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Juan Ramirez

PhD Candidate · Mila & Université de Montréal · Expected graduation: mid-2027

I work on constrained deep learning: scalable constrained optimization methods for training neural networks that must satisfy explicit requirements such as fairness, sparsity, and safety.

I am supervised by Simon Lacoste-Julien. My research spans algorithms, theory, and applications of Lagrangian methods for constrained optimization in large-scale deep learning. I also work on Feasible Learning and co-develop Cooper, an open-source PyTorch library for constrained deep learning.

Before my PhD, I completed a BSc in Mathematical Engineering at Universidad EAFIT and held research internships at Mila, McKinsey, and Tuya.

Selected Work

Learning paradigm

Feasible Learning: A Sample-Centric Paradigm

Feasible Learning trains models by solving a feasibility problem that bounds the loss on every training example, rather than optimizing for average performance. It is a sample-centric alternative to ERM for settings where tail behavior and per-example reliability matter.

Open-source software

Cooper: A PyTorch Library for Constrained Deep Learning

Cooper is an open-source package for solving constrained optimization problems in deep learning. It implements Lagrangian-based first-order update schemes and makes it easy to combine constrained optimization algorithms with PyTorch models, autograd, and modern training pipelines. See the code and docs.

Theory

Dual PI Control is the Augmented Lagrangian Method in Disguise

We show that optimistic gradient ascent (PI control) on the dual variables of a Lagrangian is equivalent to gradient descent-ascent on the Augmented Lagrangian in the single-step, first-order regime commonly used in constrained deep learning. The result helps explain the practical success of dual optimism and establish its limits.

Perspective

Position: Adopt Constraints Over Penalties in Deep Learning

We argue that fixed penalty terms are the wrong default for enforcing explicit requirements in deep learning. When a problem naturally specifies targets to satisfy, we should formulate it as a constrained optimization problem and use methods designed to enforce those requirements directly.

News

Archive

2025

2024

2023

2022

2021

Publications

* denotes equal contribution. ^ denotes equal supervision.

Preprints

  1. Juan Ramirez, M. Hashemizadeh, and S. Lacoste-Julien. Position: Adopt Constraints Over Penalties in Deep Learning. arXiv:2505.20628, 2025.
  2. J. Gallego-Posada*, Juan Ramirez*, M. Hashemizadeh*, and S. Lacoste-Julien. Cooper: A Library for Constrained Optimization in Deep Learning. arXiv:2504.01212, 2025.

Conference

  1. Juan Ramirez and S. Lacoste-Julien. Dual Optimistic Ascent (PI Control) is the Augmented Lagrangian Method in Disguise. In ICLR, 2026.
  2. Juan Ramirez*, I. Hounie*, J. Elenter*, J. Gallego-Posada*, M. Hashemizadeh, A. Ribeiro^, and S. Lacoste-Julien^. Feasible Learning. In AISTATS, 2025.
  3. M. Sohrabi*, Juan Ramirez*, T. H. Zhang, S. Lacoste-Julien, and J. Gallego-Posada. On PI Controllers for Updating Lagrange Multipliers in Constrained Optimization. In ICML, 2024.
  4. M. Hashemizadeh*, Juan Ramirez*, R. Sukumaran, G. Farnadi, S. Lacoste-Julien, and J. Gallego-Posada. Balancing Act: Constraining Disparate Impact in Sparse Models. In ICLR, 2024.
  5. J. Gallego-Posada, Juan Ramirez, A. Erraqabi, Y. Bengio, and S. Lacoste-Julien. Controlled Sparsity via Constrained Optimization or: How I Learned to Stop Tuning Penalties and Love Constraints. In NeurIPS, 2022.

Workshop

  1. Juan Ramirez, R. Sukumaran, Q. Bertrand, and G. Gidel. Omega: Optimistic EMA Gradients. LatinX in AI Workshop at ICML, 2023.
  2. Juan Ramirez and J. Gallego-Posada. L0onie: Compressing COINs with L0-constraints. Sparsity in Neural Networks Workshop, 2022.
  3. J. Gallego-Posada, Juan Ramirez, and A. Erraqabi. Flexible Learning of Sparse Neural Networks via Constrained L0 Regularization. LatinX in AI Workshop at NeurIPS, 2021.

Service

Invited Talks

Teaching Assistantships