Fix f_check_interpolation_2D/3D returning only last edge's result

[sbryngelson]

User description

Summary

• Fix f_check_interpolation_2D and f_check_interpolation_3D in m_model.fpp which only returned the interpolation decision from the last edge/triangle in the loop, silently discarding earlier true results.

Bug Details

Both subroutines loop over edges (2D) or triangles (3D), checking if any edge length exceeds the cell width. However, the interpolate flag was unconditionally overwritten on every iteration:

if (l1 > cell_width) then
    interpolate = .true.
else
    interpolate = .false.   ! ← clobbers previous .true.
end if

If edge 5 of 10 needs interpolation but the last edge doesn't, the function returns .false., causing the caller to skip interpolation when it's needed. This can produce incorrect levelset fields for OBJ models where mesh resolution varies across the surface.

Fix

Return early on the first edge that exceeds the cell width. Since interpolate is initialized to .false. before the loop, only the true case needs handling.

Test plan

• Existing OBJ model tests pass
• 3D immersed boundary cases with non-uniform triangle meshes produce correct levelsets

🤖 Generated with Claude Code

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CodeAnt-AI Description

Fix interpolation checks to correctly detect when any boundary edge/triangle needs interpolation

What Changed

• The 2D and 3D interpolation-check routines now stop and report "interpolate needed" as soon as any edge or triangle side is longer than the cell width, instead of using the last edge's result.
• Calls that previously could skip interpolation when an earlier edge required it will now trigger interpolation as intended.
• Observable behavior: OBJ and other imported meshes with non-uniform edge lengths produce correct levelset interpolation decisions.

Impact

✅ Fewer skipped interpolations for OBJ and imported meshes
✅ Correct levelset shapes for non-uniform meshes
✅ Fewer rendering/artifact errors at mesh boundaries

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Fixes #1219

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Nitpicks 🔍

🔒 No security issues identified

⚡ Recommended areas for review Early-return semantics The fix returns immediately when any long edge/triangle is found. Ensure callers expect that behavior and that no additional per-subroutine cleanup or side-effects (e.g., logging or resource handling) are needed after detection. Also confirm that empty inputs (zero edges/triangles) are handled as intended. Intent / API contract The parameter interpolate is declared intent(inout) but is always assigned by the subroutines (initialized to .false. and possibly set to .true.). This is effectively an output-only value; using intent(out) would better express intent and avoid reliance on caller-provided state. Verify all callers do not depend on prior value. Performance Issue The new checks compute Euclidean lengths with sqrt() inside tight loops (both 2D and 3D). Replacing sqrt with squared-length comparisons (compare to squared cell_width) will avoid the expensive sqrt call and be numerically equivalent for the > test.

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Pull request overview

Fixes incorrect interpolation decisions in f_check_interpolation_2D and f_check_interpolation_3D by preventing later loop iterations from overwriting a previously-detected .true. condition.

Changes:

• Return early from the 2D edge loop once any edge exceeds cell_width.
• Return early from the 3D triangle loop once any edge exceeds cell_width.

[danieljvickers]

In my last PR, I delete this subroutine entirely. You should probably just close this PR and wait for my update to come int to save the time on the compute resources.