TheoremBase

Existence of Smooth Bump Functions on Euclidean Space

Statement

Let n∈n\in N\mathbb{N}, let x0x_0 be a point of Euclidean space Rn\mathbb{R}^n, and let r,s∈Rr,s\in\mathbb{R} with 0<r<s0<r<s. Then there exists a smooth map χ:Rn→R\chi:\mathbb{R}^n\to\mathbb{R} such that, with dd denoting the Euclidean distance on Rn\mathbb{R}^n:

  1. 0≤χ(x)≤10\le\chi(x)\le 1 for every x∈Rnx\in\mathbb{R}^n;
  2. χ(x)=1\chi(x)=1 for every x∈Rnx\in\mathbb{R}^n with d(x,x0)≤rd(x,x_0)\le r;
  3. χ(x)=0\chi(x)=0 for every x∈Rnx\in\mathbb{R}^n with d(x,x0)≥sd(x,x_0)\ge s.

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