Julian Hall (University of Edinburgh)

Parallel matrix inversion for the revised simplex method: a study
ERGO Optimization day: Tuesday 13 June 2006 at 14.00, JCMB 5327

Abstract

The revised simplex method for solving linear programming LP problems requires the solution of Bãq = aq and Bπ = ep, where B is the basis matrix, aq is column q of the (sparse) constraint matrix and ep is column p of the identity matrix. Although the invertible representation of B is usually obtained by an updating procedure, periodically it is necessary to form it from scratch. As a crucial step towards the goal of a practical parallel implementation of the revised simplex method, this talk considers the scope for exploiting parallelism during basis matrix inversion.

For LP problems where the revised simplex method out-performs barrier methods, the solutions of Bãq = aq and Bπ = ep are generally sparse. This property of LP problems is referred to as hyper-sparsity. It will be shown that the basis matrices of hyper-sparse LP problems are generally highly reducible, and that the dominant cost of matrix inversion is that of identifying the irreducible component via a triangularisation procedure. This talk will describe the triangularisation procedure and discuss the scope for parallelising it.

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