return value type for complex abs; fixes #1836

[bob-carpenter]

Summary

Corrects return type for abs(const std::complex<T>& x) to T.

Tests

Added new test for return type. Other generic tests still work.

Side Effects

No.

Release notes

• return type T for abs(const std::complex&) abs(complex) should return value type, not complex type #1836

Checklist

• Math issue abs(complex) should return value type, not complex type #1836

• Copyright holder: Simons Foundation

  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/)

• 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

[stan-buildbot]

---

Name	Old Result	New Result	Ratio	Performance change( 1 - new / old )
gp_pois_regr/gp_pois_regr.stan	4.86	4.93	0.99	-1.34% slower
low_dim_corr_gauss/low_dim_corr_gauss.stan	0.02	0.02	0.97	-3.1% slower
eight_schools/eight_schools.stan	0.09	0.09	0.99	-0.95% slower
gp_regr/gp_regr.stan	0.22	0.22	1.0	0.11% faster
irt_2pl/irt_2pl.stan	6.44	6.49	0.99	-0.72% slower
performance.compilation	88.32	87.13	1.01	1.35% faster
low_dim_gauss_mix_collapse/low_dim_gauss_mix_collapse.stan	7.55	7.59	0.99	-0.51% slower
pkpd/one_comp_mm_elim_abs.stan	21.12	20.86	1.01	1.22% faster
sir/sir.stan	93.85	90.79	1.03	3.26% faster
gp_regr/gen_gp_data.stan	0.05	0.05	1.02	1.56% faster
low_dim_gauss_mix/low_dim_gauss_mix.stan	2.96	2.95	1.0	0.14% faster
pkpd/sim_one_comp_mm_elim_abs.stan	0.3	0.3	1.0	0.05% faster
arK/arK.stan	1.9	1.74	1.09	8.46% faster
arma/arma.stan	0.66	0.67	0.98	-1.98% slower
garch/garch.stan	0.51	0.51	1.0	-0.29% slower
Mean result: 1.00557078014

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Jenkins Console Log
Blue Ocean
Commit hash: 41106d8

---

Machine information

ProductName: Mac OS X ProductVersion: 10.11.6 BuildVersion: 15G22010

CPU:
Intel(R) Xeon(R) CPU E5-1680 v2 @ 3.00GHz

G++:
Configured with: --prefix=/Applications/Xcode.app/Contents/Developer/usr --with-gxx-include-dir=/usr/include/c++/4.2.1
Apple LLVM version 7.0.2 (clang-700.1.81)
Target: x86_64-apple-darwin15.6.0
Thread model: posix

Clang:
Apple LLVM version 7.0.2 (clang-700.1.81)
Target: x86_64-apple-darwin15.6.0
Thread model: posix

[bob-carpenter]

This is a bug fix that'd be nice to get in for the release.

[bob-carpenter]

Are we still merging bug fixes for the release? If so, can this one get merged?

[rok-cesnovar]

Yes of course. Merge away.