José Manuel Gutiérrez

Photonic information processing beyond Turing: an optoelectronic implementation of reservoir computing

Many information processing challenges are difficult to solve with traditional Turing or von Neumann approaches. Implementing unconventional computational methods is therefore essential and optics provides promising opportunities. Here we experimentally demonstrate optical information processing using a nonlinear optoelectronic oscillator subject to delayed feedback. We implement a neuro-inspired concept, called Reservoir Computing, proven to possess universal computational capabilities. We particularly exploit the transient response of a complex dynamical system to an input data stream. We employ spoken digit recognition and time series prediction tasks as benchmarks, achieving competitive processing figures of merit.

Sensitivity analysis in discrete Bayesian networks

This paper presents an efficient computational method for performing sensitivity analysis in discrete Bayesian networks. The method exploits the structure of conditional probabilities of a target node given the evidence. First, the set of parameters which is relevant to the calculation of the conditional probabilities of the target node is identified. Next, this set is reduced by removing those combinations of the parameters which either contradict the available evidence or are incompatible. Finally, using the canonical components associated with the resulting subset of parameters, the desired conditional probabilities are obtained. In this way, an important saving in the calculations is achieved. The proposed method can also be used to compute exact upper and lower bounds for the conditional probabilities, hence a sensitivity analysis can be easily performed. Examples are used to illustrate the proposed methodology.

How well do CMIP5 Earth System Models simulate present climate conditions in Europe and Africa

The present study assesses the ability of seven Earth System Models (ESMs) from the Coupled Model Intercomparison Project Phase 5 to reproduce present climate conditions in Europe and Africa. This is done from a downscaling perspective, taking into account the requirements of both statistical and dynamical approaches. ECMWF’s ERA-Interim reanalysis is used as reference for an evaluation of circulation, temperature and humidity variables on daily timescale, which is based on distributional similarity scores. To additionally obtain an estimate of reanalysis uncertainty, ERA-Interim’s deviation from the Japanese Meteorological Agency JRA-25 reanalysis is calculated. Areas with considerable differences between both reanalyses do not allow for a proper assessment, since ESM performance is sensitive to the choice of reanalysis. For use in statistical downscaling studies, ESM performance is computed on the grid-box scale and mapped over a large spatial domain covering Europe and Africa, additionally highlighting those regions where significant distributional differences remain even for the centered/zero-mean time series. For use in dynamical downscaling studies, performance is specifically assessed along the lateral boundaries of the three CORDEX domains defined for Europe, the Mediterranean Basin and Africa.

NONLINEAR TIME SERIES MODELING AND PREDICTION USING FUNCTIONAL NETWORKS. EXTRACTING INFORMATION MASKED BY CHAOS

Abstract Functional networks are a recently introduced extension of neural networks which deal with general functional models instead of sigmoidal-like ones. In this paper we show that functional network architectures provide simple and efficient techniques to model nonlinear time series. To this aim, the neural functions are approximated by finite combinations of known functions from a given family (polynomials, Fourier expansions, etc.) and the associated coefficients are estimated from data. In this paper we present two architectures from the same functional networks family, introducing efficient learning algorithms leading to error functions with a single global minimum that need not to be learned by an iterative process. We demonstrate the effectiveness of these models by applying them to several examples, including data from the Henon, Holmes, Lozi and Burgers maps. Finally, we show that these models can also be used to extract information masked in chaotic time series.

Reassessing Statistical Downscaling Techniques for Their Robust Application under Climate Change Conditions

AbstractThe performance of statistical downscaling (SD) techniques is critically reassessed with respect to their robust applicability in climate change studies. To this end, in addition to standard accuracy measures and distributional similarity scores, the authors estimate the robustness of the methods under warming climate conditions working with anomalous warm historical periods. This validation framework is applied to intercompare the performances of 12 different SD methods (from the analog, weather typing, and regression families) for downscaling minimum and maximum temperatures in Spain. First, a calibration of these methods is performed in terms of both geographical domains and predictor sets; the results are highly dependent on the latter, with optimum predictor sets including near-surface temperature data (in particular 2-m temperature), which appropriately discriminate cold episodes related to temperature inversion in the lower troposphere.Although regression methods perform best in terms of co...

