Questions tagged [python]

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

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1answer
124 views

Dynamic Programming - Formulating recurrence relation

We wish to apply dynamic programming techniques to find the optimal betting strategy for a pool to wager on the outcome of the NCAA men's basketball tournament 64 teams compete in a single ...
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1answer
139 views

How to balance the workload of teachers in OR-Tools (maximization of the minimum)

I am very new to optimization and OR-Tools. I am trying to solve a very simple question. Let's assume that we have $n$ students. Each student needs to be assigned to only one teacher as a supervisor. ...
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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 ...
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2answers
376 views

Pulp: slack variable to identify & measure extent infeasible in supply problem

I am currently modelling a supply problem that attempts to optimise a rail schedule which moves products from a production plant, to a warehouse to satisfy sales. The model is working fine (thanks in ...
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1answer
140 views

Branch-and-Price: return gap using SCIP

I implemented a branch-and-price tree in python. I would like to stop the process after 5 hours and return the gap in % between the best integer solution found so far and the optimal solution. How ...
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1answer
265 views

How to enforce this specific constraint in PuLP?

I am trying to implement an employee (nurse) scheduling problem and seek some advice on how to implement a specific constraint.The problem is as follows: There is a set of employees and days (both ...
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1answer
111 views

Conditional constraints in PuLP

I have the following optimization model using PuLP. ...
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1answer
242 views

How to display results from a solver during solving in Pyomo

I would like to see the current results (e.g. MIP gaps) of a solver in pyomo (as in GAMS) while solving the problem. I read that I should use the option "stream-solver" (see for instance ...
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2answers
127 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 ...
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1answer
107 views

How to display results of 2-dimensional Pyomo variables in a pandas dataframe

I would like to create a pandas dataframe from the results (and the parameters) of an optimization problem and create a csv file out of it. In my previous example (1-dimensional case) I have just one ...
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1answer
54 views

How to assign values from a list of dictionaries to a 2-dimensional parameter in Pyomo

I know how to assign values from a single dictionary to a 1-dimensional parameter in Pyomo. For that I use the following code ...
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1answer
214 views

How to display results of Pyomo variables in a pandas dataframe

I would like to display all the results of Pyomo variables in a pandas dataframe. I had a look at this question Pyomo: Looping Over A Variable Method and tried to adjust it to my case without success. ...
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1answer
33 views

How to assure a range for a specific variable in Pyomo

I would like to specify a certain range for a variable for a certain timeslot in Pyomo. I have a temperature variable $T(t)$ that is defined by using the difference equation $$T(t) = T(t-1) + \cdots,\...
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1answer
92 views

Python Gurobipy Maximum Flow: How to model "source" and "sink" in constraints

I am attempting to capture the nature of a "source" node as well as a "sink" node where the net flow for each node aside from the source and sink is zero. Here is my code so far: <...
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1answer
748 views

Pyomo can't find solver

I am new to Pyomo and I have the following optimization problem (original transport problem by Dantzig): ...
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1answer
106 views

Issues modeling portfolio optimization with rebalancing in gurobipy

I want to solve the following portfolio optimization problem by means of the Python API of Gurobi: \begin{align}\max_w&\quad w^\top\Pi\\\text{s.t.}&\quad w^\top\Sigma w=\sigma^{\rm target}\\&...
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1answer
52 views

Print Intermediate Solutions of Scheduling Problem and tackling FLAGS in jupyter notebook

I tried this code and it goes on and I'm clueless when it'll end so I manually interrupt it. Is there any way we can see intermediate solutions that are feasible solutions and can we limit time or ...
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1answer
59 views

Calculating the Obj Value manually in Gurobi

I have been working on the problem on Facility Location Problem with Gurobi using the example provided by the Gurobi team. ...
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1answer
116 views

How to make the solution of linear programming within the specified elements [duplicate]

The constraint value of a variable must be an element of the specified list.A simple example is shown as follow,in which the value of the...
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1answer
38 views

gurobipy.GurobiError: Second argument should be a list of Var

The following error was encountered when using LinExpr in gurobi: ...
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1answer
104 views

Job Shop Scheduling Problem: jobs are scheduled on the same machine at the same time

I want to solve a job shop scheduling problem. I got $n$ Jobs that have to be scheduled on $k$ Machines. A Job $i$ has 2 or 3 Tasks $j$, and there is a known sequence of the Tasks of a Job. One ...
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1answer
81 views

How can I formulate an objective function that minimises the number of items required to solve a problem

I am currently trying to solve a problem where I need to minimise transport cost through the choice of vehicle (and how many of each choice) subject to a given demand. The problem: There are currently ...
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1answer
252 views

Python, Google OR-Tools, OnlyEnforceIf() method

I am trying to solve a basic puzzle by using Google OR-Tools, this is my first try with OR-Tools and I am trying to learn. I completed almost everything and was ready to conclude the program until I ...
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1answer
130 views

Flexible Job Shop Problem with several resources per alternative - Ortools

It has been quite a journey for me to go from 0 to understanding the job shop (js) and the flexible job shop (fjs) examples given by Google's ORTOOLS team. Now the time has come for me to start ...
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1answer
75 views

How to get detail about 'OptimizationStatus.ERROR' in MIP module in Python?

