Feature/issue 2682 operands and partials 8

[Franzi2114]

Summary

Here, we adapt the operands_and_partials routine such that it works for 8 parameters. We need this feature for issue #2682. This is a split from PR #2822.

We adapted the following files:
-stan/math/prim/functor/operands_and_partials.hpp
-stan/math/rev/functor/operands_and_partials.hpp
-stan/math/fwd/functor/operands_and_partials.hpp
-stan/math/opencl/rev/operands_and_partials.hpp
-test/unit/math/prim/functor/operands_and_partials_test.cpp
-test/unit/math/rev/functor/operands_and_partials_test.cpp

Tests

We also adapted the test files:
-test/unit/math/prim/functor/operands_and_partials_test.cpp
-test/unit/math/rev/functor/operands_and_partials_test.cpp

Side Effects

No.

Release notes

operands_and_partials expanded to accept 8 parameters.

Checklist

• Math issue Adding 7-Parameter Drift Diffusion Model (DDM) PDF with partial derivatives to Stan Math #2682

• Copyright holder: (fill in copyright holder information)

  The copyright holder is typically you or your assignee, such as a university or company. By submitting this pull request, the copyright holder is agreeing to the license the submitted work under the following licenses:
  - Code: BSD 3-clause (https://opensource.org/licenses/BSD-3-Clause)
  - Documentation: CC-BY 4.0 (https://creativecommons.org/licenses/by/4.0/)

• [x]the basic tests are passing

  • unit tests pass (to run, use: ./runTests.py test/unit)
  • header checks pass, (make test-headers)
  • dependencies checks pass, (make test-math-dependencies)
  • docs build, (make doxygen)
  • code passes the built in C++ standards checks (make cpplint)

• the code is written in idiomatic C++ and changes are documented in the doxygen

• the new changes are tested

[SteveBronder]

Hi @Franzi2114 I think on my home computer I have a version of operands_and_partials that actually allows for unlimited numbers of arguments through variadic templates. A while back it didn't work because mingw would fail for the tuple, but now that we have moved off of the mingw based on gcc 4.9.3 I think it will work. Do you mind holding off on this till Thursday when I can put a PR with the variadic changes to operands and partials?

[Franzi2114]

Do you mind holding off on this till Thursday

Hey @SteveBronder, extending operands_and_partials to infinitely many inputs sounds much better than just expanding it to 8. Since I need this for my PR #2822, it would be nice to have it as soon as possible. But Thursday is totally fine for me. Your implementation should work with the call in our new wiener_full_lpdf-function, shouldn't it?
Then, your PR will be merged into develop, I merge develop into our feature-branch and then I can use your operands_and_partials, is this correct?

So, shall I close this PR then? Or does somebody else do it? Should we refer to your PR in a few days?

[SteveBronder]

Hey @SteveBronder, extending operands_and_partials to infinitely many inputs sounds much better than just expanding it to 8. Since I need this for my PR #2822, it would be nice to have it as soon as possible. But Thursday is totally fine for me. Your implementation should work with the call in our new wiener_full_lpdf-function, shouldn't it?

Yes

Then, your PR will be merged into develop, I merge develop into our feature-branch and then I can use your operands_and_partials, is this correct?

Yep!

So, shall I close this PR then? Or does somebody else do it? Should we refer to your PR in a few days?

No if I don't have time to do update the variadic PR or if something bonks in it then we can go with this version.

[SteveBronder]

@Franzi2114 see the PR below, apologies for the delay. It's a bit of a big PR so it might take till after this coming release for someone to review and merge

#2841

[Franzi2114]

Hi @SteveBronder, what do you think: Will your PR #2841 be finished in the near future so that I can use the functionality for the 7-parameter DDM (PR #2822) or could we prioritize this PR #2833 such that the PR #2822 can move forward?
Here, we made only small changes to the existing operands_and_partials routine. Basically copying existing lines and adapting them for the 6th, 7th, and 8th parameter.

[andrjohns]

Thanks @Franzi2114! I'll approve and merge this so it's compatible with your other changes

[Franzi2114]

This refers to issue #2698. I just closed that issue.