14.1. Introduction

The concept of eigenstructure placement was born in the 1970s with the works of Kimura [KIM 75] and Moore [MOO 76a]. Since then, the eigenstructure placement has undergone continuous development, in particular due to its potential applications in aeronautics. In fact, the control of couplings through these techniques makes them very appropriate for this type of application. Moore s works led to numerous studies on the decoupling eigenstructure placement. The principle consists of setting the dominant eigenvalues of the system while guaranteeing, through a proper choice of related closed loop eigenvectors, certain decoupling, non-reactivity, insensitivity, etc. Within the same orientation, Harvey [HAR 78] interprets the asymptotic LQ in terms of eigenstructure placement. Alongside this type of approach, Kimura s works on pole placement through output feedback have been supported by several researchers. In these more theoretical approaches, the exact pole placement is generalized during the output feedback. The degrees of freedom of eigenvectors are no longer used in order to ensure decoupling as in Moore s approach but in order to set supplementary eigenvalues. Recently, research in automatics has been particularly oriented towards robustness objectives (through methods such as the H _? synthesis, the ?-synthesis, etc.), the control through eigenstructure placement being limited to the aim of ensuring the insensitivity of the eigenvalues placed (insensitivity to the first order) by a particular choice of eigenvectors [APK 89, CHO 94, FAL 97, MUD 88]. It was only recently that...