  We study the problem of predicting highly localized low-lying eigenfunctions
$(-\Delta +V) \phi = \lambda \phi$ in bounded domains $\Omega \subset
\mathbb{R}^d$ for rapidly varying potentials $V$. Filoche & Mayboroda
introduced the function $1/u$, where $(-\Delta + V)u=1$, as a suitable
regularization of $V$ from whose minima one can predict the location of
eigenfunctions with high accuracy. We proposed a fast method that produces a
landscapes that is exceedingly similar, can be used for the same purposes and
can be computed very efficiently: the computation time on an $n \times n$ grid,
for example, is merely $\mathcal{O}(n^2 \log{n})$, the cost of two FFTs.
