Extension operands_and_partials to 8 edges

[Franzi2114]

Description

As I want to add a function with 8 known partials to the stan-math library (#2682), I had to extend the operands_and_partials routine such that it can work with 8 instead of 5 partial derivatives.

Example

It is possible to fill up to 8 edges for operands_and_partias:
ops_partials.edge8_.partials= ...

Questions

• Do I have to set up an own Pull Request for this? Or can it go together with the Pull Request for the new function?
• Which tests are required for this purpose before I ask can for the Pull Request?

Current Version:

v4.3.2

[bob-carpenter]

can it go together with the Pull Request for the new function?

Yes.

Which tests are required

Value tests and then derivative tests for the function. I'm not sure how operands_and_partials is tested itself, but you can follow whatever tests are already there.

[SteveBronder]

I think at the point we have 8 edges it might be good to turn the impl into having an underlying std::tuple just holding all the edges we need

[Franzi2114]

I think at the point we have 8 edges it might be good to turn the impl into having an underlying std::tuple

Yeah, maybe that makes sense. But I would suggest that somebody does it at a later point of time since right now, the new 7-parameter function works with those few changes I did. And @bob-carpenter agreed to bring these changes in the same Pull Request as the new 7-parameter function. The change of the underlying structure sounds a bit more complex.

[Franzi2114]

This was done in PR #2833.