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Backport: Relax lanczos gtest tolerance - #3142

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Backport: Relax lanczos gtest tolerance#3142
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NVIDIA:release/26.10from
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@bdice bdice commented Sep 8, 2026 •
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Backports #3137 to release/26.10 to stabilize CI.

@aamijar @bdice
Relax lanczos gtest tolerance (NVIDIA#3137)
ae910e0 
This was too tight of a tolerance causing a flaky test.
```
[ RUN      ] LanczosTests/LanczosTestD_SM.Result/0
/tmp/conda-bld-output/bld/rattler-build_libraft-headers-only/work/cpp/tests/sparse/solver/lanczos.cu:425: Failure
The difference between host_eigenvalues[i] and expected[i] is 9.9339252102037534e-12, which exceeds tol, where
host_eigenvalues[i] evaluates to 0.013678224628902495,
expected[i] evaluates to 0.01367822461896857, and
tol evaluates to 1.1695277001426182e-12.
eigenvalue 1 (which=3) is not part of the requested selection: got=0.013678224628902495 expected (from independent dense reference spectrum)=0.01367822461896857

[  FAILED  ] LanczosTests/LanczosTestD_SM.Result/0, where GetParam() = 112-byte object <02-00 00-00 14-00 00-00 A0-86 01-00 00-00 00-00 00-00 00-00 7D-1D 90-26 03-00 00-00 00-00 00-00 2A-00 00-00 00-00 00-00 90-BB A0-E2 B7-5C 00-00 24-BD A0-E2 B7-5C 00-00 24-BD A0-E2 B7-5C 00-00 10-25 A1-E2 B7-5C 00-00 10-37 A1-E2 B7-5C 00-00 10-37 A1-E2 B7-5C 00-00 20-37 A1-E2 B7-5C 00-00 20-5B A1-E2 B7-5C 00-00 20-5B A1-E2 B7-5C 00-00> (55889 ms)
[----------] 1 test from LanczosTests/LanczosTestD_SM (55889 ms total)
```

Authors:
  - Anupam (https://github.com/aamijar)
  - Divye Gala (https://github.com/divyegala)

Approvers:
  - Divye Gala (https://github.com/divyegala)

URL: NVIDIA#3137
@bdice
bdice requested a review from a team as a code owner September 8, 2026 22:16
@bdice bdice added improvement Improvement / enhancement to an existing function non-breaking Non-breaking change labels Sep 8, 2026
@bdice bdice self-assigned this Sep 8, 2026
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  • cpp/tests/sparse/solver/lanczos.cu

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📝 Summary

Summary by CodeRabbit

  • Bug Fixes
    • Improved eigenvalue solver tolerance handling across platforms.
    • Adjusted tolerance values by numeric precision to support more consistent results for single- and double-precision calculations.

Walkthrough

Changes

Lanczos eigenvalue tolerance

Layer / File(s) Summary
Precision-dependent tolerance and rationale
cpp/tests/sparse/solver/lanczos.cu		 Adds compile-time type selection for the tolerance multiplier. Double precision uses 10,000, while other types use 500. The documentation records the observed cross-platform variation and retains dimension-independent scaling.

Priority: ⬇️ Low

Estimated code review effort: 1 (Trivial) | ~5 minutes

Merge Risk: ⚪ Minimal · up to ae910

This adjusts double-precision Lanczos test tolerance to accommodate observed cross-platform variation while retaining existing correctness checks. No current merge-blocking risk remains.

Suggested reviewers: achirkin, says1117

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name Status Explanation Resolution
Docstring Coverage ⚠️ Warning Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 2 functions across 1 files. Write docstrings for the functions missing them to satisfy the coverage threshold.
✅ Passed checks (4 passed)
Check name Status Explanation
Linked Issues check ✅ Passed Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check ✅ Passed Check skipped because no linked issues were found for this pull request.
Description check ✅ Passed The description states that the change backports PR #3137 to stabilize CI. This matches the Lanczos tolerance changes.
Title check ✅ Passed The title clearly identifies the backport and the main change: relaxing the Lanczos GTest tolerance.
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@divyegala

divyegala commented Sep 8, 2026

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/merge

@rapids-bot
rapids-bot Bot merged commit 59c3daa into NVIDIA:release/26.10 Sep 8, 2026
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@divyegala divyegala divyegala approved these changes
@aamijar aamijar aamijar approved these changes

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