Questions tagged [gams]
For questions related to GAMS (General Algebraic Modeling System), a high-level modeling system for mathematical optimization.
24
questions
-2
votes
0answers
49 views
Inventory positioning Model in GAMS
I have plotted a problem in GAMS expecting to get the route and inventory level I should put in DC but it's not shown the result.
...
2
votes
0answers
72 views
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
1answer
103 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.
0
votes
1answer
78 views
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.
...
5
votes
1answer
75 views
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 ...
3
votes
2answers
188 views
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?
2
votes
2answers
177 views
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 ...
-1
votes
1answer
97 views
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 ...
1
vote
1answer
191 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
...
0
votes
1answer
115 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 ...
1
vote
1answer
81 views
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 ...
1
vote
0answers
44 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 ...
2
votes
1answer
327 views
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 ...
2
votes
1answer
190 views
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:...
5
votes
0answers
84 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 ...
2
votes
2answers
357 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 $e(h)$. ...
46
votes
15answers
10k 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 ...
10
votes
2answers
704 views
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. ...
5
votes
1answer
118 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!
3
votes
0answers
72 views
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 ...
7
votes
1answer
175 views
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{...
6
votes
1answer
64 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 ...
7
votes
1answer
97 views
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 ...
13
votes
1answer
770 views
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 ...