Questions tagged [gams]

For questions related to GAMS (General Algebraic Modeling System), a high-level modeling system for mathematical optimization.

Filter by
Sorted by
Tagged with
2
votes
0answers
69 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
73 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
74 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
176 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
170 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
175 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
108 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
80 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
254 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
157 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
320 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 $e(h)$. ...
45
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
700 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
95 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
171 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
96 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
751 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 ...