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  • Articles  (16)
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  • 1
    Publication Date: 2015-08-21
    Description: Smoothing splines provide flexible nonparametric regression estimators. However, the high computational cost of smoothing splines for large datasets has hindered their wide application. In this article, we develop a new method, named adaptive basis sampling, for efficient computation of smoothing splines in super-large samples. Except for the univariate case where the Reinsch algorithm is applicable, a smoothing spline for a regression problem with sample size n can be expressed as a linear combination of n basis functions and its computational complexity is generally O ( n 3 ). We achieve a more scalable computation in the multivariate case by evaluating the smoothing spline using a smaller set of basis functions, obtained by an adaptive sampling scheme that uses values of the response variable. Our asymptotic analysis shows that smoothing splines computed via adaptive basis sampling converge to the true function at the same rate as full basis smoothing splines. Using simulation studies and a large-scale deep earth core-mantle boundary imaging study, we show that the proposed method outperforms a sampling method that does not use the values of response variables.
    Print ISSN: 0006-3444
    Electronic ISSN: 1464-3510
    Topics: Biology , Mathematics , Medicine
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  • 2
    Publication Date: 2015-09-15
    Description: This paper deals with the distributed robust output regulation problem for the multi-agent systems with general nonlinear dynamics and uncertainty parameters. Assume that the information of active leaders or environmental disturbances cannot be completely measurable for all other agents. By employing the centre manifold theory and characteristics of the agents’ communication, the nonlinear distributed dynamic feedback controllers are designed to make the agents asymptotically track the references or reject the disturbance signals, which are generated by the exosystem. Two numerical examples are provided to show the effectiveness of the main results.
    Print ISSN: 0265-0754
    Electronic ISSN: 1471-6887
    Topics: Mathematics
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  • 3
    Publication Date: 2016-01-10
    Description: As known from the theory of centre manifolds, it is important to approximate invariant manifolds when discussing high order terms of the reduced systems in the investigation of bifurcations. In this paper, we give a method to approximate invariant manifolds which are obtained under pseudo-hyperbolicity. This method enables us to avoid the trouble of increasing dimension of the so-called approximate inertial manifold for smaller thickness of attractive neighbourhood. Unlike centre manifolds, exponential expansion and contraction may exist on such manifolds. Consequently, the technique of the contraction principle cannot be used directly. We not only overcome the difficulty so as to approximate such $C^{1}$ manifolds at a possibly higher order but also estimate, for non-local bifurcations, the lower bound of their locality radius such that the approximation is valid. Our approximation is demonstrated by examples of a wave equation and an ordinary differential equation.
    Print ISSN: 0272-4960
    Electronic ISSN: 1464-3634
    Topics: Mathematics
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  • 4
    Publication Date: 2015-07-16
    Description: This paper is concerned with the spatial dynamics of a time-delayed reaction and diffusion malaria model. We first analyse the well-posedness of the initial-boundary value problem of the model. Then, we study the global stability of the disease-free or endemic steady state for the system by structuring two Lyapunov functionals. Moreover, by applying Schauder fixed-point theorem, we establish the existence of travelling wave solutions connecting the two steady states: the disease-free steady state and the endemic steady state if the basic reproduction ratio $\mathcal {R}_0 〉 1$ , and show the non-existence of travelling wave solutions connecting the disease-free steady state to itself if $\mathcal {R}_0 〈 1$ . Our analytic results show that $\mathcal {R}_0$ is a threshold value for global dynamics and the existence of travelling wave solutions to the malaria model.
    Print ISSN: 0272-4960
    Electronic ISSN: 1464-3634
    Topics: Mathematics
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  • 5
    Publication Date: 2016-03-27
    Description: In this paper, we present a model for supply chain network design (SCND) with anticipation of variable delivered price competition in markets under deterministic and price-dependent demands and with the presence of rivals. The objective is to design a new SC under a capacity constraint in order to maximize the future profit of the SC in competing markets. The structure of the network of the new SC is assumed to be set ‘once and for all’ as a strategic decision; then the price adjustment is possible throughout the course of the competition as a decision at the operation level. In this paper, a new model for oligopolistic competitive SCND is proposed for each of the following two strategies: (1) ‘single product strategy’ and (2) ‘substitutable product strategy’. Finally, we illustrate the model through several numerical examples.
