Comment (by Erik Schnetter):

Note that #include <math.h> should not be used in this test. Another test would be the same, but with #include <math.h>. Yet another test would be the same as above, but using a single-precision argument to isnan.

--
Ticket URL: https://bitbucket.org/einsteintoolkit/tickets/issues/2407/cactus-math-work-arounds-break-carpetx