On Tue, 22 Sep 2009, Sam Seaver wrote: > Yes, I can say that the problem is almost infeasible. I also removed > the column, and applied its constraints directly to the rows involved, > and got the same almost infeasibility for some of these rows. > > As it happens, three of these rows are very highly used (this is a > large problem, 7000+ columns, 3000+ rows), and affording the > constraints of the rows some of the same slack means I get an optimal > solution.
You might want to look for a way to reformulate. Even scaling can sometimes have a consierable effect. > I read somewhere that my version of glpk may be too old to deal with > these inflexible constraints, I use 4.29, should I upgrade? Probably it wouldn't hurt. I don't know how much improvement has gone into the solver and how much into the bells and whistles. Even with a good solver, it can sometimes be hard to tell whether a basis corresponds to a feasible solution. -- Michael [email protected] "Pessimist: The glass is half empty. Optimist: The glass is half full. Engineer: The glass is twice as big as it needs to be." _______________________________________________ Help-glpk mailing list [email protected] http://lists.gnu.org/mailman/listinfo/help-glpk
