Indexing array "Assign" with type dexpr int not supported by this algorithm

Question

My question is similar to one already asked, but there was not an answer (at least not one accepted nor suitable).

I am attempting to make a constraint, which I've simplified below:

dexpr int startingWeekChanges[p in People] = 7 * y + 1;

...

for(p in People){
    Assign[startingWeekChanges[p]] == 1;
}

But I see this is not allowed (error message being "Indexing array "Assign" with type dexpr int not supported by this algorithm").

I can't change over to constraint programming. Is there an alternative strategy to get by this?

Explaining why exactly the answers provided in the question you linked would go a long way towards helping others provide the answer that you're looking for. — Xavier Nodet
– Xavier Nodet, Commented Apr 13, 2019 at 17:48

Daniel Junglas · Accepted Answer · 2019-04-14 18:00:34Z

3

I think something like this might do the trick:

forall (i in IndexSetForAssign)
   Assign[i] == (sum (p in People) (startingWeekChanges[p] == i) >= 1);

It sets Assign[i] to 1 if at least one startingWeekChanges[p] has the value i. If not then it sets Assign[i] to 0.

The expressions above exploit the fact that you can use the truth value (1 if true, 0 otherwise) of a constraint for modeling.

answered Apr 14, 2019 at 18:00

Daniel Junglas

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3 Comments

Ken Reid Over a year ago

This looks very promising but I'm a little confused - what exactly is IndexSetForAssign? Thank you for your help.

Daniel Junglas Over a year ago

IndexSetForAssign is the index set you used when you defined Assign. Assuming you did dvar int Assign[I] this would just be I.

Ken Reid Over a year ago

Ah, the problem is my simplification, as Assign is actually 4 dimensional. I now have that part working thanks to your assistance!

halfer · Accepted Answer · 2019-07-20 14:02:17Z

1

At https://www.ibm.com/developerworks/community/forums/html/topic?id=7bb1e7ff-ec3a-4e79-a8c4-c20050dfad0c&ps=25 I answered the same question and gave an example.

range r=1..5;

float value[r]=[2,3,4.5,1,0];
dvar int i in 1..5;
dexpr int j=6-i;

maximize sum(k in r) value[k]*(k==j);
subject to
{

}

execute
{
writeln("i=",i);
}

edited Jul 20, 2019 at 14:02

halfer

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answered Apr 13, 2019 at 6:28

Alex Fleischer

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Comments

Xavier Nodet · Accepted Answer · 2019-04-13 14:26:33Z

0

It seems you want to define an expression as the value of an array indexed by a variable. This is called the element constraint [1] and is only available in the context of Constraint Programming, as a Linear Programming solver can't cope with such constraints.

[1] https://www.ibm.com/support/knowledgecenter/SSSA5P_12.9.0/ilog.odms.ide.help/OPL_Studio/opllangref/topics/opl_langref_constraints_types_inCP.html#usropllangref.uss_langref_constraints.1073721__section1319017294580

answered Apr 13, 2019 at 14:26

Xavier Nodet

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