Search Results for author: Nicolas Loizou

Found 30 papers, 11 papers with code

Dissipative Gradient Descent Ascent Method: A Control Theory Inspired Algorithm for Min-max Optimization

no code implementations14 Mar 2024 Tianqi Zheng, Nicolas Loizou, Pengcheng You, Enrique Mallada

Gradient Descent Ascent (GDA) methods for min-max optimization problems typically produce oscillatory behavior that can lead to instability, e. g., in bilinear settings.

Stochastic Extragradient with Random Reshuffling: Improved Convergence for Variational Inequalities

1 code implementation11 Mar 2024 Konstantinos Emmanouilidis, René Vidal, Nicolas Loizou

The Stochastic Extragradient (SEG) method is one of the most popular algorithms for solving finite-sum min-max optimization and variational inequality problems (VIPs) appearing in various machine learning tasks.

Locally Adaptive Federated Learning via Stochastic Polyak Stepsizes

1 code implementation12 Jul 2023 Sohom Mukherjee, Nicolas Loizou, Sebastian U. Stich

We prove that FedSPS converges linearly in strongly convex and sublinearly in convex settings when the interpolation condition (overparametrization) is satisfied, and converges to a neighborhood of the solution in the general case.

Federated Learning

Communication-Efficient Gradient Descent-Accent Methods for Distributed Variational Inequalities: Unified Analysis and Local Updates

no code implementations8 Jun 2023 Siqi Zhang, Sayantan Choudhury, Sebastian U Stich, Nicolas Loizou

However, with the increase of minimax optimization and variational inequality problems in machine learning, the necessity of designing efficient distributed/federated learning approaches for these problems is becoming more apparent.

Federated Learning

Single-Call Stochastic Extragradient Methods for Structured Non-monotone Variational Inequalities: Improved Analysis under Weaker Conditions

1 code implementation NeurIPS 2023 Sayantan Choudhury, Eduard Gorbunov, Nicolas Loizou

In addition, several important questions regarding the convergence properties of these methods are still open, including mini-batching, efficient step-size selection, and convergence guarantees under different sampling strategies.

A Unified Approach to Reinforcement Learning, Quantal Response Equilibria, and Two-Player Zero-Sum Games

3 code implementations12 Jun 2022 Samuel Sokota, Ryan D'Orazio, J. Zico Kolter, Nicolas Loizou, Marc Lanctot, Ioannis Mitliagkas, Noam Brown, Christian Kroer

This work studies an algorithm, which we call magnetic mirror descent, that is inspired by mirror descent and the non-Euclidean proximal gradient algorithm.

MuJoCo Games reinforcement-learning +1

Stochastic Gradient Descent-Ascent: Unified Theory and New Efficient Methods

1 code implementation15 Feb 2022 Aleksandr Beznosikov, Eduard Gorbunov, Hugo Berard, Nicolas Loizou

Although variants of the new methods are known for solving minimization problems, they were never considered or analyzed for solving min-max problems and VIPs.

Stochastic Extragradient: General Analysis and Improved Rates

1 code implementation16 Nov 2021 Eduard Gorbunov, Hugo Berard, Gauthier Gidel, Nicolas Loizou

The Stochastic Extragradient (SEG) method is one of the most popular algorithms for solving min-max optimization and variational inequalities problems (VIP) appearing in various machine learning tasks.

Stochastic Mirror Descent: Convergence Analysis and Adaptive Variants via the Mirror Stochastic Polyak Stepsize

no code implementations28 Oct 2021 Ryan D'Orazio, Nicolas Loizou, Issam Laradji, Ioannis Mitliagkas

We investigate the convergence of stochastic mirror descent (SMD) under interpolation in relatively smooth and smooth convex optimization.

Extragradient Method: $O(1/K)$ Last-Iterate Convergence for Monotone Variational Inequalities and Connections With Cocoercivity

1 code implementation8 Oct 2021 Eduard Gorbunov, Nicolas Loizou, Gauthier Gidel

In this paper, we resolve one of such questions and derive the first last-iterate $O(1/K)$ convergence rate for EG for monotone and Lipschitz VIP without any additional assumptions on the operator unlike the only known result of this type (Golowich et al., 2020) that relies on the Lipschitzness of the Jacobian of the operator.

Stochastic Gradient Descent-Ascent and Consensus Optimization for Smooth Games: Convergence Analysis under Expected Co-coercivity

1 code implementation NeurIPS 2021 Nicolas Loizou, Hugo Berard, Gauthier Gidel, Ioannis Mitliagkas, Simon Lacoste-Julien

Two of the most prominent algorithms for solving unconstrained smooth games are the classical stochastic gradient descent-ascent (SGDA) and the recently introduced stochastic consensus optimization (SCO) [Mescheder et al., 2017].

On the Convergence of Stochastic Extragradient for Bilinear Games using Restarted Iteration Averaging

no code implementations30 Jun 2021 Chris Junchi Li, Yaodong Yu, Nicolas Loizou, Gauthier Gidel, Yi Ma, Nicolas Le Roux, Michael I. Jordan

We study the stochastic bilinear minimax optimization problem, presenting an analysis of the same-sample Stochastic ExtraGradient (SEG) method with constant step size, and presenting variations of the method that yield favorable convergence.

