Questions tagged [cplex]

Questions related to the commercial solver IBM ILOG CPLEX Optimization Studio.

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2
votes
1answer
71 views

Minimizing a quadratic binary nonconvex function by CPLEX

I am using CPLEX 12.8 to minimize a quadratic binary nonconvex function, according to quadratic function by CPLEX. In particular, my function is the following: $$ \sum_{i=1}^{m-1} \sum_{f=1}^{F} \sum_{...
3
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2answers
65 views

How to improve relative mip GAP using CPLEX in a MIP

Supose that I have an integer feasible solution for a MIP and I provide this one for CPLEX. I have tested this situation in a problem and CPLEX have reported the following: ...
3
votes
1answer
110 views

Problems finding a feasible solution in a MIP

I am using CPLEX with Julia using the package JuMP to solve a MIP problem. In a small instance, I have tested my problem but, after 10 minutes, nothing happens. I have defined the following parameters ...
3
votes
1answer
54 views

How to collect solutions within CPLEX and retrieve them from PYOMO?

I would like to seek some advice on modeling the following: I am currently to invoke solvers, CPLEX, in particular. As I am solving my problem sequentially, i.e., the top-level subproblem results are ...
6
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3answers
289 views

Gurobi and CPLEX cannot exploit more than 32 cores of machine

I have some attempts to solve a scheduling problem using the Gurobi and doCPLEX API in python and .NET on Ubuntu-server installed on a hyper-computing cluster with 64 physical cores. Unfortunately, ...
6
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1answer
55 views

GAMS: Is there a way to retrieve the gap from the final solve statement

Good evening, I am looking for a way to retrieve information from the final solve statement. Lower bound and Gap would be nice. I am working with the python api but i can only get the final obj. value ...
2
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2answers
79 views

GAMS default Solver doesn't use much of my RAM and CPU

I noticed that when i run solver via gams ide or python api i dont use more than ~33% of my RAM. Is there a artificial barrier which i can put up or disable?
3
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2answers
114 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
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1answer
91 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 ...
9
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2answers
148 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
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2answers
95 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 ...
4
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1answer
50 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. ...
1
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1answer
70 views

Solving 2d bin packing, nesting problem with Cplex

Is it possible to solve a 2d bin packing problem or nesting problem with Cplex? The solution should present the $x$ and $y$ coordinates of each item.
4
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1answer
84 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
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1answer
32 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: ...
5
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2answers
93 views

how to determine differents gap rate?

I found in the literature different gaps: a gap between a random solution and an exact solution a gap between the exact solution and a lower bound a gap between the exact solution and a lower bound a ...
5
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0answers
103 views

Obtaining the system of irredundant inequalities from a set of inequalities using CPLEX

Given a linear system of inequalities $Ax \geq b$, I would ideally like to compute the irredundant set for those set of inequalities. I know how to do so mathematically, but I was wondering if there ...
15
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4answers
2k 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
147 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
131 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 ...
5
votes
1answer
107 views

Add robustness of AMPL code through file name

I want to add robustness to my AMPL code, here is what I am actually doing: In my script I use a .txt file that contains all my parameters, lets call it "instance.txt". I want to print my ...
2
votes
2answers
91 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 ...
2
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0answers
48 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 ...
4
votes
1answer
132 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
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2answers
326 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 ...
2
votes
2answers
165 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 ...
2
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1answer
72 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 ...
3
votes
1answer
138 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
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0answers
49 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
35 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 ...
4
votes
1answer
78 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 ...
2
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0answers
47 views

CPLEX keeps restarting in Pyomo

I tried running my model by adding the following settings to CPLEX. ...
5
votes
2answers
160 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
146 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 ...
3
votes
1answer
101 views

Find a particular optimal solution

After writing an integer linear program in AMPL, I solved it using CPLEX. Now, I have some variables that must necessarily be 1, others that must necessarily be 0 and finally it is possible that some ...
0
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1answer
69 views

how can I use warm start in C#

I have been working on a MIP in C#. I want to reduce the gap, so I'm trying warm start. I use this code just before solve(). ...
2
votes
1answer
93 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 ...
7
votes
1answer
144 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 ...
9
votes
1answer
238 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
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2answers
1k 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 ...
2
votes
1answer
94 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 ...
3
votes
2answers
134 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 ...
1
vote
1answer
71 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
154 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
101 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
4
votes
1answer
172 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 ...
1
vote
0answers
66 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
170 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
200 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
139 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: ...