Noise operator on the Boolean hypercube
= Noise operator on the Boolean hypercube
{title2=$T_\rho$}
{wiki=Noise_stability}
The noise operator averages $f(y)$ over a random $y$ correlated with $x$ by $\rho$. It acts diagonally on the <Fourier-Walsh transform>:
$$
T_\rho f=\sum_S\rho^{|S|}\widehat f(S)\chi_S.
$$