Re: [Help-glpk] What does this mean?

[Andrew Makhorin]

> Hello, when I solve a problem, "PROBLEM HAS NO PRIMAL FEASIBLE SOLUTION"
> appeared immediately after the "Model has been successfully generated".
> But the problem should be calculated for a little time. Dose it mean that
>  my model is not correct?

This only means that your problem is primal infeasible, i.e. it has
no primal feasible solution. If you are in doubt, you can disable the
lp presolver with the option '--nopresol'.

> Another question is what does the sentences mean when glpsol solve the
> problem, such as this:
>     800: obj =  1.051500000e+002  infeas = 3.231e+001 (25) 
>    1000: obj =  1.403333333e+002  infeas = 8.000e-001 (2) 
> *  1038: obj =  1.379333333e+002  infeas = 5.157e-015 (1) 
> *  1200: obj =  7.906666667e+001  infeas = 4.151e-015 (0) 
> *  1225: obj =  7.820000000e+001  infeas = 5.274e-016 (0) 
> OPTIMAL SOLUTION FOUND 
> Integer optimization begins... 
> +  1225: mip =     not found yet >=              -inf        (1; 0) 
> + 30729: >>>>>  7.820000000e+001 >=  7.820000000e+001 < 0.1% (324; 0)
> + 30729: mip =  7.820000000e+001 >=     tree is empty   0.0% (0; 647) 

At first glpsol solves the lp relaxation with the simplex method,
and then, once optimal basic solution to lp relaxation has been found
(the line "OPTIMAL SOLUTION FOUND") it calls the mixed integer optimizer
to find integer optimal solution (the line "Integer optimization
begins..."). For more details see the glpk reference manual included
in the distribution. See also:
http://lists.gnu.org/archive/html/help-glpk/2007-06/msg00060.html