I think I am doing something wrong in the application of elasticity variables on each row. The non zero coefficients of the constraints matrix should contain exactly elasticity variables additional non-zeros. The logs seems to violate this
>>> 450946+220038 !=642201 Regards, Rabih Le 24 janv. 2013 à 18:41, Rabih Chaar <[email protected]> a écrit : > Hello, > Thanks for the quick reply. > Concerning your recommendation on checking my objective coefficients, I was > also outputting my relaxed problem in cplex, and everything seems fine. > > I am not having this behavior on all instances of the problem. For others I > am getting the sinf not null. > > My goal is to implement an algorithm giving a minimal iis if the problem is > infeasible, hence the relaxation. This is done programmatically via the glpk > API, making a copy of the problem, adding the additional elasticity > variables, setting there objective coefficients to one, setting the objective > coefficients of initial variables to zero, and adapting row constraints with > the elasticity variables. I will check my code again. > > I wanted to be sure that the primal simplex (on the initial problem) will > always find a feasible domain if it exists. > > Thanks in advance. > > Rabih > > Le 24 janv. 2013 à 14:40, Andrew Makhorin <[email protected]> a écrit : > >> >>> PS: here is a small log of both problems >>> >>> GLPK Simplex Optimizer, v4.47 >>> 191255 rows, 68860 columns, 450946 non-zeros >>> 0: obj = 0.000000000e+000 infeas = 5.436e+009 (28783) >>> ... >>> 17761: obj = -8.927238865e+008 infeas = 2.030e+007 (14520) >>> PROBLEM HAS NO FEASIBLE SOLUTION >>> >>> Elasticity >>> Addtional constraints 220038 for 191255 rows >>> Current column size is 68860 >>> Additional Constraints 220038 >>> Current column size after resize is 288898 >>> GLPK Simplex Optimizer, v4.47 >>> 191255 rows, 288898 columns, 642201 non-zeros >>> 0: obj = 0.000000000e+000 infeas = 5.436e+009 (28783) >>> ... >>> * 1552: obj = 0.000000000e+000 infeas = 1.490e-008 (28782) >>> OPTIMAL SOLUTION FOUND >>> Sinf is 0 >> >> BTW, in the second case the objective (Sinf, I guess) is zero on all >> iterations. Probably you forgot to assign objective coefficients to >> elastic variables. > > _______________________________________________ > 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
