Hi guys,
I am using GAMS with CPLEX as the solver. I have a really strange problem. I have a MIP model with many binary vairables which was solved within 5 minutes.
All of a sudden - without having changed anything - the same model requires quite much time to be solved. I let the solver run for 5000 seconds, but still the problem was not solved (meaning that the Gap of the best found solution is still quite high).
Has someone experienced something similar? Or could someone think about a possible reason for that? I uploaded the node log file of that run. Maybe someone of you will see something interesting in it.
Thanks a lot in advance for your comments.
Computational time of model extremely increased
Computational time of model extremely increased
- Attachments
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- Log3 - Time 5000.txt
- Node Log File
- (167.81 KiB) Downloaded 472 times
Re: Computational time of model extremely increased
Does nobody have a clue?
Do you think the I should let the model run for more than 5000 Seconds? The improvement for the last 3000 senconds were 0 % with regard to the gap (sett uploaded logfile). This is why I stronlgy doubt that a higher runtime will significantly improve the results.
Do you think the I should let the model run for more than 5000 Seconds? The improvement for the last 3000 senconds were 0 % with regard to the gap (sett uploaded logfile). This is why I stronlgy doubt that a higher runtime will significantly improve the results.
- Gideon Kruseman
- User
- Posts: 24
- Joined: 6 years ago
Re: Computational time of model extremely increased
same model and same data?
Gideon Kruseman
ex-ante and foresight lead @CIMMYT, big data focal point @CIMMYT, coordinator CoP socio-economic data @CGIAR_BigData
ex-ante and foresight lead @CIMMYT, big data focal point @CIMMYT, coordinator CoP socio-economic data @CGIAR_BigData
Re: Computational time of model extremely increased
Hi PeterBe,
I get the same error in my simulation. Did you find any solution about?
Larissa
Thank you.
I get the same error in my simulation. Did you find any solution about?
Larissa
Thank you.
Re: Computational time of model extremely increased
GAMS/Cplex (in default mode) runs deterministically when executed on the identical model instance on the same machine. There are a few options that can make it behave non-deterministically (only with option thread<>1). But even slight changes (e.g. the order of variables and equations, or a coefficient slightly changed) can result in a different path of the algorithm and hence in different performance of the solver. This is known as performance variability. Here are a few good entries on this topic:
- http://www.thequestforoptimality.com/pe ... -readings/
- Section 5 in MIPLIB 2010 paper http://mpc.zib.de/index.php/MPC/article/viewFile/56/28
Re: Computational time of model extremely increased
Hi guys,
sorry for not responding for so long. I was busy with other things.
Now again the problem still remains that the computational time of my model has extremely increased altough I am not aware of any changes.
I read about mipemphasis parameters: https://www.gams.com/latest/docs/S_CPLE ... ipemphasis
How can I use them with GAMS? I tried different syntax like:
I always got a syntax error. Could anyone tell me which syntax I have to use to specify this parameter?
sorry for not responding for so long. I was busy with other things.
Now again the problem still remains that the computational time of my model has extremely increased altough I am not aware of any changes.
I read about mipemphasis parameters: https://www.gams.com/latest/docs/S_CPLE ... ipemphasis
How can I use them with GAMS? I tried different syntax like:
Code: Select all
mipemphasis 0;
mipemphasis =0;
mipemphasis (0);
modelname.mipemphasis =0;
Re: Computational time of model extremely increased
Peter,
It seems that you try to set the mipemphasis option in your GAMS program. However, mipemphasis is a CPLEX solver option (https://www.gams.com/latest/docs/S_CPLE ... ipemphasis) that needs to be specified via a solver option file and then you also need to instruct the solver to read that option file , e.g as follows:
For details see the following chapter in the documentation: https://www.gams.com/latest/docs/UG_Sol ... PTION_FILE
I hope this helps!
Fred
It seems that you try to set the mipemphasis option in your GAMS program. However, mipemphasis is a CPLEX solver option (https://www.gams.com/latest/docs/S_CPLE ... ipemphasis) that needs to be specified via a solver option file and then you also need to instruct the solver to read that option file , e.g as follows:
Code: Select all
[...]
$echo mipemphasis 0 > cplex.opt
modelname.optfile = 1;
[...]
I hope this helps!
Fred
Re: Computational time of model extremely increased
Thanks for your answer Fred,
I inserted the following code in GAMS:
then I created a file called cplex.opt and this file looks like this:
I changed the number but nothing seemed to have an effect on the results. I always get the same results (when specifying the maximal running time of the solver to 100). Do you think this is just a coincidence or did I made a mistake?
I inserted the following code in GAMS:
Code: Select all
mymodel.optfile = 1;
Code: Select all
* CPLEX options file
mipemphasis 2
Re: Computational time of model extremely increased
Would anyone mind telling me whether my insereted code and the file are correct?
- Gideon Kruseman
- User
- Posts: 24
- Joined: 6 years ago
Re: Computational time of model extremely increased
$echo mipemphasis 0 > cplex.opt
modelname.optfile = 1;
The first statement writes the cplex options file
the second statement tells gams to use the cplex options file
modelname.optfile = 1;
The first statement writes the cplex options file
the second statement tells gams to use the cplex options file
Gideon Kruseman
ex-ante and foresight lead @CIMMYT, big data focal point @CIMMYT, coordinator CoP socio-economic data @CGIAR_BigData
ex-ante and foresight lead @CIMMYT, big data focal point @CIMMYT, coordinator CoP socio-economic data @CGIAR_BigData