If H ∞ control laws are built on high-order models, then reduced computational speed and memory problems are likely to arise. This article proposes an algorithm for computing H ∞ controllers which is similar to the Matlab procedure hinfsyn.m, but of low order. The method consists in introducing dependencies between the differential equations of the controller by means of a rank minimisation problem. As a consequence, all differential equations of the controller are expressed as a linear

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... ion of a smaller number of differential equations. Redundant states are then removed.