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A Stable Primal-Dual Approach for Linear Programming
"... This paper studies a primal-dual interior/exterior-point path-following approach for linearprogramming that is motivated on using an iterative solver rather than a direct solver for the search direction. We begin with the usual perturbed primal-dual optimality equations Fu(x, y, z) = 0. Under nonde ..."
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This paper studies a primal-dual interior/exterior-point path-following approach for linearprogramming that is motivated on using an iterative solver rather than a direct solver for the search direction. We begin with the usual perturbed primal-dual optimality equations Fu(x, y, z) = 0. Under nondegeneracy assumptions, this nonlinear system is well-posed,i.e. it has a nonsingular Jacobian at optimality and is not necessarily ill-conditioned as the iterates approach optimality. We use a simple preprocessing step to eliminate boththe primal and dual feasibility equations. This results in a single bilinear equation that maintains the well-posedness property. We then apply both a direct solution techniqueas well as a preconditioned conjugate gradient method (PCG), within an inexact Newton framework, directly on the linearized equations. This is done without forming the usualnormal equations, NEQ, or augmented system. Sparsity is maintained. The work of aniteration for the PCG approach consists almost entirely in the (approximate) solution of this well-posed linearized system. Therefore, improvements depend on efficient preconditioning.

