Check the existing historical GDP parameter first

[Jihoon]

I find the line in read_data() below checks whether gdp_calibrate (imported from external excel input files) has at least 2 periods before the model horizon.

https://github.com/iiasa/message_ix/blob/2045b07c13322ce0224ce809ca1c64c1e5f64398/message_ix/macro.py#L275-L286

But this can be also imported from self.s.par("historical_activity", {"technology":"GDP"}). So the condition can first check the parameter and, if so, import historical values directly. If not, then it can ask for external historical GDP inputs.

[khaeru]

Good idea!

self.s.par("historical_activity", {"technology":"GDP"})

Is having a specific "technology" set element with the ID "GDP" a generic feature of message_ix/MESSAGE-MACRO, or something particular to the MESSAGEix-GLOBIOM model family? The latter case would make it a little harder (not impossible) to have a generic implementation.

[khaeru]

Working on #719, I think the solution here is to provide an example in the docs and maybe a test. The example code should essentially:

• Load MACRO calibration data, e.g. from a file.
• data["historical_gdp"] = scenario.par("historical_activity", filters={"technology": "GDP"}) —and mention that the user is free to create a "historical_gdp" parameter or retrieve this from wherever else they like.
• scenario.add_macro(data).