What is Nonlinear system?
{{Complex systems}} In [[mathematics]] and science, a '''nonlinear system''' is a [[system]], where the change of the [[output]] is not [[Proportionality|proportional]] to the change of the [[input]].<ref>{{Cite news|title=Explained: Linear and nonlinear systems|work=MIT News|url=https://news.mit.edu/2010/explained-linear-0226|access-date=2018-06-30}}</ref><ref>{{Cite web|title=Nonlinear systems, Applied Mathematics - University of Birmingham|url=https://www.birmingham.ac.uk/research/activity/mathematics/applied-maths/nonlinear-systems.aspx|access-date=2018-06-30|website=www.birmingham.ac.uk|language=en-gb}}</ref> In [[nature]], most systems are non-linear. Nonlinear problems are interesting to [[Engineer|engineers]], [[Biologist|biologists]],<ref>{{Citation|date=2007|pages=181–276|publisher=Springer Berlin Heidelberg|language=en|doi=10.1007/978-3-540-34153-6_7|isbn=9783540341529|title=The Nonlinear Universe|series=The Frontiers Collection|chapter=Nonlinear Biology }}</ref><ref>{{cite journal|last1=Korenberg|first1=Michael J.|last2=Hunter|first2=Ian W.|date=March 1996|title=The identification of nonlinear biological systems: Volterra kernel approaches|journal=Annals of Biomedical Engineering|language=en|volume=24|issue=2|pages=250–268|doi=10.1007/bf02667354|issn=0090-6964|pmid=8678357|s2cid=20643206}}</ref><ref>{{cite journal|last1=Mosconi|first1=Francesco|last2=Julou|first2=Thomas|last3=Desprat|first3=Nicolas|last4=Sinha|first4=Deepak Kumar|last5=Allemand|first5=Jean-François|last6=Vincent Croquette|last7=Bensimon|first7=David|date=2008|title=Some nonlinear challenges in biology|url=http://stacks.iop.org/0951-7715/21/i=8/a=T03|journal=Nonlinearity|language=en|volume=21|issue=8|pages=T131|bibcode=2008Nonli..21..131M|doi=10.1088/0951-7715/21/8/T03|s2cid=119808230 |issn=0951-7715}}</ref> [[Physicist|physicists]],<ref>{{cite journal|last1=Gintautas|first1=V.|date=2008|title=Resonant forcing of nonlinear systems of differential equations|journal=Chaos|volume=18|issue=3|pages=033118|arxiv=0803.2252|bibcode=2008Chaos