footnoted

One post, underlined term by term, each one pointing to a plain-English footnote with a real paper or page behind it. First entry: the ablation post that started this thread.

A note on the byline: the ask named "Rev. Howard Arson" as the post's author. Nobody in the actual thread goes by that — so consider him the fictional, overcredentialed exegete narrating these footnotes (doctorate unverified, opinions confident), while the post itself is reproduced exactly as @theophite.bsky.social actually wrote it.

@theophite.bsky.social · replying to a thread about diffusion models

one thing that i've been doing is literally running an before doing literally anything and i have learned more about as an architecture than my total knowledge of all two months ago

i'm using basically the training recipe with (i think, although i haven't checked) the swapped for for my ablations. i'm using as my big testbed, but that's multiday. i can experiment with packing the big on CIFAR like hourly.

  1. 1ablation study

    Turn one thing off — or swap it out — and rerun, so any change in behavior is attributable to that one thing and not vibes. In ML this usually means retraining a small, cheap version of a model with one component removed or substituted, purely to isolate what that piece actually contributes.

  2. 2diffusion transformers

    A diffusion model — one trained to reverse a step-by-step noising process, turning static back into an image — that uses a Transformer as the network doing the noise-predicting, instead of the convolutional U-Nets earlier diffusion models used.

  3. 3transformers

    The architecture behind basically everything since 2018: instead of reading a sequence step by step, self-attention lets every token (or image patch) look at every other one at once and learn which ones matter to it.

  4. 4HybViT (Yang et al.)

    A recipe for training one Vision Transformer to do double duty: classify images and generate them through diffusion, sharing a single backbone instead of training two separate networks for the two jobs.

  5. 5MLPs

    Multi-Layer Perceptrons — the plain feedforward block inside a Transformer layer (two linear layers with a nonlinearity between them) that processes each token on its own, right after attention has let tokens compare notes with each other.

  6. 6SwiGLUs

    A drop-in replacement for that plain MLP block: it gates one linear projection through a Swish activation and multiplies it elementwise against a second projection, instead of a single activation sandwiched in the middle. Slightly more compute per layer, usually a better loss for the same parameter count.

  7. 7CIFAR-10

    A small (60,000 image, 32×32px, 10-class) labeled image dataset from 2009 — small enough to train dozens of variants of a model on in an afternoon, which is exactly why it's the go-to for ablations: you're not testing whether an idea scales, just whether it helps at all.

  8. 8Krea 2

    A commercial image/video generation product. Mentioned here as the "big testbed" — the actual full-scale model being iterated toward, as opposed to the cheap CIFAR-10 sandbox that can be retrained hourly instead of over multiple days.

  9. 9Shampoo

    A second-order optimizer — unlike Adam or SGD, which only track first-order gradient statistics, Shampoo approximates a per-layer preconditioner from the shape of each weight tensor. Converges in fewer steps than Adam; each step costs more, because of the matrix math below.

  10. 10Gram matrices

    The matrix math Shampoo actually does each step: for a weight tensor, it builds a matrix of all pairwise dot products between its rows (or columns) as a stand-in for the full curvature. That matrix is the expensive part — it grows with the layer size, which is why it fits hourly on the small CIFAR run and not on the multiday Krea 2 one.