Questions tagged [gams]
For questions related to GAMS (General Algebraic Modeling System), a high-level modeling system for mathematical optimization.
34
questions
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1
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How to print/display a specific element of a set in GAMS?
I have the follwoing set in GAMS
set i /10,13,15/;
how can I display the second element of this set ?
- 1,275
1
vote
0
answers
19
views
Using Neos Server to submit GAMS file
When I submit a GAMS file along with a GDX file to the Neos Server upon clicking the submit button I don't get any error but the following webpage which is not loading and nothing is displayed. I ...
- 163
3
votes
5
answers
613
views
Convert MCP model from GAMS to Pyomo
I have a Mixed Complementarity Problem (MCP) that represents a market under perfect competition. The model is written in GAMS and works as expected. But when translating it to Python, using Pyomo, the ...
- 315
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votes
1
answer
258
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gams syntax issue - "set identifier or quoted element expected"
Writing some GAMS code, getting some syntax errors:
Anyone recognize the problem?
- 171
2
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1
answer
159
views
How to solve infeasible cplex model in GAMS?
I am facing this kind of error
"Row 'eq1(14)' infeasible, all entries at implied bounds"
in a problem that a GAMS script gets data from MATLAB. I have seen some posts about conflict ...
- 21
2
votes
1
answer
50
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Piecewise constraints in GAMS
I'm trying to solve the network problem below in GAMS Cplex. I have a piecewise constraint that are depending on the node situations (whether a node is an origin (o) node, inbetween node, and ...
2
votes
1
answer
136
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multiple solutions to a nonlinear problem in GAMS
Good afternoon, I have the following doubts
Is there a command in GAMS that lets me know when my problem has multiple optimal solutions?
Suppose my nonlinear optimization problem has multiple global ...
- 193
4
votes
3
answers
1k
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Is it better to use GAMS or Python for Optimization Models?
I have been using GAMS for several years, and I would like to do my new research in Python programming language. It is simple to do coding stuff in GAMS, however, it takes much time in complex ...
- 139
3
votes
2
answers
451
views
Write constraints with relationship sets in Pyomo
I would like to write the following constraint in the most compact form possible using Pyomo.
$$\sum_{o\in O}y_{n,o} = \sum_{o\in O} \sum_{n'\in LN}y_{n',o}\qquad \forall n$$
Where, the important part,...
- 81
2
votes
0
answers
128
views
Defining a highly non-linear function of integer variables
I have a complicated non-linear objective function of positive integer variables subject to linear constraints:
$\mathop {Min}\limits_{\underline x} f(\underline x)$
s.t.
$A\underline x\leq \underline ...
1
vote
0
answers
59
views
Ordering a set in GAMS
I'm trying to solve a problem very similar to this one, where I'm trying to find an optimal order. How would I actually plug this into GAMS?
It gives out a single value rather than an ordering. I ...
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0
answers
236
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Building model takes so much time in Cplex
I am a beginner in CPLEX. I have a model with about 1 million constants and 800k rows and 1.6 million columns. I implemented in both GAMS and CPLEX (C# as the platform). The final solution for both is ...
2
votes
1
answer
120
views
Any good resource for solving power system optimization in GAMS?
I am looking for some resources to learn the modelling tricks of GAMS in power system optimisation problems.
- 1,275
0
votes
1
answer
225
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GAMS summing over subset
I am trying to sum over a subset between $t+1$ and $t+U-1$ as follows $$y_i^t+\sum_{k=t+1}^{t+Ut_i-1}z_i^k\le1$$ but I could not define the condition within sum.
...
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4
votes
1
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196
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GAMS: Is there a way to retrieve the gap from the final solve statement
Good evening,
I am looking for a way to retrieve information from the final solve statement. Lower bound and Gap would be nice. I am working with the python api but i can only get the final obj. value ...
- 533
3
votes
2
answers
377
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GAMS default Solver doesn't use much of my RAM and CPU
I noticed that when I run the solver via the GAMS IDE or Python API I don't use more than ~33% of my RAM. Is there an artificial barrier which I can put up or disable?
