feat: add constants/float16/gamma-lanczos-g

[Amansingh0807]

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Resolves none

Description

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This pull request:

• add constants/float16/gamma-lanczos-g

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This pull request has the following related issues:

• Resolves None

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[stdlib-bot]

Coverage Report

Package	Statements	Branches	Functions	Lines
constants/float16/gamma-lanczos-g	$\color{green}47/47$ $\color{green}+0.00%$	$\color{green}1/1$ $\color{green}+0.00%$	$\color{green}0/0$ $\color{green}+0.00%$	$\color{green}47/47$ $\color{green}+0.00%$

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

[Planeshifter]

Thanks!

[stdlib-bot]

PR Commit Message

feat: add `constants/float16/gamma-lanczos-g`

PR-URL: https://github.com/stdlib-js/stdlib/pull/9022

Co-authored-by: Philipp Burckhardt <pburckhardt@outlook.com>
Reviewed-by: Philipp Burckhardt <pburckhardt@outlook.com>
Signed-off-by: Philipp Burckhardt <pburckhardt@outlook.com>

Please review the above commit message and make any necessary adjustments.

[kgryte]

@Amansingh0807 How did you derive the value of this constant? Do you have any sources you can share?

[kgryte]

cc @Planeshifter

[kgryte]

@Amansingh0807 After a bit of sanity checking, what you chose for the constant in this PR is a common value for approximating the gamma function in double-precision. That is not appropriate for half-precision. As observed for constants/float64/gamma-lanczos-g and constants/float32/gamma-lanczos-g, what value we use for g depends on what approximation we use in our gamma function implementations. What you provided here would not be what we used.

So, unfortunately, this PR should not have been merged, and I've reverted the addition in e2902df. For future reference, for some of these constants, they only make sense within the context of actual implementations, and, as we will not be adding a half-precision approximation of the gamma function anytime soon, this constant is not needed. Accordingly, it can be useful to first sanity check with maintainers to determine which constants, if any, we are interested in adding to the project.

Hope this clarifies things, and sorry for the miscommunication.

[Amansingh0807]

Thanks for the clarification @kgryte.

This context helps a lot. From my side, I treated this similar to other constants that already exist across precisions and followed commonly used Lanczos parameters as a reference, assuming consistency would be acceptable.

I understand that gamma-lanczos-g is tightly coupled to the specific Gamma implementation and its chosen approximation, and since there’s no planned float16 Gamma implementation, adding this constant independently doesn’t really fit.

Thanks for explaining the rationale and reverting the change, the reasoning is clear now. I will make sure to check in advance for constants that are implementation-dependent rather than intrinsic.