Re: GMPL/GLPK display objective function value

[Domingo Alvarez Duarte]

Hello Andrew !

Again thank you very much for your help !

After replying to your comments I reviewed again the wikibook link 
(https://en.wikibooks.org/wiki/GLPK/Troubleshooting#Objective_shift_term_ignored_when_exported) 
and realized that somehow I've got lost because of the of the misleading 
AMPL result and both solvers report of the objective value.

Also I think that like in the exported LP file we get a comment about 
the constant term, the solution file also somehow should have a comment 
about it.

So in this case AMPL has a bug.

I think that this function (and similares) should have a return value 
that could tell about this:

====

void glp_mpl_build_prob(glp_tran *tran, glp_prob *prob)

to

int glp_mpl_build_prob(glp_tran *tran, glp_prob *prob)

{

int ret = 0;

...

if (mpl_get_row_c0(tran, i) != 0.0) {
            xprintf("glp_mpl_build_prob: row %s; constant term %.12g ig"
               "nored\n",
               mpl_get_row_name(tran, i), mpl_get_row_c0(tran, i));

            ret = WARNING_CONST_TERM_IGNORED;

}

...

return ret;

}

====

Cheers !

On 29/8/20 11:01, Domingo Alvarez Duarte wrote:
> Hello Andrew !
>
> Thanks for reply !
>
> The problem is that the GMPL is not informed/knows anything about the 
> warning/divergence in the results and goes blindly.
>
> Te exit code of glpsol also doesn't reflect anything that could be 
> detected, only by visual inspection of the output or redirect the 
> output and scan it for possible warnings.
>
> Somehow GMPL should have a way to acknowledge situations like these.
>
> ===
>
> >Exit code: 0
>
> ===
>
> Cheers !
>
> On 29/8/20 0:46, Andrew Makhorin wrote:
> > > While trying to implement multi solve statements I found that in GMPL
> > > the display of an objective function after solving do not show the
> > > optimal value.
> > BTW, glpsol warns about that:
> >
> > [...]
> > 38 lines were read
> > Generating Reduced_Cost...
> > Generating Width_Limit...
> > Model has been successfully generated
> > glp_mpl_build_prob: row Reduced_Cost; constant term 1 ignored
> > [...]