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Nonlinear objectives, nonlinear constraints, non-convex objective, non-convex feasible region.

4 votes

Maximize $f(0)+\cdots+f(n-1)$ subject to $f(x)f(y) + f(x+y) \leq 1$

Gerhard Paseman's solution is correct, and shows that $f \equiv 1/\phi$ is the unique maximizer of $d_n$ for each $n\geq 0$. Just reproducing here in as few words as I can, for the purpose of succinct …
Sean Eberhard's user avatar
10 votes

Elementary inhomogeneous inequality for three non-negative reals

Write $x = 1-X$, $y=1-Y$, $z=1-Z$. Then the inequality reduces to $$2XYZ \leq X^2 + Y^2 + Z^2$$ for $X, Y, Z \leq 1$. If $X, Y, Z < 0$ then the inequality is trivial, since LHS < 0. Otherwise suppose …
Sean Eberhard's user avatar