[Help-glpk] A suggestion concerning a new option

[Pietro Scionti]

Hi,
I'm working with the code in these days to add a new option, that I tentatively 
called "outlp": it allows the user to write the solution of the LP relaxation 
to file, before entering the MIP solver.
It is a feature I would really like to see implemented: I mostly work with hard 
instances (unfortunately), and so sometimes when I see that the solver is not 
giving me an answer in a reasonable amount of time it is useful to at least 
work on the non-integer optimal solution.
The only way I know to do that now is use the --nomip option, save the solution 
to file and then solve everything back again without --nomip, which almost 
doubles the time spent.

The way I thought of it, I edited the routine glp_main, added a new member, 
"const char out_lp" to the csa struct and then triggered the lpx_print_sol in 
two different regions: for the no presolve case, in the problem solution region 
(the one which now starts at line 1032), after the glp_simplex call of glp_main 
(file glpapi20.c) and, for the presolve case, before the resolution of the 
transformed mip in the preprocess_and_solve_mip routine (around line 390), file 
glpapi09.c.
However, everything is not smooth yet, so before I waste any more time, do you 
think there is a cleverer way to do it? Or a workaround that doesn't involve 
cutting the code?

Thank you,
Pietro

PS: I noticed a couple of omittions in the manual, glpsol appendix: the 
--fpump, --nointopt and --mipgap options were missing and --cbg was repeated 
twice instead of --cgr. I attach the corrected .tex


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glpk10.tex
Description: glpk10.tex