cyclus/cyclus — pull request #440 by katyhuff (2013-02-04 20:53:35+00:00)
Title: Nan from atom frac

I was getting nan when asking for the atomFraction of an isotope that exists as an index in an empty CompMap. I think the real answer should either be 0 or to throw an exception.

I opted for 0, wrote a test to that effect, and implemented the solution.

Katy