The Experts below are selected from a list of 10587 Experts worldwide ranked by ideXlab platform
Michael Ghil - One of the best experts on this subject based on the ideXlab platform.
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multivariate singular spectrum analysis and the road to phase synchronization
Physical Review E, 2011Co-Authors: Andreas Groth, Michael GhilAbstract:We show that multivariate singular spectrum analysis (M-SSA) greatly helps study phase synchronization in a large system of coupled oscillators and in the presence of high observational noise levels. With no need for detailed knowledge of individual subsystems nor any a priori phase definition for each of them, we demonstrate that M-SSA can automatically identify multiple oscillatory modes and detect whether these modes are shared by clusters of phase- and frequency-locked oscillators. As an essential modification of M-SSA, here we introduce variance-maximization (Varimax) Rotation of the M-SSA eigenvectors to optimally identify synchronized-oscillator clustering.
Dale R Nyholt - One of the best experts on this subject based on the ideXlab platform.
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a simple correction for multiple testing for single nucleotide polymorphisms in linkage disequilibrium with each other
American Journal of Human Genetics, 2004Co-Authors: Dale R NyholtAbstract:In this report, we describe a simple correction for multiple testing of single-nucleotide polymorphisms (SNPs) in linkage disequilibrium (LD) with each other, on the basis of the spectral decomposition (SpD) of matrices of pairwise LD between SNPs. This method provides a useful alternative to more computationally intensive permutation tests. A user-friendly interface (SNPSpD) for performing this correction is available online (http://genepi.qimr.edu.au/general/daleN/SNPSpD/). Additionally, output from SNPSpD includes eigenvalues, principal-component coefficients, and factor “loadings” after Varimax Rotation, enabling the selection of a subset of SNPs that optimize the information in a genomic region.
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a simple correction for multiple testing for single nucleotide polymorphisms in linkage disequilibrium with each other
Faculty of Health; Institute of Health and Biomedical Innovation, 2004Co-Authors: Dale R NyholtAbstract:In this report, we describe a simple correction for multiple testing of single-nucleotide polymorphisms (SNPs) in linkage disequilibrium (LD) with each other, on the basis of the spectral decomposition (SpD) of matrices of pairwise LD between SNPs. This method provides a useful alternative to more computationally intensive permutation tests. Additionally, output from SNPSpD includes eigenvalues, principal-component coefficients, and factor "loadings" after Varimax Rotation, enabling the selection of a subset of SNPs that optimize the information in a genomic region.
Luis A Aguirre - One of the best experts on this subject based on the ideXlab platform.
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matrix formulation and singular value decomposition algorithm for structured Varimax Rotation in multivariate singular spectrum analysis
Physical Review E, 2016Co-Authors: Leonardo L Portes, Luis A AguirreAbstract:Groth and Ghil [Phys. Rev. E 84, 036206 (2011)PLEEE81539-375510.1103/PhysRevE.84.036206] developed a modified Varimax Rotation aimed at enhancing the ability of the multivariate singular spectrum analysis (M-SSA) to characterize phase synchronization in systems of coupled chaotic oscillators. Due to the special structure of the M-SSA eigenvectors, the modification proposed by Groth and Ghil imposes a constraint in the Rotation of blocks of components associated with the different subsystems. Accordingly, here we call it a structured Varimax Rotation (SVR). The SVR was presented as successive pairwise Rotations of the eigenvectors. The aim of this paper is threefold. First, we develop a closed matrix formulation for the entire family of structured orthomax Rotation criteria, for which the SVR is a special case. Second, this matrix approach is used to enable the use of known singular value algorithms for fast computation, allowing a simultaneous Rotation of the M-SSA eigenvectors (a Python code is provided in the Appendix). This could be critical in the characterization of phase synchronization phenomena in large real systems of coupled oscillators. Furthermore, the closed algebraic matrix formulation could be used in theoretical studies of the (modified) M-SSA approach. Third, we illustrate the use of the proposed singular value algorithm for the SVR in the context of the two benchmark examples of Groth and Ghil: the Rossler system in the chaotic (i) phase-coherent and (ii) funnel regimes. Comparison with the results obtained with Kaiser's original (unstructured) Varimax Rotation (UVR) reveals that both SVR and UVR give the same result for the phase-coherent scenario, but for the more complex behavior (ii) only the SVR improves on the M-SSA.
Canan Tosunoglu - One of the best experts on this subject based on the ideXlab platform.
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exploratory and confirmatory factor analyses of an environmental attitude scale eas for turkish university students
The Journal of Environmental Education, 1995Co-Authors: Giray Berberoglu, Canan TosunogluAbstract:Abstract The authors developed a 4-dimensional Environmental Attitude Scale (EAS) on a sample of 639 university students in Turkey. Forty-seven attitude statements from the pool of 172 items were given to 192 students. Items from the four different dimensions resulted from a principal component analysis with a Varimax Rotation. Both exploratory and confirmatory factor analyses indicated that the scale measures 4-dimensional traits, such as attitudes toward population growth, environmental problems, nuclear energy, and energy conservation. Differences in the factor structures between the present study and studies conducted in Western countries may reflect cultural differences.
Janet G Hamilton - One of the best experts on this subject based on the ideXlab platform.
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viability of exploratory factor analysis as a precursor to confirmatory factor analysis
Structural Equation Modeling, 1996Co-Authors: David W Gerbing, Janet G HamiltonAbstract:As part of the development of a comprehensive strategy for structural equation model building and assessment, a Monte Carlo study evaluated the effectiveness of different exploratory factor analysis extraction and Rotation methods for correctly identifying the known population multiple‐indicator measurement model. The exploratory methods fared well in recovering the model except in small sample sizes with highly correlated factors, and even in those situations most of the indicators were correctly assigned to the factors. Surprisingly, the orthogonal Varimax Rotation did as well as the more sophisticated oblique Rotations in recovering the model, and generally yielded more accurate estimates. These results demonstrate that exploratory factor analysis can contribute to a useful heuristic strategy for model specification prior to cross‐validation with confirmatory factor analysis.
