Questions tagged [python]
For questions about solving Operations Research problems using the Python programming language.
66
questions with no upvoted or accepted answers
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What distuingishes a model-and-run framework solver from a programmatic solver?
I am looking for examples to understand what kind of benefits a model-and-run framework solver offers that a more programmatic solver doesn't do or doesn't do as well.
What distinguishes a model-and-...
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7
votes
0
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810
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 ...
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6
votes
0
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378
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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 ...
- 61
5
votes
0
answers
144
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How to use interpolation for problem parameters in Pyomo
I'm working on my first Pyomo DAE project to teach myself how to use it for trajectory optimization. I have generated an atmosphere lookup table with density and speed of sound as a function of ...
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5
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answers
110
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Reduce overhead Gurobi Python getting and setting attributes
I am using Gurobi 9.5.1 in Python 3.10. In the context of column generation I request the duals of the master problem and set them in the objective of the subproblem. This is done repeated times.
<...
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5
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139
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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}_{...
- 1,133
4
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answers
96
views
4
votes
0
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62
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Changing a parameter while branching in SCIP
I use pyscipopt. I know how to add constraints while branching using handlers (kind of), but now I want also to change some parameters. I imagine is similar, but couldn’t found an example.
What I want ...
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4
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227
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Does anyone have the criss cross algorithm programming code to solve linear programming problems?
I have a project that requires programming code for the simplex algorithm and criss-cross algorithm. The purpose of this project is to compare the two methods. I've tried to find it, but the ...
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4
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84
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Problem related to machine's performance while solving an LP-relaxation of a set-covering problem using the Column Generation
PS: I am familiar with performance variability encountered while solving large-scale MIPs. My question may not be explicitly related to it but maybe to the inefficiency of python packages.
I have ...
- 668
3
votes
1
answer
72
views
Solver options in Pyomo as long as using the NEOS solvers
I am working on a scheduling problem that is already coded in Pyomo. To solve the problem, I have used the NEOS solver, CPLEX. Now, to test and run some of the instances, I need to call some CPLEX ...
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3
votes
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39
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Pygmo2: What is the point of evolving an archipelago in a loop if number of generations already set in algo
I want to solve a multi-objective problem with nsga2 or moead taking advantage of the parallelism available in pygmo library. I have seen a very nice example on github posted below. However I am not ...
- 31
3
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85
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Minimize total cost to buy unique products over timespan
I am looking for some guidance on how to better state my problem formally and practically (e.g., relevant Python libraries).
Let's assume I have a set of $X$ unique products to buy. I have $Y$ days in ...
- 31
3
votes
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answers
107
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Proving convexity for a function with summation and integer variable
I would like to show that the function $f$ is convex in $\rho\in [0,1)$ under $s\in \mathbb{Z}^+$. When I use Sympy packages of Python to find $\displaystyle\frac{\partial^2 f(\rho)}{d\rho^2}$. I get ...
- 1,239
3
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0
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229
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Add Variables in Bulk for ortools
I am using the Python ortools to solve large LPs where the number of variables and constraints are in the hundred thousands ($10^5$). Surprisingly, it takes longer ...
- 131
3
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69
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PuLP Python: How to linearize an inequality involving an integer variable
I am working on a Copper payables problem where the objective function is to maximise the sum of copper payable over a time period, T.
The total amount of payable tonnes i.e. what the customer will ...
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3
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0
answers
585
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How can I see the engine log when solving a LP using pulp (python)?
I wonder which command should I use to see how the steps the pulp solver is doing when solving a linear program.
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3
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0
answers
92
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Constraint equivalence in PuLP
I'm working on an optimization problem in PuLP and I have to enforce a daily minimum of shifts and a daily maximum of assigned shifts. I have the following constraints to ensure each day has a minimum ...
- 101
3
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0
answers
175
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Power of variable or tools
I'm working with OR Tools in Python and I need to define the objective function an expression of the variables. In particular, the objective function is
$$\frac{c_j}{1.7^{s_j}}$$
with $c_j$ ...
- 131
2
votes
0
answers
65
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Pyomo Terminal Condition: other
I have written a huge optimization code in pyomo. The code serves for any planning horizon. The variables are indexed in time (t). When I set t to have 365 days, the termination condition is feasible/...
- 21
2
votes
1
answer
96
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Using networkx predecessors in Pyomo initialize method
I am working on the directed graph by using the Networkx package and what I need is to use its predecessors' method on an optimization model. Let's say, there exists a directed graph with just $12$ ...
- 7,664
2
votes
1
answer
80
views
Control load per trip in multi trip VRP in ORTools
I have implemented multitrip VRP in ortools (To be specific, solved CVRPTW with virtual depots). Maximum number of trips per vehicle is limited to 2. I want to put a hard constraint that load carried ...
- 181
2
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0
answers
128
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OR constraint in Gurobi - Python
I'm new to Gurobi in Python and I am wondering if there is way to code the following constraints:
1- $\sum x_i =0$ for all $i\in A$ OR for all $i \in B$
where A and B are distinch sets of integers ...
- 185
2
votes
0
answers
520
views
Add lower and upper bounds on decision variables in Pyomo
I have the following optimization model in pyomo:
...
