## Scaled Relative Graph: Nonexpansive operators via 2D Euclidean GeometryErnest Ryu, Robert Hannah, Wotao YinSubmitted: ## OverviewHave you ever fallen asleep while reading a mathematical proof? Have you ever read a proof of convergence but felt you couldn't digest it? Most convergece proofs of iterative algorithms are written in algebraic equalities and inequalities. Compared to figures, those equations look dull. Even when they are easy to verify, they may still be difficult to understand. Their core ideas of some proofs can be illustrated with figures, but, for the sake of rigor, we write them down with unfriendly equations. It is fair to say that lack of an intuitive way to present a proof creates a barrier between the author and the reader. The good news is, for nonexpansive operators that constitute popular optimization methods such as forward-backward, alternative projection, Douglas-Rachford, and ADMM, there exist simple 2D graphs that not only capture the core ideas of their convergence proofs but is also a tool to write rigorous proofs and even find best parameters. In this paper, we introduce a geometric approach to analyzing contractive and
nonexpansive fixed point iterations with a new tool called the While the reader must see our paper for SRG's definition and examples, below we illustrate how a statement is easily proved by SRG. ## Citation
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