Forward: hand-written tiled GEMM vs cuBLAS sgemm on random matrices
(square / non-tile-aligned rect / 256³), max relative error < 1e-3, using
the row-major⟺col-major identity to drive cuBLAS without explicit
transposes. Backward: scalar loss L = sum(W∘C) (so dC = W), dA/dB from
matmul_backward checked against the finite-diff harness. Gated behind
not(no_cuda).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
