Duality

Transportation problem is defind as (Primal model)

  • we have muktiple factory and multiple customer
  • each factory has a capacity amount of items
  • each customer place an order amount of items
  • there are a different cost of sending 1 item from factoryABC to customerABCD
  • To minimize transportation cost,
    • which factory should send item to each customer
    • and how many items do that factory send.

In another view of problem (Duality model – provide vital economic interpretations)

  • If we want to expand a factory (to increase a capacity per factory), How much cost will be reduced.
  • If customers order more items, How much profit we will get.

shadow price  :the optimal values of dual variables associate with each constraint

  • is a price that paid for 1 unit of resource.

reduced cost : associate with each decision variable. defined as the change in objective function value

  • is also called opportunity cost.