Line search algorithms for nonlinear programming must include safeguards to enjoy global convergence properties. This paper describes an exact penalization approach that extends the class of problems that can be solved with line search SQP methods. In the new algorithm, the penalty parameter is adjusted at every iteration to ensure sufficient progress in linear feasibility and to promote acceptance of the step. A trust region is used to assist in the determination of the penalty parameter (but not in the step computation). It is shown that the algorithm enjoys favorable global convergence properties. Numerical experiments illustrate the behavior of the algorithm on various difficult situations. 1

Abstract. We present a two-phase algorithm for solving large-scale quadratic programs (QPs). In the first phase, gradient-projection iterations approximately minimize a bound-constrained augmented Lagrangian function and provide an estimate of the optimal active set. In the second phase, an equality-constrained QP defined by the current active set is approximately minimized in order to generate a second-order search direction. A filter determines the required accuracy of the subproblem solutions and provides an acceptance criterion for the search directions. The resulting algorithm is globally and finitely convergent. The algorithm is suitable for large-scale problems with many degrees of freedom, and provides an alternative to interior-point methods when iterative methods must be used to solve the underlying linear systems. Numerical experiments on a subset of the CUTEr QP test problems demonstrate the effectiveness of the approach. Key words. Large-scale optimization, quadratic programming, gradient-projection, active-set methods, filter methods, augmented Lagrangian. AMS subject classifications. 65K05, 90C06, 90C20, 90C26, 90C52 1. Introduction. Quadratic programs (QPs) play a fundamental role in optimization. They are useful across a rich class of applications, such as the simulation

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Summary. This papers studies the performance of several interior-point and activeset methods on bound constrained optimization problems. The numerical tests show that the sequential linear-quadratic programming (SLQP) method is robust, but is not as effective as gradient projection at identifying the optimal active set. Interiorpoint methods are robust and require a small number of iterations and function evaluations to converge. An analysis of computing times reveals that it is essential to develop improved preconditioners for the conjugate gradient iterations used in SLQP and interior-point methods. The paper discusses how to efficiently implement incomplete Cholesky preconditioners and how to eliminate ill-conditioning caused by the barrier approach. The paper concludes with an evaluation of methods that use quasi-Newton approximations to the Hessian of the Lagrangian. 1

Sequential quadratic programming (SQP) methods form a class of highly efficient algorithms for solving nonlinearly constrained optimization problems. Although second derivative information may often be calculated, there is little practical theory that justifies exact-Hessian SQP methods. In particular, the resulting quadratic programming (QP) subproblems are often nonconvex, and thus finding their global solutions may be computationally nonviable. This paper presents a secondderivative SQP method based on quadratic subproblems that are either convex, and thus may be solved efficiently, or need not be solved globally. Additionally, an explicit descent-constraint is imposed on certain QP subproblems, which “guides ” the iterates through areas in which nonconvexity is a concern. Global convergence of the resulting algorithm is established. Key words. Nonlinear programming, nonlinear inequality constraints, sequential quadratic programming, ℓ1-penalty function, nonsmooth optimization

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This paper addresses the need for nonlinear programming algorithms that provide fast local convergence guarantees no matter if a problem is feasible or infeasible. We present an active-set sequential quadratic programming method derived from an exact penalty approach that adjusts the penalty parameter appropriately to emphasize optimality over feasibility, or vice versa. Conditions are presented under which superlinear convergence is achieved in the infeasible case. Numerical experiments illustrate the practical behavior of the method.

Stebel Tvarová optimalizace pro Navierovy–Stokesovy rovnice s viskozitou Katedra numerické matematiky

This paper presents an active-set algorithm for large-scale optimization that occupies the middle ground between sequential quadratic programming (SQP) and sequential linear-quadratic programming (SL-QP) methods. It consists of two phases. The algorithm first minimizes a piecewise linear approximation of the Lagrangian, subject to a linearization of the constraints, to determine a working set. Then, an equality constrained subproblem based on this working set and using second derivative information is solved in order to promote fast convergence. A study of the local and global convergence properties of the algorithm highlights the importance of the placement of the interpolation points that determine the piecewise linear model of the Lagrangian. 1

Abstract. We analyze an abridged version of the active-set algorithm FPC AS proposed in [18] for solving the l1-regularized problem, i.e., a weighted sum of the l1-norm ‖x‖1 and a smooth function f(x). The active set algorithm alternatively iterates between two stages. In the first “nonmonotone line search (NMLS) ” stage, an iterative first-order method based on “shrinkage” is used to estimate the support at the solution. In the second “subspace optimization ” stage, a smaller smooth problem is solved to recover the magnitudes of the nonzero components of x. We show that NMLS itself is globally convergent and the convergence rate is at least R-linearly. In particular, NMLS is able to identify of the zero components of a stationary point after a finite number of steps under some mild conditions. The global convergence of FPC AS is established based on the properties