Questions tagged [python]

For questions about solving Operations Research problems using the Python programming language.

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6
votes
1answer
218 views

Interface for Cbc - COIN-OR

I would like to code some IP/MIP models in python and test them with an open-source solver. As of now, I only know the Cbc - COIN-OR open-source solver. I have already tried the or-tools interface, ...
8
votes
1answer
618 views

Travelling salesman problem with given number of locations to visit

There's a great example here of how to find a solution to the travelling salesman problem: ...
6
votes
1answer
549 views

Constraint Programming OR-Tools finding Matrix Combinations

As a similar post of mine Find all Combinations of a Matrix I am trying to find matrix combinations with entries $>0$ meaning for a matrix \begin{bmatrix} 0 & 1 & 3 \\ 5 & 2 & 1 \\ ...
5
votes
3answers
1k views

Finding a solution to a linear program with a small number of zeros

It is known that, in a linear program with $k$ constraints, there exists a basic feasible solution in which at most $k$ variables are non-zero. How can I find such a solution? Is there a polynomial-...
8
votes
2answers
2k views

Python does not identify the academic version of CPLEX

Python does not identify the academic version of CPLEX. I am using Linux, Ubuntu. I have Python 3.6. I installed CPLEX studio 12.9 (academic version installed via the file ...
8
votes
2answers
1k views

Implementing solvers with Object Oriented Programming

I would like to know what are some best practices in designing a solver implementation with Object Oriented Programming. We have implemented a solver with procedural programming paradigm, using python,...
12
votes
3answers
2k views

YALMIP-like modeling environment in Python

What are the handiest optimization parsers out there? Is COIN-OR's PyPy being used actively? I am currently trying to do an optimization project in Python, but I am used to using MATLAB + YALMIP ...
5
votes
1answer
175 views

Scheduling with transition costs - DOCPLEX

I am dealing with a kind of scheduling problem. I have a set of tasks to be executed by a set of machines. It is known that different machines are able to execute the same task, but each machine can ...
10
votes
4answers
1k views

Integer programming problem with simple quadratic objective function in Python

I have $n$ objects that need to be divided among $k$ groups. Each group must receive at least $5$ objects. In addition, the percentage of objects in group $i$ should be as close as possible to $p_i$ ...
10
votes
1answer
442 views

TSP problem: traveller does not visit all nodes - Google OR-tools

Context: I am dealing with a kind of scheduling problem, in which I have a set of tasks and machines. All tasks must be assigned to machines (not necessary all of them). In addition to that, I must ...
5
votes
0answers
56 views

How to handle constraints in docplex to states the relation between two variables?

I am using docplex.cp and I need to state the following constraint: $$\sum_{c}(X_p{_w}_{cj}+X_{p+1}{_{w'}}_{cj+1})\leqslant T_w{_{w'}}_{,jj+1} + 1$$ Knowing that the binary variables are: $X_p{_w}...
6
votes
0answers
253 views

How to make constraints satisfy disciplined convex programming guidelines?

How do I turn my convex constraints (described below) into constraints that are DCP so that I can solve them in CVXPy? Is there some ``cheat sheet'' of standard tricks? I'm trying to implement the ...
7
votes
1answer
97 views

DOCPLEX: tips to manipulate data input (binary parameter)

I am coding a MIP problem in docplex and I would like to ask for some tips. I would like to input a binary parameter that states a compatibility relation: I have a set of characteristics $H$ to be ...
7
votes
0answers
487 views

Having trouble with objective function in Python: “GurobiError: Variable not in model”. What else could I try?

I am trying to figure out how I can write this objective function into python using Gurobi. I have to minimize the sum of the product of three dictionary's values. The reason I am confused is that ...
8
votes
2answers
2k views

How can I add this conditional constraint to my model in Python?

I am creating an optimization model with 2 sets of binary decision variables. The first, site, is regarding which of 380 cities to place manufacturing sites in, and ...
5
votes
2answers
455 views

How to establish constraint between variables with multiple indexes using CPLEX in Python

I am new in CPLEX and I am using docplex in Python to solve an ILP. I would like to translate the following constraint in docplex: $$\sum_{c}(X_p{_w}_{cj}+X_{p+1}{_{w'}}_{cj+1})\leqslant T_w{_{w'}}_{,...
9
votes
2answers
1k views

Reading an LP/MPS file using Pyomo software

I would like to know is it possible to read an LP/MPS file into the Pyomo software and solve the problem? If so, how can I do that?
9
votes
1answer
786 views

Pyomo: Looping Over A Variable Method

I am trying to extract my variable values into unique lists so that I can pass them to a panadas dataframe and eventually export the dataframe to Excel after I solve my model. The idea is to have the ...
8
votes
3answers
725 views

Maximize assigned tasks to each worker

In a scheduling problem I want to assign the maximum number of tasks to one worker before assigning it to another. For example, if I have $10$ tasks and $2$ workers, the best assignment would be $(10, ...
9
votes
2answers
159 views

When should I use a solver for IP and MIP and can I just use a library from Python, R, Matlab, etc…?

