Tomomichi Hagiwara Kenichi Morioka Koichiro Okada Quasi-finite-rank approximation of compression operators in sampled-data systems and time-delay systems. 2385-2394 2010 83 Int. J. Control 11 https://doi.org/10.1080/00207179.2010.523849 db/journals/ijcon/ijcon83.html#HagiwaraMO10