Validation and Stability

TIDE includes built-in checks for stability and parameter consistency.

CFL Condition

Use cfl_condition(grid_spacing, dt, max_vel) to evaluate whether dt is stable.

Return values: - inner_dt: stable internal time step - step_ratio: number of internal steps per external step

maxwelltm and maxwell3d call this internally, but explicit checks are useful when designing survey parameters.

Sampling and Resampling

Resampling helpers provide deterministic signal transforms used in CFL sub-stepping: - upsample: low-pass upsample on last time axis - downsample: low-pass downsample on last time axis - downsample_and_movedim: convenience transform for receiver tensors

Use freq_taper_frac and time_pad_frac to reduce FFT edge artifacts.

Padding Helpers

• create_or_pad: create zeros or pad existing tensors
• reverse_pad: convert natural pad order into torch.nn.functional.pad order
• zero_interior: keep CPML activity near boundaries while clearing non-PML interior

Validation Helpers

• validate_model_gradient_sampling_interval
• validate_freq_taper_frac
• validate_time_pad_frac

These are simple but effective front-line guards for user-facing numeric controls.