- 533
2
votes
2
answers
406
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CPLEX output log
Whats the difference between MIP solution and Final Solve? I am trying to benchmark some solution approaches and I am not sure which of those is the more significant... sometimes they have the same ...
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votes
1
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124
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GAMS CPLEX solver solves big problem instances suspiciously fast
I am having trouble with my Problem Instances, which seem to be not "complicated" enough..
Is there a way to find out what the problem is? It is being solved in a matter of seconds even if ...
- 533
1
vote
1
answer
403
views
How can one iterate over all instances and solve them in GAMS?
I wrote my model down in GAMS:
all sets
parameter
obj. function
constraints
and used $include in order to feed the model differently sized data...
I am currently using
...
- 533
0
votes
1
answer
287
views
GAMS export to excel in a loop
I am looking for a way to write data from several iterations during a loop process into my excel.
How can i change the location it is written to during every loop iteration?
those 2 lines would keep ...
- 533
1
vote
1
answer
136
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Looking for an example of a heuristic implementation in GAMS
I am new to GAMS and the documentation is not helping me to make fast progress.
I am looking for an example implementation similar to Relax and Fix heuristic
where in several iterations subsets of ...
- 533
1
vote
0
answers
54
views
How to automatize instance generation for GAMS?
Gams problem instances can be saved in a .inc file what is basically just a .txt file and u can make gams read from that, but how can i automatize the generation process for those problem instances? I ...
- 533
3
votes
1
answer
2k
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How to build a GAMS model in python
I looked at the GAMS python API but the documentation only describing already predefined models (run .gms with some tweaking options).
My question is now: Can I somehow build a gams model from scratch ...
- 533
2
votes
1
answer
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How to set solver options in Pyomo with GAMS Python API?
Did anyone have experiences with Pyomo and GAMS as solver? I had looked into the pyomo documentation (GAMSShell Solver) and in the CPLEX Manuals, but doesnt find the correct syntax.
My Code looks like:...
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5
votes
0
answers
87
views
Quantifying Feasibility
I have a scheduling model formulation ( experimental setup) that takes in product states as input (sample points) and checks the model status (response) and returns feasible or infeasible.
My plan is ...
- 51
2
votes
2
answers
975
views
GAMS Sum over a subset
I have the following sets, variables, and parameters in a GAMS model.
set \quad h/1*3/;
alias (h,t);
Positive variables are $p_d(h)$, $p_c(h)$ and $e(h)$. ...
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52
votes
15
answers
13k
views
Are Python and Julia used for optimization in industry?
I am giving a small computer exercise that aims at teaching students the basics of a modelling language to model small optimization problems. So far I have been using the modelling language GAMS as ...
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10
votes
2
answers
808
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Modeling and solvers
I have just started to dive into OR world on my work. Currently we are using GAMS with Gurobi but some of us have strong programming background and would like to have more programmatic approach to OR. ...
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5
votes
1
answer
277
views
Tolerance for equality in GAMS/CPLEX
Is there an option in GAMS that sets the tolerance for declaring two real numbers to equal?
For example, how can I tell GAMS or GAMS/CPLEX that $0.999100 = 0.99909$?
Thank you for your help!
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3
votes
0
answers
77
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How can I do this in GAMS?
I am mimicking a GAMS model that was introduced in Soler et al. (2013)1 to compare my new model with its results.
In a nutshell, assume we have a variable $t$ that is supposed to only take certain ...
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votes
1
answer
217
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Is this formulation linear or non-linear?
Can you help me figure out if this formulation constitutes a non-linear problem? I believe It is a linear problem but my solver (GAMS) is unable to produce a acceptable solution.
$x,y$ and $\text{...
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6
votes
1
answer
75
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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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7
votes
1
answer
144
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Get a MPS file using NEOS/GAMS web interface
I'm trying to use Neos/GAMS to solve an optimization problem. I will need to get a MPS file from the model. With using GAMS IDE it is easy to use an option file to get it but, it needs a licence file ...
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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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