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Real-valued functions of real variable, analytic properties of functions and sequences, limits, continuity, smoothness of these.

5 votes

Functions that map open balls to open balls of different radius?

For $n\ge 2$ every balloon map is a composition of a scaling, a translation and a rotation/reflection. The following proof is incomplete as it relies on the fact that the boundary of a ball is mappe …
Martin Kell's user avatar
2 votes
Accepted

Kantorovich duality with pseudometrics

Yes the Kantorovich Duality holds for continuous cost functions by following the proof in Villani's book without any change. The proof for general cost functions needs compactness of the set of coupli …
Martin Kell's user avatar
10 votes

Derivative of distance function to a closed, rectifiable set

The distance $f: x \mapsto \mathsf{dist}(x,\Gamma)$ to a closed set $\Gamma$ in $\mathbb{R}^n$ is differentiable in $x \notin \Gamma$ iff the nearest point projection is unique; denote this by $x_\Gam …
Martin Kell's user avatar