M9: gradient conformance and training primitives - #18
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Lifts indexed_add/indexed_put/gather off the via_binary fallback onto
native mx::scatter_add / mx::scatter / mx::gather, and adds the test
scaffolding needed to trust a gradient on Emily.
Backend: shared apply_scatter/6 + index-split + updates-shape rewrap
helpers translate Nx's {N, rank} indices + {batch ++ non_indexed_dims}
updates into MLX's per-axis index arrays + {batch ++ per_axis_slot}
updates. The single-axis gather fast path now reshapes to out.shape —
fixes a latent shape lie that only surfaced when grad chains dot
downstream of gather.
Tests:
- grad_equivalence_test.exs: 8-property zoo (sum, dot, reshape∘transpose,
broadcast, gather, indexed_add + two composition cases), each run
under Emily.Compiler and Nx.Defn.Evaluator, plus a PRNG-key-threading
test through a grad-computed dropout.
- finite_diff_test.exs + support/grad_helper.ex: 4-op numerical oracle
with per-op tolerance tables.
- mlp_curve_test.exs + transformer_block_curve_test.exs +
support/training_helper.ex: 50-step SGD curves matched per-step
(rtol=1e-3, drift canary) and final-loss (rtol=1e-4, convergence).
- soak/training_test.exs: 1k training-step memory-stability soak.
- mnist_full_test.exs: opt-in `:training_full` MNIST Axon MLP →
>97% test accuracy in 5 epochs under Emily.Compiler.
Docs: RELEASE.md updated; PLAN.md renumbered — M10 (conv-pool) and
M11 (1.0 release) follow.
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Summary
indexed_add/indexed_put/gatheroff thevia_binaryfallback onto nativemx::scatter_add/mx::scatter/mx::gather; grad through these ops no longer round-trips toNx.BinaryBackend.gatherfast path that only surfaced onceNx.Defn.gradchaineddotdownstream ofgather.See
RELEASE.mdfor the full M9 entry andPLAN.md § M9for scope.Test plan
mix precommit— 1 doctest, 64 properties, 219 tests, 0 failuresmix test --only conformance— 16 tests, 0 failures (DistilBERT / Qwen3 / ViT / Whisper tiny-random unaffected by the gather shape-lie fix)mix test --only training_full— 1 test, 0 failures; Axon MLP on MNIST converges to ~97% in 5 epochs underEmily.Compiler(~10 s wall time on Apple Silicon)