XPRESS Mosel - Wrong logical operator

Question

I am begginer at Xpress Mosel, i am trying to calculate a surplus = max(0;production-consumption) The production is calculated based on the power installed which is a decision variable. The model gives me an error : Wrong logical Operator. Please if anyone can help

Answer 1

In order to get the maximum of things that involve decision variables, you can use the fmax function from the mmxnlp package, see the documentation here.

A short example for a surplus definition is

model Surplus

uses "mmxprs"
uses "mmxnlp"

declarations
 production: mpvar
 consumption: mpvar
end-declarations

surplus := fmax(0.0, production - consumption)
  
minimize(surplus)

end-model