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How can I find an extremal for the following functional: $$J[y] = \int_0^1 e^y (y')^2 dx $$

with the boundary conditions $y(0)=1, y(1)=\log(4)$? I have tried computing the Euler-Lagrange equation but it becomes overly complicated.

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2 Answers

The E-L equation is $- e^y (y')^2 - 2 e^y y'' = 0$. Divide by $e^y$ and first solve the first-order equation for $y'$, then integrate to get $y$. Then put in the boundary conditions.

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The Euler-Lagrange equation simplifies down to $y''+(y')^{2}=0$. Set $u=y'$ to get a seperable ODE, then integrate to find $y$.

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