Use the approach in the question you linked. Expression
Max(c4 * x4, c5 * x5)
can be replaced with a variable x6provided that you add the following additional restrictions:
x6 >= c4 * x4
x6 >= c5 * x5
So your general set becomes:
Minimize (c1 * x1) + (c2 * x2) + (c3 * x3) + x6 + (c6 * x4) + (c7 * x5)
given that:
some equality and inequality constraints
and new requirements:
x6 >= c4 * x4
x6 >= c5 * x5
, Max(c4 * x4, c5 * x5) c4 * x4, c5 * x5. x6 , max-. x6 max-. .