[gecode-users] Re: Var indexes-help

[penche]

<pekczynski at ...> writes:

> 
> Hi there,
> I think using the element constraint is the correct choice.
> Maybe the little example I attached will help you out.
> At least you can use the element constraint to model
> 
> B[C[i-1]]=A[i]
> 
> and indeed the alg also does
> 
> A[i]=B[C[i-1]]
> 
> see http://www.gecode.org/gecode-doc-latest/group__TaskIntIntElement.html
> 
> > 2) I also tried 'element' to express this constraint
> >
> > Int Var x;
> > element(this, B, C.get(i - 1), x);
> > rel(this,A.get(i),IRT_EQ,x);
> 
> So this was quite right, but you can directly use
> 
>  element(this, B, C[i - 1], A[i]);
> 
> so you don't need the rel constraint.
> 
> If there are any further questions, let us know.
> :-D
> Cheers
> Patrick
> 
> 
> Attachment (arrayex.cc): application/octet-stream, 1932 bytes
> 
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Thank you, I now see rel is useless and element is just enough. 
But one point is; we will need Var indexes inevitable when the relations 
get nested.

For example; A[i] = B [ C [A[j]] ]

1) obviously rel does not work. 
rel(this, A.get(i), IRT_EQ, B.get(C.get(A.get(j))))

2) I tried to introduce new Vars, but below did not work also. 

IntVar intermediate1= new IntVar(this,min,max);
IntVar intermediate2= new IntVar(this,min, max);

element(this, C, A.get(j), intermediate1);
element(this, B, intermediate1, intermediate2);

rel(this, A.get(i), IRT_EQ, intermediate2);

3) Any way to write this constraint?

Thanks!