# Questions tagged [ampl]

For questions related to the algebraic modeling language AMPL.

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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 ...
1k views

### 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 ...
217 views

### 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 ...
470 views

### 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 ...
249 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 (+...
63 views

### 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 ...
138 views

### 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 ...
220 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: ...
117 views

### 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 ...
70 views

### 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: ...
68 views

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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: ...
108 views

### 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 ...
136 views

### 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\...
162 views

### 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 ...
62 views

### Integer variable optimization - decreasing execution time

I have a variable declared as follows in AMPL: ...
172 views

### 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 ...
47 views

### 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 ...
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 \$...