Fix Mamba2.step() handling of D when D_has_hdim=True#901
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When D_has_hdim=True, self.D has shape (nheads * headdim,) instead of
(nheads,). The forward() method correctly reshapes D from (h*p,) to
(h, p) in this case, but step() always treated D as if it had shape
(nheads,), leading to incorrect results during autoregressive decoding.
Fix both code paths in step() (with and without selective_state_update)
to use rearrange("(h p) -> h p") when D_has_hdim=True, consistent with
forward().
Fixes #887
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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Closing in favor of #903 (duplicate) |
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Summary
Mamba2.step()to correctly handleself.DwhenD_has_hdim=True, whereDhas shape(nheads * headdim,)instead of(nheads,)step()(with and withoutselective_state_update) now userearrange("(h p) -> h p")whenD_has_hdim=True, consistent withforward()D_has_hdim=TruebecauseDis misinterpreted as per-head rather than per-head-dimFixes #887
Test plan
step()output matchesforward()output for a single token whenD_has_hdim=TrueD_has_hdim=False(default behavior unchanged)selective_state_updateavailable and with the fallback path🤖 Generated with Claude Code