Thanks again for the response.
> You could write your instance also in cplex format specifying the
> option '--wcpxlp outfile' along with '--wopb' and then check both
> the files. AFAIK cplex lp format is very similar to opb format.
>
I did as you suggested and it was quite illustrative. The formats are indeed
very similar. For my empty LHS constraints in OPB:
<= 15
<= 15
etc.
The cplex format has:
Departure_Rate(LAS,3): 0 w(AC12_11,DUMMY_DST,151) <= 15
Departure_Rate(LAS,4): 0 w(AC12_11,DUMMY_DST,151) <= 15
etc.
So it does look like these constraints are trivially satisfied if I am
interpreting the output correctly. So I guess that would be a good little
patch in the lpx_write_pb() function. Line 129 looks like this:
k=glp_get_mat_row(lp, j, ndx, val);
Immediately following this line I added:
if( k == 0 ) continue;
And the empty LHS inequalities went away. It may have broken something else
for all I know, but maybe Oscar could let us know if adding that line hurts
anything else.
I realized something else I had to do to the output OPB file for acceptance by
minisat+. For some reason, minisat+ doesn't like brackets or commas. This is
a problem since my binary variables are 3-dimensional and all have brackets and
commas in there respective names. This is clearly a minisat+ problem though
and not a GLPK issue. The reason I bring it up is that maybe I hurt the file
when I remove/replace these symbols with sed. I don't think I hurt the
integrity of the file, but will have to verify that. The only clue I have that
I may have damaged the file is the fact that I am still getting a different
solution out of minisat+.
But at least now I am pretty sure the problem isn't with glpk. If I discover
anything more regarding this issue, I'll be sure to update the thread for
posterity. Thanks for the help Andrew and Oscar.
Joey
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