stan-dev / stan-dev/stanc3

[FR] Add `lower_upper` constrain

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feature good first issue
Dominant language
OCaml
Stars
160
Forks
59
Avg merge
21h 45m
Merged PRs (30d)
26

Description

With the merge of stan-dev/math#3087, the lub_* constrain and free functions now support a single tuple of bounds. It would be great to add the lower_upper bounds type so that both bounds can be specified in a single function call.

Example pseudo-stan:

functions {
  (vector, vector) make_bounds(...) { ... }
}

...

parameters {
  vector<lower_upper = make_bounds(...)> x;
}

This would be great for situations where parameter bounds depend on functions of other parameters, and there is some non-trivial computation shared by both bounds

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First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

The issue names no source files or tests. Start by reviewing the existing lub_* constrain and free-function support from stan-dev/math#3087, then determine how a single lower_upper bounds specification should be represented; done means bounds returned together by make_bounds can be used in one parameter declaration.

Written by the indexing model from the issue text.

Assessment

Tech stack
ocaml
Domain
compilers
Issue type
Feature
Difficulty
5/5
Estimated time
Over a week
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
38/100

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