Hi,
I am trying to use the summing function (over regions, periods and timeslices), and the results seems to tell me this funtion will add a non-negative constraint to related variables. Is that true and/or possible to change?
The thing is, I use the cumulative emissions as a constraint to generate mitigation scenarios, while the constrainted variable (i.e. CO2) has to stay positive (zero the lowest) no matter how limited the emission space is. In this case, the model cann't use negative-emission technologies BECCS, therefore I have trouble modelling the zero-emission / negetive-emission target.
Please let me know if I have misunderstanding here, or there is some other ways to realize this modelling. Thanks a lot!
Regards,
Huan.

By default, most variables are non-negative in TIMES (including VAR_COMNET and VAR_COMPRD). If you want to allow for negative CO2 emissions, you should define the corresponding variables free, or with sufficiently negative lower bounds. Usually defining a few VAR_COMNET variables free is sufficient (e.g. TOTCO2, GHG). A shortcut for defining -INF as the lower bound of VAR_COMNET(r,t,c,s) in each period is to set:
COM_BNDNET(r,'0',c,'ANNUAL','N')=-1;
In VEDA-FE, it would mean putting 0 in the Year column, and N in the LimType column in a ~TFM_INS table. Of course you can also directly set lower bounds (LO), but then you must choose some reasonable negative number (not too large in absolute value).

Just in case the previous post does not seem to help, some more information:
I have myself modelled scenarios with negative emissions for many years in TIMES, and I have not seen any problems with that, as long as I define the total net CO2 and GHG variables (VAR_COMNET) free, i.e. with negative bounds. However, if you are also referring to the VAR_COMPRD variables of the emissions in your model, then you may need to define those variables free as well (or having negative bounds).
Defining cumulative constraints on the emissions should not make any difference in that respect. Even if you use UC_CUMCOM, which creates new variables for cumulative amounts, TIMES automatically sets the lower bound of the cumulative variables to negative infinity, whenever the corresponding period-wise variables have been set with negative lower bounds. But if the problem persists, please provide some more info about the way you are defining the constraints and bounds.

Thanks a lot Antti-L!
I followed your instruction, and now it perfectly worked! I really appreciate your detailed explanation.
Best regards,
Huan.