Among the continuous functions on , the positive definite functions are those functions which are the Fourier transforms of nonnegative Borel measures.
Bochner's Theorem
Explore with Wolfram|Alpha
Cite this as:
Weisstein, Eric W. "Bochner's Theorem." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/BochnersTheorem.html