A public utility, which is divided into six regional districts, wishes to allocate ten power generation contracts to its regions as cheaply as possible. The cost per unit of power generated by each region for each contract is known. If part of a contract is allocated to a region then it must be at least as big as a certain minimum size (5 units). For reliability reasons, no contract may be placed exclusively with only one district. Each district has a limited power generation capacity.

Further explanation of this example: 'Xpress teaching material', Section 2.2 'Semi-continuous variables: contract allocation'; 'Applications of optimization with Xpress-MP'', Section 3.4.3 'Semi-continuous variables'

! Data file for `contract.mos'

OUTPUT: [50 40 10 20 70 50]              ! Maximum output per district

COST:   [50 20 25 30 45 40]              ! Cost per district

VOLUME: [20 10 30 15 20 30 10 50 10 20]  ! Volume of contracts