Pointer & CryptaMind
Pointer Pointer
I’ve been trying to reduce the parameter count of transformer models without a drop in performance—think of it as a pruning algorithm that stays near the theoretical lower bound for model size. Got a moment to dissect the math and see if we can squeeze more out of the architecture?
CryptaMind CryptaMind
Sure, let's dive in. Start by looking at the Hessian of the loss—pruning based on second‑order importance tends to preserve capacity better than plain magnitude pruning. Then, consider re‑weighting the attention heads: instead of dropping entire heads, scale their weights according to mutual information with the output. That keeps the representational budget tight but avoids losing expressive power. Also, explore low‑rank factorization of the weight matrices; a carefully chosen rank can get you close to the information‑theoretic lower bound. Keep the regularization tight during fine‑tuning to prevent over‑compensation. Let me know which of these you want to formalize.
Pointer Pointer
Let’s formalize the Hessian‑based pruning first, then sketch the head re‑weighting. The Hessian, \(H=\nabla^2 L(\theta)\), gives a second‑order importance measure; we’ll approximate its diagonal or use a block‑diagonal structure to keep it tractable. For each parameter \( \theta_i \), we compute \(g_i^2/H_{ii}\) and prune where that ratio is below a threshold—this keeps the parameters with the largest curvature impact. Once we prune, we’ll replace the dropped entries with zero, then recompute the loss and retrain for a few epochs with a very small learning rate to let the remaining parameters adapt. After that, we’ll move to the attention heads: compute mutual information between each head’s output and the final logits, scale each head’s weights by \( \alpha_i = \frac{I_i}{\sum_j I_j}\), then fine‑tune with L2 regularization to keep the weights from blowing up. Finally, we’ll apply a low‑rank factorization—\(W \approx U V^T\) with rank chosen to satisfy \(\text{rank} \leq \log_2(\text{dim})\) so we stay near the information‑theoretic bound. We’ll test each step’s impact on perplexity and FLOPs before moving on. Does that workflow line up with what you had in mind?