The Discrete Lot Sizing problem considered here is a multi-item, single machine problem with capacity of production limited to one per period.
There are storage costs and sequence-dependent changeover costs, respecting the triangle inequality.
The changeover cost q^{i, j} is induced when passing from the production of item i to another one j with q^{i, i} = 0 for all i.
Backlogging is not allowed, each order has to be produced before the corresponding demand time,
