Community Digest

Top new questions this week:

Unpopular/Obscure solvers/algorithms that you used

There are many (numeric) optimizers which solve some subset of the set of multi-objective, black-or-grey-or-white box, robust, stochastic, mixed-integer, non-linear, non-smooth, manifold-constrained ...

asked by worldsmithhelper 9 votes

Formulating two non-negative variables without binary and/or big-M

There are two non-negative integer variables $q$ and $p$, where only one of them can take a positive value. To impose this relation, I write: \begin{align} q &\leq M(1 - y) \tag1 \\ p &\leq M(...

mixed-integer-programming modeling binary-variable big-m  
asked by Mostafa 6 votes
answered by RobPratt 8 votes

Are there strategies/rules/systematic approaches to derive alternative formulations for an optimization problem?

For a given optimization problem there are often many known math programming formulations. For example for the TSP here is a survey of many ...

asked by user3680510 5 votes
answered by LocalSolver 4 votes

Column generation for a linear optimization problem

I have an LP that has exponentially many constraints, and just linearly many variables. The dual of the problem, therefore, has exponentially many variables, while just linearly many constraints. My ...

linear-programming column-generation duality  
asked by independentvariable 5 votes
answered by mtanneau 12 votes

What are useful plots/statistics/metrics when analyzing the solution sensitivity in multi-objective optimization?

Consider an optimization problem with $n>3$ objectives. For handling this there exists often two approaches: a) some weighting of the objectives, b) fix an order of objectives and then optimize ...

mixed-integer-programming multi-objective-optimization  
asked by user3680510 5 votes

Ipopt (probably) fails to solve a nonlinear problem, what is next?

I am trying to solve a nonlinear problem with only a set of continuous variables (where the nonlinearity stems from negative inconsistent - across differently indexed variables - large powers), e.g., ...

nonlinear-programming pyomo open-source  
asked by Taner Cokyasar 4 votes
answered by Nikos Kazazakis 2 votes

TSP with Repeated City Visits

Suppose that we have a standard TSP, except that it is required to visit each city at least once instead of exactly once. The challenge is: how to transform this problem to a standard TSP? To that ...

asked by DSPinfinity 3 votes
answered by worldsmithhelper 6 votes

Greatest hits from previous weeks:

How do I access the value of a variable in PuLP?

In Python's PuLP package, how can I get the value of a decision variable? For example, if I declare a variable— ...

python pulp  
asked by LarrySnyder610 9 votes
answered by LarrySnyder610 12 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 ...

asked by Kevin Dalmeijer 35 votes
answered by Kevin Dalmeijer 51 votes

How to improve the quality of code in OR?

So I noticed, that a lot of students taking OR-classes come from non-computer science backgrounds (e.g. buissiness administration). They typically had only one other class in their first semester ...

reference-request software or-careers  
asked by Luke599999 8 votes
answered by Richard 8 votes

Are there any COVID-19 (coronavirus) related optimization problems with input datasets that we can "crowd solve"?

Is anyone aware of a medicine/vaccine related challenges with a good problem definition and some available input datasets, ideally related to COVID-19? What kind of constraint solving challenges would ...

asked by Geoffrey De Smet 41 votes
answered by Sebastiaan van den Broek 16 votes

Is there any relationship between KKT and duality?

I noticed the similarities between KKT and complementary slackness, but I do not fully understand it.

linear-programming duality kkt-conditions  
asked by Amos 8 votes
answered by Kevin Dalmeijer 21 votes

What is the purpose of libraries like Pyomo and Google OR tools?

I'm new to the OR world, and trying to learn the various tools available. I originally thought that Pyomo and Google OR tools were open source alternatives to commercial solvers like Gurobi or CPLEX. ...

cplex pyomo gurobi modeling-languages  
asked by Skander H. 17 votes
answered by Bethany Nicholson 16 votes

Solving a minimization problem using a Simplex method

There is a method of solving a minimization problem using the simplex method where you just need to multiply the objective function by -ve sign and then solve it using the simplex method. All you need ...

linear-programming simplex  
asked by John adams 6 votes
answered by oszkar 15 votes

Can you answer these questions?

Find multiple solutions in Pyomo with Gurobi

I am fairly new to Pyomo and Gurobi. I'd like to find 20 sets of different solutions that meet the following constraints. ...

gurobi pyomo  
asked by ssswokao 1 vote

CPU time on Linux with Gurobi

I am solving a MILP model in C++ using Gurobi 10.1. I retrieve the CPU time of my C++ program under Linux via the following commands: ...

optimization gurobi c++  
asked by Pratim 2 votes
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