From differential equation solvers to accelerated first-order methods for convex optimization

Convergence analysis of accelerated first-order methods for convex optimization problems are presented from the point of view of ordinary differential equation solvers. A new dynamical system, called Nesterov accelerated gradient flow, has been derived from the connection between acceleration mechanism and $A$-stability of ODE solvers, and the exponential decay of a tailored Lyapunov function along with the solution trajectory is proved. Numerical discretizations are then considered and convergence rates are established via a unified discrete Lyapunov function. The proposed differential equation solver approach can not only cover existing accelerated methods, such as FISTA, G\"{u}ler's proximal algorithm and Nesterov's accelerated gradient method, but also produce new algorithms for composite convex optimization that possess accelerated convergence rates.