[Help-glpk] post-processing without defined variables?

[Kevin Hunter]

Hello GLPK List,

I see from the GLPK Wikibook that there's no ability to create reporting 
variables (err, just learned that others call them "defined variables").

https://en.wikibooks.org/wiki/GLPK/GMPL_Workarounds#Mimicking_an_AMPL_defined_variable

I want to explore the last sentence in that section ("But you can use a 
structural variable and a constraint instead to achieve the same effect 
— the downside being that this formulation may render your problem 
harder to solve").  The models that I'm working with are necessarily 
large (roughly 1e5 [C] x 1e5 [R], give or take an order of magnitude 
depending on the input), and I'd like to avoid adding any more variables 
to the solver's matrix.

Given that I can't create constraints /after/ a solve statement (i.e. to 
re-solve starting from the previous solution), does that mean that my 
only option is a post-GMPL step with another tool (e.g. C, Perl, Python)?

Thanks,

Kevin