We consider a problem of optimizing multi-cell downlink throughput in multiple-input single-output (MISO) beamforming with single user per sub-channel in the wireless communication system. Previous work based on the g...
详细信息
We consider a problem of optimizing multi-cell downlink throughput in multiple-input single-output (MISO) beamforming with single user per sub-channel in the wireless communication system. Previous work based on the generalization of uplink-downlink duality has already reformulated the maximum achievable downlink throughput into dual uplink throughput maximization problem. Since the dual uplink problem is nonconvex, it is difficult to find its optimal solution. The main contribution of this paper is a novel practical algorithm based on heuristic to find the solution of beamforer design satisfying the necessary optimality conditions of the dual uplink problem. Meanwhile the converged beamforming vectors can in turn improve the system sum rate significantly. As the dual problem is a mixed optimization, we also provide algorithms for its two sub-optimal problems. Simulation results validate the convergence and the efficiency of proposed algorithms.
In this paper, we consider a linear quadratic regulator control problem for spacecraft rendezvous in an elliptical orbit. A new spacecraft rendezvous model is established. On the basis of this model, a linear quadrati...
详细信息
In this paper, we consider a linear quadratic regulator control problem for spacecraft rendezvous in an elliptical orbit. A new spacecraft rendezvous model is established. On the basis of this model, a linear quadratic regulator control problem is formulated. A parametric Lyapunov differential equation approach is used to design a state feedback controller such that the resulting closed-loop system is asymptotically stable, and the performance index is minimized. By an appropriate choice of the value of a parameter, an approximate state feedback controller is obtained from a solution to the periodic Lyapunov differential equation, where the periodic Lyapunov differential equation is solved on the basis of a new numerical algorithm. The spacecraft rendezvous mission under the controller obtained will be accomplished successfully. Several illustrative examples are provided to show the effectiveness of the proposed control design method. Copyright (c) 2014 John Wiley & Sons, Ltd.
Here we investigate the optimal harvesting problem for some periodic age-dependent population dynamics;namely, we consider the linear Lotka-McKendrick model with periodic vital rates and a periodic forcing term that s...
详细信息
Here we investigate the optimal harvesting problem for some periodic age-dependent population dynamics;namely, we consider the linear Lotka-McKendrick model with periodic vital rates and a periodic forcing term that sustains oscillations. Existence and uniqueness of a positive periodic solution are demonstrated and the existence and uniqueness of the optimal control are established. We also state necessary optimality conditions. A numerical algorithm is developed to approximate the optimal control and the optimal harvest. Some numerical results are presented.
The paper discusses recursive computation problems of the criterion functions of several least squares type parameter estimation methods for linear regression models, including the well-known recursive least squares (...
详细信息
The paper discusses recursive computation problems of the criterion functions of several least squares type parameter estimation methods for linear regression models, including the well-known recursive least squares (RLS) algorithm, the weighted RLS algorithm, the forgetting factor RLS algorithm and the finite-data-window RLS algorithm without or with a forgetting factor. The recursive computation formulas of the criterion functions are derived by using the recursive parameter estimation equations. The proposed recursive computation formulas can be extended to the estimation algorithms of the pseudo-linear regression models for equation error systems and output error systems. Finally, the simulation example is provided. (C) 2013 Elsevier Inc. All rights reserved.
In this paper we present magnetic control of a spacecraft using the Dichotomous Coordinate Descent (DCD) algorithm with box constraints. What is common for most work on magnetic spacecraft control is the technique for...
详细信息
In this paper we present magnetic control of a spacecraft using the Dichotomous Coordinate Descent (DCD) algorithm with box constraints. What is common for most work on magnetic spacecraft control is the technique for solving for the control variables of the magnetic torquers where a cross product is included which is well known to be singular. The DCD algorithm provides a new scheme which makes it possible to use a general control law and then adapt it to work for magnetic torquers including restrictions in available magnetic moment, instead of designing a specialized controller for the magnetic control problem. A non-linear passivity-based sliding surface controller is derived for a fully actuated spacecraft and is then implemented for magnetic control by utilizing the previous mentioned algorithm. Results from two simulations are provided, the first comparing the results from the DCD algorithm with older results, and the second showing how easily the derived sliding surface controller may be implemented, improving our results.
Over any field F every square matrix A can be factored into the product of two symmetric matrices as A = S-1 . S-2 with S-i = S-r(T) is an element of F-n,F-n and either factor can be chosen nonsingular;as was discover...
