Unanswered Questions
41 questions with no upvoted or accepted answers
6
votes
0
answers
651
views
Cplex is stuck after root node relaxation solution
I am solving an MIP through Benders decomposition (coded both generic and legacy callback versions), by employing Java with Cplex 12.9. For some of the instances, Cplex is stuck for two hours (time ...
- 5,442
5
votes
0
answers
124
views
Scale of largest CPLEX/Gurobi execution
I am trying to understand the CO2 emission of large scale optimization using CPLEX or Gurobi. Is there a published literature which addresses the compute usage of large scale executions?
- 1,895
4
votes
0
answers
159
views
4
votes
0
answers
385
views
CPLEX Python: Current subproblem model in branch and bound
I have an MILP problem and use CPLEX (Python interface). I am working on user heuristics for branching in the branch-and-bound procedure. With HSCallback I managed to get the information about the ...
- 251
3
votes
1
answer
210
views
Implementing Logic-based Benders decomposition on a single search tree
Currently, I am working on a scheduling problem and trying to approach it by the logic-based Benders decomposition method. Theoretically, I have everything, i.e., the master and sub problem(s), the ...
CommunityBot
- 1
3
votes
0
answers
101
views
cplex callbacks: getting the branching variable
I would like to obtain the number of the variable cplex branches on at the current node during B&B.
I try this by using the callback
...
- 75
2
votes
0
answers
156
views
Why the column generation algorithm remains stuck at the same solution?
I was trying to solve a MILP by a column generation algorithm, and I noticed that the algorithm was stuck at the same solution, I tried to diversify the pool of initial columns, but the problem I ...
- 429
2
votes
0
answers
107
views
Automated Benders Using Annotations
I'm trying to solve an optimization model using Automated Benders with annotations using CPLEX library in C++. I've defined a master problem and N (number of supply nodes in my model's network) ...
- 1
2
votes
0
answers
67
views
Discrepancy between CPLEX interface solution and C API
I have a C API program uploaded here in Dropbox that is an LP. Here is the problem: When I compile the C file it gives me "1017 Not available for mixed-integer problems" while the problem is ...
- 5,874
2
votes
0
answers
94
views
MIP start in cplex using Java
When I am reading an "lp" file for the problem and using a MIP start reading from a "sol" file it works.
But when I pass on the same model directly to cplex (without writing lp) ...
- 5,874
2
votes
0
answers
64
views
Where is the relative gap from cplexbilp?
I am invoking cplexbilp (CPLEX 12.9) from Matlab R2022a. I request all 4 return arguments:
...
- 223
2
votes
0
answers
135
views
Defining a highly non-linear function of integer variables
I have a complicated non-linear objective function of positive integer variables subject to linear constraints:
$\mathop {Min}\limits_{\underline x} f(\underline x)$
s.t.
$A\underline x\leq \underline ...
- 1,895
2
votes
0
answers
116
views
Achieve true determinism in CPLEX
I'm unable to achieve true determinism in CPLEX (I'm using the DOCplex python API).
Even if the best integer optimal solution is found without going to timeout (so it is expected to be unique), two ...
- 91
2
votes
0
answers
77
views
Making multiple branches in make_branch function of Cplex
In my current python code, I have used MyBranch call back of Cplex to make 2 branches and solve my model.
However, I now need to generate 4 branches after the first incumbent is generated. I need ...
- 1,895
2
votes
0
answers
271
views
Pyomo + Cplex - OSError: [Errno 22] Invalid argument
I am trying to get Cplex working with pyomo.
I have followed Cplex installation instructions has explained here: Downloading and setting up CPLEX for Pyomo
However when calling Cplex via pyomo I get ...
CommunityBot
- 1
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