Unanswered Questions
41 questions with no upvoted or accepted answers
2
votes
0
answers
268
views
Building model takes so much time in Cplex
I am a beginner in CPLEX. I have a model with about 1 million constants and 800k rows and 1.6 million columns. I implemented in both GAMS and CPLEX (C# as the platform). The final solution for both is ...
- 4,037
2
votes
0
answers
117
views
How to implement CPLEX user cuts using CPXaddusercuts in C API?
I am trying to use CPXaddusercuts to add cutting planes, which have not been violated yet but are likely to be violated as we go down the branch & bound tree, to the list (pool) of constraints. As ...
2
votes
0
answers
122
views
how to convert type of variable in CPLEX
I have an Integer Linear Problem which is solved quickly when I change my variable type to double. now I'm developing a fix and relax algorithm and I used conversion to change data type which takes a ...
- 8,677
1
vote
0
answers
48
views
Approximate Solutions and Solver Settings in CPLEX and Gurobi
CPLEX offers functionalities to approximate solutions for nonconvex optimization problems rather than guaranteeing global optimality. It includes an option to find solutions satisfying first-order ...
1
vote
0
answers
73
views
Getting error in callback (lazy constraints) for docplex with Python to solve MILP
I am trying to use lazy constraints to solve my MILP problem. The details are given as follows.
...
- 9,068
1
vote
0
answers
83
views
CPLEX gets stuck in "Performing restart"
During solving my problem using generic lazy cuts (in Benders decomposition fashion), the solver gets stuck logging out "Performing restart 2" for several hours (while the time limit is 30 ...
- 1,895
1
vote
0
answers
37
views
Calling Cplex from R through a MPS-like file
I have a working - and long - R code to generate a mps file to be read by cplex.
Because I work with large instances I am finding troubles (too much time) in producing a large mps file.
Is there a way ...
- 1,895
1
vote
0
answers
89
views
Weird behavior when using Automatic Benders Decomposition in CPLEX
I've encountered some weird behavior when using the Automatic Benders Decomposition in CPLEX.
I initially solved the MIP without BD and then I compared the results against the Full, Workers and User ...
- 1,895
1
vote
0
answers
92
views
Linearization of Conditional Constraints for MIP using Cplex
I'm currently working on a mixed-integer programming (MIP) problem and I'm trying to implement a set of conditional constraints in CPlex. These constraints involve decision variables that are indexed ...
- 1,895
1
vote
0
answers
85
views
Information about number of simplex and barrier iterations in OPL CPLEX
I would like to know how can I obtain the exact number of simplex and barrier iterations used by CPLEX in OPL. The solution reports the total number of iterations but I want them to be separated (...
- 5,874
1
vote
0
answers
51
views
CPLEX OPL - Problem of arrangements and increments
I have a problem involving work shifts and assembly stations.
Work shifts have the subscript = T
Workstations have the subscript = J
My decision variable is X[t][j]
For each turn (T) I am trying to ...
- 11
1
vote
0
answers
147
views
User callback doing nothing slows down Cplex
I am trying to do something with user callbacks in Cplex using Python API. For instance, I will need a callback that only counts the number of explored nodes.
While testing something I noticed that ...
- 251
1
vote
0
answers
384
views
How to make unconstrained variables non-negative (as in excel solver) in AMPL?
This is a sequencing problem.
I've got this variables
...
- 1,895
1
vote
0
answers
310
views
CPLEX callback in pyomo
I am trying to figure out what is the correct use of cplex callbacks in pyomo. In particular I am looking for the translation of the following example from gurobi to cplex:
...
1
vote
0
answers
485
views
CPLEX ignores a feasible solution given as start one
Assume we have 100% feasible solution for the model with decision variable a[i].
Then we are changing the objective function on something similar to ...
- 5,874