Boundaries of conditional quadratic forms - a comment on "Stabilization via static output feedback"

Motivated by the above paper, (Trofino-Neto and Kucera, ibid., vol.38, no.5, p.764-65, 1993) this note considers the boundaries of a quadratic form with all possible constraints over a given subspace. Essential upper (or lower) bounds are presented provided they exist. It mends a mild incompleteness in the proof of the main result.<
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