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Posts by Pablo Samuel Castro

We have the keynote speakers for RLC2026 now!

Thrilled to welcome Rika Antonova, Sheila McIlraith, Marc G. Bellemare, Danijar Hafner, Balaraman Ravindran!

Details: rl-conference.cc/index.html

The RL community is coming together this August in Montréal, Québec, Canada. Hope you make it!

2 weeks ago 22 10 0 3
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Google PhD fellowship program The Google PhD Fellowship Program recognizes outstanding graduate students doing exceptional work in computer science, related disciplines, or promising research areas.

Applications for the global Google PhD Fellowship Program are open! Fellowships directly support grad students doing exceptional and innovative research in computer science and related fields as they pursue their PhD. Learn more and apply by April 30 at goo.gle/phdfellowship.

1 month ago 10 3 0 1

Exploring SigReg regularization for RL has been on my "todo when I have time" list for a while.

While I haven't fully read this paper yet, it appears to do a fantastic thorough investigation, and it looks quite promising!

1 month ago 12 2 0 0
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GitHub - asahebpa/IsoGaussian-DRL: Repository for paper: Stable Deep Reinforcement Learning via Isotropic Gaussian Representations Repository for paper: Stable Deep Reinforcement Learning via Isotropic Gaussian Representations - asahebpa/IsoGaussian-DRL

Code is available at: github.com/asahebpa/Iso...

This project was led by my students Ali Saheb Pasand & @johanobandoc.bsky.social , and in collaboration with Aaron Courville & @bashivan.bsky.social

Read the full paper: arxiv.org/abs/2602.19373

1 month ago 4 1 0 0

🖼️ Big picture takeaway 🖼️
Representation collapse and neuron dormancy aren't just symptoms to treat, they're predictable consequences of unconstrained representation geometry under non-stationarity.

🔑 Fixing the geometry fixes the learning 🔑

1 month ago 7 0 1 0
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And beyond Atari: on Isaac Gym continuous control (AllegroHand, ShadowHand, Humanoid, Ant…), SIGReg improves training stability and reduces variance across all tasks.

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On Atari with PQN, SIGReg improves performance in 51/57 games (89.5%), with a mean AUC improvement of 889% and median of 138%. These gains are broad, not driven by a few outliers. The benefits extend to PPO too in which 70% of games’ performance are improved.

1 month ago 5 0 1 0
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We first validate on non-stationary CIFAR-10 (shuffled labels protocol). Without SIGReg: rank collapse, dormant neurons, poor recovery after each shift. With SIGReg: stable rank, near-zero dormancy, fast recovery.

1 month ago 2 0 1 0
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To enforce this in practice, we use SIGReg (Sketched Isotropic Gaussian Regularization) proposed by Balestriero & LeCun, 2025:
💡Project embeddings onto random directions and match each projection to a Gaussian.
Simple✅
differentiable✅
computationally cheap✅

1 month ago 5 0 1 0
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3️⃣ Maximum entropy — Gaussians maximize entropy under a fixed variance budget. This keeps all representational dimensions active and useful.

1 month ago 5 0 1 0
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2️⃣ Gaussianity controls drift variance — among all isotropic distributions, Gaussians minimize fluctuations in the drift term. Heavier-tailed distributions (Laplacian, Logistic) introduce higher-order moments that cause destabilizing spikes.
See the red term in Theorem 3.1:

1 month ago 3 0 1 0
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1️⃣ Isotropy equalizes contraction — when the feature covariance Σ = σ²I, the tracking error is uniformly damped across ALL directions. Anisotropic representations amplify drift along poorly conditioned directions, destabilizing learning.
See the blue term in Theorem 3.1:

1 month ago 4 0 1 0
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We ask: what structure should learned representations have to remain stable under continuously evolving targets? 🤔

Answer: Isotropic Gaussian representations are provably advantageous. 💡

Why? Three reasons:

1 month ago 4 0 1 0
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The core problem: deep RL is inherently non-stationary.