详细信息
Over any field F every square matrix A can be factored into the product of two symmetric matrices as A = S-1 . S-2 with S-i = S-r(T) is an element of F-n,F-n and either factor can be chosen nonsingular;as was discovered by Frobenius in 1910. Frobenius' symmetric matrix factorization has been lying almost dormant for a century. The first successful method for computing matrix symmetrizers, i.e., symmetric matrices S such that SA is symmetric, was inspired by an iterative linear systems algorithm of Huang and Nong (2010) in 2013 [29,30]. The resulting iterative algorithm has solved this computational problem over R and C, but at high computational cost. This paper develops and tests another linear equations solver, as well as eigen- and principal vector or Schur Normal Form based algorithms for solving the matrix symmetrizer problem numerically. Four new eigendata based algorithms use, respectively, SVD based principal vector chain constructions, Gram-Schmidt orthogonalization techniques, the Arnoldi method, or the Schur Normal Form of A in their formulations. They are helped by Datta's 1973 method that symmetrizes unreduced Hessenberg matrices directly. The eigendata based methods work well and quickly for generic matrices A and create well conditioned matrix symmetrizers through eigenvector dyad accumulation. But all of the eigen based methods have differing deficiencies with matrices A that have ill-conditioned or complicated eigen structures with nontrivial Jordan normal forms. Our symmetrizer studies for matrices with ill-conditioned eigensystems lead to two open problems of matrix optimization. (C) 2015 Elsevier Inc. All rights reserved.
An efficient and accurate numerical method is presented for computing invariant manifolds of maps which arise in the study of dynamical systems. A quasi-interpolation method due to Hering-Bertram et al. is used to dec...
详细信息
An efficient and accurate numerical method is presented for computing invariant manifolds of maps which arise in the study of dynamical systems. A quasi-interpolation method due to Hering-Bertram et al. is used to decrease the number of points needed to compute a portion of the manifold. Bezier triangular patches are used in this construction, together with adaptivity conditions based on properties of these patches. Several numerical tests are performed, which show the method to compare favorably with previous approaches. (C) 2012 Elsevier B. V. All rights reserved.
We propose a new interpolation technique for the CIP method applied to curvilinear coordinates. The CIP method can hardly maintain third-order accuracy on curvilinear coordinates. The reason for the degeneracy in accu...
详细信息
We propose a new interpolation technique for the CIP method applied to curvilinear coordinates. The CIP method can hardly maintain third-order accuracy on curvilinear coordinates. The reason for the degeneracy in accuracies has not been discussed in detail. This paper reveals the problems of the CIP method on curvilinear coordinates and presents an improved CIP method to solve the advection equation accurately. The features of the presented method are: (1) the metric computation on the upwind stencil is defined in the same manner as in the advection phase of the CIP method;and (2) gradient values in the physical domain in the computation on the curvilinear coordinates are used. Various test problems show that the improved CIP method has approximate third-order accuracy. (C) 2010 Elsevier Inc. All rights reserved.
With the energy consumption rising in rail transport, the railway sector is showing increasing interest in the energy-efficient operation of freight trains. Freight trains require more complicated driving strategies t...
详细信息
With the energy consumption rising in rail transport, the railway sector is showing increasing interest in the energy-efficient operation of freight trains. Freight trains require more complicated driving strategies than ordinary passenger trains do due to their heavy loads, especially in the long-distance steep downhill (LDSD) sections that are very common in freight rail lines in China. This paper studies the energy-efficient operation of a freight train considering LDSD sections. An optimal control model including regenerative and pneumatic braking is developed for the freight train. Then, when a train leaves/enters the LDSD section, we verify the uniqueness of control transitions and discuss the speed profile linkage between LDSD and its adjacent sections, which indicates that the periodic braking should be applied on LDSD sections for optimality. Additionally, given the same running time for the entire journey, our analysis shows that electrical braking-full braking strategy is more energy-efficient than coasting-full braking strategy on LDSD sections. Finally, a numerical algorithm for the optimal driving solution is proposed. The simulation results demonstrate that the driving strategies generated by the proposed algorithm performs better than those from fuzzy predictive control and field operation regarding energy saving.
Based on Ahmadzadeh-Varvani hardening rule (A-V model), multiaxial ratcheting effect of Z2CND18.12N austenitic stainless steel is simulated by ABAQUS with user subroutine UMAT. The results show that the predicted resu...
详细信息
Based on Ahmadzadeh-Varvani hardening rule (A-V model), multiaxial ratcheting effect of Z2CND18.12N austenitic stainless steel is simulated by ABAQUS with user subroutine UMAT. The results show that the predicted results of the origin multiaxial A-V model are lower than the experimental data, and it is difficult to control ratcheting strain rate. In order to improve the predicted capability of A-V model, the A-V model is modified. In this study. Moreover, under the assumption of the von Mises yield criterion and normal plasticity flow rule, we develop a numerical algorithm of plastic strain with the improved model to implement the finite element calculation of the model. Internal iteration in the numerical algorithm was implemented with the Euler backward method, which calculated the trial strain for each equilibrium iteration using the consistent tangent matrix. With a user subroutine, the proposed model is programmed into ABAQUS for a user -executable version. By simulating the uniaxial ratcheting of a round bar made of Z2CND18.12N austenitic stainless steel, we observe that the predicted results simulated by ABAQUS with UMAT are compared with the experimental data. The predicted results of the improved multiaxial A-V model are consistent well with the experimental data.
暂无评论