Optimization Question Pollution Taxes

[mbr1818]

Dear Forum,

I am running the EPAUS9rT TIMES-MARKAL model, which tracks the emissions of CO2, SO2, PM2.5, and NOx.
When I implement a tax for the entire time horizon on SO2, PM2.5, and NOx simultaneously the model solves and reaches an optimal solution. When I tax PM2.5 alone the model also solves.

However, when I tax NOx or SO2 alone, the model does not find an optimal solution. This seems strange to me. Any insight on why this may be occurring and what I may do to trouble shoot this problem?

Thank you,

Mike

[Antti-L]

You are not very clear what you mean by "the model does not find an optimal solution". If the solver reports the model as "proven infeasible", then it is indeed very strange. Merely adding some more (positive) objective function coefficients to a model does not affect its feasibility, unless some constraints are also being changed. But if the solver gets into numerical difficulties and just cannot reach optimality, it is not at all so strange. If the model is badly scaled or it has some redundant equality constraints, numerical problems may arise in a "random" manner.

For some suggestions for troubleshooting scaling issues, see:
http://iea-etsap.org/forum/showthread.php?tid=162