Introducing a parameter (''solve_param'') 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 been introduced to allow users to select whether they want to solve sequentially or concurrently for all regions. This is determined by the ''solve_param'' parameter, defined in ''MESSAGE-MACRO_run''. The default solving is sequential (for ''solve_param''=1), so if the user doesn't update the solving mechanism, the macro is solved as it used to be. In terms of efficiency, the concurrent solving is slightly more efficient. 

For the concurrent solving mechanism (for ''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.

Introducing a parameter (''solve_param'') 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.

Defining ''solve_param'' in ''MESSAGE-MACRO_run.gms'' creates a problem in testing. Therefore, ''solve_param'' is defined in ''macro_data_load.gms'' instead.