Setting namelist defaults with multiple physics suites?

[nusbaume]

There are multiple CAMDEN namelist options whose default values depend on the physics option (phys) chosen. Normally this could be taken directly from the physics-suites config option, except currently the code allows for multiple physics suites to be listed even when there is only one model instance.

What should be done for the namelist defaults in the case of multiple physics suites but only a single host model instance? I can see a few possibilities:

1. Simply disallow situations where the number of physics suites listed is greater than the number of instances (NINST), and assume each instance only has one associated physics suite.

2. Have buildnml automatically choose a particular physics suite as the namelist default (e.g. the first suite listed in --physics-suites).

3. Have the namelist defaults depend on the specific compset chosen (e.g. FKESSLER) instead of the physics suites listed.

Any thoughts or opinions? To be honest this might tie into a bigger question of what to do with multiple physics suites that conflict with each other in several different ways, such as containing schemes that represent the exact same physical processes (which could result in either double-counting or one scheme never running, both of which seem bad).

[nusbaume]

After discussion, it was decided that if there is more than one physics suite listed, then the user MUST state which physics suite is being used in user_nl_cam. If not, then buildnml will throw an error.

This feature will be brought in as part of the PR dealing with issue #44 .