Based on the proof given in the action article of wiki (http://en.wikipedia.org/wiki/Action_(physics)#Euler-Lagrange_equations_for_the_action_integral), it would seems that the statement of the "central thm of calculus of variation"(http://en.wikipedia.org/wiki/Euler-Lagrange_equations#Statement) is in fact an [itex]\Leftrightarrow[/itex] one. I.e. not just "IF action is extremized, THEN L satisfies E-L", but rather "Action is extremized, iff L satisfies E-L"(adsbygoogle = window.adsbygoogle || []).push({});

someone can confirm?

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# What does the central thm of calculus of variation says?

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