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Abstract With the appearance of approach named "robust alignment by sparse and low-rank decomposition" (RASL), a number of linearly correlated images can be accurately and robustly aligned despite significant corruptions and occlusions. It has been discovered that this aligning task can be characterized as a sequence of 3-block convex minimization problems which can be solved efficiently by the accelerated proximal gradient method (APG), or alternatively, by the directly extended alternating direction method of multipliers (ADMM). However, the directly extended ADMM may diverge although it often performs well in numerical computations. Ideally, one should find an algorithm which can have both theoretical guarantee and superior numerical efficiency over the directly extended ADMM. We achieve this goal by using the intelligent symmetric Gauss–Seidel iteration based ADMM (sGS-ADMM) which only needs to update one of the variables twice, but surprisingly, it leads to the desired convergence to be guaranteed. The convergence of sGS-ADMM can be followed directly by relating it to the classical 2-block ADMM and with a couple of specially designed semi-proximal terms. Beyond this, we also add a rank-correction term to the model with the purpose of deriving the alignment results with higher accuracy. The numerical experiments over a wide range of realistic misalignments demonstrate that sGS-ADMM is at least two times faster than RASL and APG for the vast majority of the tested problems. [ABSTRACT FROM AUTHOR]

For solving large-scale unconstrained minimization problems, the nonlinear conjugate gradient method is welcome due to its simplicity, low storage, efficiency and nice convergence properties. Among all the methods in the framework, the conjugate gradient descent algorithm — CG_DESCENT is very popular, in which the generated directions descend automatically, and this nice property is independent of any line search used. In this paper, we generalize CG_DESCENT with two Barzilai–Borwein steplength reused cyclically. We show that the resulting algorithm owns attractive sufficient descent property and converges globally under some mild conditions. We test the proposed algorithm by using a large set of unconstrained problems with high dimensions in CUTEr library. The numerical comparisons with the state-of-the-art algorithm CG_DESCENT illustrate that the proposed method is effective, competitive, and promising. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we give some notes on the two modified spectral gradient methods which were developed in . These notes present the relationship between their stepsize formulae and some new secant equations in the quasi-Newton method. In particular, we also introduce another two new choices of stepsize. By using an efficient nonmonotone line search technique, we propose some new spectral gradient methods. Under some mild conditions, we show that these proposed methods are globally convergent. Numerical experiments on a large number of test problems from the CUTEr library are also reported, which show that the efficiency of these proposed methods. [Copyright &y& Elsevier]

Abstract: In this paper, we propose a modified BFGS (Broyden–Fletcher–Goldfarb–Shanno) method with nonmonotone line search for unconstrained optimization. Under some mild conditions, we show that the method is globally convergent without a convexity assumption on the objective function. We also report some preliminary numerical results to show the efficiency of the proposed method. [Copyright &y& Elsevier]

Abstract: In this paper, we propose a family of derivative-free conjugate gradient methods for large-scale nonlinear systems of equations. They come from two modified conjugate gradient methods [W.Y. Cheng, A two term PRP based descent Method, Numer. Funct. Anal. Optim. 28 (2007) 1217–1230; L. Zhang, W.J. Zhou, D.H. Li, A descent modified Polak–Ribiére–Polyak conjugate gradient method and its global convergence, IMA J. Numer. Anal. 26 (2006) 629–640] recently proposed for unconstrained optimization problems. Under appropriate conditions, the global convergence of the proposed method is established. Preliminary numerical results show that the proposed method is promising. [Copyright &y& Elsevier]

Abstract: In this paper, a subspace limited memory BFGS algorithm for solving large-scale bound constrained optimization problems is developed. It is modifications of the subspace limited memory quasi-Newton method proposed by Ni and Yuan [Q. Ni, Y.X. Yuan, A subspace limited memory quasi-Newton algorithm for large-scale nonlinear bound constrained optimization, Math. Comput. 66 (1997) 1509–1520]. An important property of our proposed method is that more limited memory BFGS update is used. Under appropriate conditions, the global convergence of the method is established. The implementations of the method on CUTE test problems are presented, which indicate the modifications are beneficial to the performance of the algorithm. [Copyright &y& Elsevier]