Fix GRCBC subsonic inflow using wrong L index

[sbryngelson]

User description

Summary

• In the GRCBC subsonic inflow boundary condition, the wave amplitude array was indexed as L(2) instead of L(i) inside a do i = 2, momxb loop
• This meant only L(2) was repeatedly overwritten rather than setting each L(i) for the corresponding wave

Test plan

• Verify GRCBC subsonic inflow test cases produce correct results
• May need golden file regeneration if prior results silently used the buggy index

🤖 Generated with Claude Code

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CodeAnt-AI Description

Fix GRCBC subsonic inflow to assign each wave amplitude correctly

What Changed

• The subsonic inflow boundary now sets each wave amplitude L(i) inside the loop instead of repeatedly overwriting L(2), so every wave entry is updated.
• This changes the computed inflow boundary state for cases using the GRCBC subsonic option and can affect any dependent simulation outputs or comparisons.

Impact

✅ Correct subsonic boundary wave amplitudes
✅ More accurate GRCBC inflow results
✅ Fewer silent simulation result mismatches

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Summary by CodeRabbit

• Bug Fixes
  • Fixed an issue with subsonic inflow boundary condition handling in simulations to ensure corrections are applied consistently across all relevant parameters.

[cubic-dev-ai]

No issues found across 1 file

Confidence score: 5/5

• Automated review surfaced no issues in the provided summaries.
• No files require special attention.

[Copilot]

Pull request overview

This pull request fixes a critical indexing bug in the GRCBC (Generalized Relaxation Characteristic Boundary Condition) subsonic inflow implementation within the characteristic boundary condition module. The bug caused incorrect wave amplitude calculations by repeatedly overwriting a single array element instead of populating the entire wave amplitude array.

Changes:

• Fixed indexing bug in GRCBC subsonic inflow where L(2) was incorrectly used instead of L(i) inside a loop
• This ensures each wave amplitude L(i) is correctly computed for i = 2 to momxb

[codecov]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 44.05%. Comparing base (d048c4b) to head (224c548).
⚠️ Report is 19 commits behind head on master.

Files with missing lines	Patch %	Lines
src/simulation/m_cbc.fpp	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1224      +/-   ##
==========================================
- Coverage   44.07%   44.05%   -0.02%     
==========================================
  Files          70       70              
  Lines       20431    20498      +67     
  Branches     1974     1990      +16     
==========================================
+ Hits         9004     9030      +26     
- Misses      10291    10329      +38     
- Partials     1136     1139       +3     

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[sbryngelson]

Superseded by #1242 (batched HPC-sensitive fixes)