24,427 research outputs found
Autonomous frequency domain identification: Theory and experiment
The analysis, design, and on-orbit tuning of robust controllers require more information about the plant than simply a nominal estimate of the plant transfer function. Information is also required concerning the uncertainty in the nominal estimate, or more generally, the identification of a model set within which the true plant is known to lie. The identification methodology that was developed and experimentally demonstrated makes use of a simple but useful characterization of the model uncertainty based on the output error. This is a characterization of the additive uncertainty in the plant model, which has found considerable use in many robust control analysis and synthesis techniques. The identification process is initiated by a stochastic input u which is applied to the plant p giving rise to the output. Spectral estimation (h = P sub uy/P sub uu) is used as an estimate of p and the model order is estimated using the produce moment matrix (PMM) method. A parametric model unit direction vector p is then determined by curve fitting the spectral estimate to a rational transfer function. The additive uncertainty delta sub m = p - unit direction vector p is then estimated by the cross spectral estimate delta = P sub ue/P sub uu where e = y - unit direction vectory y is the output error, and unit direction vector y = unit direction vector pu is the computed output of the parametric model subjected to the actual input u. The experimental results demonstrate the curve fitting algorithm produces the reduced-order plant model which minimizes the additive uncertainty. The nominal transfer function estimate unit direction vector p and the estimate delta of the additive uncertainty delta sub m are subsequently available to be used for optimization of robust controller performance and stability
Temporal Cross-Media Retrieval with Soft-Smoothing
Multimedia information have strong temporal correlations that shape the way
modalities co-occur over time. In this paper we study the dynamic nature of
multimedia and social-media information, where the temporal dimension emerges
as a strong source of evidence for learning the temporal correlations across
visual and textual modalities. So far, cross-media retrieval models, explored
the correlations between different modalities (e.g. text and image) to learn a
common subspace, in which semantically similar instances lie in the same
neighbourhood. Building on such knowledge, we propose a novel temporal
cross-media neural architecture, that departs from standard cross-media
methods, by explicitly accounting for the temporal dimension through temporal
subspace learning. The model is softly-constrained with temporal and
inter-modality constraints that guide the new subspace learning task by
favouring temporal correlations between semantically similar and temporally
close instances. Experiments on three distinct datasets show that accounting
for time turns out to be important for cross-media retrieval. Namely, the
proposed method outperforms a set of baselines on the task of temporal
cross-media retrieval, demonstrating its effectiveness for performing temporal
subspace learning.Comment: To appear in ACM MM 201
Testing consumers' asymmetric reaction to wealth changes
This study contains several tests to show that individuals overreact to negative wealth changes, relative to positive wealth changes. This asymmetry, that is found using micro data, suggests that economists should not treat symmetrically the relation between economic variables (consumption for instance) and wealth in their models when wealth decreases. We find that this asymmetry increases with age and picks at retirement.
Culture, nationality and demographics in ultimatum games
We use experimental data collected in Russia and in the United States using a simple ultimatum game to evaluate two alternative hypotheses that may account for previously observed behavior in multinational experiments. One hypothesis postulates that behavioral differences observed in bargaining experiments arise from country-specific cultural environments. We submit the alternative hypothesis that different behavior in such experiments stems from differences in the demographic characteristics of the subject pools within each country. Because of its simplicity, our experimental design allows us to discriminate between these two hypotheses. Our findings support the alternative hypothesis.multinational experiments, ultimatum bargaining
Classification methods for Hilbert data based on surrogate density
An unsupervised and a supervised classification approaches for Hilbert random
curves are studied. Both rest on the use of a surrogate of the probability
density which is defined, in a distribution-free mixture context, from an
asymptotic factorization of the small-ball probability. That surrogate density
is estimated by a kernel approach from the principal components of the data.
The focus is on the illustration of the classification algorithms and the
computational implications, with particular attention to the tuning of the
parameters involved. Some asymptotic results are sketched. Applications on
simulated and real datasets show how the proposed methods work.Comment: 33 pages, 11 figures, 6 table
Non-Parametric Calibration of Probabilistic Regression
The task of calibration is to retrospectively adjust the outputs from a
machine learning model to provide better probability estimates on the target
variable. While calibration has been investigated thoroughly in classification,
it has not yet been well-established for regression tasks. This paper considers
the problem of calibrating a probabilistic regression model to improve the
estimated probability densities over the real-valued targets. We propose to
calibrate a regression model through the cumulative probability density, which
can be derived from calibrating a multi-class classifier. We provide three
non-parametric approaches to solve the problem, two of which provide empirical
estimates and the third providing smooth density estimates. The proposed
approaches are experimentally evaluated to show their ability to improve the
performance of regression models on the predictive likelihood
Diffusion Maps Kalman Filter for a Class of Systems with Gradient Flows
In this paper, we propose a non-parametric method for state estimation of
high-dimensional nonlinear stochastic dynamical systems, which evolve according
to gradient flows with isotropic diffusion. We combine diffusion maps, a
manifold learning technique, with a linear Kalman filter and with concepts from
Koopman operator theory. More concretely, using diffusion maps, we construct
data-driven virtual state coordinates, which linearize the system model. Based
on these coordinates, we devise a data-driven framework for state estimation
using the Kalman filter. We demonstrate the strengths of our method with
respect to both parametric and non-parametric algorithms in three tracking
problems. In particular, applying the approach to actual recordings of
hippocampal neural activity in rodents directly yields a representation of the
position of the animals. We show that the proposed method outperforms competing
non-parametric algorithms in the examined stochastic problem formulations.
Additionally, we obtain results comparable to classical parametric algorithms,
which, in contrast to our method, are equipped with model knowledge.Comment: 15 pages, 12 figures, submitted to IEEE TS
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