Originally posted by: CynthiaLi

Hi,I have a question about get dual value in main script. I'm a beginner, so I am not even sure that the question is right...
Anyway, I basically modified the cutstock example. In the cutstock model, there is a part:
for(var i in masterOpl.Items) {
subData.Duals[i] = masterOpl.ctFill[i].dual;
}
I believe it means to pass the dual value from the master problem to the sub problem.
I want to do a similar thing. The difference is that I want to take the dual value from the master problem first, then do some calculation to put in the subproblem. Here is my code:
var duals;
for(var t=1;t<=MasterData.NbDual;t++)
{
duals[t]=MasterOpl.ctFill[t].dual;
}
for (var i=1; i<= MasterOpl.NbX;i++)
{
for(var j=1; j<= MasterOpl.NbDual;j++) Big[i]=Big[i]+duals[j]*MasterOpl.T[i][j];
}

However, there is error sign pointing at the line of duals[t]=MasterOpl.ctFill[t].dual;
And it says "Scripting runtime error: cannot add properties to this value, "undefined".
Where did I go wrong?
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Originally posted by: SystemAdmin

If you need to treat duals in your script as array then you should declare it as:

var duals = new Array();

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Originally posted by: SystemAdmin

I need a little help in the same context :
I am trying to get duals for constraints using Opl dual function

Syntax
dual(ct)

Description
This function is available in a post-processing context.
is there any example showing usage?
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Originally posted by: SystemAdmin

Yes, you may want to look at 'custock' example that comes with distribution. Specifically, in cutstock_main.mod file, 'FillDuals' script accesses dual value of constraints to fill an array that is then passed to sub-model.

Regards,
Faisal
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Originally posted by: SystemAdmin

Thanks Faisal, that was helpful.

I have a few questions ( if you are from IBM team):
the syntax mentioned in Opl Reference manual is
Opl.dual(ct) > i took ct for constraint name
am i missing something here? because i get error if i try that.
Also i tried the following (similar) in the post processing code
execute DISPLAY_RESULT{
for ( var i in Rows )

write ( ct i . dual , " " ) ;
}

but it gives me dual value as 'undefined' in the script log
and it is not displayed in problem browser either ( all other outputs are displayed in problem browser)
Thank you
Mandar
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Originally posted by: SystemAdmin

I also have the same problem...
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Originally posted by: SatishKumarA

Try this,

execute DISPLAY_RESULT{
 
for ( var i in Rows )
write ( ct i . dual , " " ) ;
writeln("Dual value:",i,ct[i].dual); (or)
writeln("Dual Value:,ct[i].dual);
}

And AFAIK, dual value will be given as "undefined" when the corresponding constraint is undefined.

I hope this helps,

Thanks,
Satish Kumar A
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Originally posted by: SatishKumarA

Try this,

execute DISPLAY_RESULT{ 
for ( var i in Rows )
writeln("Dual value:",i,ct[i].dual); (or) writeln("Dual Value:",ct[i].dual);
}

And AFAIK, dual value will be given as "undefined" when the corresponding constraint is undefined.

I hope this helps,

Thanks,
Satish Kumar A
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Originally posted by: Mathsg

Hi, i am facing same problem with dual variables. I am getting an error in scripting part of my master problem when passing dual variable constriant from master problem to sub model. i have tried my best to fix it but i am unable to locate it. Kindly guide me 

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Hi,

in cutstock_main

you may read

      // Using data elements from the master model.
      var subData = new IloOplDataElements();
      subData.RollWidth = masterOpl.RollWidth;
      subData.Size = masterOpl.Size;
      subData.Duals = masterOpl.Duals;     
      subOpl.addDataSource(subData);
      subOpl.generate();

 

regards

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Originally posted by: Mathsg

Hi Alex, 

 

Thank you so much for your continued help throughout my research. I have read your refrance but i have not get much about it weather my problem is same as that problem. I am unable to locating the problem why it give me an error while passing dual variables constraint from master problem to another model may be the error is due to accesing of array with false way or i dont know. Can you help me to fix the error ? I am looking forward to hearing from you. thank you

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Have you tried

subData.Duals = masterOpl.Duals;   

from cutstock_main example ?

 

regards

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Originally posted by: Mathsg

Hi,

 

Thank you so much for your help. The problem has been fixed which was due to some mistakes in my constraint but now it give me another error while writing next iteration part in script for updating the master problem from sub opl. In my orignal master problem i was cosidering subset of light paths which has given me current solution and then sub model give me negative reduce cost which means that still there are light paths that can improve our Master problem. Now i am writing it in script part of OPL to get the light paths from sub model and update the master problem. i have looked upon the cut stock example but i am unable getting an idea from this example. can you help me ?  i would appreciate it very much if anyone can fix the error or give me some kind suggestions. thank you

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and what is the type of routes ?

regards

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Originally posted by: Mathsg

Hi,

 

thank you very much for your time. I am solving networking planing problem by column generation approache in which i have 6 node topology. Source and destination are connected through k shortest path.

i have decompose the problem into master and sub problem. i am going to minimize the cost of flow. In the master problem i have cosider 2 k shortest path for each flow between source and destination which give me current solution for the flows and sub problem can generate new path which can imporve our objective i.e., minimize the cost. path is made up of connecting different link and combine them i.e., hope count. Now i am confused that how to write the next iteration for updating the master problem as i have get reduced cost from sub problem which means there a path i.e., links that can improve our master prblem objective. i have written it but it give me an error

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Originally posted by: Mathsg

Hi,

 

thank you very much for your time. I am solving networking planing problem by column generation approache in which i have 6 node topology. Source and destination are connected through k shortest path.

i have decompose the problem into master and sub problem. i am going to minimize the cost of flow. In the master problem i have cosider 2 k shortest path for each flow between source and destination which give me current solution for the flows and sub problem can generate new path which can imporve our objective i.e., minimize the cost. path is made up of connecting different link and combine them i.e., hope count. Now i am confused that how to write the next iteration for updating the master problem as i have get reduced cost from sub problem which means there a path i.e., links that can improve our master problem objective. i have written it but it give me an error

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Hi,

see https://www.ibm.com/developerworks/community/forums/html/topic?id=f17e0fc6-54f9-4903-8eba-ab9a4af860eb

about how to get info from sub model in the main model

regards

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