test: migrate stats/base/dists/gamma/entropy to ULP-based assertions

[kgryte]

Resolves a part of #11352.

Description

What is the purpose of this pull request?

This pull request:

• migrates the tests for stats/base/dists/gamma/entropy from relative tolerance testing to ULP difference testing, replacing the computed delta/tol comparisons with @stdlib/assert/is-almost-same-value.
• applies the same change to both test/test.js and test/test.native.js.
• uses a ULP bound of 188416 in both test files. This is the measured minimum: a binary search over the full 200-case Julia fixture set shows that 188416 ULPs passes every case while 188415 fails, for both the JavaScript and the native implementation.

The bound is large because the differential entropy of a gamma distribution is computed as a sum of terms of opposing sign (alpha - ln(beta) + lngamma(alpha) + (1-alpha)*digamma(alpha)), so fixture cases where the result falls close to zero suffer catastrophic cancellation. The worst case is alpha = 16.524296224667474, beta = 16.463066273781664, where the result is -2.4488832308833e-4 — roughly five orders of magnitude smaller than the individual summands — and the absolute error is ~1e-20. The previous relative tolerance of 1e-10 * abs( expected[ i ] ) admitted the same cases. For comparison, the already-migrated sibling package stats/base/dists/invgamma/entropy settled on a bound of 90112 ULPs for the same reason.

Measurements were taken with the native add-on built locally, so the native implementation was exercised rather than skipped. Both implementations required exactly the same minimum bound.

Only the two test files are changed.

Related Issues

Does this pull request have any related issues?

This pull request has the following related issues:

• [RFC]: Migrate math/base/special packages from relative tolerance testing to ULP difference testing (tracking issue) #11352

Questions

Any questions for reviewers of this pull request?

No.

Other

Any other information relevant to this pull request? This may include screenshots, references, and/or implementation notes.

The package test suite was run twice at the final ULP bound to confirm determinism (214 assertions passing in each of test/test.js and test/test.native.js on both runs), and make lint-javascript-tests TESTS_FILTER=".*/stats/base/dists/gamma/entropy/.*" is clean for both files.

Checklist

Please ensure the following tasks are completed before submitting this pull request.

• Read, understood, and followed the contributing guidelines.

AI Assistance

When authoring the changes proposed in this PR, did you use any kind of AI assistance?

• Yes
• No

If you answered "yes" above, how did you use AI assistance?

• Code generation (e.g., when writing an implementation or fixing a bug)
• Test/benchmark generation
• Documentation (including examples)
• Research and understanding

Disclosure

If you answered "yes" to using AI assistance, please provide a short disclosure indicating how you used AI assistance. This helps reviewers determine how much scrutiny to apply when reviewing your contribution. Example disclosures: "This PR was written primarily by Claude Code." or "I consulted ChatGPT to understand the codebase, but the proposed changes were fully authored manually by myself.".

This PR was authored by Claude Code, which mirrored the migration idiom from previously merged conversions in the same family (e.g. stats/base/dists/invgamma/entropy) and determined the minimum passing ULP bound empirically.

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https://claude.ai/code/session_01H6NQ1XGDBg2vzphpvakfVr

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Coverage Report

Package	Statements	Branches	Functions	Lines
stats/base/dists/gamma/entropy	$\\color{green}202/202$ $\\color{green}+100.00\\%$	$\\color{green}10/10$ $\\color{green}+100.00\\%$	$\\color{green}2/2$ $\\color{green}+100.00\\%$	$\\color{green}202/202$ $\\color{green}+100.00\\%$

The above coverage report was generated for the changes in this PR.