Inline index addition in gams

Question

I want to use an index equation to iterate over a tensors, whereas I always want to extract the value at index i and index i+1. An example:

Variable x; x.up = 10;

Parameter T /1=1,2=2,3=3,4=4,5=5/;
Set a /1,2,4/;

equation eq(a); eq(a).. x =g= T[a+1];
*x ist restricted by the values of T at the indices 2,3 and 5.

Model dummy /all/;
solve dummy min x use lp;

I am aware that gams sees the indices as string-keys rather than numerical ones, so the addition is not intended. Is this possible anyway? This e.g. can be solved by defining another tensor, unfortunaly my given conditions require the index operation inline (i.e. I am not allowed to define additional parameters or sets.

Answer 1

Does this work for you?

Variable x; x.up = 10;

Set aa /1*6/;
Parameter T(aa) /1=1,2=2,3=3,4=4,5=5/;
Set a(aa) /1,2,4/;

equation eq(a); eq(a(aa)).. x =g= T[aa+1];
*x ist restricted by the values of T at the indices 2,3 and 5.

Model dummy /all/;
solve dummy min x use lp;