stan-dev/stan — pull request #873 by PeterLi2016 (2014-08-14 18:35:11+00:00)
Title: Feature/issue 860 erf nan

#### Summary:
Fixes issue #860.

#### Intended Effect:
agrad/rev/erf should now return NaN for gradients and value when passed in NaN.

#### How to Verify:
Run test/unit-agrad-rev/functions/erf

#### Side Effects:
None.

#### Documentation:
None. Should document behavior of function when given NaN together with other functions.

#### Reviewer Suggestions:
Anyone