Most Popular
1500 questions
4
votes
1 answer
Average time between two dispatches in a taxi fleet (probably a batch processing queuing system)
We have a fleet of taxis with $t$ taxis available. All taxis are identical in the sense that they have the same capacity for $p$ passengers and each taxi is dispatched only when its capacity is full.
Each taxi takes passengers from district A to…
Vitamin Z
- 103
- 5
4
votes
3 answers
Have we understood the limitations of the Simplex method on nonlinear programs?
We are always told that the Simplex Algorithm is meant for solving linear equations with linear constraints.
But how badly would the Simplex Algorithm perform if we implemented it on a typical non-linear problem that is better suited for algorithms…
stats_noob
- 1,831
- 7
- 30
4
votes
1 answer
Edit .NL files to reformulate problem instances
I would like to run a solvers comparison on several instances of MINLPLib. I can get the .NL files for each instance. Now, I would like to reformulate several instances and I need to edit the .NL files (in particular I would like to add a term to…
Luca
- 59
- 2
4
votes
1 answer
How do you know if Column Generation is any faster than standard MIP formulations?
I'm currently in the process of learning about column generation, so I apologize in advance if I show a gross lack of understanding about it.
Anyways, what I've gathered so far is that Column Generation approaches typically run faster than standard…
lobstersalesman
- 43
- 2
4
votes
1 answer
"Sensitivity Analysis" vs. "Machine Learning"
I have the following question that compares how "Sensitivity Analysis" is perceived in the field of Optimization compared to that of Machine Learning.
Sensitivity Analysis in Machine Learning:
At the core of every successful Machine Learning model…
stats_noob
- 1,831
- 7
- 30
4
votes
3 answers
VRPTW: is there a way to prevent waiting at a node before starting service?
In a typical VRPTW MIP formulation there are constraints that keep service at each node between node-specific lower and upper bounds. Using $x_{ijk}$ as a binary variable representing whether or not vehicle $k$ travels from node $i$ to node $j$,…
JBinggeli
- 41
- 2
4
votes
1 answer
Exploiting ordering to removing infeasible solutions in MILP
I kindly ask for some ideas or references to exploit ordering in MILPs.
In particular, there are resources $ r = [r_1, r_2, ..., r_K] $ such that $r_{i} \leq r_{i+1} $. These are input to the problem.
In addition, there are binary variables $ x =…
Duns
- 303
- 1
- 10
4
votes
2 answers
Eliminating Variables in Semidefinite Programs Using Equality Constraints
Suppose I have an SDP
\begin{align}\min_{X \in \mathbb{S}^{n}_{+}}&\quad f(X)\\\text{s.t.} &\quad X_{i,j} = c_{i,j} \quad \forall (i,j) \in I,\end{align}
where $I \subseteq [n] \times [n]$ and $f$ is convex on the set of positive semidefinite…
Robert Bassett
- 625
- 7
- 12
4
votes
1 answer
How to retrieve the variable's value in DOCplex
I am trying to write a simple optimization problem by using DOCPLEX. I am pretty new on python+DO and What I have tried to do is:
# Set and parameters
I = ["i1"];
J = ["j1"];
Parameters form = {("i1", "j1"): number}
# model
mdl =…
A.Omidi
- 8,832
- 2
- 13
- 49
4
votes
1 answer
Adding a group constraint to binary decision variables
I have a problem where I have N binary decision variables where each one of them belongs to a group (Where the number of groups G is less than N) and I have to choose a subset of them to maximize some criteria but there are two constraints on the…
A. H
- 147
- 2
4
votes
1 answer
Can we simplify (perhaps linearize) this constraint?
We are dealing with a stochastic model and one of the constraints is
\begin{align}
y_j=\frac{\sum_{i \in I}\sum_{k \in K}\mathbb{E}\left[X_{ik}^2\right]x^k_{ij}}{\sum_{i \in I} \sum_{k \in K} \mathbb{E}\left[X_{ik}\right]x^k_{ij}}.
\end{align}
Here,…
user9659
4
votes
1 answer
Why are the final value and reduced cost 0 in excel sensitivity report for multiple variables even though there exists a unique optimal solution?
In solving a linear program (in specific a network optimization problem of the shortest path type) with the Excel solver, I noticed two things after running a sensitivity report on the solution suggested by the solver:
First, both the allowable…
AVAS
- 43
- 9
4
votes
1 answer
Can you calculate the mean of some MIP variables using linear constraints?
got a lingering question from a graduate course in integer programming that's been bugging me ever since.
Is it possible to find the mean of some variables in a MIP without resorting to quadratic constraints?
Here's an example of what I…
gjgutier545
- 150
- 8
4
votes
0 answers
Linearize a highly non-linear objective function
[EDIT] : The formula below is updated to remove the radical, 0.5 in the term $(I_{i,v} \cdot \Delta t)$ and constant temperature $T$ replces temperature as function of current.
[EDIT] :The values of the constants are added
[EDIT] : Plot of $$…
Jose_Peeterson
- 349
- 2
- 10
4
votes
1 answer
Is Google's OR-tools for professional work? Specially VRP module
So I've been given at work a project which consist on finding optimal pathing for trucks in certain custom scenarios. When I discovered this tool I thought it worked wonders for what I understood the project was back then, but obviously we are…
