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variablesoptimizationconditional-statementssetgams-math

Splitting GAMS equation using if else statements

I have a working GAMS optimization model using LP. I want to modify one of my equations so that it excludes one of the terms when t = 1. Here's the simplification of this problem:

Set t "time in hours" / 1 * 8760/ ;

If t = 1: vDemand(t) =e= p1*(vInternal(t) - pAmbient(t))

else: vDemand(t) =e= p1*(vInternal(t) - pAmbient(t)) + p2*(vInternal(t) - vInternal(t-1))

How do I modify this vDemand equation while keeping my optimization linear?

I looked up and tried the different ways to incorporate conditional statements on GAMS, but not successful so far.

Solution 
  • vDemand(t) =e= p1*(vInternal(t) - pAmbient(t)) + (p2*(vInternal(t) - vInternal(t-1)))$(ord(t)>1);

    The $ condition at the end of the second term makes sure, that that part is only used, if it is not the first element of the set t.