▁If ▁the ▁parameters ▁of ▁any ▁second - order ▁linear ▁differential ▁equation ▁are ▁varied ▁period ically , ▁Flo quet ▁analysis ▁shows ▁that ▁the ▁solutions ▁must ▁vary ▁either ▁sin us oid ally ▁or ▁expon entially . ▁ ▁The ▁ ▁equation ▁above ▁with ▁period ically ▁varying ▁ ▁is ▁an ▁example ▁of ▁a ▁Hill ▁equation . ▁If ▁ ▁is ▁a ▁simple ▁sin us oid , ▁the ▁equation ▁is ▁called ▁a ▁Math ieu ▁equation . ▁ ▁See ▁also ▁Harm onic ▁oscill ator ▁Math ieu ▁equation ▁Opt ical ▁paramet ric ▁ampl ifier ▁Opt ical ▁paramet ric ▁oscill ator ▁ ▁References ▁ ▁Further ▁reading ▁Kü hn ▁L . ▁( 1 9 1 4 ) ▁Ele kt rote ch . ▁Z ., ▁ 3 5 , ▁ 8 1 6 - 8 1 9 . ▁ ▁P ungs ▁L . ▁DR GM ▁Nr . ▁ 5 8 8 ▁ 8 2 2 ▁( 2 4 ▁October ▁ 1 9 1 3 ); ▁DR P ▁Nr . ▁ 2 8 1 4 4 0 ▁( 1 9 1 3 ); ▁Ele kt rote ch . ▁Z ., ▁ 4 4 , ▁ 7 8 - 8 1 ▁( 1 9 2 3 ? ); ▁Pro c . ▁I RE , ▁ 4 9 , ▁ 3 7 8 ▁( 1 9 6 1 ). ▁ ▁External ▁articles ▁El mer , ▁Franz - Jose f , ▁" Param et ric ▁Res on ance ▁P end ul um ▁Lab ▁University ▁of ▁Bas el ". ▁un ib as . ch , ▁July ▁ 2 0