Questions tagged [python]

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

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1answer
47 views

Varible vector violates upper and lower bounds when I hit iteration limit

I have an application where I want to monitor the variables over time. I declare all the variables in my model like this: ...
9
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4answers
2k views

What are technologies or libraries which greatly improve the speed or ease of use for delivering of OR software?

There are many great technologies/libraries out there to improve the speed and quality of implementing and deploying OR applications. However in my experience i "stumbled" upon many of them ...
1
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0answers
57 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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1answer
127 views
1
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1answer
105 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: ...
1
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0answers
80 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 $w, v$...
1
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1answer
114 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...
1
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1answer
36 views

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

The following error was encountered when using LinExpr in gurobi: ...
1
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2answers
160 views

How to make the elements of the solution of gurobi belong to the elements of the specified list?

If I want to use the elements of the list as the range of the solution, like list1 = [10,20,50,60,30],and the elements of the solution must belong to the elements of the list The sample example as ...
1
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0answers
67 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: ...
2
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1answer
101 views

Obtaining solver timings from Pyomo

I would like to seek some advice on the following: I am currently using Pyomo to generate my MILP model in Pyomo and solve it using Gurobi, respectively. As the solution process is iterative, I would ...
1
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0answers
41 views

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

I tried solving my model with xpress: pip install xpress And then in the model: ...
2
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1answer
99 views

Capacitated Maximum Coverage Location Problem, Python and Gurobi

I am building a variant of the maximum coverage location model and want to limit the amount of points that each "facility" can cover. I am using Gurobi optimization . I have tried using the ...
1
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1answer
90 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 ...
2
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1answer
101 views

Find multiple solutions using pyomo and gurobi

I am solving a MILP using Gurobi and Pyomo. I would like to obtain as many optimal solutions as possible. Here is what I have so far: ...
0
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1answer
49 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: ...
1
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0answers
73 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}\...
1
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1answer
50 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 ...
2
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1answer
54 views

Returning the best possible value found when the search direction is becoming too small (IPOPT via Pyomo)

I'm using Pyomo to solve an optimization problem and I'm using as a solver IPOPT. Now I'm getting an error from IPOPT. EXIT: Search Direction is becoming Too Small. according to the docs, this means:...
-4
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1answer
94 views

Multiple If else constraints in Mixed integer programming

How to formulate the following as constraints in MILP? a[0][0] = y, if x[0]= 0, a[0][0] = 0, if x[0] != 0, . . . . a[i][j] = b[i][j-1] + y, if x[j]=i, a[i][j] = a[i][j-1], if x[j] != i, ... . . . b[0]...
1
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0answers
53 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 ...
2
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2answers
96 views

OR-Tools: Partial Solution ignored due to “unknown rate is too large”

With SetHint() from the OR-tools linear solver I am trying to pass a feasible solution to my problem. But I receive the following warning: ...
1
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1answer
122 views

Travelling salesman problem variant without returning to the starting point

I tried the code provided on the link : https://developers.google.com/optimization/routing/tsp The actual requirement is to traverse all paths without returning to the start point with minimum ...
1
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1answer
138 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. ...
4
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3answers
108 views

warmstarting simplex algorithm- how much can problems differ from each other?

I'm working on an implementation of the simplex algorithm. I want to solve problems in real time every 30 minutes. They could be interpreted as a classic transportation problem. I couldn't really say ...
3
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1answer
117 views

Is the Dynamic programming in Operations Research book the same dynamic programming in software industry?

Mostly when I search dynamic programming in google I get : dynamic programming (DP) in python, in C++, in java from web pages like geekforgeeks, litecode, codechef, and so on. But in the operation ...
2
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1answer
160 views

Efficient solver for multiway number partitioning

I am interested in the following problem. The input is a set of $n$ integers, and a fixed integer $k$. The required output is a partitioning of the integers into $k$ subsets, such that the smallest ...
0
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1answer
84 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 ...
3
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1answer
44 views

Control & Experimental Group Selection Methodology using STDEV and T-Test?

I would like to know if my methodology was 'correct': I am trying to conduct an experiment on my stores. I would like to find out the effect of a marketing campaign on the number of transactions. Only ...
0
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0answers
161 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-...
2
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2answers
119 views

Trouble with optional nodes in a VRP model using Gurobi for python

I am currently working on a VRP problem where the vehicles are electric. This means that I have range restrictions, and charging stations as nodes which are optional to visit. In my model I have the ...
1
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1answer
30 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,\...
1
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1answer
121 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 ...
4
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1answer
66 views

Clustering problem involving multidepots and customers requiring commodities located exclusively in an specific depot

I'm trying to solve a clustering problem that's similiar to a VRP Pickup and Delivery problem with multiple depots and customers. Each customer demands a commodity that is exclusively found on one ...
2
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1answer
97 views

Impose binary constraint on integer matrix with CVXPY

So I have the following matrix: \begin{equation} P_{i,j}= \begin{bmatrix} x_0 & x_1 & x_2 \\ y_0 & y_1 & y_2 \\ z_0 & z_1 & z_2 \end{bmatrix} \end{equation} where ...
1
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0answers
69 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 ...
3
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0answers
82 views

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
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1answer
78 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 ...
2
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0answers
54 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: ...
2
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0answers
39 views

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 ...
2
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1answer
224 views

Pyomo can't find Gurobi solver

I have a pyomo model that I can solve using the GLPK solver by just using the code: ...
3
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1answer
117 views

Referencing of sets in Pyomo objectives

I have a question about referecing set in Pyomo objectives. Basically I have 2 options and I do not understand why one of it works whereas the other yields an error. Here you see them: ...
1
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1answer
146 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 ...
1
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1answer
96 views

Solving general minimum cost flow problems using only one demand and one supply node

This is a practice in using reduction. Suppose I have a solver that only allows input to a MCF that specifies only one demand and one supply node. How could I use this solver to solve general MCF ...
3
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1answer
63 views

How to implement a difference equation in Pyomo

I would like to define a difference equation in pyomo for a temperature variable. The equation (simplified) looks like: $Temperature(t) = Temperature (t-1) + x(t)$ , for t>0 $Temperature (0) = 20 $ ...
1
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1answer
72 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: <...
3
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0answers
36 views

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 ...
2
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1answer
63 views

Generating a different optimal solution from CPLEX for each run

I recently chanced upon the idea of solution diversity through the setting of random seeds within CPLEX. However, the documentation page on the settings does not shed any light with regard to the ...
1
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1answer
445 views

Pyomo can't find solver

I am new to Pyomo and I have the following optimization problem (original transport problem by Dantzig): ...
2
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1answer
97 views

How to define constraints in Pyomo using sets and variables

I am trying to model the transportation problem of Dantzig in Pyomo (see the GAMS code here https://www.gams.com/latest/gamslib_ml/libhtml/gamslib_trnsport.html or the description here https://www....