_ADD_SOURCE_ sets source term (and does not add to it)

[JensWyrwa]

In my tests the "call" af the preprocessor directive ADD_SOURCE does set the source term for a specified state variable. A second call for the same variable does not take effect. Second here means, the model is mentioned lower in the fabm.yaml file.
I would like to reassure that I observed this correctly and that this is the intended behaviour.

[jornbr]

Could you post the contents, or relevant snippet of, of your fabm.yaml?

[JensWyrwa]

Hi Jorn,

qsim_decay.F90:
...
_ADD_SOURCE_(self%id_tracer, -1.0_rk * self%decay_rate * tracer)
...

qsim_tracerzone.F90:
...
_ADD_SOURCE_(self%id_tracer, zone_hop)
...

fabm.yaml:

instances:
  qsim_tracerzone:
    initialization:
      tracer: 0.0
      bottom_variable: 0.0
    model: uzweijens/qsim_tracerzone
    parameters:
      tracered_zone: 7.0
      tracering_time: 1324800.0
  qsim_decay:
    initialization:
      tracer: 0.0
    model: uzweijens/qsim_decay
    parameters:
      decay_rate: 0.0011574 # 0.000011574=1/d

Depending on which model is first in the fabm.yaml, the tracer behaves according to that sink/source.

Hope it helps

Yours Jens

[jornbr]

Thanks Jens! If the tracer variable in both qsim_tracerzone and qsim_decay is registered with register_state_variable, that above fabm.yaml will give each module its own independent tracer. You'll thus have two: "qsim_tracerzone_tracer" and "qsim_decay_tracer". Each module's sources will apply only to its "own" tracer. If you'd like the two modules to share the same tracer variable, you'll need to make an explicit coupling, e.g.,

  qsim_decay:
    model: uzweijens/qsim_decay
    parameters:
      decay_rate: 0.0011574 # 0.000011574=1/d
    coupling:
      tracer: qsim_tracerzone/tracer

Note that you can then also drop the "initialization" section under qsim_decay, since the variable is now "owned" (and initialized) by qsim_tracerzone. A recent post with some related info: #146

Best

Jorn

[JensWyrwa]

Hi Jorn,

I did some more tests, more carefully.

Further calls to _ADD_SOURCE_ only do add to the sink/source term of a state variable, if the variables are coupled in fabm.yaml (same name inside the models is not sufficient).

The position of the model in fabm.yaml is irrelevant for this behaviour (sorry for this error in the initial post).

It is irrelevant for the result, wether the variables are both registered with register_state_variable or one of them uses register_state_dependency as long as they are coupled in fabm.yaml. If one is registered with register_state_dependency then FABM throws an error if the variables are not coupled.
This is further described in #146 .

yours Jens

[jornbr]

Hi Jens, thanks for the update.

That all sounds correct, assuming you did indeed get two separate tracers - "qsim_tracerzone_tracer" and "qsim_decay_tracer" - in your original example, with sources set in "qsim_tracerzone" being applied to the former, and the source from "qsim_decay" applied to the latter. If so, everything is behaving as expected, and I guess this isssue is settled.

Best,

Jorn

[JensWyrwa]

yes, thanks for the help again.