Questions tagged [cplex]
Questions related to the commercial solver IBM ILOG CPLEX Optimization Studio.
147
questions
2
votes
2answers
155 views
CPLEX output log
Whats the difference between MIP solution and Final Solve? I am trying to benchmark some solution approaches and I am not sure which of those is the more significant... sometimes they have the same ...
-1
votes
1answer
94 views
GAMS CPLEX solver solves big problem instances suspiciously fast
I am having trouble with my Problem Instances, which seem to be not "complicated" enough..
Is there a way to find out what the problem is? It is being solved in a matter of seconds even if ...
4
votes
1answer
60 views
splittable multicommodity problem with CPLEX
I am working on a splittable multicommodity flow problem, where each commodity can be split into k orders. However, I don't know the value of k in advance. Here is my code.
...
9
votes
2answers
162 views
Objective Integrality Cuts
Consider a mixed integer linear program with an objective function that includes only integer variables. Objective integrality cuts are known as a class of valid inequalities that can be added to ...
2
votes
2answers
101 views
Constraint to handle the machine-configuration's change between initial position and its first occurrence in the process
I am working with a kind of a reconfigurable process planning, meaning that the same machine can have different configurations and perform multiple operations. Each machine has an initial ...
3
votes
1answer
241 views
Why does the getTime() function from cplex concert returns wrong value?
I am running a MILP formulation (implemented in C++) with the Cplex Concert Technology 12.10, and I am trying to get the total elapsed time. So till the moment, I have tried three approaches:
Be ...
3
votes
1answer
86 views
Bioinformatics / Genomics Optimization Problems?
I am a third year bioinformatics student and would like to apply my knowledge from an introductory course in Optimization Methods to some problems in the field of genomics or bioinformatics.
Do you ...
1
vote
1answer
40 views
Get array of sequences for array of interval arrays in OPL
So I want to define multiple sequences (an array of them).
I have this:
...
2
votes
2answers
183 views
implementation of heuristics using C++ to solve operations research problems
can anyone suggest some good books with the implementation of heuristics and matheuristics using C++ to solve operations research problems especially routing problems such as TSP and VRP. also, I need ...
18
votes
4answers
3k views
What are the advantages of commercial solvers like Gurobi or Xpress over open source solvers like COIN-OR or CVXPY?
I come from an ML background, and occasionally have to dive into the OR world. I am trying to figure out whether I need to purchase a commercial solver license for a certain problem set.
In the ML ...
4
votes
1answer
282 views
MILP Minimum set Vertex cover coding by Python or MATLAB?
As a following up for my question for modeling a simple moded of the minimum set vertex cover problem, which is shown next. I would like to have your help in modeling this problem using Python or ...
3
votes
1answer
192 views
How do I interpret the CPLEX Optimization Studio MIP gap output?
I'm having difficulties understanding my FlowControl output compared to what the Engine Log shows me.
My output from the FlowControl into the Scripting Log (yellow marks) is ...
0
votes
1answer
172 views
How to form math model to solve this problem using cplex
Hiring company has the following requirement within a year;
week 1 to 5: 20
week 6 to 20: 40
week 21 to 40: 35
week 41 to 60: 55
week 61 to 80:75
week 81 to 100: 60
Training time for an ...
1
vote
2answers
116 views
Issue with number of threads on Cplex
I'm solving a bunch of similar problems and I want to compare them. To do so, I need everything to run on one thread. Even by setting the number of threads to 1, the model still runs on 8 threads. Has ...
1
vote
0answers
50 views
Making distinct modifications on a model
How can I apply different modifications separately on a model? The example in CPLEX documentation shows how to make modifications on a single solved model. However, unlike this example, I want to make ...
3
votes
1answer
150 views
Implementation of Local Branching
I've been recently reading some papers where the authors use local branching specifically in Benders Decomposition (see for reference). Although I understand up to some extend how the algorithm works, ...
