mollifier

A mollifier is a smooth function $f:{ℝ}^n\to ℝ$ such

1. $f(x)\ge 0$ for all $x\in {ℝ}^n$,

2. $f$ is normalized such that

   $${\int }_{{ℝ}^n}f(x)𝑑x=1,$$

3. $f(0)=1$.