I am using MIP (Mixed Integer Programming) module in Python to solve one of my optimization problems. for some of the scenarios, model returns "ERROR" (OptimizationStatus.ERROR) status after ...
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1answer
95 views

Pyomo: Struggling to get a constraint to work

I am trying to model an Electric Vehicle scheduling to minimise the electricity bill. Of course, the EV will only be able to charge every time that is plugged into a charging station (i.e. it cannot ...
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0answers
59 views

Adding sequence constraints to the assignment problem- Python

This is an online assignment problem and yet can be considered as an assignment problem with a sequence. Assume that workers are coming into the system sequentially and I want to assign a task to them ...
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0answers
23 views

How to count the number of Stale variables in Pyomo?

How to check if a variable is Stale or not? How to count them? For example let's have a variable like instance.x[i] (i in instance.i set). Let's assume some of ...
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0answers
32 views

MLE application with gekko in python

I want to implement MLE (Maximum likelihood estimation) with gekko package in python. Suppose that we have a DataFrame that ...
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0answers
73 views

Optimisation Multiple Constraints

I am trying to solve a linear algebra problem: an optimisation problem and I am using CVXOPT. I've split the problem into 3 components In its simplest form, The general formulation for CVXOPT is \...
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0answers
88 views

How do I define multiple indices for the same set in python? (using CPLEX to solve a MILP)

I am using docplex in Python to solve a MILP and I am having some trouble defining the indices and sets of my model. I want to translate $w,v,a\in W$ into Python. In this case, $W$ is a set, and $w, v$...
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0answers
70 views

How can I set the solution of gurobi to be a multiple of 10 instead of all integers?

For example, the solution for gurobi has two solutions, as follows: [10,20,50,70] [55,79,30,80] I only want to output solutions that contain only multiples of 10. The sample example as follow: ...
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0answers
52 views

Solver issue? Xpress (slp) - Nonlinear - Python - Pyomo

I tried solving my model with xpress: pip install xpress And then in the model: ...
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0answers
79 views

Implement sequential formulation in TSP (Miller, Tucker, Zemlin)

I'm trying to solve a TSP in different ways. I already did it with the formulation of Dantzig, Fulkerson and Johnson und now I want to do use the Miller, Tucker, Zemlin constraint. $$u_i-u_j+nx_{ij}\...
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0answers
91 views

Value Error in Pyomo: Constraint rule returned None

I get an error in Pyomo that I do not understand. I habe 288 timeslots t and a binary variable y (which I call here ...
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0answers
74 views

Strange Result from GurobiPy

I am trying to understand why GurobiPy gives me a strange result for a simple linear programming model coded as below? Why is the optimality gap is 0%? Please let me know if you spot any errors in the ...
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0answers
136 views

Doesn't Pyscipopt handle nonlinear objective functions?

I am trying to solve a large-scale nonlinear problem. Below is the objective function coded for pyscipopt. I have some loops over a list of tuples (r,p,s) in the list RouteTimeStop, and the only ...
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0answers
61 views

Modeling the multiplication of two binary decision variables in undirected graph in python

In an undirected graph, I'm trying to model a constraint that forcing the optimizer to set an edge $(u,v)$ between two nodes to only exist (= $1$) if the two nodes have been selected to be $1$. The ...
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0answers
22 views

Implement geometric constraint using DOCplex

currently I'm working on a wind farm layout optimization problem. I found an appropriate model in literature (Fischetti et al.) and now I'm trying to reproduce it using the Python API of cplex with ...
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0answers
28 views

MILP formualtion for Two-level minimum dominating set (MDS) problem?

I'm working on an optimization problem which is kind of finding the minimum dominating set (MDS) or the minimum vertex set (MVS) in an undirected graph. given the MILP formulation for both problems, I ...
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0answers
120 views

Resource constrained LP problem

I am working on Diet Allocation problem. Where we need to provide food piece for protein deficiency. The data is as below: ...
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0answers
53 views

CPLEX keeps restarting in Pyomo

I tried running my model by adding the following settings to CPLEX. ...
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1answer
1k views

How to solve knapsack problem with simulated annealing?

I was going through the course contents of Optimization with Metaheuristics in Python in udemy , where they have solved a quadratic assignment problem using Simulated annealing in python , i was ...
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1answer
56 views

How to create constraint-equations in Pyomo with empty set inputs

I would like to crate an constraint-equation that depends on 4 sets. For that I use the following code: ...
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1answer
137 views
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1answer
123 views

Gurobi: How to define constraints that can accept multiple different values? [duplicate]

I have a question about Gurobi. How do I define a constraint that can accept multiple different values? For example, a sample constraint is shown as follows: ...
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1answer
146 views

Mutable parameter in Pyomo causes a problem

I am defining a Pyomo model that should have some mutable Big-M parameters whose values should be dynamically assigned (once). However, I am having a problem with a difference equation as described in ...
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0answers
111 views

Set Covering and Column Generation

I need some set covering and column generation examples in OR-Tools python. If anyone can provide or direct me to some resources that would be great..!
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0answers
277 views

Use if-statements when defining a constraint in Pyomo

I would like to define the value of a variable model.variable_costsPerTimeSlot [t] in pyomo and I would like to use if-statements. Depending on the value of the if-...
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1answer
178 views

Optimized Production Planning & Scheduling

I want to create an optimized schedule and production to meet demand of four different buyers. I am starting with Pulp but not able to account for continuous production variable and discrete dispatch ...