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AcousticLSRTM

sweep.equations.AcousticLSRTM 

AcousticLSRTM(spatial_order=4, device='cpu', backend='torch')

Bases: sweep.equations.base.SecondOrderEquation

Second-order 2-D acoustic Born / LSRTM wave equation.

Two coupled scalar wave equations: a background pressure-like field h1 propagating through the smooth velocity vp, and a scattered pressure-like field sh1 driven by the reflectivity perturbation mp acting on the background Laplacian (linearised Born scattering). Both fields share an independent set of CPML memory variables. Defaults: source on the background field h1, receivers on the scattered field sh1 — the standard layout for least-squares reverse-time migration.

Models (constructor input order)

  • vp (m/s): Background acoustic velocity model.
  • mp: Acoustic reflectivity perturbation used for LSRTM.

Wavefields

  • h1 (aliases: pressure, p, background): Background acoustic pressure-like wavefield; default source.
  • h2 (aliases: pressure_prev, background_prev): Previous-step background wavefield (internal).
  • psix: Background CPML memory variable for the x-derivative term (internal).
  • psiz: Background CPML memory variable for the z-derivative term (internal).
  • zetax: Background CPML auxiliary wavefield for the x-direction update (internal).
  • zetaz: Background CPML auxiliary wavefield for the z-direction update (internal).
  • sh1 (aliases: scattered, scattered_pressure, data): Scattered acoustic wavefield used for LSRTM data prediction; default receiver.
  • sh2 (aliases: scattered_prev): Previous-step scattered wavefield (internal).
  • spsix: Scattered-wave CPML memory variable for the x-derivative term (internal).
  • spsiz: Scattered-wave CPML memory variable for the z-derivative term (internal).
  • szetax: Scattered-wave CPML auxiliary wavefield for the x-direction update (internal).
  • szetaz: Scattered-wave CPML auxiliary wavefield for the z-direction update (internal).

Defaults

  • source_type: ['h1']
  • receiver_type: ['sh1']
  • pml_type: 'cpmlr'

Build the 2-D acoustic LSRTM equation operator.

Parameters:

  • spatial_order –

    FD accuracy order of the spatial Laplacians applied to both the background and scattered fields — e.g. spatial_order=4 is fourth-order accurate. Internally the half-stencil width is M = spatial_order // 2 (used for loop bounds and PML padding). Must be an even integer (2, 4, 6, 8, 10, …). Performance note (impl='c' on CUDA): the compiled kernels ship template specialisations only for spatial_order ∈ {2, 4, 6, 8}. Above 8 the dispatcher drops to a generic runtime path (order = -1 in src/sweep/csrc/cuda/equations/acoustic_lsrtm2d/forward.cu) which uses more registers and runs noticeably slower. The PyTorch eager path is unaffected. Defaults to 4.

  • device –

    Device for the operator's static kernels. Use 'cuda' / a torch.device for GPU runs so the propagator can follow without a host↔device copy. Defaults to 'cpu'.

  • backend –

    Array / programming backend, 'torch' or 'jax'. When you later want impl='c', leave this on 'torch'. Defaults to 'torch'.