Estudo Geralhttps://estudogeral.sib.uc.ptThe DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Mon, 13 Jul 2020 18:23:03 GMT2020-07-13T18:23:03Z5051Complementarity Active-Set Algorithm for Mathematical Programming Problems with Equilibrium Constraintshttp://hdl.handle.net/10316/7719Title: Complementarity Active-Set Algorithm for Mathematical Programming Problems with Equilibrium Constraints
Authors: Júdice, J.; Sherali, H.; Ribeiro, I.; Faustino, A.
Abstract: Abstract In this paper, an algorithm for solving a mathematical programming problem with complementarity (or equilibrium) constraints (MPEC) is introduced, which uses the active-set methodology while maintaining the complementarity restrictions throughout the procedure. Finite convergence of the algorithm to a strongly stationary point of the MPEC is established under reasonable hypotheses. The algorithm can be easily implemented by adopting any active-set code for nonlinear programming. Computational experience is included to highlight the efficacy of the proposed method in practice.
Mon, 01 Jan 2007 00:00:00 GMThttp://hdl.handle.net/10316/77192007-01-01T00:00:00ZOn finding global optima for the hinge fitting problemhttp://hdl.handle.net/10316/4642Title: On finding global optima for the hinge fitting problem
Authors: Queiroz, M.; Humes, C.; Júdice, J.
Abstract: This paper considers the data fitting of n given points in by a hinge function, as it appears in Breiman (IEEE Trans. Inform. Theory 39(3) (1993) 999) and Pucar and SjÃ¶berg (IEEE Trans. Inform. Theory 44(3) (1998) 1310). This problem can be seen as a mathematical programming problem with a convex objective function and equilibrium constraints. For the euclidean error, an enumerative approach is proposed, which is a polynomial method in the sample size n, for a fixed dimension m. An alternative formulation for the l1 error is also introduced, which is processed by a Sequential Linear Complementarity Problem approach. Some numerical results with both algorithms are included to highlight the efficiency of those procedures.
Thu, 01 Jan 2004 00:00:00 GMThttp://hdl.handle.net/10316/46422004-01-01T00:00:00ZThe directional instability problem in systems with frictional contactshttp://hdl.handle.net/10316/4641Title: The directional instability problem in systems with frictional contacts
Authors: Pinto da Costa, A.; Martins, J. A. C.; Figueiredo, I. N.; Júdice, J. J.
Abstract: The research summarized in this paper addresses the directional instability of finite dimensional systems with unilateral frictional contacts. Conditions for the occurrence of this divergence type instability are discussed, complementarity formulations are developed, and numerical procedures are proposed for the solution of the corresponding non-smooth stability eigenproblems. Various examples are analytically or numerically solved and discussed, namely some finite element examples that have instability modes involving evolution towards slip or stick in different portions of the contact surface.
Thu, 01 Jan 2004 00:00:00 GMThttp://hdl.handle.net/10316/46412004-01-01T00:00:00ZA block active set algorithm for large-scalequadratic programming with box constraintshttp://hdl.handle.net/10316/7748Title: A block active set algorithm for large-scalequadratic programming with box constraints
Authors: Fernandes, L.; Fischer, A.; Júdice, J.; Requejo, C.; Soares, J.
Abstract: Abstract An algorithm for computing a stationary point of a quadratic program with box constraints(BQP) is proposed. Each iteration of this procedure comprises a guessing strategy whichforecasts the active bounds at a stationary point, the determination of a descent direction bymeans of solving a reduced strictly convex quadratic program with box constraints and anexact line search. Global convergence is established in the sense that every accumulationpoint is stationary. Moreover, it is shown that the algorithm terminates after a finite numberof iterations, if at least one iterate is sufficiently close to a stationary point which satisfiesa certain sufficient optimality condition. The algorithm can be easily implemented for sparselarge-scale BQPs. Furthermore, it simplifies for concave BQPs, as it is not required to solvestrictly convex quadratic programs in this case. Computational experience with large-scaleBQPs is included and shows the appropriateness of this type of methodology.
Thu, 01 Jan 1998 00:00:00 GMThttp://hdl.handle.net/10316/77481998-01-01T00:00:00ZMultiple- and single-objective approaches to laminate optimization with genetic algorithmshttp://hdl.handle.net/10316/7765Title: Multiple- and single-objective approaches to laminate optimization with genetic algorithms
Authors: Costa, L.; Fernandes, L.; Figueiredo, I.; JĂºdice, J.; Leal, R.; Oliveira, P.
Abstract: In this paper an application of a genetic algorithm to a material- and sizing-optimization problem of a plate is described. This approach has obvious advantages: it does not require any derivative information and it does not impose any restriction, in terms of convexity, on the solution space. The plate optimization problem is firstly formulated as a constrained mixed-integer programming problem with a single objective function. An alternative multiobjective formulation of the problem in which some constraints are included as additional objectives is also presented. Some numerical results are included that show the appropriateness of the algorithm and of the mathematical model for the solution of this optimization problem, as well as the superiority of the multiobjective approach.
Thu, 01 Jan 2004 00:00:00 GMThttp://hdl.handle.net/10316/77652004-01-01T00:00:00Z