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1500 questions
4
votes
1 answer
Solution time of different formulation
In MIP, what's the difference of solving time between the following two formulations?
$x_i = 0$ for $i\in I$, and
$\sum_{i\in I} x_i = 0$.
Suppose that $x_i, \forall i\in I$ are all binary variables.
nousername
- 41
- 1
4
votes
1 answer
Accelerating an integer programming model
I am working on a scheduling problem, where I am solving it through column generation. The pricing problem of this algorithm is an integer programming model as follows:
\begin{equation}
F_1 \Big\{V^0 + \sum_{k \in \mathcal{K}} \sum_{o \in…
mdslt
- 615
- 3
- 8
4
votes
1 answer
Reduce optimality gap and get a solution faster
I have a maximization problem that I know that the maximum value of the objective function should be 6000. When solving the problem using Xpress, I end up on something like the following:
Node BestSoln BestBound Sols Active Depth …
christouandr7
- 73
- 5
4
votes
3 answers
Is this ILP formulation for Group Closeness Centrality a column generation approach?
I want to solve the Group Closeness Centrality problem where the input is a graph $G=(V,E)$ and integer $k$ and we want to find a vertex set $S$ of size $k$ minimizing the total distance of the vertices in $V\setminus S$ to $S$. Here, the distance…
Christian Komusiewicz
- 143
- 5
4
votes
0 answers
How to invoke a solution pool and access all the solutions in cplex using PYOMO ? this is the structure of my pyomo code
model = pyo.ConcreteModel()
opt = SolverFactory('cplex', executable = cplex_executor_path)
model.x = Var(ftHc, within = NonNegativeIntegers)
model.y = Var(ftHc, within = NonNegativeIntegers)
model.obj = pyo.Objective(expr = xyz,…
Prachi Patki
- 41
- 2
4
votes
2 answers
Phase I of the simplex method and Farkas certificates
Phase I of the simplex method solves an auxiliary optimization problem to determine an initial basic feasible solution, or concludes that no such exists. Is there a way to use the solution of this auxiliary problem to construct a Farkas certificate…
fmg
- 223
- 1
- 6
4
votes
1 answer
Upper bound on number of pivots to escape a degenerate point
Is it always possible to escape a degenerate point by a single pivot, or is it possible that several pivots are required?
In other words is it possible to get away from a degenerate point by a single pivot regardless of which of the possible bases…
gmn
- 666
- 4
- 10
4
votes
1 answer
Geometric Programming with Simple Affine Equality Constraint
Consider a Geometric Program (GP),
$$
\begin{array}{cl}
\operatorname{minimize} & f_{0}(x) \\
\text { subject to } & f_{i}(x) \leq 1, \quad i=1, \ldots, m, \\
& g_{i}(x)=1, \quad i=1, \ldots, p,
\end{array}
$$
where $f_i$ are posynomial functions,…
Apprentice
- 215
- 1
- 9
4
votes
1 answer
Subtour elimination implementation (DFJ) using Python (PULP). While loop never exits
The simple test problem I'm trying to implement is
\begin{align}
\min &\quad c_{ij}x_{ij} \\
\text{s.t} &\quad \\
&\quad \sum_{j\in N}x_{ij} = 1, \quad i\in N\\
&\quad \sum_{i\in N}x_{ij} = 1, \quad j\in N\\
&\quad x_{ii} = 0, \quad i\in…
Parseval
- 207
- 1
- 6
4
votes
4 answers
Visualizing results to the RCPSP
Bot for getting better insight and reporting purposes, I am looking for a way to visualize results to the Resource-Constrained Project Scheduling Problem (RCPSP). I am aware that such results are most often represented by a resource Gantt chart. An…
Rutger
- 115
- 4
4
votes
0 answers
Conditional constraint formulation
How can I create constraints to make sure $x=1$ if $k\geq 0$ and $x=0$ if $k<0$, where $x\in \{0,1\}$ and $k\in \mathbb{R}$?
Here is my attempt:
\begin{equation}\label{cons:1}
\begin{aligned}
k\leq Mx
…
tcokyasar
- 1,249
- 5
- 12
4
votes
0 answers
If and then constraint for a special case
I have the following constraint:
$$f\geq C_1\left(d-z-E_1-E_2\right)+C_2\left(E_1+E_2\right).$$
Here $f, d,z\in \mathbb{R}_{\geq 0}$ and $y\in \{0,1\}$ are variables and $C_1$, $C_2$, $E_1$, and $E_2$ are parameters.
I want to have this constraint…
tcokyasar
- 1,249
- 5
- 12
4
votes
1 answer
large scale optimization with Python
I am dealing with the following optimization problem:
$$
\underset{x}{\min} q(x)
$$
subject to
$$
l_{x} \leq x \leq u_{x} \,\,\,\, \text{ and } \,\,\,\, l_{a} \leq Ax \leq u_{a}.
$$
where $q(x)$ is a quadratic objective function.
In my case the…
AnTlr
- 43
- 4
4
votes
0 answers
What is the ACM Queue for operations research (or sub-disciplines)?
In his 2016 Usenix presentation Bryan Cantrill highlighted an issue with how conferences work in operating system research. He mentioned an alternative format called Queue by ACM which he describes as leading practitioners are gathered and in loose…
worldsmithhelper
- 4,007
- 6
- 21
4
votes
2 answers
Modeling an either-or-constraint
We would like to model a constraint for an assignment problem that dictates that either assign a specific subset of nodes $I\subset\mathcal{I}$ to a specific subset of nodes $J\subset\mathcal{J}$, or don't assign them at all.
In other words, for…
user9659