Minimum activity level

Continuous production rate make that may be 0 (the plant is not operating) or between allowed production limits MAKEMIN and MAKEMAX

• Introduce a binary variable ifmake to mean

  ifmake :	0 if plant is shut
  	1 plant is open

  MIP formulation:

  make ≥ MAKEMIN · ifmake	[1]
  make ≤ MAKEMAX · ifmake	[2]

  Note: see Section Minimum activity level for an alternative formulation using semi-continuous variables
• The ifmake binary variable also allows us to model fixed costs
  • FCOST: fixed production cost
  • VCOST: variable production cost
  MIP formulation:

  cost = FCOST · ifmake + VCOST · make	[3]
  make ≥ MAKEMIN · ifmake	[1]
  make ≤ MAKEMAX · ifmake	[2]