2
votes
1answer
76 views
Can CPLEX output LP solution with primal variables only?
CPLEX writeSolution method outputs both primal and dual variable values of a LP. I know how to parse through the solution file to extract specific primal variable ...
2
votes
2answers
333 views
How can I identify the reason that makes a MILP model hard for solvers such as CPLEX?
I'm solving a MILP model whose native lower bound (via linear relaxation) is very poor. We could provide a lower bound by providing a given value (derived based on the problem itself). I know that ...
7
votes
2answers
504 views
How can I implement a user-written lazy constraint callback in concert CPLEX with C++?
I am trying to implement a user-written lazy constraint callback in concert CPLEX with C++. Although I know there exists a way to implement callbacks in concert CPLEX with C++ via macros, I am looking ...
3
votes
1answer
175 views
Semi continuous constraints in CPLEX Python
I have a semi-continuous optimization problem reformulated as a MIQP optimization problem.
My objective has a quadratic form $x^{T}Qx$ and my $x_{i}$ are such as $x_{i} \in [m,M] \cup \{0\}$.
...
2
votes
0answers
53 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 ...
3
votes
1answer
40 views
How can I change decision variable type in Concert Technologies (with Java)
I have a MILP model with continuous variables ($y_{ij}$) and binaries ($x_{ij}$).
I am using Java and cplex 12.8 for implementation.
Is there a way by which - using the Java-cplex API - I would be ...
3
votes
1answer
104 views
Benders implementation on Cplex is very slow
I'm working on a location problem and I have an issue with the Benders decomposition. I'm using Cplex with Python. I coded a single cut and a multi-cut to compare.
The single-cut implementation takes ...
1
vote
0answers
50 views
CPLEX keeps restarting in Pyomo
I tried running my model by adding the following settings to CPLEX.
...
7
votes
1answer
168 views
CPLEX MIP warm start seems slow down the program?
I have been working on a combinatorial optimization problem which can be modeled as an integer linear programming. I implemented it as a c++ project in visual studio 2017 and CPLEX1271. With the hope ...
5
votes
2answers
187 views
How to linearize a quadratic constraint to add it then via a callback function
Suppose we have a positive continuous variables $0 \le x \le UB$ where $UB$ is a known upper bound.
How can we linearize the term $x^2$?
Detailled problem:
Suppose that via a callback we compute a ...
3
votes
1answer
187 views
CPLEX Python API Manual with References
I am currently attempting to code a model using the Python API.
However, the IBM Site seems to not have one that is similar in formating and content depth such as those for C++ or Java (examples and ...
2
votes
1answer
96 views
Problem with implementing squared terms in the objective function
I'm trying to implement either one of these objective functions, but I'm having a hard time with the squared terms. I'm attaching both so you can take a look at the structure and see if you can give ...
11
votes
2answers
414 views
CPLEX Auto-Benders: How do I get the number of optimality and feasibility cuts?
I am using CPLEX's 12.9 auto-Benders decomposition feature (from the CPLEX Java API). Following the documentation I let CPLEX decide the decomposition strategy as
...
8
votes
1answer
301 views
Optimization software for ARM Architecture
Given that tomorrow Apple will likely announce the first ARM Macs (per bloomberg), I was wondering what the current status of ARM support in optimization software. For instance, does anyone know if ...
1
vote
2answers
2k views
Downloading and setting up CPLEX for Pyomo
I have just installed Anaconda and am intending to use Spyder as it is able to display variable, parameter values for debugging. After which, I am planning to use Pyomo to code my MIP model and invoke ...
3
votes
2answers
139 views
Using R for coding Matheuristic for Research Publication
Given that R possesses superior data pre-processing and post-processing packages, I am thinking of coding a matheuristic using R for publishing in an academic research journal.
However, I am unable ...
2
votes
1answer
118 views
How to determine whether the solution is integer feasible in a CPLEX heuristic callback?
