Quantitative feedback theory-reply to criticisms

Oded Yaniv, Isaac Horowitz*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

20 Scopus citations


Quantitative feedback theory (QFT) consists of a steadily growing body of design techniques for achieving prespecified system performance tolerances, despite prespecified large plant parameter and disturbance uncertainties. Since 1959, QFT has been extended to SISO and MIMO, linear and non-linear, time-invariant and time-varying, output feedback and internal variable feedback, lumped and distributed plants. Design examples in all the above classes have been described in great detail. In contrast, modern control theory almost completely ignored the uncertainty issue in feedback theory until about five years ago. There has since been much activity in this subject, which it denotes as the robustness problem. Despite this activity, hardly a single detailed design example involving large plant parameter uncertainty has been described. Nevertheless, researchers in robustness have ignored QFT. This conspiracy of silence has recently been broken with a list of criticisms by Doyle. These provide a very welcome means of explanation and elaboration of important QFT properties, including some new results.

Original languageEnglish
Pages (from-to)945-962
Number of pages18
JournalInternational Journal of Control
Issue number3
StatePublished - Sep 1987


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