Operations Research Stack Exchange
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Is it possible to solve VRP using OR-Tools CpModel, instead of RoutingModel?

Is it possible to solve VRP using OR-Tools CpModel, instead of RoutingModel? I want to do synchronized VRP, which is combining vehicle routing and scheduling constraints
Rizky Luthfianto
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3 answers

Fast algorithm for Transportation Problem in Python?

The Transportation Problem can be solved with a simplex algorithm, but it's time-consuming. I'm wondering if there exists a specific Python-implemented algorithm with low complexity.
dgamboz
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Polynomially solvable cases of zero-one programming

I am dealing with a problem having two types of variables: binary variables, and continuous variables. In some cases, the continuous variables are not used, and so the problem contains those binary variables only. These cases are then very easy to…
Mostafa
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How to convert this if-then constraint to MIP constraint?

How to convert this if-then constraint to MIP constraint? $\text{if } a \geq 0 \text{ then } b=K_1 \text{ else(a <0 ) } \ b =K_2$
SAH
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What is the difference between root relaxation and LP relaxation

(I apologize. I saw this question but, I do not know these may be the same or not.) I am trying to solve a MIP problem and have an issue about that. The problem's LP relaxation has the objective value about $63$ but, when the problem is solved by…
A.Omidi
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2 answers

Monte-Carlo Simulations in inventory management

I am using Monte-Carlo simulations in Microsoft Excel to determine optimum reorder points and safety stock levels. I have the demand patterns of the last one year of the product. Using that I can construct a cumulative distribution function of the…
Nishant Kumar Gupta
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1 answer

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 many months with 0 demand, the demand distribution…
Nishant Kumar Gupta
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A good memoryless elevator strategy?

Could you OR whizkids please help me out with this one: https://stackoverflow.com/questions/61854621/a-good-memoryless-elevator-strategy Surely somebody has solved this before. How do you classify this problem? A 1D transportation problem? A routing…
Henrik4
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1 answer

Physical Interpretation of a dual of an LP

I was recently asked to physically interpret a dual of an LP for an audience who does not know mathematics/OR (without LP, dual, bounds, etc.). Though I attempted it and was very close to what the person wanted to hear (he said that), I did not meet…
Divyam Aggarwal
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3 answers

Linear programming convexity

Is it possible for a linear programming model to be non-convex ? If it is, please, provide a simple 2 variables example and explain why it is non-convex. EDIT 1: I have been wondering, maybe the following constraints are…
G Oliveira
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Complexity of determining whether a LP or MIP is infeasible

What is the best complexity for the worst case scenario and the algorithm associated with it to determine if a linear programming (LP) is infeasible ? Further, what if we consider a mixed integer programming (MIP) ? Note that I only would like to…
G Oliveira
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1 answer

Deterministic termination criteria for CBC

I'm running CBC on problems for which not always an integer solution can be found in a given time, so the command line option sec 120 is set (2 minutes maximum). The random seeds are also set to avoid that the same run returns different results…
orange
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2 answers

Estimating optimal inventory in times of high uncertainty due to coronavirus

I'm trying to help out a relative of mine who runs a small highly seasonal business in the clothing/textiles industry. 80% of sales are in Q1 of every year, and the purchasing and manufacturing decisions must usually be placed around May-July given…
leonsas
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5
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1 answer

How to write quantity discount constraint?

In a simple transportation problem like below image, how to model a constraint for shipment discount e.g. if quantity transported from any origin to any destination is more than 100 unit then the supplier will offer 10% discount in the cost of…
Ritu Rathore
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3 answers

Problem with binary decision variable constraints in VRP

I would like to create non-linear violation costs in my VRP. I already created my whole VRP with time windows in which I have these decision variable: dvar float+ w[N][D]; // violation time for late arrivals for every node and every day These dvars…
Jeroen
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