# Operations Research Stack Exchange Community Digest

## Top new questions this week:

### Restoring a list from differences

Given a list of (absolute valued) pair differences ordered and with duplicates removed, how can we recover/reconstruct the list that generated these differences? We do not know anything about the ...

combinatorial-optimization difference-lists picat asked by hakank 10 votes

### How fair is limit solver threads when publishing?

Reading gurobi reference manual I found this: We have also found that certain classes of MIP models benefit from reducing the thread count, often all the way down to one thread. Starting multiple ... asked by seimetz 9 votes answered by prubin 5 votes

### Column generation for TSP

For teaching purposes, I would like to solve the Travelling Salesman Problem with a column generation approach. In the academic literature, an approach is proposed (for example here), where columns ...

modeling column-generation traveling-salesman dantzig-wolfe-decomposition asked by Kuifje 8 votes

### Convex Optimization: Separation of Cones

I am trying to solve Exercise 2.39 at Boyd and Vandenberghe's Convex Optimization book. In one source, the answer is given as: 2.39 Separation of cones. Let $K$ and $\tilde K$ be two convex cones ...

convexity convex-optimization cone asked by independentvariable 7 votes answered by independentvariable 2 votes

### Operations Research books by world-famous authors made available on the web, despite not being "completed"

Are there any books on Operations Research subjects by world-famous authors which have been made available for free access on the web, despite never having been "completed" to the standard to which ...

online-resources books manuscripts asked by Mark L. Stone 7 votes answered by EhsanK 9 votes

### Why is there a constant in the objective function of the *best subset selection problem*?

This article presents the following formulation of the best subset selection problem $$\min_{\|\beta\|_0\leq k}\frac{1}{2}\|y-X\beta\|^2_2$$ I wonder where the $1/2$ comes from. Help appreciated. asked by k88074 7 votes answered by Mark L. Stone 8 votes

### Precedence Constraint in OR-Tools

I'm trying to write this constraint in C++ and add it to my model (addLessOrEqual): $$\text{start}_{i}+\text{duration}_{i}\le\text{start}_{j}$$ for an $(i,j)$ arc of precedence. Starts (IntVar) and ...

constraint-programming or-tools c++ asked by Diego R. Troncoso 5 votes answered by Stradivari 6 votes

## Greatest hits from previous weeks:

### How to determine the correct level of detail when modelling?

"All models are wrong, but some are useful" - George E. P. Box I usually work on what one could call operational problems. There I usually do not have too much trouble figuring out the level of ...

modeling strategic-planning asked by Renaud M. 32 votes answered by E. Tucker 23 votes

### "Best practices" for formulating MIPs

Often there are many alternatives ways for formulating a MIP. For example: The model contains inequality constraints that must hold with equality in an optimal solution. The model contains ...

mixed-integer-programming linear-programming solver cplex asked by Rolf van Lieshout 26 votes answered by Marco Lübbecke 18 votes

### What is a "hard problem" in the context of Mixed-integer programming?

As a practical (real-world problems) point of view, it's important we could solve optimization problems as quickly as possible (for instance, to release a daily schedule). Maybe a problem with many ...

mixed-integer-programming optimization modeling asked by A.Omidi 12 votes answered by prubin 7 votes

### Soft constraints and hard constraints

The terms "soft constraints" and "hard constraints" are used in the context of optimization modeling. Is there any standard way to figure out which is which in some of the complicated models?

optimization modeling constraint asked by A.Omidi 11 votes answered by Dipayan Banerjee 19 votes

### What are common and not so common abbreviations in Operations Research?

Many abbreviations are used in Operations Research. For example, we have abbreviations for problem classes (LP, MIP), solution methods (IPM), and specific problems (TSP, VRP). Which abbreviations are ...

terminology asked by Kevin Dalmeijer 31 votes answered by Kevin Dalmeijer 40 votes

### Is there a SQL/English like language that lets you define formulations given some data?

It would be very useful for beginning and non technical users to be able to define models in a way that was natural for them. Further this could perhaps assist generating some kind of generic ...

mixed-integer-programming applications modeling asked by fhk 13 votes answered by LarrySnyder610 11 votes

### Optimization terminology: "Exact" v. "Approximate"

In optimization literature, I frequently see solution methods termed "exact" or "approximate". (I use the term "method" here because I suspect exactness, or its lack, is a function of both algorithm ...

combinatorial-optimization terminology asked by prubin 25 votes answered by Michael Feldmeier 23 votes

## Can you answer these questions?

### Gurobi stuck at start - 16GB RAM exhausted

I'm solving a large instance using Gurobi 7.0, 64-bit version on machine with 16GB of RAM. Gurobi is stuck at the start and all the memory is exhausted. Here is the output: 5378534 variables, all ...

integer-programming gurobi asked by lazar 4 votes

### Demonstrating a given solution is basic for a MCFP?

Given a minimum-cost flow problem, how could I go about demonstrating that a specific solution (as sets of basic and non-basic (!) arcs that build a rooted spanning tree for a given graph) is basic ...

simplex network-flow asked by Johnny Bueti 5 votes

### 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 ...

mixed-integer-programming linear-programming modeling journals asked by anoop yadav 4 votes
You're receiving this message because you subscribed to the Operations Research community digest.
Unsubscribe from this community digest       Edit email settings       Leave feedback       Privacy Stack Overflow, 110 William Street, 28th floor, New York, NY 10038

 <3