Clustering methods for statistical downscaling in short-range weather forecasts

In this paper an application of clustering algorithms for statistical downscaling in short-range weather forecasts is presented. The advantages of this technique compared with standard nearest-neighbors analog methods are described both in terms of computational efficiency and forecast skill. Some validation results of daily precipitation and maximum wind speed operative downscaling (lead time 1‐5 days) on a network of 100 stations in the Iberian Peninsula are reported for the period 1998‐99. These results indicate that the weighting clustering method introduced in this paper clearly outperforms standard analog techniques for infrequent, or extreme, events (precipitation . 20 mm; wind . 80 km h21). Outputs of an operative circulation model on different local-area or large-scale grids are considered to characterize the atmospheric circulation patterns, and the skill of both alternatives is compared.

VALUE - A Framework to Validate Downscaling Approaches for Climate Change Studies

VALUE is an open European network to validate and compare downscaling methods for climate change research. VALUE aims to foster collaboration and knowledge exchange between climatologists, impact modellers, statisticians, and stakeholders to establish an interdisciplinary downscaling community. A key deliverable of VALUE is the development of a systematic validation framework to enable the assessment and comparison of both dynamical and statistical downscaling methods. In this paper, we present the key ingredients of this framework. VALUEs main approach to validation is user- focused: starting from a specific user problem, a validation tree guides the selection of relevant validation indices and performance measures. Several experiments have been designed to isolate specific points in the downscaling procedure where problems may occur: what is the isolated downscaling skill? How do statistical and dynamical methods compare? How do methods perform at different spatial scales? Do methods fail in representing regional climate change? How is the overall representation of regional climate, including errors inherited from global climate models? The framework will be the basis for a comprehensive community-open downscaling intercomparison study, but is intended also to provide general guidance for other validation studies.

Some Applications of Functional Networks in Statistics and Engineering

Functional networks are a general framework useful for solving a wide range of problems in probability, statistics, and engineering applications. In this article, we demonstrate that functional networks can be used for many general purposes including (a) solving nonlinear regression problems without the rather strong assumption of a known functional form, (b) modeling chaotic time series data, (c) finding conjugate families of distribution functions needed for the applications of Bayesian statistical techniques, (d) analyzing the problem of stability with respect to maxima operations, which are useful in the theory and applications of extreme values, and (e) modeling the reproductivity and associativity laws that have many applications in applied probability. We also give two specific engineering applications—analyzing the Ikeda map with parameters leading to chaotic behavior and modeling beam stress subject to a given load. The main purpose of this article is to introduce functional networks and to show their power and usefulness in engineering and statistical applications. We describe the steps involved in working with functional networks including structural learning (specification and simplification of the initial topology), parametric learning, and model-selection procedures. The concepts and methodologies are illustrated using several examples of applications.

On the Use of Reanalysis Data for Downscaling

AbstractIn this study, a worldwide overview on the expected sensitivity of downscaling studies to reanalysis choice is provided. To this end, the similarity of middle-tropospheric variables—which are important for the development of both dynamical and statistical downscaling schemes—from 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40) and NCEP–NCAR reanalysis data on a daily time scale is assessed. For estimating the distributional similarity, two comparable scores are used: the two-sample Kolmogorov–Smirnov statistic and the probability density function (PDF) score. In addition, the similarity of the day-to-day sequences is evaluated with the Pearson correlation coefficient. As the most important results demonstrated, the PDF score is found to be inappropriate if the underlying data follow a mixed distribution. By providing global similarity maps for each variable under study, regions where reanalysis data should not assumed to be “perfect” are detected. In contrast ...

Working with differential, functional and difference equations using functional networks

Abstract In this paper we first analyze the problem of equivalence of differential, functional and difference equations and give methods to move between them. We also introduce functional networks, a powerful alternative to neural networks, which allow neural functions to be different, multidimensional, multiargument and constrained by link connections, and use them for predicting values of magnitudes satisfying differential, functional and/or difference equations, and for obtaining the difference and differential equation associated with a set of data. The estimation of the differential or difference equation coefficients is done by simply solving systems of linear equations, in the cases of equally or unequally spaced or missing data points. Some examples of applications are given to illustrate the method.