GAMS Sum over a subset

Question

I have the following sets, variables, and parameters in a GAMS model.

set \quad h/1*3/;
alias (h,t);

Positive variables are $p_d(h)$, $p_c(h)$ and $e(h)$. Parameters are $\eta = 0.9$ and $e(0) = 0$.

I want to write the following equation in GAMS: $$e(h) = e(0)-\sum_{t=1}^h p_d(t)+\eta\cdot\sum_{t=1}^hp_c(t).$$

Answer 1

Eq(h) .. e(h) =e= E0 - sum(t$(ord(t) <=Ord(h) ), pd(t)+n*sum(t, pc(t));

It's better to define E0 as a scalar in GAMS. you should also define alias(h,t);

Answer 2

In GAMS, you are not allowed to perform a sum in the same set as the one the equation is defined.

The answer by Optimization team is correct, although it has a small mistake in the formulation.

For this case:

EQ(h)..    e(h) =E= e("0") - sum(t$(ord(t) le ord(h)), pd(t)) + n*sum(t$(ord(t) le ord(h)), pc(t));

Or, if you put the sums together:

EQ(h)..    e(h) =E= e("0") + sum(t$(ord(t) le ord(h)), n*pc(t) - pd(t));