# Uncertainty principle

Long time ago, I read in a math textbook a statement about functions of complex variables. It was a named uncertainty principle. The name attached was NOT Heisenberg. I know of Heisenberg's uncertainty principle. The one I read in that textbook was similar but seemed more fundamental. Are there any uncertainty principles in the theory of complex variables?

• Cf. this Jun 29, 2021 at 1:21
• @J.W.Tanner I was Hardy's uncertainty principle! (I remember now: the book was Hörmander's) Thank you. Jun 29, 2021 at 1:26
• Heisenberg uncertainty principle in $d$ dimensions says that $$\frac{\|xf(x)\|_2}{\|f(x)\|_2}\frac{\|\xi\hat{f}(\xi)\|_2}{\|\hat{f}(x)\|_2}\ge\frac{d}{4\pi}$$
– robjohn
Jun 29, 2021 at 5:17