity function. On the contrary, the
simulation with cold dark matter predicts a steep rise in the velocity function
towards lower velocities; for V_max=35 km/s, it forecasts ~10 times more
sources than the ones observed. If confirmed by the complete ALFALFA survey,
our results indicate a potential problem for the cold dark matter paradigm or
for the conventional assumptions about energetic feedback in dwarf galaxies.Comment: 24 pages, 14 figures, 1 table, accepted for publication in Ap
Improved constraints on the expansion rate of the Universe up to z~1.1 from the spectroscopic evolution of cosmic chronometers
We present new improved constraints on the Hubble parameter H(z) in the
redshift range 0.15 < z < 1.1, obtained from the differential spectroscopic
evolution of early-type galaxies as a function of redshift. We extract a large
sample of early-type galaxies (\sim11000) from several spectroscopic surveys,
spanning almost 8 billion years of cosmic lookback time (0.15 < z < 1.42). We
select the most massive, red elliptical galaxies, passively evolving and
without signature of ongoing star formation. Those galaxies can be used as
standard cosmic chronometers, as firstly proposed by Jimenez & Loeb (2002),
whose differential age evolution as a function of cosmic time directly probes
H(z). We analyze the 4000 {\AA} break (D4000) as a function of redshift, use
stellar population synthesis models to theoretically calibrate the dependence
of the differential age evolution on the differential D4000, and estimate the
Hubble parameter taking into account both statistical and systematical errors.
We provide 8 new measurements of H(z) (see Tab. 4), and determine its change in
H(z) to a precision of 5-12% mapping homogeneously the redshift range up to z
\sim 1.1; for the first time, we place a constraint on H(z) at z \neq 0 with a
precision comparable with the one achieved for the Hubble constant (about 5-6%
at z \sim 0.2), and covered a redshift range (0.5 < z < 0.8) which is crucial
to distinguish many different quintessence cosmologies. These measurements have
been tested to best match a \Lambda CDM model, clearly providing a
statistically robust indication that the Universe is undergoing an accelerated
expansion. This method shows the potentiality to open a new avenue in constrain
a variety of alternative cosmologies, especially when future surveys (e.g.
Euclid) will open the possibility to extend it up to z \sim 2.Comment: 34 pages, 15 figures, 6 tables, published in JCAP. It is a companion
to Moresco et al. (2012b, http://arxiv.org/abs/1201.6658) and Jimenez et al.
(2012, http://arxiv.org/abs/1201.3608). The H(z) data can be downloaded at
http://www.physics-astronomy.unibo.it/en/research/areas/astrophysics/cosmology-with-cosmic-chronometer
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