Title: Simple Spectral Graph Convolution from an Optimization Perspective. Abstract: Recent studies on SGC, PageRank and S\textsuperscript{2}GC have demonstrated that several graph diffusion techniques are straightforward, quick, and effective for tasks in the graph domain like node classification. Even though these techniques do not even need labels, they can nevertheless produce more discriminating features than raw attributes for downstream tasks with different classifiers. These methods are data-independent and thus primarily rely on some empirical parameters on polynomial bases (e.g., Monomial and Chebyshev), which ignore the homophily of graphs and the attribute distribution. They are more insensitive to heterophilous graphs due to the low-pass filtering. Although there are many approaches focusing on GNNs based on heterophilous graphs, these approaches are dependent on label information to learn model parameters. In this paper, we study the question: are labels a necessity for GNNs with heterophilous graphs? Based on this question, we propose a framework of self-representation on graphs related to the Least Squares problem. Specifically, we use Generalized Minimum RESidual (GMRES) method, which finds the least squares solution over Krylov subspaces. In theoretical analysis, without label information, we enjoy better features with graph convolution. 
The proposed method, like previous data-independent methods, is not a deep model and is, therefore, quick, scalable, and simple. We  also show performance guarantees for models on real and synthetic data. On a benchmark of real-world datasets, empirically, our method is competitive with existing deep models for node classification.