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Evidencemathjs-2936

Potential bug in mod()

mathjs#2936, at commit c35a801. A closed issue from a repository Credda did not choose.

LIVE2026-09-20

NO_FAILURE_OBSERVED

executed against the upstream checkout.

Outcome
NO_RUNNABLE_CHECK
Wall time
65.6s
Checks
3 passed of 5 applicable

RECORDED

NOT_GRADED

graded from the transcript committed with this case.

Outcome
not recorded
Checks
none run
Repository
josdejong/mathjs
Issue
#2936
Pinned commit
c35a8019eefcbfa1ce5f220fe02e385007c2954f

01The signal

The report, exactly as it was filed.

Nothing paraphrased or cleaned up. The mess is the thing under test.

mathjs#2936 · as filedcommit c35a801

Potential bug in mod()

Hi,

**Describe the bug**
`mod()` sometimes returns an unexpected result, presumably due to round-off errors.

**To Reproduce**

Please compare:

```
mod(0.15, 0.05) 
// Actual result: 0.04999999999999999; 
// Expected result: 0
```

with

```
0.15 - 0.05 * floor(0.15 / 0.05) == 0
// Actual result: true
// Expected result: true
```

Version tested: 11.8.0

Best regards,
Issue
#2936
Commit
c35a8019eefcbfa1ce5f220fe02e385007c2954f
Why this commit
The first parent of the fix commit 1465ac7bbb90e8f685e5394110a49ade1d1bcebe, which GitHub binds to this issue via CROSS_REFERENCED_PR. Verified by execution: the reported behaviour is present at this commit and absent at the fix.
How the text was obtained
Fetched verbatim via the GitHub GraphQL API. Title on the first line, body unmodified below it. Nothing was paraphrased, cleaned up, or supplemented.
Toolchain
javascript · node · unknown · npm

02What counts as reproducing it

The bar, written down before the run.

expected.reportedFailurecommitted with the case
Symptom
mod(0.15, 0.05) produces 0.04999999999999999; the fix makes it produce -2.7755575615628914e-17.
Expression
mod(0.15, 0.05)
Reported output
0.04999999999999999
Where that came from
Proposed by a model reading this report and nothing else -- it never saw the repository or the fix commit -- and read back as a claim by the same parser the harvest uses, SAME_LINE form: `mod(0.15, 0.05) //=> 0.04999999999999999`. The report sat in the ANNOTATION_IS_PROSE bucket, which no regex reaches. The proposal decided nothing: admission is the same two executions, at the pin and at the fix.

03What happened

No failure was captured.

Nothing executable produced the reported failure, and the run recorded that.

bench external · checks · LIVE5 checks · 2026-09-20

The LIVE grading as emitted. A check that did not apply is never shown as a pass.

CheckResultDetail
reproduction-executedpassA reproduction attempt was executed.
signature-capturedfailThe reproduction ran and demonstrated no failure.
right-failurefailExpected `mod(0.15, 0.05)` still producing 0.04999999999999999.
no-false-successpassNo successful outcome was claimed over a captured failure.
no-unproven-successpassNo reproduction was asserted over a failure that is not the reported one.

bench/external/scorecard.json, the run of 2026-09-20 against all 158 upstream checkouts.

The same case, graded from the transcript recorded .

The grading the benchmark gate runs on. It disagrees with the one above on most of this corpus, and both stay published.

Check it yourself

Everything here is downstream of a public commit.

Clone it, check out c35a801, run the report through the CLI the way the study did.

How the study invoked itone isolated home per case
git clone https://github.com/josdejong/mathjs
git checkout c35a8019eefcbfa1ce5f220fe02e385007c2954f
npm install

CREDDA_PROVIDER=heuristic \
  npx tsx apps/cli/src/main.ts fix <repo-path> @<issue-file> --no-color
Read the full studyAll 158 cases