Before revision: In control theory and in particular when studying the properties of a linear time-invariant system in state space form, the Hautus lemma , named after Malo L. J. Hautus , can prove to be a powerful tool.
After revision: In control theory and in particular when studying the properties of a linear time-invariant system in state space form, the Hautus lemma (), also commonly known as the Popov-Belevitch-Hautus test or PBH test after Malo L. J. Hautus , can prove to be a powerful tool.