> I have a small integer program whose optimal solution value is 49. > Root relaxation is 48.5454. Since all the variables are integer, one > expects it to stop when a solution with value 49 is found. Instead, > GLPK takes a long time to converge.
> I also tried lp-solve, it found an optimal solution quickly (less > than 0.1 second). Here is the output: > Optimal solution 49 after 72 iter, 34 nodes > (gap 0.0%). > Value of objective function: 49 > Branch Bound depth: 18 > Nodes processed: 34 > Simplex pivots: 72 > Number of equal solutions: 1 > I don #39;t think lp-solve is doing anything particular. It did not > generate cuts and just branched on the first fractional integer > variable. > An mps file is attached. I would appreciate if someone can explain why > it is taking so long. Most probably lp_solve detects integrality of the objective that helps it to finish the search once the gap becomes zero. A similar feature was implemented in earlier versions of the glpk mip solver, however, currently it is disabled due to some technical reasons. I would like to note that your mip instance is hard, and there is just a happy chance that the glpk solver (as well as lp_solve) finds the optimum on the first try. _______________________________________________ Help-glpk mailing list [email protected] http://lists.gnu.org/mailman/listinfo/help-glpk
