RLSG Grid-Spacing Utility

rlsg-spacing compares auxiliary-grid spacings for a saved CMIM interface without advancing the flow. It requires Python 3 and MPI and supports 2-D interior interfaces reconstructed with rlsg_seed_type: volumeFit.

Writing a Snapshot

Add rlsgSpacingSnapshot to plot_output. Each output event writes output/rlsg-spacing.<postfix>/. Keep all rank files in that directory. These snapshots are read by rlsg-spacing.

Comparing Spacings

For a cycle-zero snapshot, run:

rlsg-spacing output/rlsg-spacing.0 --work spacing-study --ranks 4

Each additional split halves the auxiliary spacing. The snapshot’s rlsg_grid_max_splits setting (default 3) limits the study. --max-splits N lowers this limit; --all-levels evaluates every depth.

Comparison tolerances
Option	Default	Quantity
`--relative-tolerance`	`0.05`	Relative curvature change.
`--absolute-tolerance`	`1e-8/base_length`	Absolute curvature change, in inverse metres.
`--distance-tolerance`	`0.01`	Distance change divided by `base_length` (dimensionless).

base_length is the unsplit auxiliary-grid spacing recorded in the snapshot. These comparisons measure sensitivity to grid spacing; they do not measure error against an exact interface.

The work directory contains summary.json with curvature and distance changes, grid counts, runtime, and peak memory per rank. When adjacent depths meet the tolerances, spacing.vars records the coarser passing spacing.