We provide some new necessary and sufficient conditions which guarante
e arbitrary pole placement of a particular linear system over the comp
lex numbers. We exhibit a nontrivial real linear system which is not c
ontrollable by real static output feedback and discuss a conjecture fr
om algebraic geometry concerning the existence of real linear systems
for which all static feedback laws are real. (C) 1998 Elsevier Science
B.V. All rights reserved.