text: 444,2,1524255968011321344,23024823,Yang Cai,"Very excited about our new paper with @ArgyrisOikonom1 @WeiqiangZheng3. We obtain the tight last-iterate convergence rates for the Extragradient (EG) and Optimistic Gradient (OG) algorithms, settling an open problem raised by @KonstDaskalakis. <LINK> We study the convex-concave min-max optimization (and more generally the monotone variation inequalities) in the constrained setting. The EG algorithm by Korpelevich '1976 and the OG algorithm by Popov '1980 are among the most classical and popular algorithms for such problems. For both EG and OG, we know that the last-iterate asymptotically converges, but the rate was not known despite having been studied for a long time. We obtain tight last-iterate convergence rates for both EG and OG. Our proof builds on a new natural potential function, whose monotonicity is established using a sum-of-squares programming based computer-aided proof. For more details, see my talk at the Simons Institute for our result on EG. <LINK>",https://arxiv.org/abs/2204.09228,"The monotone variational inequality is a central problem in mathematical programming that unifies and generalizes many important settings such as smooth convex optimization, two-player zero-sum games, convex-concave saddle point problems, etc. The extragradient algorithm by Korpelevich [1976] and the optimistic gradient descent-ascent algorithm by Popov [1980] are arguably the two most classical and popular methods for solving monotone variational inequalities. Despite its long history, the following major problem remains open. What is the last-iterate convergence rate of the extragradient algorithm or the optimistic gradient descent-ascent algorithm for monotone and Lipschitz variational inequalities with constraints? We resolve this open problem by showing that both the extragradient algorithm and the optimistic gradient descent-ascent algorithm have a tight $O\left(\frac{1}{\sqrt{T}}\right)$ last-iterate convergence rate for arbitrary convex feasible sets, which matches the lower bound by Golowich et al. [2020a, b]. Our rate is measured in terms of the standard gap function. At the core of our results lies a new performance measure -- the tangent residual, which can be viewed as an adaptation of the norm of the operator that takes the local constraints into account. We use the tangent residual (or a slight variation of the tangent residual) as the performance measure in our analysis of the extragradient algorithm (or the optimistic gradient descent-ascent algorithm). To establish the monotonicity of these performance measures, we develop a new approach that combines the power of the sum-of-squares programming with the low dimensionality of the update rule of the extragradient or the optimistic gradient descent-ascent algorithm. We believe our approach has many additional applications in the analysis of iterative methods. ","Tight Last-Iterate Convergence of the Extragradient and the Optimistic