Editing Systems thinking (section)

===Feedback control systems===
[[File:Ideal feedback model.svg|thumb|left|upright=1.5|System output can be controlled with [[feedback]].]]
By 1824, the [[Carnot cycle]] presented an engineering challenge, which was how to maintain the operating temperatures of the hot and cold working fluids of the [[physical plant]].<ref name="carnot1824">Sadi Carnot (1824) [[Reflections on the Motive Power of Fire]]</ref> In 1868, [[James Clerk Maxwell]] presented a framework for, and a limited solution to, the problem of controlling the rotational speed of a physical plant.<ref name="jcmaxwell1868">James Clerk Maxwell [[:File:On Governors.pdf| (1868) On Governors]] 12 pages</ref> Maxwell's solution echoed [[James Watt|James Watt's]] [[:File:SteamEngine_Boulton&Watt_1784.png| (1784) centrifugal moderator (denoted as element '''Q''')]] for maintaining (but not enforcing) the constant speed of a physical plant (that is, ''Q'' represents a moderator, but not a governor, by Maxwell's definition).<ref name="mayr1971">Otto Mayr
 [https://www.jstor.org/stable/229816 (1971) Maxwell and the Origins of Cybernetics] ''Isis'', Vol. '''62''', No. 4 (Winter, 1971), pp. 424-444 (21 pages)</ref>{{efn|name=stabilityOfSolution|1=A solution to the equations for a dynamical system can be afflicted by instability or oscillation.<ref name="sepulchre">The Royal Society of Edinburgh [https://www.youtube.com/watch?v=U8MFOoa61k4&t=150s (2016) Celebrating Maxwell's Genius and Legacy: Prof Rodolphe Sepulchre]</ref>{{rp|7:33}} The Governor: A corrective action against error can solve the dynamical equation by integrating the error.<ref name="sepulchre" />{{rp|29:44}}<ref name="ÅströmMurray">Karl Johan Åström and Richard M. Murray (2021) [https://press.princeton.edu/books/hardcover/9780691193984/feedback-systems Feedback Systems: An Introduction for Scientists and Engineers, Second Edition]</ref> }}

Maxwell's approach, which linearized the equations of motion of the system, produced a tractable method of solution.<ref name="mayr1971" />{{rp|428–429}} [[Norbert Wiener]] identified this approach as an influence on his studies of [[cybernetics]]{{efn|name=seeSystemScience |1="cybernetics: ''see system science.''";<ref name="ieee1972" />{{rp|135}} "system science: —the systematized knowledge of [[#System|system]]s"<ref name="ieee1972" />{{rp|583}} }} during [[World War II]]<ref name="mayr1971" /> and Wiener even proposed treating some [[#subsystem|subsystem]]s under investigation as [[#black box|black box]]es.<ref name="ontologyOfTheEnemy">Peter Galison [https://www.jstor.org/stable/1343893 (1994) The Ontology of the Enemy: Norbert Wiener and the Cybernetic Vision] ''Critical Inquiry'', Vol. '''21''', No. 1 (Autumn, 1994), pp. 228–266 (39 pages) ''JSTOR''</ref>{{rp|242}} Methods for solutions of the systems of equations then become the subject of study, as in [[feedback control system]]s, in [[stability theory]], in [[constraint satisfaction problem]]s, the [[unification algorithm]], [[Hindley–Milner type system|type inference]], and so forth.