Search found 16 matches

by feifan
1 month ago
Forum: Solvers
Topic: Solvers cannot get a feasible solution for a feasible model
Replies: 0
Views: 306

Solvers cannot get a feasible solution for a feasible model

Dear All, When I tried to solve a feasible MISOCP model, the solvers cannot return a feasible solution even after 10 hours. The model is feasible for sure because it returns a solution when I fix some variables. I attached my model and data below, could someone help me figure out what was happening?...
by feifan
11 months ago
Forum: Syntax
Topic: why is the elapsed seconds smaller than the total seconds
Replies: 1
Views: 335

why is the elapsed seconds smaller than the total seconds

Dear GAMS users, I was trying to get the time required for solving the model. I got a step summary like this, STEP SUMMARY: 0.000 0.000 STARTUP 0.047 0.047 COMPILATION 0.547 0.547 EXECUTION 0.000 0.000 CLOSEDOWN 0.594 0.594 TOTAL SECONDS 0.593 0.593 ELAPSED SECONDS 5.191 5.191 MAX HEAP SIZE (MB) I r...
by feifan
1 year ago
Forum: Modeling
Topic: Speed up model generation time when using loop
Replies: 3
Views: 542

Re: Speed up model generation time when using loop

Hi, Fred, Thanks for your answers. In my model, parameters are updated according to the solutions obtained in the last iteration. So, we do not know the parameters in advance. I totally understand what you were referring to. I think the model generation time is acceptable to me because the model is ...
by feifan
1 year ago
Forum: Modeling
Topic: Speed up model generation time when using loop
Replies: 3
Views: 542

Speed up model generation time when using loop

Hi, all, I am using a loop function to calculate a model with adjustable parameters repeatedly. In each iteration, I change a part of the parameters in the model and solve it again. However, since my model is quite huge, it takes 5-6 seconds to implement model generation. In each iteration, GAMS has...
by feifan
1 year ago
Forum: Modeling
Topic: GAMS/CPLEX return infeasibility while DICOPT give a solution
Replies: 3
Views: 1154

Re: GAMS/CPLEX return infeasibility while DICOPT give a solution

Hi, Fred, thanks for your answers. I use the old version GAMS 24.5.6. Is the infeasibility issue caused by the old version? Unfortunately, I don't have license for the latest GAMS. Then, what am I gonna do? Kind regards, feifan Hi, What version did you use? With the latest GAMS 26.1.0/CPLEXD, Cplex ...
by feifan
1 year ago
Forum: Modeling
Topic: Cplex did not give optimal solution for MISOCP problem after removing a redudant constraint
Replies: 7
Views: 1149

Re: Cplex did not give optimal solution for MISOCP problem after removing a redudant constraint

thank you very much! Michael We got some answer on this. So it turns out to be a Cplex bug which can be easily worked around by setting good bounds to the free variables. Here is the original reply: I found the primary source of trouble, which probably occurred on this model but not previous ones be...
by feifan
1 year ago
Forum: Modeling
Topic: GAMS/CPLEX return infeasibility while DICOPT give a solution
Replies: 3
Views: 1154

GAMS/CPLEX return infeasibility while DICOPT give a solution

Hi, all, My model is a MISOCP problem. When I used GAMS/CPLEXD to solve the model, the solver returned infeasibility. However, when I fixed my binary decision variables as zero and solved it again using CPLEXD, it did give a feasible solution. Especially, the DICOPT solver could give a feasible solu...
by feifan
1 year ago
Forum: Modeling
Topic: Problem with integer infeasiblity
Replies: 1
Views: 393

Problem with integer infeasiblity

Hi, all, In my model, I have three kinds of decision variables, they are Y_l(n1,n2), X_z(zn), and belta(n1,n2); When I define these variables as positive continuous variables and fix them as zero (Y_l.fx=0; X_z.fx=0, and belta.fx=0), I got a obvious solution with all variables being zero. However, w...
by feifan
1 year ago
Forum: Modeling
Topic: Cplex did not give optimal solution for MISOCP problem after removing a redudant constraint
Replies: 7
Views: 1149

Re: Cplex did not give optimal solution for MISOCP problem after removing a redudant constraint

Hi Indeed, it is not the optimal solution, although you have this in the listing: MIP Solution: -375.869834 (1430 iterations, 15 nodes) Best possible: -375.869834 Absolute gap: 0.000000 Relative gap: 0.000000 If I use couenne or bonmin (both are free and global solvers), I get the "correct" answer....
by feifan
1 year ago
Forum: Modeling
Topic: Cplex did not give optimal solution for MISOCP problem after removing a redudant constraint
Replies: 7
Views: 1149

Re: Cplex did not give optimal solution for MISOCP problem after removing a redudant constraint

Hi Feifan How do you know that the solution is not optimal? Constraint 4 and 5 could have an impact on the choice of the variables. (It is hard to check without the Gams code). Cheers Renger Hi, Renger, I found out that if I fixed the decision variables as the values obtained without removing those...