Hi Joey!
The OPB export has (at least) one issue. However, I'm not sure if this is
related to your problem (I do not think so from what you are writing, but
still):
It is assumed that the coefficients are integers.
But, from your explanation it seems like all the coefficients are zero,
which is strange. Especially since you get an incorrect result when
removing the empty constraints. (Clearly it would be good to check if
there are any non-zero coefficients.)
One possible reason is that your model generates some dummy constraints
that breaks the model and that you also have fractional coefficients that
are not well handled by the export function leading to an incorrect
solution.
Regards
Oscar
On Fri, 29 Feb 2008, Joey Rios wrote:
Hello,
Using the --wpb flag to glpsol, I am getting an invalid OPB file as output.
The original input to glpsol is written in mathprog and is solved correctly by
glpsol, also, for the 0-1 problems in the GLPK examples directory all seem to
come out fine as OPB files (the ones I tried at least--sudoku, todd, and
something else) and are solved with a PB SAT solver just fine. The OPB file
that is output using my files has several lines that look like this:
<= 15
<= 15
<= 12
etc...
It is expected that there would be a LHS to these inequalities if they are
being printed at all. I looked at glplpx19.c which handles the writing of this
file. I added a simple fprintf statement before line 136:
if( k == 0 ) fprintf(fp, "k was zero");
where k was defined earlier as
k=glp_get_mat_row(lp, j, ndx, val);
The result was as expected, for each of the anomalous inequalities above I now
have lines like this:
k was zero<=15
So it looks like I have some rows where all coeff's are zero. I am not sure
how to interpret this. When I manually remove all of these inequalities from
the OPB file, my PB SAT solver (minisat+) is happy with the file, but produces
the wrong solution (i.e. different from the correct/expected result from
glpsol). So these inequalities are probably necessary to obtain the correct
solution.
I'm just a little lost as to where to start looking or how to interpret what
the problem is exactly. Any insight appreciated. I'm happy to provide more
info if it would be helpful.
Thanks,
Joey
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