Operations Research Stack Exchange
Operations Research Stack Exchange

Most Popular

more tags
1500 questions
9
votes
1 answer

Rules of thumb for using classic methods (e.g. branch and bound) vs. meta-heuristics (G.A, S.A, etc..) for non-convex problems?

Are there any rules of thumb for when to use classical methods like branch and bound, branch and cut, etc...for non-convex problems, vs using meta-heuristic methods like genetic algorithms, evolutionary algorithms, simulated annealing, etc....? When…
Skander H.
  • 2,139
  • 2
  • 11
  • 21
9
votes
0 answers

Ill-conditioned LP in Benders decomposition

I have implemented a Benders decomposition for a constrained network flow but the LP solver (Gurobi) warns me of the ill-conditioning of the subproblem dual LP. As you can see below, the coefficients seem well behaved but I still get warnings like…
Mauricio Zambon
  • 191
  • 2
9
votes
1 answer

Binary variable to count appearances

Let $x \in \mathbb{R}^n$ be an optimization variable. Now, at a constraint, I would like to count how many times a value, say $2$, appears in $x$ decision. I think we can have a binary variable $y_i$ indicating whether $x_i =2$. So, $x_i - 2 = 0$…
independentvariable
  • 3,980
  • 10
  • 36
9
votes
2 answers

Integer Decision Variables Always Forced to Zero in Minimization Problem (MINLP)

I am trying to write out a MINLP problem of optimal control for an invasive species and the code that I have for my PYOMO model is below. Some of the initialization values take from an Excel spreadsheet, so they are not made explicit in the…
GrayLiterature
  • 2,309
  • 7
  • 27
9
votes
0 answers

For the solution of complex gaming are we to leave behind approximation and fixed algorithms in favor of agents?

For an evolutionary extensive form game is the use of multi-agent systems a necessity or can more traditional approximate Nash equilibria and mean-field interactions suffice? Few games can be represented completely by a simple tree and solved…
Rob
  • 2,110
  • 1
  • 13
  • 34
9
votes
2 answers

Common structures in Gurobi - Python

I'm new to Gurobi in Python and I was wondering if someone knows how to code some common structures of linear constraints. I'm trying to understand how you'll code something like the following constraints: \begin{alignat}2\sum_{i\in A\mid i\ne…
SantiagoAm16
  • 103
  • 4
9
votes
3 answers

To which area does constraint programming belong?

The problem I solved is a flow-shop scheduling problem with parallel machines. I solved it with the IBM ILOG CPLEX Optimization framework. There I used the constraint programming (CP). The question is now to what kind of field of operations research…
Tobias M.
  • 343
  • 1
  • 5
9
votes
3 answers

Matlab fmincon for a problem with many nonlinear constraints

Using Matlab to solve a problem which has linear objective function and many nonlinear constraints, I am trying to generate the inequality nonlinear constraints by a function and pass it to fmincon solver via nonlcon option. My question is if there…
Oguz Toragay
  • 8,652
  • 2
  • 13
  • 41
9
votes
1 answer

Using Spatial Multi Criteria Analysis for simultaneously locating various facilities?

Is it possible to use SMCA (Spatial Multi Criteria Analysis) for determining simultaneously where to locate various facilities? Suppose, for example, I'm planing to build a new city and everything has already been determined, with the exception of…
Saul Berardo
  • 191
  • 1
9
votes
1 answer

pyomo - pass time limit to NEOS

I am sending a pretty complex Pyomo MINLP to NEOS using Couenne. I'm getting an error message that the solve time is too long (sorry, I don't have it still in my Python console). Is there a way to set a max time and return the best feasible result?…
Ralph
  • 371
  • 2
  • 5
9
votes
1 answer

Profit Maximization vs Cost Minimization for Employee Scheduling

I wanted to write two objective functions for an employee scheduling problem (MIP) until it occurred to me, that one objective function may be redundant. Is there a difference between the cost minimization and profit maximization for this assigning…
Georgios
  • 1,193
  • 5
  • 21
9
votes
2 answers

How to determine the convexity of my problem and categorize it?

My problem is: \begin{align}\min\limits_{x_{ij}}\qquad&{\sum_{i\in N}\sum_{j\in M}\frac{x_{ij}}{C_j-\sum\limits_{i\in N} x_{ij}a_i}}\\\text{s.t.}\qquad&0
Ben
  • 101
  • 6
9
votes
1 answer

Extreme rays in polymake

I am trying to find extreme rays of a polyhedral cone using polymake. My understanding is that in a cone, every feasible solution is also a ray and an extreme ray is a ray that cannot be written as the convex combination of two other rays. The…
Florian Pommerening
  • 385
  • 1
  • 7
9
votes
1 answer

Real world demand dataset

I am looking for a publicly available real world demand data to compare the performance of some algorithms. The dataset should include some products with data of a sufficiently long period of time. I know the FoodMart dataset, whose structure you…
Afshin Oroojlooy
  • 835
  • 8
  • 15
9
votes
1 answer

Stochastic VRP: Sources of uncertainty and modeling approaches

In one of the archived research topics of mine, I tried to model and solve SVRPs using Multiple Tandem Queues. I have two related questions: What are the sources for uncertainty in Stochastic VRPs? In other words, what causes the stochasticity in…
Oguz Toragay
  • 8,652
  • 2
  • 13
  • 41
1 2 3
…
99 100