391 research outputs found
Risks of Large Portfolios
Estimating and assessing the risk of a large portfolio is an important topic
in financial econometrics and risk management. The risk is often estimated by a
substitution of a good estimator of the volatility matrix. However, the
accuracy of such a risk estimator for large portfolios is largely unknown, and
a simple inequality in the previous literature gives an infeasible upper bound
for the estimation error. In addition, numerical studies illustrate that this
upper bound is very crude. In this paper, we propose factor-based risk
estimators under a large amount of assets, and introduce a high-confidence
level upper bound (H-CLUB) to assess the accuracy of the risk estimation. The
H-CLUB is constructed based on three different estimates of the volatility
matrix: sample covariance, approximate factor model with known factors, and
unknown factors (POET, Fan, Liao and Mincheva, 2013). For the first time in the
literature, we derive the limiting distribution of the estimated risks in high
dimensionality. Our numerical results demonstrate that the proposed upper
bounds significantly outperform the traditional crude bounds, and provide
insightful assessment of the estimation of the portfolio risks. In addition,
our simulated results quantify the relative error in the risk estimation, which
is usually negligible using 3-month daily data. Finally, the proposed methods
are applied to an empirical study
A semi-free weighting matrices approach for neutral-type delayed neural networks
AbstractIn this paper, a new approach is proposed for stability issues of neutral-type neural networks (DNNs) with constant delay. First, the semi-free weighting matrices are proposed and used instead of the known free weighting matrices to express the relationship between the terms in the Leibniz–Newton formula to simplify the system synthesis and to obtain less computation demand. Second, global exponential stability conditions which are less conservative and restrictive than the known results are derived. At the same time, based on the above approach, fewer variable matrices are introduced in the construction of the Lyapunov functional and augmented Lyapunov functional. Two examples are given to show their effectiveness and advantages over others
Complex-valued wavelet network
AbstractIn this paper, a complex-valued wavelet network (CWN) is proposed. The network has complex inputs, outputs, connection weights, dilation and translation parameters, but the nonlinearity of the hidden nodes remains a real-valued function (real-valued wavelet function). This kind of network is able to approximate an arbitrary nonlinear function in complex multi-dimensional space, and it provides a powerful tool for nonlinear signal processing involving complex signals. A complex algorithm is derived for the training of the proposed CWN. A numerical example on nonlinear communication channel identification is presented for illustration
Passivity and Passification of Fuzzy Systems with Time Delays
AbstractTakagi-Sugeno (T-S) fuzzy model provides an effective representation of complex nonlinear systems in terms of fuzzy sets and fuzzy reasoning applied to a set of linear input/output submodels. Recently, a number of authors studied the T-S fuzzy systems with time delays. In this paper, the passivity and feedback passification of T-S fuzzy systems with time delays are considered. Both delay-independent and delay-dependent results are presented, and the theoretical results are given in terms of linear matrix inequalities (LMIs). Numerical examples are given which illustrate the effectiveness of the theoretical results
Cluster Consensus on Discrete-Time Multi-Agent Networks
Nowadays, multi-agent networks are ubiquitous in the real world. Over the last decade, consensus has received an increasing attention from various disciplines. This paper investigates cluster consensus for discrete-time multi-agent networks. By utilizing a special coupling matrix and the Kronecker product, a criterion based on linear matrix inequality (LMI) is obtained. It is shown that the addressed discrete-time multi-agent networks achieve cluster consensus if a certain LMI is feasible. Finally, an example is given to demonstrate the effectiveness of the proposed criterion
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Contractual practices between the consultant and employer in Chinese BIM-enabled construction projects
The management of building information modeling (BIM)-enabled construction projects is challenging and unstructured in nature, particularly in terms of contract administration. Even though previous studies have revealed various legal issues related to BIM, little is known regarding the contractual practices of BIM. Hence, this study was carried out to explore the contractual practices between the BIM consultant and employer in detail. An explanatory case study was carried out on four large BIM-enabled construction projects in China.
The contractual practices differed from one project to another in terms of ownership and intellectual property rights of the BIM model, roles of the BIM consultant, liability of the BIM consultant in the event of errors and delays of the BIM model, and BIM-related costs and payments. Some of the interesting findings are as follows: (a) the employer shall retain the ownership and intellectual property rights of the BIM model, (b) the BIM consultant shall provide a warranty to ensure usability of the BIM model after project handover, (c) the BIM consultant shall pay for damages or losses if the BIM model fails to deliver, and (d) the costs of BIM implementation shall be borne by both contracting parties. This study provides a fresh, realistic insight on the development of plausible contractual practices between the BIM consultant and employer and the findings can be used to improve BIM contract protocols in future projects
Hopf Bifurcation and Chaos in a Single Inertial Neuron Model with Time Delay
A delayed differential equation modelling a single neuron with inertial term
is considered in this paper. Hopf bifurcation is studied by using the normal
form theory of retarded functional differential equations. When adopting a
nonmonotonic activation function, chaotic behavior is observed. Phase plots,
waveform plots, and power spectra are presented to confirm the chaoticity.Comment: 12 pages, 7 figure
Hopf Bifurcation and Chaos in Tabu Learning Neuron Models
In this paper, we consider the nonlinear dynamical behaviors of some tabu
leaning neuron models. We first consider a tabu learning single neuron model.
By choosing the memory decay rate as a bifurcation parameter, we prove that
Hopf bifurcation occurs in the neuron. The stability of the bifurcating
periodic solutions and the direction of the Hopf bifurcation are determined by
applying the normal form theory. We give a numerical example to verify the
theoretical analysis. Then, we demonstrate the chaotic behavior in such a
neuron with sinusoidal external input, via computer simulations. Finally, we
study the chaotic behaviors in tabu learning two-neuron models, with linear and
quadratic proximity functions respectively.Comment: 14 pages, 13 figures, Accepted by International Journal of
Bifurcation and Chao
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