Need universal small value for denominators

[katsmith133]

There are a few places where a small, but non-zero value is needed in a denominator to prevent dividing by zero (and perhaps needed for other purposes too?), such as:

Omega/components/omega/src/ocn/VertMix.h

Lines 110 to 111 in 012f9a5

	Real RichardsonNum = BruntVaisalaFreqSq(ICell, K) /
	Kokkos::max(1.0e-12_Real, ShearSquared);

It would be helpful to have a universal variable, something like Eps, Puny, or Tiny defined somewhere that can be used by all. My first thought is to put it in GlobalConstants.h, but open to suggestions on both the name and location where its defined. So far it looks like 1.0e-12 is the value used most places (both MPAS-O and Omega), is there a need for a value other than this?

[philipwjones]

Agree on location. We don't want a too-small number (eg the machine limit) since that will cause overflows on the division, especially if the numerator is on the large size, so 1.0e-12 is a reasonable compromise. I don't believe any of those names causes conflicts with stdlib numerical limits or other libs. Puny or Tiny might better a better description - Eps might refer to a meaningful actual epsilon in an algorithm so could be riskier.