Schwarz function

A Schwarz function, also known as a "test function" in the context of distribution theory, is a smooth function that rapidly decreases at infinity along with all its derivatives. More formally, a function \( f: \mathbb{R}^n \to \mathbb{R} \) is called a Schwarz function if it satisfies the following conditions: 1. \( f \) is infinitely differentiable (i.e., \( f \in C^\infty \)).