- 21
2
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252
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 ...
- 424
2
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0
answers
128
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Multiple Depot/Crew Office Bus Driver Scheduling Modelling
I'm working on Bus Driver Schedule with multiple add-on constraints that are complex and hence trying to figure out how this can be achieved.
Reference of Bus Driver Scheduling using OR-Tools:-
https:/...
- 21
2
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0
answers
484
views
How to assign a single value to Pyomo parameter without a dictionary
I would like to assign a single value to a paramter that depends on a created set in Pyomo. I have the following code:
...
- 1,636
2
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0
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265
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Gurobi is unable to give an optimal solution even when it exists
I am trying to solve Logarithmic Fuzzy Preference Programming (LFPP) for criteria weight evaluation, based on fuzzy comparisons between criteria, and I am solving it with Gurobi in Python 2.7. It is a ...
- 21
2
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0
answers
94
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Efficient way to do user rescaling of variable in Gurobi
Is there a better way than the code below to the rescaling of variable in a model after the model has been build with Gurobi? Like some build in function or a direct manipulation of the column object? ...
- 3,607
2
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145
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How to solve an LPP with summation
Up until this point I have only solved simple LPP problems with maybe 2 to 3 variables that looked like this, using pen and paper.
I need to solve
This Problem using Simplex, Dual Simplex, Big M and ...
- 21
1
vote
0
answers
31
views
Which Python package is suitable for finding the optimal non dominated set in multiobjective optimization?
I would like to know how to use pyhon or Cplex or both for finding the whole optimal pareto front for a biobjective mixed integer linear programming problem?
Thanks
- 11
1
vote
1
answer
205
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MIQP — CVXPY unable to treat summation of variables as a variable
I have a quadratic integer programming assignment problem. The goal is to assign riders seats on a bus such that distance between any two riders is maximized; however, the importance of each objective ...
- 471
1
vote
0
answers
151
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Resetting Pyomo model after computation
I am aware that the types provided by pyomo are immutable and often cause issues when we feed the same data twice in consecutive computations (e.g. when trying to solve an instance a couple of times) ...
- 392
1
vote
0
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173
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Apply Benders decomposition approach in CPLEX with python while using docplex class
I am new to cplex with python. I want to solve a problem using the Benders decomposition approach. Where I want to use UserCutCallback and LazyConstraintCallback. I am writing code in script format (...
1
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0
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111
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Profit Optimization in Python with Difficult Constraints to Maximize Net Revenue
I am currently trying to work on this problem that determines the best constraints on how to place these 'bids'- please see the second column in the screenshot:
The ask at hand is to uncover a model ...
- 11
1
vote
0
answers
48
views
Pyomo error about evaluating value of 'ScalarParam' parameter
I'm trying to optimize a huge model, but here is a part of it capable of creating an understanding of my question:
...
1
vote
0
answers
39
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batch file for docplex
I have a mathematical model written in docplex python. For analysis, I have to generate different sized data with batch file which can be input for the problem. How can I generate this type of batch ...
- 307
1
vote
0
answers
36
views
Blended or hierarchical objectives if solving speed is more important
When optimizing a two objective task assignment problem, is it generally better to use blended objectives or hierarchical objectives if
the speed to obtaining a near-optimal solution is more ...
- 179
1
vote
0
answers
133
views
How to see fix constraint violations found with IIS
I'm running a simple MCNF model to see if my network is balanced. I'm using Gurboi in Python and with the IIS I can see that there are 2 constraint violations making it infeasible. How do I fix these ...
- 109
1
vote
0
answers
406
views
How to eliminate large matrix coefficients and large RHS warning in Gurobi
I'm solving a large network flow problem using Gurobi to do Benders decomposition in Python. The imported .csvs contain values that typically fall in either zero, the range of [20,200], or with a ...
- 109
1
vote
0
answers
462
views
In DOcplex, how can I get value of variable for objective function before solved?
In terms of python based atypical math model as shown below, which is unlike nonlinear or quadratic form in my opinion, I have difficulty in accessing value of variable before optimization as ...
1
vote
0
answers
72
views
Meaning of zeros in the column best bound in docplex?
I am trying to solve a large-scale MIP problem in docplex(python). I give to the model a MIP start solution, I remark that after 20 hours, the best integer still the cost of the MIP start and the best ...
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1
vote
0
answers
257
views
Problem with Piecewise constraint in Gurobi
I am facing a problem in my model with piecewise constraints that is making my one of the decision variables equal to zero for every value.
My objective function is:
\begin{equation}
\min \sum_{t=...
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1
vote
0
answers
303
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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1
vote
0
answers
265
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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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1
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0
answers
92
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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 ...
- 125
1
vote
0
answers
155
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Optimization Multiple Constraints
I am trying to solve a linear algebra problem: an optimization problem and I am using CVXOPT. I've split the problem into 3 components
In its simplest form, The general formulation for CVXOPT is \...
- 173
1
vote
0
answers
429
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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1
vote
0
answers
126
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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1
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205
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Solver issue? Xpress (slp) - Nonlinear - Python - Pyomo
I tried solving my model with xpress:
pip install xpress
And then in the model:
...
- 111