Unified Analysis of Stochastic Gradient Methods for Composite Convex and Smooth Optimization

no code implementations20 Jun 2020 Ahmed Khaled, Othmane Sebbouh, Nicolas Loizou, Robert M. Gower, Peter Richtárik

We showcase this by obtaining a simple formula for the optimal minibatch size of two variance reduced methods (\textit{L-SVRG} and \textit{SAGA}).

Quantization

SGD for Structured Nonconvex Functions: Learning Rates, Minibatching and Interpolation

no code implementations18 Jun 2020 Robert M. Gower, Othmane Sebbouh, Nicolas Loizou

Stochastic Gradient Descent (SGD) is being used routinely for optimizing non-convex functions.

A Unified Theory of Decentralized SGD with Changing Topology and Local Updates

no code implementations ICML 2020 Anastasia Koloskova, Nicolas Loizou, Sadra Boreiri, Martin Jaggi, Sebastian U. Stich

Decentralized stochastic optimization methods have gained a lot of attention recently, mainly because of their cheap per iteration cost, data locality, and their communication-efficiency.

Stochastic Optimization

Stochastic Polyak Step-size for SGD: An Adaptive Learning Rate for Fast Convergence

1 code implementation24 Feb 2020 Nicolas Loizou, Sharan Vaswani, Issam Laradji, Simon Lacoste-Julien

Consequently, the proposed stochastic Polyak step-size (SPS) is an attractive choice for setting the learning rate for stochastic gradient descent (SGD).

Randomized Iterative Methods for Linear Systems: Momentum, Inexactness and Gossip

no code implementations26 Sep 2019 Nicolas Loizou

In the era of big data, one of the key challenges is the development of novel optimization algorithms that can accommodate vast amounts of data while at the same time satisfying constraints and limitations of the problem under study.

Revisiting Randomized Gossip Algorithms: General Framework, Convergence Rates and Novel Block and Accelerated Protocols

no code implementations20 May 2019 Nicolas Loizou, Peter Richtárik

In this work we present a new framework for the analysis and design of randomized gossip algorithms for solving the average consensus problem.

Convergence Analysis of Inexact Randomized Iterative Methods

no code implementations19 Mar 2019 Nicolas Loizou, Peter Richtárik

We relax this requirement by allowing for the sub-problem to be solved inexactly.

SGD: General Analysis and Improved Rates

no code implementations27 Jan 2019 Robert Mansel Gower, Nicolas Loizou, Xun Qian, Alibek Sailanbayev, Egor Shulgin, Peter Richtarik

By specializing our theorem to different mini-batching strategies, such as sampling with replacement and independent sampling, we derive exact expressions for the stepsize as a function of the mini-batch size.

A Privacy Preserving Randomized Gossip Algorithm via Controlled Noise Insertion

no code implementations27 Jan 2019 Filip Hanzely, Jakub Konečný, Nicolas Loizou, Peter Richtárik, Dmitry Grishchenko

In this work we present a randomized gossip algorithm for solving the average consensus problem while at the same time protecting the information about the initial private values stored at the nodes.

Privacy Preserving

Stochastic Gradient Push for Distributed Deep Learning

3 code implementations ICLR 2019 Mahmoud Assran, Nicolas Loizou, Nicolas Ballas, Michael Rabbat

Distributed data-parallel algorithms aim to accelerate the training of deep neural networks by parallelizing the computation of large mini-batch gradient updates across multiple nodes.

General Classification Image Classification +2

Provably Accelerated Randomized Gossip Algorithms

no code implementations31 Oct 2018 Nicolas Loizou, Michael Rabbat, Peter Richtárik

In this work we present novel provably accelerated gossip algorithms for solving the average consensus problem.

Accelerated Gossip via Stochastic Heavy Ball Method

no code implementations23 Sep 2018 Nicolas Loizou, Peter Richtárik

In this paper we show how the stochastic heavy ball method (SHB) -- a popular method for solving stochastic convex and non-convex optimization problems --operates as a randomized gossip algorithm.

Momentum and Stochastic Momentum for Stochastic Gradient, Newton, Proximal Point and Subspace Descent Methods

no code implementations27 Dec 2017 Nicolas Loizou, Peter Richtárik

We prove linear convergence of several stochastic methods with stochastic momentum, and show that in some sparse data regimes and for sufficiently small momentum parameters, these methods enjoy better overall complexity than methods with deterministic momentum.

Stochastic Optimization

Linearly convergent stochastic heavy ball method for minimizing generalization error

no code implementations30 Oct 2017 Nicolas Loizou, Peter Richtárik

In this work we establish the first linear convergence result for the stochastic heavy ball method.

Privacy Preserving Randomized Gossip Algorithms

no code implementations23 Jun 2017 Filip Hanzely, Jakub Konečný, Nicolas Loizou, Peter Richtárik, Dmitry Grishchenko

In this work we present three different randomized gossip algorithms for solving the average consensus problem while at the same time protecting the information about the initial private values stored at the nodes.

Optimization and Control

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