Inverse function theorem: Difference between revisions

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===Banach spaces===
 
The inverse function theorem can also be generalized to differentiable maps between [[Banach space]]s. Let ''X'' and ''Y'' be Banach spaces and ''U'' an open neighbourhood of the origin in ''X''. Let ''F''&nbsp;:&nbsp;''U''&nbsp;&rarr;&nbsp;''Y'' be continuously differentiable and assume that the derivative (d''F'')<sub>0</sub>&nbsp;:&nbsp;''X''&nbsp;&rarr;&nbsp;''Y'' of ''F'' at 0 is a [[bounded linear map|bounded]] linear isomorphism of ''X'' onto ''Y''. Then there exists an open neighbourhood ''V'' of ''F''(0) in ''Y'' and a continuously differentiable map ''G''&nbsp;:&nbsp;''V''&nbsp;&rarr;&nbsp;''X'' such that ''F''(''G''(''y''))&nbsp;=&nbsp;''y'' for all ''y'' in ''V''. Moreover, ''G''(''y'') is the only sufficiently small solution ''x'' of the equation ''F''(''x'')&nbsp;=&nbsp;''y''. The first Banach space version of the inverse function theorem has been proved by Lawrence Graves in 1950.
 
==References==