Added "append_array" function to address Issue 481

[bbbales2]

Submission Checklist

• Run unit tests: ./runTests.py test/unit
• Run cpplint: make cpplint
• Declare copyright holder and open-source license: see below

Summary:

Addresses: #481

This replaces pull request: #531

Sorry for axing the old pull req, but the outdated fvar stuff was causing issues and I thought it would be better to rebase onto the updated Stan than try to figure it out. I've checked the fvar<fvar<var>>/fvar<fvar<double>> behavior and I think these tests make sense (though they are kinda verbose).

Side effects

Hopefully none

How to Verify:

./runTests.py test/unit/math/prim/arr/fun/append_array_test
./runTests.py test/unit/math/rev/arr/fun/append_array_test
./runTests.py test/unit/math/fwd/arr/fun/append_array_test
./runTests.py test/unit/math/mix/arr/fun/append_array_test

Reviewer Suggestions

Anyone

Copyright and Licensing

Please list the copyright holder for the work you are submitting (this will be you or your assignee, such as a university or company): University of California, Santa Barbara

By submitting this pull request, the copyright holder is agreeing to 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/)

[stan-buildbot]

Can one of the admins verify this patch?

[bob-carpenter]

Those tests are way more verbose and detailed than they need to be. We can leave them, or you can simplify them. To test append(a, b), you only need to test that the results are equal to the results from a or from b---you shouldn't need to run autodiff, etc.

I'm OK with it going in as is, though. I'm going to go through and unify a lot of the higher-order testing in a testing framework that should make this all a lot easier. So maybe not much point trying to simplify for just this one test.