I am working with a MILP formulation of a routing problem using Concert CPLEX 12.10. And I am implementing a greedy heuristic that uses the variables fractional values to attempt to construct an ...
9
votes
1answer
362 views
Integrating genetic algorithm (or other heuristic methods) with CPLEX
[Topic to discuss GA and CPLEX]
I've seen some papers trying to integrate genetic algorithm with CPLEX, such as here and here. Although they integrated both, it is done in 2 different steps; that ...
1
vote
1answer
82 views
Cplex giving different solutions for equivalent Linear problems
I'm trying to simplify a linear problem by removing "useless" variables and constraints.
After simplifying my initial problem and solving both instances with Cplex, it seems like the results differ ...
2
votes
2answers
175 views
How to use tight upper and lower bounds to get to the optimal value via branch and bound?
I have algorithms that get me a tight upper (UB) and lower (LB) bound to a maximization binary integer program (a routing problem). My formulation is non-compact and requires the addition of sub-tour ...
2
votes
1answer
135 views
shortest path problem,I want to write constraints in closed form
the constraints in the photo ,I need to translate to the closed-form I don't know how can I do this.
Can you help?
I need to write the mod file and dat file in Cplex for this problem
1
vote
0answers
71 views
Ways to improve lower bounds while solving MIPs
What are the ways to improve lower bounds while solving a minimization problem (MILP)?
3
votes
1answer
225 views
Cplex : The cutting stock problem
The problem below aims to minimize the cutting leftovers from each cut :
A company manufactures desks for kids gardens and primary schools, colleges and high schools. The leg of these deks all have ...
5
votes
3answers
206 views
Problem with binary decision variable constraints in VRP
I would like to create non-linear violation costs in my VRP. I already created my whole VRP with time windows in which I have these decision variable:
...
2
votes
1answer
205 views
Nested set in OPL/CPLEX
I'm trying to solve a scheduling problem using OPL/CPLEX. In the model, there are nine tasks in which each task has its specific precedence. the precedence relationship is as follows:
...
1
vote
1answer
77 views
5
votes
3answers
450 views
How can I represent null or dashes in a cost matrix or incidence matrix in CPLEX?
In the image below, the cost matrix of customers and supplier has several dashes which indicates the impossibility of certain suppliers with certain customers. How can I represent these dashes in ...
7
votes
1answer
124 views
Duals in CPLEX generic callback
When using a generic callback in the "relaxation" context, it is fairly clear how to get values of the primal variables in the LP relaxation (along with a bunch of other stuff), but I can't seem to ...
0
votes
1answer
260 views
What is wrong with my linear programming model?
I tried solving this problem
Here is my cplex code
I have mentioned stored[month] as float+ but in the final result I get negative values. What is wrong with my model?
5
votes
1answer
425 views
Where can I find resources to learn mathematical modelling for real life operation research problems like combinatorial optimization?
I find it hard to form math models for real life operations research problems, how can I learn this? Any books, tutorials available?
2
votes
1answer
132 views
How to formulate logical or constraint in cplex?
How to write the following constraint in cplex?
the cost for full truck load is $700
and the cost of fractional truck load is \$800 *fraction up to $700
4
votes
1answer
497 views
How to read a solution file (.sol) in cplex python API?
I've been to trying to read a .sol file in cplex python API before solving the problem but couldn't find any command to do so. There are analogous commands for this ...
8
votes
1answer
204 views
Can Gurobi or CPLEX handle nonlinearly constrained problems?
Though my title is quite general (please feel free to edit), indeed, I wonder if the following models can be solved in Gurobi or CPLEX. Model 2 is just an alternative one to Model 1. Although we ...
4
votes
1answer
104 views
Constraint programming in OPL: intervals covering time slots
I am trying to model the following:
There is a shop open from xx AM to yy PM.
In each 30 min time slot, there have to be demand[timeSlot] = x employees present.
E.g. the shop is open from 08am to ...
