# Questions tagged [modeling]

For questions related to the process of converting a real-world problem into a mathematical model. Can include questions related to linearization, logical constraints, tightness of formulations, and so on.

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### MIP formulation for graph planarity test

In this question, it was asked wether a MIP formulation exists to test for a graph's planarity. The inputs are the graph's nodes and edges, and the output would be a certificate which guarantees that ...
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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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### Modeling traffic in a city

I am trying to model traffic in a city, $(i,j)$ represents a road in a city. There are $H$ vehicles in a city they have some prescheduled set of destinations to visit, $A_{j,h}$ denotes arrival time ...
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### Why does PuLP call copy for addition and how can I avoid it?

Using a for loop to append terms to an expression seems to be much faster than summing a group of terms all at once. Constructing the expression using a for loop uses __iadd__, which does not include ...
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### Modelling a simple ordering problem to have balanced delivery days

Assuming that I should buy 50 items from 25 different vendors with pre-known delivery duration between 2-7 day for each, which day of a week should I place each order so that the delivery days be even ...
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### Issue of Dense columns in the formulation

I'm working on a price-selection model where we need to identify price point for each time-period (could be day/week). Objective of the model is to figure out optimal price-point for each time-point ...
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### Airline revenue management re-solving problem

I am considering a bid prices (shadow price of the capacity constraint) problem (from Chen, L. and Homem-de Mello, T. (2009)., page 14) where the acceptable classes for booking requests for ...
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### Estimating multistop routing costs

In many OR problems, it is sometimes a good idea (or necessary) to relax routing constraints. An example of this occurs in the classical facility location problem, where a warehouse can send out a ...
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### Data Formulation for Mixed-Integer-Programming Models

Until now, I have used the Gurobi, CPLEX and OR-Tools (GCO) interface to formulate mixed-integer-programming models. Recently, I have discovered MiniZinc and want to utilize it to formulate big ...
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### Help in solving resource allocation optimization problem

I've been pondering on this question for some work optimization, and I need some help in being directed to the right direction. I have multiple customers that require an amount of $X$, $Y$ and $Z$ ...
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### Publishing paper that uses LP solver to solve equation

I was reading this paper by Cerna et al. (2018)1. In the paper there are only CPLEX-solvable equations given by the authors and the results. How valuable is this paper, and what is its quality? Can ...
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### Optimization model testing tooling: likes, dislikes, and wishes

Weāre [1] in the thick of building out a testing suite for decision models, starting with a focus on route optimization. There are several angles we care about [2] and are considering: unit testing, ...
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### System Stability constraints formulation

I am working with a system having a massless 2D plane and on that plane there is a rigid object with some mass placed on it. I want to support the plane with wooden sticks such that the system is ...
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### Resources on the soft aspects of modelling

Usually, the modeling involves those steps : Fuzzy Description ----(1)----> Clearer Description -----(2)-----> Mathematical model. Of course, it's not linear and a lot of iteration and re-...
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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 ...
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### Assignment/scheduling how to formulate considering job time and job cost

I have the following problem that I do not know how to formulate. There are a fixed number of workers $w_i \in W$ for $i \in [1ā¦N]$. Also, there are a fixed number of jobs that must be assigned to ...
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### How to construct a restriction for a blending problem that has 2 inputs that are blended, and as result we get 2 outputs?

THE PROBLEM A refinery has 10 million barrels of type A crude and 6 million barrels of Type B crude oil. The refinery has 3 plants to produce Gasoline (it makes a profit of 2 USD / barrel) and Naphtha ...
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### Recommendations on Operations Statistics/Analytics Approaches/Materials

I'm an operations data analyst. I was wondering if I can get recommendations on books/videos on statistical models specific to optimizing business operations through analytics and statistical modeling....
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### How to use NEOS without using Pyomo

I am new to modelling language and specifically NEOS server. I aim to solve MINLP using Baron, through the NEOS server. So, far I have been able to write model file, data file and command file as ...
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### Hardness Reduction for assigning Users to Servers

Suppose there are $x$ servers, and $y$ users. The $y$ users are to be assigned to the $x$ servers similar to classic scheduling problems. The cost of using servers is given by $c(|x|)$ which is an ...
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### Dynamic Programming problem of affecting equipment with budget constraint

I have a problem that I must formulate as a DP problem and solve. A hospital is split up into 4 sections, each section has 1 or 2 or 3 backup generators. We have to maximize the likelihood that no ...
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### Analysis model vs. executable implementation of model?

In my post-graduate research and subsequent career in operational analysis, the difference between following seems to have become clearer with the years: (1) a model of a problem or operations in the ...
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There are $N - \{1 \ldots N\}$ jobs, each with processing time $p_j$, to be scheduled on $M - \{1 \ldots M\}$ machines over span of $D - \{1 \ldots D\}$ days and while working $T - \{1 \ldots E \ldots ... 2 votes 0 answers 110 views ### Efficient way to do user rescaling of variable in Gurobi Is there a better way than the code below to the rescaling of variable in a model after the model has been build with Gurobi? Like some build in function or a direct manipulation of the column object? ... • 3,655 2 votes 0 answers 135 views ### Montoya et al. 2017 benchmark Results I am testing Montoya et al. 2017 dataset and trying to replicate the Result from this paper The electric vehicle routing problem with capacitated charging stations. I am unable to replicate the exact ... • 1,589 2 votes 0 answers 170 views ### How to solve an LPP with summation Up until this point I have only solved simple LPP problems with maybe 2 to 3 variables that looked like this, using pen and paper. I need to solve This Problem using Simplex, Dual Simplex, Big M and ... 2 votes 0 answers 90 views ### Problem classification: optimal weights for Weighted Arithmetic Mean I want to write an optimization problem then solve it, to get optimized weights to compute a final score using a weighted arithmetic mean. The problem is as follows. I have an entity (an input vector$...
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I have a set of tasks $I$ with processing times $p_i, \forall i \in I$. There exists a set of machines $M$ and each machine has availability time ranges in a given time horizon. For instance, given a ...