Hello Andrew, GLPK is a linear programming solver. A constraint with an IF would not be linear.
In linear programming you might introduce binary variables for your purpose. Or use a constraint programming solver. Best regards Heinrich Schuchardt http://www.xypron.de Am 07.05.13 um 07:48 schrieb Jay Hutfles > Oh, I don't think there's anything wrong with them. Well, except for how > > I'm trying to use them. > > > > I see that the examples only use them in computable parameters, though. I > > was trying to use them in constraints, and was getting errors along the > > lines of "forall function does not exist" (sorry, I don't have the exact > > error with me). The constraints were of the form: > > > > for all a in A, if x[a] =1 then there exists a b in B such that > > (something or another based on a) > > > > I was having trouble directly implementing constraints of this form, so I > > changed the "if p then q" form to "not p or q" like this: > > > > subject to C {a in A} : > > (1 - x[a]) + (if exists {b in B} (...something or other based on a..) > > then 1 else 0) >= 1; > > > > I'll have to try again in the morning when I'm more awake. Thanks for the > > guidance, Andrew. > > > > > > > > On Mon, May 6, 2013 at 11:36 PM, Andrew Makhorin <[email protected]> wrote: > > > > > > > > > Can you provide a link to an example of each? Any help would be > > > > appreciated. > > > > > > > > > > Please see glpk/examples/color.mod (for 'exists') and > > > glpk/examples/egypt.mod (for 'forall'). > > > > > > What is wrong with these operators? > > > > > > > > > > > _______________________________________________ > > Help-glpk mailing list > > [email protected] > > https://lists.gnu.org/mailman/listinfo/help-glpk _______________________________________________ Help-glpk mailing list [email protected] https://lists.gnu.org/mailman/listinfo/help-glpk
