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.

23 questions with no upvoted or accepted answers
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OR-TOOLS : delivery node with multiple possible pickup nodes

I am using ortools to model a VRP with pickup and delivery constraints, where pickups can be done at different nodes. For example, if node A has a demand, it must be picked at node B or C. Here is how ...
7
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136 views

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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66 views

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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63 views

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 ...
6
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53 views

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 ...
6
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114 views

Modelling issue with precedence constraint in OR-Tools

I'm trying to solve an RCPSPDc model It is infeasible, although Ilog Cplex solves it, so I think I have a modelling issue. I have more constraints but the precedence is the one that makes it ...
6
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62 views

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 ...
6
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110 views

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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75 views

Modelling issue with rcpsp and boolean expressions

I'm trying to solve an RCPSPDc problem in OR-Tools with CP-SAT solver. In my RCPSPDc model (with discount rate) i want to set this objective: $$\max_{s}\sum_{j\in J}\text{profit}_{j}\cdot \frac{1}{(1+...
4
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91 views

Can this problem be modelled with a transformation from a known TSP with profits?

The profitable tour problem (PTP) is defined on a graph $G=(V,E)$ with $|V|=n$, where each vertex $i \in V$ has an associated prize $m_i \geq 0$ and each edge $e \in E$ has an associated cost $c_e \...
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66 views

Adding redundant inequality to a model

The following relationship is part of my optimization model ($W_k$ denotes a binary variable) $$W_{1} \le \cdots \le W_{k-1} \le W_{k} \le W_{k+1} \le \cdots \le W_{k^{\max}}$$ My question is, do ...
4
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161 views

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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188 views

How can I formulate this multi-objective optimization problem?

Now, for each system $X$ $(X=A,B,C,E)$, my objective is $$\max\min\frac{s_{x_u}}{d_{x_u}}$$ here, $x=a$ for system A, $x=b$ for system B and follows... and for the whole system, my objective is $$\max\...
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49 views

What are the efficient ways to model this scheduling problem and ways to improve running time

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 ...
3
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0answers
46 views

Discrete optimization in transport economics

I was working on a problem in transport economics where the optimal number of trips in a given duration of time is to be found out. The profit is a function of the price vector $p$ and time cost $c$ ...
2
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69 views

Production planning for a video game economy

I'm a software developer who likes to play a video game that has a complex economy. I realized that the type of problem I'm trying to solve mimics real life operations research problems, and I am ...
2
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68 views

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 ...
2
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0answers
63 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? ...
2
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0answers
105 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 ...
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58 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 ...
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59 views

Problem classification: optimal weights for Weighted Arithmetic Mean

I want to write an optimisation problem then solve it, to get optimised 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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50 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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111 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: ...