On Fri, 18 Mar 2011 22:43:03 +0300 Andrew Makhorin <[email protected]> wrote: > > It may take a little while to get the "glp_write_prob" output > because I > > don't access to the computer resources needed to re-run these > examples > > (they were run by a colleague on a parallel research cluster) but I > do > > have a printout the LP coefficient matrices that caused a problem. > I'm > > including a number of these instances. Note that I'm not printing > out > > the last row, the last column, nor the r.h.s. because they are the > same > > for every LP of a given size. The last column contains a -1.0 in > every > > entry except the lower-right corner entry which is a zero. The > last > > constraint row contains a 1.0 in every entry except the lower-right > > corner which again is a zero. Every constraint row except the last > is > > <= 0 (in glpk form, you add an artificial variable and have the > > constraint = 0). The last constraint is = 1.0. All of the output > was > > generated by the application program except for two lines that were > > output by glpk saying that it was unable to factorize the basis > matrix > > and that basis recovery hadn't been implemented yet. The fifth and > > seventh LPs listed below were the only two in which there wasn't > two or > > more identical constraint rows. Sorry about the mail facility word > > wrapping the longer constraint rows; there doesn't seem to be a way > to > > avoid it. If this information isn't sufficient and you really need > to > > see the output from glp_write_prob, let me know and I'll get that > to > > you when I can. Thanks very much for your time. > > It seems to me that the error in solution is caused by some other > reason, at least not by linearly dependent rows. Since all your > instances are of small size, I'd recommend the following: remove any > calls to glp_scale_prob, and every time you need to solve a newly > generated lp instance, call glp_std_basis and then glp_simplex with > the > lp presolver disabled (don't forget to check the return code from > glp_simplex). If the error will not disappear, please post me the > instances written in cplex lp or glpk format. Thanks.
removing the call to glp_scale_prob fixed the problems! When we initially ran into these error, we made two changes; reset tiny numbers that are effectively zero to exactly zero and add the call to glp_scale_prob. Removing the scaling and leaving in the resetting of "effective zeroes" solves the problem. :-) Thanks for your suggestions. -- Glenn C. Rhoads _______________________________________________ Help-glpk mailing list [email protected] http://lists.gnu.org/mailman/listinfo/help-glpk
