feat(lsrtm): RWI vp gradient for AcousticLSRTM (c backend, 2-D/3-D, DD) - #108
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impl='c' AcousticLSRTM/3D returned vp.grad = 0. Full and bs now compute terms II+III+IV (Wu & Alkhalifah 2015): a background adjoint driven by the coupling transpose plus the scattered field (u_tt stored in full, reconstructed in bs). Only when vp requires grad: the layout follows it per call, so a fixed-vp LSRTM keeps the old buffers and cost (V100 x1.00; with vp.grad x1.5-1.8 time, x1.4-2.0 memory). vs eager, mp reaching the CPML band: rel 2.4e-4 (2-D) / 6.2e-4 (3-D).
With SWEEP_LSRTM_SPLIT_III=1 the full/bs backward writes the image-point term III to BackwardInput.grad_split_iii_out (new ABI field, generated files regenerated): vp.grad keeps II+IV and last_grad_split_iii() returns III on the model grid, for (II+IV) + beta*III (eq. 18-20). (II+IV) + III equals the unsplit vp.grad to rel <1e-7.
Forward and bs backward run stepped segments and honour the cut mask; the slot tables let ModelParallel rotate and halo-exchange both fields (LSRTM_DD, serial forward). The capture follows each model's requires_grad (mp only: 3 reconstruction grids; re-captured once vp wants its gradient). The NOPML reconstruction guard was abcn-based on every face and skipped cells beside each cut; now per face. Record and gradients bitwise vs one card on 4x V100, with and without vp.
Notebook 32: the paper's Fig. 1 anatomy in 2-D and 3-D, the eq. 15 identity, the beta-III split and the memory modes; gallery card and nav.
This was referenced Oct 5, 2026
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impl='c'AcousticLSRTM / AcousticLSRTM3D returnedvp.grad = 0. This branch adds the RWI tomographic vp gradient (Wu & Alkhalifah, 2015, terms II+III+IV) to the c backward, then domain decomposition and a docs notebook.Commits
ad2babb3vp gradient in full and boundary-saving modes: a background adjoint driven by the coupling transpose, plus the scattered field (u_ttstored in full mode, reconstructed in bs). The coupling also runs inside the CPML band (pml_field); without it vp.grad was 8–10 % off eager once mp reached the edges.3d9ede9eSWEEP_LSRTM_SPLIT_III=1returns term III on its own (last_grad_split_iii()), for (II+IV) + β·III. NewBackwardInputfield; generated files regenerated.dc569060DD for AcousticLSRTM 2-D/3-D: stepped segments, cut mask, slot tables for both fields. The NOPML reconstruction guard is now per face (it skipped the cells beside every cut).ca48c33anotebook 32: Acoustic vs AcousticLSRTM gradient anatomy in 2-D and 3-D, the β-III split, memory modes; gallery card and nav.Cost follows
vp.requires_grad, per callA classic LSRTM (mp only) keeps dev's buffers and kernels. The RWI layout is allocated only when vp asks for its gradient; under DD the capture is redone the first time it does.
Checks
-fmad=false; ≤7e-7 in the default build (FMA contraction).test/on KW60443: 1888 passed; the one failure,test_shipped_core, always fails with an in-place build. Newtest/test_lsrtm_rwi_vp_gate.pypins both layouts.backend_gradient_matrix.py(acoustic_lsrtm2d/3d): 2-D passes; 3-D fails only on the wavelet gradient, as on dev.Not covered: checkpointing modes still return vp.grad = 0 (declared in
test/gradient_cases.py).🤖 Generated with Claude Code