Questions tagged [python]

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

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5
votes
2answers
163 views

Priority List Constraint

I used the Vehicle Routing Problem example that has the objective of minimizing total distance traveled for each vehicle. Suppose that each order to pick up for each vehicle at each node has a ...
2
votes
0answers
124 views

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 ...
1
vote
2answers
190 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 ...
4
votes
3answers
681 views

Branch and bound algorithm programming code

I want to solve an integer programming problem using the branch and bound method, but I'm having trouble finding the programming code. From what I saw, almost all algorithms use it for traveling ...
27
votes
9answers
10k views

MATLAB vs. Python in industry

I am a beginning PhD student in math, and I would like to focus on optimization. I am learning programming for the first time, and I have written out some rudimentary optimization algorithms in both ...
2
votes
0answers
65 views

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? ...
5
votes
1answer
113 views

Adding a hard and soft upper bound constraint of number of locations to visit (VRP)

I went through the Vehicle Routing Problem example and was able to replicate it. On the example, there is a constraint added for vehicle maximum distance as shown below: ...
0
votes
1answer
484 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 ...
8
votes
3answers
1k views

Open source MILP solver for quick “good enough” solution

I have a problem that I have already posted elsewhere in OR.stack, but the question is focused around a large binary MILP (about 1 million decision variables). Ultimately, I am more time constrained ...
4
votes
0answers
106 views

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 ...
4
votes
2answers
149 views

Suggest me good books to learn heuristics to solve Operations Research problems using python

Suggest me some good books with implementation of heuristics using python to solve operations research problems
10
votes
3answers
645 views

Settings for a faster solution of a MILP (GUROBI, python)

Using GUROBI with python. When solving a MILP, I notice that the incumbent is very early (25sec) at the optimal point but the best bound is so slow to fall (maximization problem) that it takes ages (...
3
votes
0answers
33 views

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 ...
4
votes
1answer
237 views

How to set these constraints in a linear optimization problem (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 ...
3
votes
0answers
64 views

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 ...
2
votes
0answers
80 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 ...
2
votes
1answer
135 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 ...
4
votes
1answer
187 views

How to make a copy of a Gurobi model in Python?

Suppose I have made a Gurobi model in Python model = Model(), defined variables, constraints, objective function, and solved it. However, I want to make a deepcopy ...
4
votes
1answer
200 views

PuLP Transport Problem - How to add outcomes of decision variables together

I am working on a rail scheduling problem that moves product from a production plant to a storage facility to satisfy demand. I am new to PuLP so finding this difficult to understand why this isn't ...
37
votes
13answers
8k views

Are Python and Julia used for optimization in industry?

I am giving a small computer exercise that aims at teaching students the basics of a modelling language to model small optimization problems. So far I have been using the modelling language GAMS as ...
3
votes
1answer
162 views

Convexity Analysis

For the following function, I am testing the convexity in $\lambda$. All parameters are in $\mathbb{R}^+$. $$\frac{\left(- \lambda \left(b + \frac{p}{\beta}\right) + 1\right) \left(\left(1 + \frac{p}{...
8
votes
1answer
147 views

Heuristic Search Planning Tree Leading to Worse TSP Solutions than Naive Greedy

I'm doing a Traveling Salesman Problem (TSP) homework for a coursera optimization course. My first attempt was a regular naive greedy approach, from each point, moving to the closest node (that hadn't ...
6
votes
1answer
199 views

Advanced Heuristics for MIP vehicle routing problem in PuLP

I am currently trying to speed up an MIP. An approach I was considering was to implement a cut callback heuristic with PuLP (one which rounds relaxed integer variables greater than .9 to 1). ...
2
votes
0answers
59 views

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 ...
3
votes
2answers
135 views

Rotated Second-Order Cone Constraints in docplex

I have programmed the model in here using Gurobi 9.0 in Python 3.7. To ensure playing within the boundaries of the licensing, I am trying to program it using CPLEX where we have broader flexibility ...
4
votes
1answer
310 views

How to read a solution file (.sol) in cplex python API?

I've been to trying to read a .sol file in cplex python API before solving the problem but couldn't find any command to do so. There are analogous commands for this ...
4
votes
1answer
64 views

Inputting logical constraints into a binary programming model in Gurobi

I am very new to Gurobi and OR in general (I'm in my first class for it now), so apologies if this is a very obvious answer. For a project in that class, I am generating a flight schedule for a ...
3
votes
1answer
100 views

Logical operation on an array in DOCplex

Here is a simple example of logical operation in docplex taken from here. Code below works fine. ...
9
votes
2answers
637 views

Modeling and solvers

I have just started to dive into OR world on my work. Currently we are using GAMS with Gurobi but some of us have strong programming background and would like to have more programmatic approach to OR. ...
8
votes
2answers
804 views

Is there a way to view added constraints in Gurobi (Python)?

I should note that I am very new to Gurobi so apologies if this is obvious. I am working on a project for a class to maximize profit on a theoretical flight network by deciding which routes to fly at ...
5
votes
1answer
391 views

How to run MOSEK solver in CVXOPT

I have written a small code to do a simple min variance optimisation using CVXOPT, you can see the whole code below By using solvers.qp(P, q, G, h, A, b) in CVXOPT ...
4
votes
1answer
47 views

Access LpVariable as input to another Keras sequential network

I want to use LpVariable as an input argument to a sequential CNN network layer, which is in Keras. When I tried to call the function I got the error as follows: <...
8
votes
1answer
390 views

Creating a Continuous Decision Variable between 0 and 1 in Python-MIP Interface

This task appears to be harder than it seems to me. I want to create a continuous variable $x \in [0,1]$. To test this, I did use the open-source Python-MIP interface which uses the CBC-Solver out ...
6
votes
1answer
250 views

Creating a Decision Variable in Python-MIP with Dictionaries

I have already seen in the Python-MIP documentation on how to implement a variable with multiple indices. In each example I read, this is done with the use of lists and integers as indices. This is ...
9
votes
4answers
861 views

Open Source MILP software for Python with user-friendly API to define the optimization problem

Following the accepted answer to Assignment problem where assignments must be done sequentially I would like to write a Python script which can solve the problem defined there. It's a Mixed Integer ...
3
votes
0answers
99 views

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 $c_j$ ...
9
votes
1answer
409 views

Floating points in ORtools

I'm trying to solve an RCPSPDc model (maximizing the net present value instead of a makespan). The objective function is: $\sum\limits_{j \in \text{Tasks}} e^{-\theta\cdot s_{j}}\cdot p_{j}$, where $...
4
votes
1answer
327 views

CPLEX Python API

I am trying to run the following optimization problem at Python by using the CPLEX API: $$\min \{x_1 + x_2\ | \ x_1 \geq 3, x_2 \geq 2, 2x_1 + x_2 \geq 9\} $$ I just want to give a matrix of ...
7
votes
1answer
191 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
591 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: ...
7
votes
1answer
466 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-...
9
votes
2answers
1k 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,...
13
votes
3answers
1k 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
143 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 ...
11
votes
4answers
947 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
407 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
29 views

Restricted assignment problem with variable required tasks: feasibility in docplex.cp

I am trying to solve a kind of restricted assignment problem in which the tasks required are dependent of the user input. Let me suppose that the user can enter a set of requirements. According to ...
5
votes
0answers
46 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}...