Adding the option to solve concurrently for all regions in MACRO

[daymontas1]

This PR introduces the option to solve for all regions concurrently in MACRO. A parameter (''solve_param'') has been added to ''MESSAGE-MACRO'' to control the solving mechanism for MACRO. Setting ''solve_param'' to 1 (the default value) triggers sequential solving across regions, whereas setting it to 2 enables concurrent solving.

An if statement has also been introduced in ''macro_solve'' that dictates whether sequential or concurrent solving is applied in MACRO, based on the value of the ''solve_param'' parameter defined in ''MESSAGE-MACRO_run''. The default solving is sequential (''solve_param''=1), so if the user doesn't update the solving mechanism, MACRO is solved as it used to be. In terms of efficiency, the concurrent solving is subtly more efficient.

For the concurrent solving mechanism (''solve_param''=2), all nodes are activated from the beginning, thereby enabling simultaneous solving for all regions. This setting allows for factoring in interregional interactions into the optimization process. We want this concurrent optimization option, as we intend to incorporate interregional feedback mechanisms into MACRO, e.g., interregional investments. Given that in the current version of MACRO regions are independent, both solving mechanisms should produce the same results.

How to review

Required: It must be verified that both versions produce the same results (considering there are no interregional interactions in the current version of MACRO).

If the changes are accepted, the model's documentation must be updated to include the concurrent option and instructions on how to trigger it. Additionally, it may be worthwhile to consider making the concurrent solving mechanism for MACRO the default, in case it reduces solving times.

PR checklist

• [ ] Continuous integration checks all ✅

• [x] Add or expand tests; coverage checks both ✅
• [ ] Add, expand, or update documentation.

• [ ] Update release notes.

[CLAassistant]

All committers have signed the CLA.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 95.4%. Comparing base (c359123) to head (376e97f). Report is 1 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #808 +/- ## ======================================= - Coverage 95.4% 95.4% -0.1% ======================================= Files 46 46 Lines 4354 4354 ======================================= - Hits 4156 4155 -1 - Misses 198 199 +1 ``` [see 1 file with indirect coverage changes](https://app.codecov.io/gh/iiasa/message_ix/pull/808/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=iiasa)

[glatterf42]

Thanks for this PR @daymontas1 :)

Currently, all test failures complain about a GAMS compilation error:

FAILED message_ix/tests/test_macro.py::test_calc_valid_years - ixmp.model.base.ModelError: GAMS errored with return code 2:
    There was a compilation error

For details, see the terminal output above, plus:
Listing   : /Users/runner/work/message_ix/message_ix/message_ix/model/MACRO_run.lst
Log file  : /Users/runner/work/message_ix/message_ix/message_ix/model/MACRO_run.log
Input data: /Users/runner/work/message_ix/message_ix/message_ix/model/data/MsgData_Westeros_Electrified_test_calc_valid_years_macro.gdx
FAILED message_ix/tests/test_macro.py::test_calc_data_missing_ref - ixmp.model.base.ModelError: GAMS errored with return code 2:
    There was a compilation error

For details, see the terminal output above, plus:
Listing   : /Users/runner/work/message_ix/message_ix/message_ix/model/MACRO_run.lst
Log file  : /Users/runner/work/message_ix/message_ix/message_ix/model/MACRO_run.log
Input data: /Users/runner/work/message_ix/message_ix/message_ix/model/data/MsgData_Westeros_Electrified_test_calc_data_missing_ref_macro.gdx
FAILED message_ix/tests/test_macro.py::test_calibrate - ixmp.model.base.ModelError: GAMS errored with return code 2:
    There was a compilation error

For details, see the terminal output above, plus:
Listing   : /Users/runner/work/message_ix/message_ix/message_ix/model/MACRO_run.lst
Log file  : /Users/runner/work/message_ix/message_ix/message_ix/model/MACRO_run.log
Input data: /Users/runner/work/message_ix/message_ix/message_ix/model/data/MsgData_Westeros_Electrified_test_macro_calibration.gdx
FAILED message_ix/tests/test_macro.py::test_calibrate_roundtrip - ixmp.model.base.ModelError: GAMS errored with return code 2:
    There was a compilation error

For details, see the terminal output above, plus:
Listing   : /Users/runner/work/message_ix/message_ix/message_ix/model/MACRO_run.lst
Log file  : /Users/runner/work/message_ix/message_ix/message_ix/model/MACRO_run.log
Input data: /Users/runner/work/message_ix/message_ix/message_ix/model/data/MsgData_Westeros_Electrified_test_calibrate_roundtrip_macro.gdx
FAILED message_ix/tests/test_macro.py::test_sector_map - ixmp.model.base.ModelError: GAMS errored with return code 2:
    There was a compilation error

For details, see the terminal output above, plus:
Listing   : /Users/runner/work/message_ix/message_ix/message_ix/model/MACRO_run.lst
Log file  : /Users/runner/work/message_ix/message_ix/message_ix/model/MACRO_run.log
Input data: /Users/runner/work/message_ix/message_ix/message_ix/model/data/MsgData_Westeros_Electrified_test_sector_map_macro.gdx

If you run these tests on your system, do they work? If not, could you please try troubleshooting what's blocking them from working?

[daymontas1]

@glatterf42 The error arises because the tests cannot read ''solve_param'' when it is defined in ''MESSAGE-MACRO_run.gms''. As a result, an error occurs in ''model_solve'' since the solving mechanism is dictated by ''solve_param''. However, when ''solve_param'' is defined within ''macro_data_load.gms'', the tests are successful. Therefore, ''solve_param'' should be defined in ''macro_data_load.gms'' instead of ''MESSAGE-MACRO_run.gms''.

[khaeru]

I've updated the PR description to re-add the checklist that appears in the PR template.

If, for a certain PR, one feels that certain items in the checklist are not necessary, ~use strikeout~ and put a note to explain why. In this case, however, I do think documentation and an entry in the release notes are needed.

If the branch contains "Merge …" commits, we use squash-and-merge; if it is rebased and these disappear, we can use an ordinary merge.