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4
votes
5
answers
622
views
Elementary inequality generalizing convexity of a function on a segment
I am looking for a proof of the following statement which is known to be true as far as I heard.
Let $g\colon [a,b]\to \mathbb{R}$ be a smooth function. Assume that
$$b-a< \pi.$$
Assume also $$g(a)\ge …
0
votes
1
answer
162
views
A property of convex cones in Euclidean spaces
EDIT: Let $K$ be a closed convex cone in a Euclidean space of finite dimension. Assume it is non-zero and not the whole space.
Does there exist a non-zero point $x\in K$ such that
$$(x,y)\geq …
7
votes
0
answers
892
views
Geometry of level sets of a convex function
EDIT: Let $\Omega\subset \mathbb{R}^n$ be an open subset. Let $f\colon \Omega\to\mathbb{R}$ be a function such that for some $\lambda$ the function $f(x)+\lambda |x|^2$ is convex. Assume that the grap …
4
votes
0
answers
63
views
Length of curves on convex hypersurfaces
Let $\gamma\colon[a,b] \to \mathbb{R}^n$ be a smooth curve.
Let $f_i\to f$ be a sequence of convex functions on $\mathbb{R}^n$ converging uniformly on compact subsets to $f$.
Let $\hat\gamma(t):=(\gam …
5
votes
1
answer
632
views
When minimum of two supporting functionals of convex bodies is convex?
For a convex compact set $K\subset \mathbb{R}^n$ let us denote by $h_K$ its supporting functional
$$h_K(\xi):=\sup_{x\in K}\langle\xi,x\rangle.$$
Thus $h_K\colon \mathbb{R}^n\to \mathbb{R}$ is a conv …