    Print ISSN: 1471-678X
    Electronic ISSN: 1471-6798
    Topics: Mathematics
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  • 6
    Publication Date: 2015-05-26
    Description: In this paper, we analyse the connection between approximate non-linear self-adjointness of perturbed partial differential equations (PDEs) and non-linear self-adjointness of the corresponding unperturbed PDEs, and consequently provide a simple approach to discriminate approximate non-linear self-adjointness of perturbed PDEs. Moreover, a succinct approximate conservation law formula by virtue of the known conservation laws of the corresponding unperturbed PDEs is given in an explicit form. As an application, we classify a class of perturbed wave equations to be approximately non-linearly self-adjoint and construct its general approximate conservation law formula. The specific examples demonstrate that approximate non-linear self-adjointness can be used to construct new approximate conservation laws of perturbed PDEs.
    Print ISSN: 0272-4960
    Electronic ISSN: 1464-3634
    Topics: Mathematics
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  • 7
    Publication Date: 2012-04-19
    Description: The mean residual life provides the remaining life expectancy of a subject who has survived to a certain time-point. When covariates are present, regression models are needed to study the association between the mean residual life function and potential regression covariates. In this paper, we propose a flexible class of semiparametric mean residual life models where some effects may be time-varying and some may be constant over time. In the presence of right censoring, we use the inverse probability of censoring weighting approach and develop inference procedures for estimating the model parameters. In addition, we provide graphical and numerical methods for model checking and tests for examining whether or not the covariate effects vary with time. Asymptotic and finite sample properties of the proposed estimators are established and the approach is applied to real life datasets collected from clinical trials.
    Print ISSN: 0006-3444
    Electronic ISSN: 1464-3510
    Topics: Biology , Mathematics , Medicine
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  • 8
    Publication Date: 2012-04-19
    Description: Several optimality properties of Dorfman’s (1943) group testing procedure are derived for estimation of the prevalence of a rare disease whose status is classified with error. Exact ranges of disease prevalence are obtained for which group testing provides more efficient estimation when group size increases.
    Print ISSN: 0006-3444
    Electronic ISSN: 1464-3510
    Topics: Biology , Mathematics , Medicine
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  • 9
    Publication Date: 2011-11-24
    Description: The H filtering problem for continuous-time linear systems is considered in which the amplitude saturation of the measurements of the system and the input of the filter are taken into account. An linear matrix inequality-based design approach is presented for the desired filter such that the resulting error system is local exponential asymptotical stable while regional L 2 gain satisfies a prescribed H -norm bound constraint. Both the filter design with the minimum attenuation level bound and the estimation of the largest domain of attraction are formulated into convex optimization problems.
    Print ISSN: 0265-0754
    Electronic ISSN: 1471-6887
    Topics: Mathematics
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  • 10
    Publication Date: 2018-03-06
    Description: In this article, we construct a $C^0$ linear finite element method for two fourth-order eigenvalue problems: the biharmonic and the transmission eigenvalue problems. The basic idea of our construction is to use gradient recovery operator to compute the higher-order derivatives of a $C^0$ piecewise linear function, which do not exist in the classical sense. For the biharmonic eigenvalue problem, the optimal convergence rates of eigenvalue/eigenfunction approximation are theoretically derived and numerically verified. For the transmission eigenvalue problem, the optimal convergence rate of the eigenvalues is verified by two numerical examples: one for constant refraction index and the other for variable refraction index. Compared with existing schemes in the literature, the proposed scheme is straightforward and simpler, and computationally less expensive to achieve the same order of accuracy.
    Print ISSN: 0272-4979
    Electronic ISSN: 1464-3642
    Topics: Mathematics
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