Community Digest

Top new questions this week:

Can presolve reductions change the value of the linear programming relaxation?

For integer programs solvers (like Gurobi, Cplex, ...) report the value of the linear programming relaxation for integer programs, i.e. Root relaxation: objective 2.648400e+02, 233 iterations, 0.01 ...

mixed-integer-programming linear-programming  
asked by user3680510 10 votes
answered by Marco Lübbecke 14 votes

What is the definition for an integer-friendly constraint?

I have seen some papers claiming that their proposed model is integer-friendly. I would like to get more information about what type of constraints we can call integer-friendly. Probably, it can be ...

mixed-integer-programming modeling terminology  
asked by Mostafa 6 votes
answered by Nikos Kazazakis 3 votes

Is there a name for this variation of the assignment problem?

I'm given two matrices: $A$, an $n\times n$ adjacency matrix of a graph. The graph is unweighted, undirected and has no self-edges or multi-edges. $X$, an $n\times n$ symmetric matrix of edge ...

asked by user3636 6 votes
answered by user3680510 8 votes

Safety stock for lumpy demand

I have a product for which the monthly demand pattern for the last year looks like the following. The product is ordered only 22 days out of 366 days in batch sizes of 272 kgs. Since there are so ...

asked by Nishant Kumar Gupta 5 votes
answered by LarrySnyder610 5 votes

How to use tight upper and lower bounds to get to the optimal value via branch and bound?

I have algorithms that get me a tight upper (UB) and lower (LB) bound to a maximization binary integer program (a routing problem). My formulation is non-compact and requires the addition of sub-tour ...

cplex vehicle-routing branch-and-bound bounds branch-and-cut  
answered by prubin 2 votes

Simplex - Network flow problem : Arc from 1 to P with infinite capacity

The Network - Maximum flow problem below aims to find the maximum flow using simplex method : With the LP as follow : LP : \begin{Bmatrix} Z(Max) = \sum_{i=1}^{m} fi \\ Af =0 \end{Bmatrix} ...

optimization simplex graphs network-flow  
asked by JirenOppaik 1 vote

Greatest hits from previous weeks:

Counter-intuitive results in OR

When teaching introductory OR courses I have often found that presenting counter-intuitive or paradox-like results is a great eye-opener for the students. I use these examples and results as a ...

asked by Sune 36 votes
answered by LarrySnyder610 27 votes

Solving pricing problem heuristically in column generation algorithm for VRP

In the set covering/column generation approach for the VRP (Balinski and Quandt (1964), or e.g. this tutorial), the basic idea is: Generate some routes. Solve the set covering problem using those ...

reference-request vehicle-routing heuristics column-generation set-covering  
asked by LarrySnyder610 21 votes
answered by Kevin Dalmeijer 19 votes

How is Big M calculated?

Because of excessive pollution on the Momiss River, the state of Momiss is going to build pollution control stations. Three sites (1, 2, and 3) are under consideration. Momiss is interested in ...

optimization mixed-integer-programming integer-programming big-m  
asked by The Poor Jew 5 votes
answered by RobPratt 6 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

Allocating credit card points

I’m interested in the idea behind this in general, so I thought this would be the best place to post, though I have a practical and semi-urgent need of allocating the points on my credit card towards ...

optimization integer-programming finance knapsack  
asked by Dave 12 votes
answered by CMichael 9 votes

Polyhedra, Polyhedron, Polytopes and Polygon

About Polyhedra, Polyhedron, Polytopes and Polygon, what do they mean in the context of linear programming and what is the difference between them?

linear-programming terminology polyhedra  
asked by A.Omidi 14 votes
answered by TheSimpliFire 19 votes

Linear Programming with additional "if-then"/"Default to zero" constraints?

What approaches can I use for a Linear Programming problem with the additional constraint that if a decision variable falls below a certain threshold, then it should just be forced to 0. I'm ...

linear-programming convexity  
asked by Alex Kinman 15 votes
answered by David Bernal 9 votes
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