Boundaries and PML

TIDE uses CPML (Convolutional Perfectly Matched Layer) boundaries to absorb outgoing waves and reduce reflections from computational edges.

pml_width

Accepted formats: - 2D: - int: same width on all sides - [top, bottom, left, right] - 3D: - int: same width on all sides - [z0, z1, y0, y1, x0, x1]

Larger PML widths reduce boundary reflection but increase memory and compute cost.

fd_pad

Finite-difference padding is extra halo space required by stencil order.

Interaction with PML: - FD padding and PML are both outside the physical model interior. - Callback views expose full, pml, and inner regions to separate these areas. - CPML auxiliary fields are zeroed in non-PML interior regions.

Accuracy and Stencils

Supported stencil orders: 2, 4, 6, 8.

Trade-offs: - Higher order reduces numerical dispersion at fixed grid spacing. - Higher order increases arithmetic cost and halo width. - Order 2 is fastest per step but may need finer grids for equivalent accuracy.

Practical recommendation: - Start with stencil=2 for quick iteration. - Increase to 4 or 6 for production-quality inversion when dispersion error dominates.