stan-dev / stan-dev/docs

motivate Cholesky factor parameterizations in functions reference and elsewhere

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enhancement good first issue
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Description

Summary:

We define the Cholesky-based parameterization, but don't mention that they're more efficient and more numerically stable.

Description:

This should go in the functions reference for the Cholesky-based parameterizations (LKJ, Wisharts, and multi-normal).

This arose through an issue on the Stan forums from jachymb, which also describes why the Cholesky parameterizations are better:

https://discourse.mc-stan.org/t/what-is-the-point-of-the-multi-normal-cholesky-parametrization/38483/2

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First steps

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  3. Fork the repository and make your change on a branch.
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Research direction

Start in the functions reference at the Cholesky-based parameterization entries for LKJ, Wishart, and multi-normal. Read the linked Stan forum discussion for the rationale, then update those entries to explain their efficiency and numerical-stability benefits; done means all three parameterizations are covered.

Written by the indexing model from the issue text.

Assessment

Domain
documentation
Issue type
Documentation
Difficulty
3/5
Estimated time
1-2 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
38/100

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