Forward: compare via matrix relative error (max abs error / max|ref|)
instead of a per-element ratio, so near-zero outputs where two correct
f32 GEMMs differ only in rounding order don't inflate the metric.
Backward: L = sum(W∘C) is bilinear, so central differences are
truncation-free — use eps=1e-2 (sharper f32 resolution of the
difference) and atol=1e-3 to floor near-zero-gradient subtraction noise.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Gahow Wang
88fbe0a85d