# Questions tagged [combinatorial-optimization]

For questions about optimization over a discrete solution space.

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### Unable to find good solution for CVRP with Time Window

I am trying to solve Capacitated VRP with Time Window for 50 demand points. I was trying to optimize this in Gurobi Solver but it doesn't give good answer like optimality gap is 30% or more. Any idea ...
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### Shift roster (calendar) - mathematic optimization algorithm

I have question about heuristic searching problem - I need to plan shift roster for workers. My solution is to use some bio-inspired algorithm. My implementation is: I created list of timeframes (...
150 views

### optimizing choosing subset of best items

I have a simple problem that doesn't perform well at the moment. I have a set of ~1000 candidates, from which I want to choose ~10 optimal candidates. They all have a score, and the optimal subset is ...
104 views

### Solving a Variant of Bin Packing

We have a set of bins that are partitioned into fixed blocks of size $S = \{S_1, S_2, \ldots S_n\}$, and the items are all of sizes from $S$. An item can be allocated to a bin partition if the size of ...
1 vote
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### 2D bin packing where some items must be packed in the same bin?

I am solving a 2D bin packing problem, however, there is an additional constraint where some items must be in the same bin. The problem is at industry scale (up to 1000 items and ~200 bins of ...
58 views

I am looking for guidance on a solution to the problem of picking the best special offers that can be applied to a given basket of items. In the system, a special offer has N collections of qualifying ...
1 vote
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### What reasons would cause lazy constraints to degrade the performances when reoptimizing with a different objective?

We are currently solving a hard MILP problem on optimality. Once it has been solved, several times (from 5 to 10 times), we change one coefficient of the objective function and reoptimize. Thus the ...
213 views

### Best known results on the flexible jobshop benchmarks

Is there a website that compiles the best known results on the flexible jobshop problem ? I know there was a blog post/article by Quintiq, a (deleted) blog post on CP Optimizer, some more recent ...
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### Problem 8.17 of Korte and Vygen

An airline wants to conduct a given set of scheduled flights with as few airplanes as possible. All available airplanes are of the same type. For each flight we know the departure time and the flight ...
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### Assignment of colored boxes to groups

I am working on a problem that I think can be solved as an extension to the assignment problem, but am open to hear about other ways to solve. PROBLEM There are a lot of colored boxes. For each color ...
63 views

### How to Group IDs Based on the Difference of Each IDās Min and Max Value?

I have a dataset that contains IDs along with their corresponding minimum and maximum values. Hereās a sample of the data: ...
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### Grouping of a list of elements in fixed order to maximize the total return of all the groups

I'd like to ask about if there's an existing type of problems that fits to my question. (Searching it for a while but cannot get to the point) Basic Problem Description: Given a sequenced list (order ...
52 views

### updating cliques for an updated graph

A graph $G$ has nodes $V$ and edges $E$. Let's say I have found the maximum clique or all the cliques in $G$ with any algorithm, such as the Bron-Kerbosch algorithm. After a while, $E$ has been ...
1 vote
114 views