For the stated class of undirected weighted simple graphs, adding positive self-loops leaves the smallest normalized-Laplacian eigenvalue at zero and strictly decreases the largest eigenvalue; on Cora/citation-network examples the paper reports an approximate shrinkage from 2 to 1.5, enabling augmented SGC propagation to act as a low-pass-type filter.

来源：paper:PDF pp.4-5, Theorem 1 and Figure 2; PDF p.14, propagation discussion