Questions tagged [ampl]
For questions related to the algebraic modeling language AMPL.
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it is possible to have a constraint that does not contain any decision variables
I had formulated an optimization model, and along the way I had to change a variable into a parameter. In doing so, one of my constraints that contained the variable I changed no longer contained a ...
- 23
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3
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120
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Optimization solver that satisfies variable values within set membership
Is there a solver that can handle an AMPL model of this sort:
...
3
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1
answer
240
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Unexpected runtime error
I have a model that contains the sets (both ordered and Days also circular): Days and Personnel, and I'm trying to make a restriction run exaclty once per Day for every member of Personnel. I'm using ...
3
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2
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62
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Constrained shift assignment problem using ilogcp solver can´t find an optimal solution
I´ve been trying to solve a contrained assignation problem given a set of constraints based in a real-world problem. I modeled the problem in AMPL as follows:
...
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0
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208
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How to make unconstrained variables non-negative (as in excel solver) in AMPL?
This is a sequencing problem.
I've got this variables
...
- 11
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0
answers
139
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How to use ampl.lic in Pyomo
I have the licence of some solvers and I want to use these solvers in Pyomo. The licence file is ampl.lic and my machine is Macbook.
I have an executable file for Baron solver which is only for demo ...
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0
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1
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122
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How do I get the first and last item of a set in GLPK
I have a college exercise that I need to create a linear programming model from an academic paper. This has to be written in Gusek software which uses GLPK as a resolver.
The article defines sets in ...
- 111
1
vote
1
answer
153
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Why is the value negative? AMPL
I developed an LP model where it allocates the number of cassava crackers to the declared number of stores depending on their minimum demand.
I have a concern because when I ran the code in AMPL, ...
- 29
15
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2
answers
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Is Apple's M1 suitable for Operations Research?
I am curious about the performance of Apple's M1 chip solving optimizations models, MIP, LP, and in solutions approach as benders or columns generations.
I read that is a spectacular cpu to perform ...
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2
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1
answer
157
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Error defining a binary parameter in AMPL
I have to define this binary parameter in AMPL:
param h{k in K, j in Jk, t in T, r in R}; binary
which equals 1 if a bus of type $k$ and age $j$ can be assigned to ...
- 21
2
votes
2
answers
226
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AMPL Gurobi Define Variables Bounds
I am trying to define both upper and lower bounds for a vector of variables in AMPL (solver Gurobi). However, after solving to optimal solution, the variables violate the bounds. The only way these ...
- 159
3
votes
1
answer
291
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VRPTW implementation
Does anybody have an example of the vehicle routing problem with time windows (VRPTW), implemented on Python with CPLEX library, AMPL, or MiniZinc? So far I've looked into ...
- 175
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1
answer
135
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Add robustness of AMPL code through file name
I want to add robustness to my AMPL code, here is what I am actually doing:
In my script I use a .txt file that contains all my parameters, let's call it "instance.txt". I want to print my ...
- 113
5
votes
2
answers
479
views
Overwrite on a txt file from AMPL
I have a result I want to save in a .txt file. So I use this line to save a result k:
...
- 113
1
vote
1
answer
156
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Handy way to index set of tuples in AMPL
I am dealing with a discrete math optimization problem on a complete graph. My variables are the arcs but I want to delete the arcs that "cost too much". I have $n$ nodes which means I have $...
- 113
3
votes
1
answer
174
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Find a particular optimal solution
After writing an integer linear program in AMPL, I solved it using CPLEX. Now, I have some variables that must necessarily be 1, others that must necessarily be 0 and finally it is possible that some ...
- 133
4
votes
2
answers
363
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Combinatorial Optimization using AMPL
I want to solve the following integer programming problem using AMPL. The problem is the following (It was already asked on mathstackexchange.com, but I need to know how to solve it using AMPL):
Let $...
- 41
3
votes
1
answer
256
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How to define hybrid variables without using additional binary variables?
I am working on a large NLP model with equilibrium equations in which the variables are defined in the following form:
$$x_i \in [L_B, U_B] \cup\{0\} \quad \text{where} \quad L_B \ \& \ U_B \in\...
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3
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0
answers
71
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Integer variable optimization - decreasing execution time
I have a variable declared as follows in AMPL:
...
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3
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1
answer
330
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How to set combined stop condition in AMPL/CPLEX?
I would like to set a stop condition combined of a timelimit and a relative MIP gap.
So I would like AMPL/CPLEX to look for the solution of my LP for an hour and if there isn't a solution stop if or ...
- 287
7
votes
3
answers
395
views
Constraint that checks for an undirected graph whether it is connected?
I would like to create a constraint with AMPL that checks whether I am able to reach from one node $v$ to all other nodes of a set but I don't really know how to formulate it (especially in AMPL (+...
- 287
5
votes
2
answers
78
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AMPL implement constraint
I'm trying to implement the following in AMPL:
$$ i \in [N], j \in[N] \backslash \{i\}, t \in [T] $$
I have so far written the following:
...
- 129
5
votes
1
answer
77
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How to formulate case distinctions in AMPLs objective function?
This is my first real optimisation problem I formulated and now trying to solve by using AMPL.
The following objective function is from a linear 0-1 LP means all variables $x_i^b\in\{0,1\}$, with $i\...
- 287
6
votes
1
answer
74
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Issue interpreting sets of constraints in AMPL
I'm new to AMPL and am trying to model the following constraints.
\begin{align}y_{ij3}&\le\sum_\ell X_{j\ell2}\quad(m=2,k=3)\\y_{ijk}&\le\sum_\ell\sum_mx_{j\ell m},\quad\forall i\in I,\forall ...
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0
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Magic square in AMPL: presolve: constraint cannot hold [duplicate]
I'm solving the magic square problem without using the alldiff operator.
To insert different values in the matrix, I initialized a variable:
...
- 223
7
votes
4
answers
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Matrix in ampl: constraint that the values are all different
I'm solving the magic square problem for my operational research exam.
The constraints of my model are that the sum of the elements on the lines must be equal to a constant (var constant), that the ...
- 223
8
votes
1
answer
791
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Understanding the AMPL Solver LIbrary within Pyomo
For anyone familiar with the Pyomo book, it occasionally makes reference to the AMPL Solver Library, and to my understanding, if you can manage to hook up to the solver library then you are able to ...
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6
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1
answer
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Obtaining the intermediate solutions in AMPL
I know that for some solvers, for example, the constraint programming solver in Google OR-Tools, it is possible to see all the intermediate solutions that the solver finds while it searches for an ...
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14
votes
1
answer
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Comparison of Algebraic modelling languages and general programming languages
Some optimization software/frameworks (commercial or open-source) such as AMPL, GAMS, Cplex, ... have a specific Algebraic modelling language. Some of them have another type of programming that uses ...
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4
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1
answer
286
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Declare numerical-sequence set in AMPL .dat file
Suppose I want an AMPL set to contain the integers 1 through 5. How can I declare this in the .dat file?
I can do it in the .mod file, like this:
things.mod:
...
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