Originally posted by: istenc

Hi,

I have two decision variable A and B that are interval and integer variable respectively. I am trying to  use element method so as to define a variable like A_k such that k=B_i. In other words, I am trying to use a decision variable as a subscript of another but I fail.

I would be very glad if you can help me.

Best,

İstenç

Hi,

indeed today you cannot write

using CP;

int n=5;

dvar interval A[i in 1..n] in i..i+1 size 1;

dvar int B[i in 1..n] in 1..n;

subject to
{
allDifferent(B);

forall(i in 1..n-1) startOf(A[B[i]])>=startOf(A[B[i+1]]);
}

but you could manage by using elements within an array:

using CP;

int n=5;

dvar interval A[i in 1..n] in i..i+1 size 1;
dvar int startA[i in 1..n];
dvar int B[i in 1..n] in 1..n;

subject to
{
allDifferent(B);

 

forall(i in 1..n) startA[i]==startOf(A[i]);
forall(i in 1..n-1) startA[B[i]]>=startA[B[i+1]];
}

Could that help ?

regards

Originally posted by: istenc

Yes, it totally helps. I have tried to use element method like "element(all(i in 1..n) A[i],B[i])" but i think this method is incompatible with interval variables.

Thanks a lot.

Best,

İstenç

Originally posted by: GGR

Hi istenc

Actually you're right, the element expression is an integer expression. 

Is it possible you told us why you need it for a scheduling problem?

Cheers

Originally posted by: istenc

Hi,

I need it for a scheduling problem with batch delivery. At the end of some orders, a batch is delivered in our problem. So,  let a batch be delivered immediately after order 1 is completed. If order 2 is also in this batch, i should ensure that order 1 is completed after order 2; at this point, i should ensure that  endOf(A[2]])<endOf(A[1]). In a closed form, it would be  like

endOf(A[i])<endOf(A[B[i]]) where B[i] is the order that has the maximum completion time in the batch by which order i is delivered.

Thanks to the post by Alex Fleischer, i can model this constraint easily.

Best,

İstenç

Originally posted by: GGR

Hi

Thanks a lot for the model issue.