📉As the agent learns, its data distribution and learning targets keep shifting. This causes representations to degrade, neurons to go dormant, and performance to plateau or collapse.

1 month ago 4 0 1 0
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New paper 🚨
"Stable Deep Reinforcement Learning via Isotropic Gaussian Representations"

Deep RL suffers from unstable training, representation collapse, and neuron dormancy. We show that a simple geometric insight, isotropic Gaussian representations, can fix this. Here's how 👇

1 month ago 24 4 2 2

In light of the ongoing conflict in the Middle East, RLC decided to remove the abstract deadline: rl-conference.cc/callforpaper...

The only deadline is for the full paper: Mar 5(AOE) openreview.net/group?id=rl-...

Affected folks may also contact the PCs to discuss deadline extensions before Mar 5.

1 month ago 14 8 1 2

RLC 2026 Call for Workshop is live on OpenReview!

Submission deadline: Mar 12 (AoE).
Full details here: rl-conference.cc/call_for_wor...

@glenberseth.bsky.social @eugenevinitsky.bsky.social @twkillian.bsky.social @schaul.bsky.social @sologen.bsky.social @audurand.bsky.social @bradknox.bsky.social

1 month ago 10 3 0 1

It's been such a pleasure working with @caroline-wang.bsky.social the last few months. She is a fantastic researcher, engineer, & person, and I really hope we can work together again.
Check out the paper that came out of her time with us, comparing strategic behavior of humans and LLMs!👇🏽

2 months ago 18 0 0 0
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The Formalism-Implementation Gap in Reinforcement Learning Research The last decade has seen an upswing in interest and adoption of reinforcement learning (RL) techniques, in large part due to its demonstrated capabilities at performing certain tasks at "super-human l...

This is something I talk about in my paper, where I suggest being explicit about {\gamma}_train (some methods use multiple gammas during training) and \gamma_eval.
One of my students is empirically investigating this and, as one would expect, it can have a huge impact.

arxiv.org/abs/2510.16175

2 months ago 12 1 1 1
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Today's wordle spoke volumes.

Wordle 1,677 2/6

⬛🟩⬛🟩🟩
🟩🟩🟩🟩🟩

P.S. here's a selfie of my x-country ski commute this morning 😃🎿

3 months ago 2 0 0 0

Today's wordle energized me

Wordle 1,662 2/6

🟨🟩🟩⬛⬛
🟩🟩🟩🟩🟩

3 months ago 3 0 1 0
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How I started 2026, hoping to keep this spirit up throughout the year!
Happy new year!

3 months ago 10 0 0 0

Another one of my favorite spots in Ecuador: El Pailón del Diablo 🇪🇨

3 months ago 5 0 0 0
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Gets better the closer you get 🏔️🇪🇨

3 months ago 12 0 0 1

Quito, Ecuador

3 months ago 3 0 1 0
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Will never tire of this view ❤️🇪🇨

3 months ago 13 0 1 1
RLJ | RLC Call for Papers

Hi RL Enthusiasts!

RLC is coming to Montreal, Quebec, in the summer: Aug 16–19, 2026!

Call for Papers is up now:
Abstract: Mar 1 (AOE)
Submission: Mar 5 (AOE)

Excited to see what you’ve been up to - Submit your best work!
rl-conference.cc/callforpaper...

Please share widely!

3 months ago 62 29 1 9

Today's wordle made me feel warm.

Wordle 1,646 2/6

⬛🟨🟩⬛⬛
🟩🟩🟩🟩🟩

3 months ago 3 0 0 0

Despite some of its flaws, OpenReview has had a tremendously positive impact on our research community.
This is a great initiative! Join me, and many others, in donating to ensure OpenReview not only remains a positive force, but is able to improve.

4 months ago 1 0 0 0

It was really great to chat with so many friends that I don't always get a chance to see, and to meet new ones, especially during our morning runs.
I really enjoyed this #NeurIPS2025 , but am also exhausted 🥰🫩

Until next time!

bsky.app/profile/did:...

4 months ago 2 0 0 0