Here’s an improved version of your message with clearer details about the error and your model setup:

Hello,

I’m working on a GAMS model where I have a variable `L`

representing the battery’s level of charge in MWh over time periods `t`

. One of my constraints involves limiting the change in charge level between consecutive time periods.

Here’s the formula I’m trying to use:

*pow[t] = (L[t+1] - L[t]) <= C*

However, I encounter this error:

*TypeError: Domain item must be type Set, Alias, ImplicitSet or str but found <class 'gamspy._algebra.expression.Expression'>*

It seems the error arises because of `L[t+1]`

.

How can I reference the next value of `L`

(i.e., `L[t+1]`

) within the same constraint, so I can calculate the difference with `L[t]`

?