Decision Optimization

Originally posted by: trebron

Howdy,

I run into an exception with cplex.addMIPStart() that  I do not understand. I ocuurs only on one of my larger instances that is solved using an iterative approach.

Everything  works fine for a couple of iterations, but in the 6-th I end up with the error message

*** ERROR[ENGINE_001] at 61:0 ./MyApplication.mod: Exception from IBM ILOG Concert: addMIPStart: arrays with diffferent sizes.
### CONCERT exception: addMIPStart: arrays with diffferent sizes

A dump of the array-sizes just before the call of addMIPStart() does not indicate any differences

    writeln("sizes; x="+subModel.x.size +";  edge-solution="+theModel.Current_Edge_Solution.size)
    cplex.addMIPStart(subModel.x, theModel.Current_Edge_Solution)

leads to

sizes; x=126135;  edge-solution=126135

Are there any known issues related to that topic? I am using version: 12.8.0.0

Cheers

   Norbert

Hi,

1) Can you try with 12.10 ?

2) In https://www.linkedin.com/pulse/making-decision-optimization-simple-alex-fleischer/

you chose

Warm start through API : addMIPStart

can you try

Write and read MST files : warm start ?

3) Then it's time to log a support request

regards

Originally posted by: trebron

Dear Alex,

thanks for the hints. I'll give it a try.

In a first attempt I modified your zoo-example a bit and was wondering what the working directory of OPL-IDE is.

main
{
    thisOplModel.generate();

    var filenameLp = "zoo.lp";
    cplex.exportModel(filenameLp);

    cplex.solve();
    var filename = "zooSolution.mst";
   //var filename = "c://temp//zooSolution.mst";
    thisOplModel.postProcess();

    cplex.writeMIPStarts(filename, 0, 1);
}

The dump of the lp-work fine whereas the dump of the solution file yields

Ausnahme von IBM ILOG CPLEX: CPLEX Error  1422: Could not open file 'zooSolution.mst' for writing. 
Ausnahme von IBM ILOG CPLEX: CPLEX status = 1422.    zoo.mod   

Moreover
* It works fine with oplrun and the mst-file is written.

* The mst-file is as well written within the IDE if I specify a complete path (e.g., "c://temp//zooSolution.mst")

I'm confused. Is that behaviour to be expected?

(mod file is enclosed).

Cheers

   Norbert

Hi,

I tried your model zoo.mod

The .mst file is written in folder CPLEX_Studio1210\opl\oplide when you do not specify an absolute path.

The error you got is probably because you do not have write access in that folder

Knowing this you could use a relative path from there, for instance

var filename = "../../zooSolution.mst";

works fine and writes the .mst file in a parent folder

regards

Originally posted by: trebron

Hi Alex,

thanks for your answer - that is what I expected. What I still do not understand is why we have a different behaviour for  exportModel() and  writeMIPStarts().

For exportModel() the file is always written relative to the mod-file, while writeMIPStarts() only for oplrun, otherwise realtive to the installation path. That is not really intuitive. Is there a sound reason for that?

By the way: The workaround with writing and reading the mst-file worked for CPLEX 12.8. I'll give a newer CPLEX-version a try as well...

Take care and stay healthy!

Cheers

   Norbert

Hi,

we know about this and do not hesitate to log a wish in Aha https://ibm-data-and-ai.ideas.aha.io/?project=CPLEX

regards

Originally posted by: trebron

Hi Alex,

I did so, knowing that the feature is only "nice-to-have".

Thanks.

Norbert