Are there any rules of thumb for figuring out when you need to use a solver like Gurobi or CPLEX, and when you can just solve you problems directly with a Python, R, or Matlab package? Is it just a ...
4
votes
1answer
282 views

Machine Allocation & optimal Utilization using python

Problem statement: Meet the demand which can be met across 2 facilities each having multiple machines where several components are made. The objective is to find the optimal solution to meet the ...
8
votes
1answer
175 views

Specific filter on the set using Python

I'm trying to write an optimization model using an open-source solver's Python API. I'm new to use Python. The model objective function is as follows: \begin{equation} \sum_{k=1}^{K} \sum_{j=1}^{n}\...
9
votes
2answers
237 views

Common structures in Gurobi - Python

I'm new to Gurobi in Python and I was wondering if someone knows how to code some common structures of linear constraints. I'm trying to understand how you'll code something like the following ...
11
votes
1answer
470 views

How to solve the Cumulative Traveling Salesman Problem using or-tools in python?

The objective of the Cumulative Traveling Salesman Problem (CTSP) is to minimize the sum of arrival times at customers, instead of the total travelling time. This is different than minimizing the ...
10
votes
1answer
1k views

Simulation in Python

What is the most common package for discrete-event simulation in the OR community? I have found SimPy package.
10
votes
2answers
959 views

How to get GAMS's solvers to work from Pyomo?

I want to run a model written in Pyomo language with CPLEX solver of GAMS. However I get the following error: ...
7
votes
1answer
334 views

Can docplex (module for Constraint Programming optimizer CPLEX for Python) read .lp or .mps file?

I want to solve a problem with docplex.cp (module for Constraint Programming optimizer CPLEX for Python), and the problem is available in ...
10
votes
2answers
158 views

Are there examples of spatially explicit MIP problems?

Disclosure: I am an MSc student in economics, but not an expert by any means in OR. I am trying to model a spatial MIP problem of an invasive species similar to this academic paper, however, my ...
11
votes
1answer
537 views

Change coefficient in PuLP

Once a model is implemented in PuLP, how do you change a coefficient (e.g., $a_{ij}$, $b_i$ or $c_j$) of a program of the from $\min\{c^{\top}x: Ax=b, x\geq0\}$? Specifically: How to update ...
10
votes
1answer
419 views

Termination Criteria of Solver in Pyomo

I am solving a nonlinear optimization problem using Pyomo with Ipopt as solver. The solver exits with the status: EXIT: Optimal Solution Found. This I can cross ...
8
votes
3answers
3k views

Python API and CPLEX

Note: See the EDIT below for one possible solution. I apologize if this is not appropriate but I don't really have anywhere else to turn. I was hoping that someone would be able to post how they ...
12
votes
3answers
1k views

How to model a mixed-integer linear programming formulation in Python using Gurobi?

I can remember that I spent some time in understanding how to formulate my first model. So I aimed at presenting a complete model here, wishing to save some time for students or researchers needing it....
8
votes
1answer
722 views

Read an LP/MPS file in the PuLP

I was trying to read a MPS file by using the PuLP package in the Python, but I can't find any related documents on it. Does ...
9
votes
1answer
6k views

How do I access the value of a variable in PuLP?

In Python's PuLP package, how can I get the value of a decision variable? For example, if I declare a variable— ...
8
votes
2answers
2k views

Gurobi's “Out of memory” error without exhausting the RAM?

I wrote a branch-and-price algorithm in Python 2.7 which solves several small LP and MIP models by Gurobi 8.1 in each node. The algorithm runs fine at first, it produces both lower bound and upper ...
5
votes
1answer
331 views

Python PuLP - Unable to Model Non-Square Matrix

I am having issues with setting up constraints using both input arrays from excel and variable arrays within PuLP. It appears the model only works with square matrices and my final code has a matrix ...
9
votes
1answer
216 views

pyomo - pass time limit to NEOS

I am sending a pretty complex Pyomo MINLP to NEOS using Couenne. I'm getting an error message that the solve time is too long (sorry, I don't have it still in my Python console). Is there a way to set ...

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